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Title: Kant's Prolegomena - To Any Future Metaphysics
Author: Kant, Immanuel
Language: English
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The Open Court Publishing Co.

[Transcriber's note: ** Supplemental material and table of contents
are omitted from this etext. ** ]




Kant's Prolegomena,{1} although a small book, is indubitably the most
important of his writings. It furnishes us with a key to his main
work, The Critique of Pure Reason; in fact, it is an extract
containing all the salient ideas of Kant's system. It approaches the
subject in the simplest and most direct way, and is therefore best
adapted as an introduction into his philosophy. For this reason, The
Open Court Publishing Company has deemed it advisable to bring out a
new edition of the work, keeping in view its broader use as a
preliminary survey and explanation of Kant's philosophy in general. In
order to make the book useful for this broader purpose, the editor has
not only stated his own views concerning the problem underlying the
Prolegomena (see page 167 et seq.), but has also collected the most
important materials which have reference to Kant's philosophy, or to
the reception which was accorded to it in various quarters (see page
241 et seq.). The selections have not been made from a partisan
standpoint, but have been chosen with a view to characterising the
attitude of different minds, and to directing the student to the best
literature on the subject.

{1} Prolegomena means literally prefatory or introductory remarks. It is
the neuter plural of the present passive participle of
προλέγειν, to speak before, i.e., to make introductory
remarks before beginning one's regular discourse.

It is not without good reasons that the appearance of the Critique of
Pure Reason is regarded as the beginning of a new era in the history
of philosophy; and so it seems that a comprehension of Kant's
position, whether we accept or reject it, is indispensable to the
student of philosophy. It is not his solution which makes the sage of
Königsberg the initiator of modern thought, but his formulation of
the problem.

* * *

The present translation is practically new, but it goes without saying
that the editor utilised the labors of his predecessors, among whom
Prof. John P. Mahaffy and John H. Bernard deserve special credit.
Richardson's translation of 1818 may be regarded as superseded and has
not been consulted, but occasional reference has been made to that of
Prof. Ernest Belfort Bax. Considering the difficulties under which
even these translators labored we must recognise the fact that they
did their work well, with painstaking diligence, great love of the
subject, and good judgment. The editor of the present translation has
the advantage of being to the manor born; moreover, he is pretty well
versed in Kant's style; and wherever he differs from his predecessors
in the interpretation of a construction, he has deviated from them not
without good reasons. Nevertheless there are some passages which will
still remain doubtful, though happily they are of little consequence.

As a curiosum in Richardson's translation Professor Mahaffy mentions
that the words widersinnig gewundene Schnecken, which simply means
"symmetric helices,"{2} are rendered by "snails rolled up contrary to
all sense"—a wording that is itself contrary to all sense and makes
the whole paragraph unintelligible. We may add an instance of another
mistake that misses the mark. Kant employs in the Appendix a word that
is no longer used in German. He speaks of the Cento der Metaphysik as
having neue Lappen and einen veränderten Zuschnitt. Mr. Bax
translates Cento by "body," Lappen by "outgrowths," and Zuschnitt by
"figure." His mistake is perhaps not less excusable than Richardson's;
it is certainly not less comical, and it also destroys the sense,
which in the present case is a very striking simile. Cento is a Latin
word[3] derived from the Greek κεντρων,[4] meaning "a garment of
many patches sewed together," or, as we might now say, "a crazy

{2} Mahaffy not incorrectly translates "spirals winding opposite ways,"
and Mr. Bax follows him verbatim even to the repetition of the

{3} The French cento is still in use.

{4} κέντρων, (1) one that bears the marks of the κέντρο,
goad; a rogue, (2) a patched cloth; (3) any kind of patchwork,
especially verses made up of scraps from other authors.

* * *

In the hope that this book will prove useful, The Open Court
Publishing Company offers it as a help to the student of philosophy.



These Prolegomena are destined for the use, not of pupils, but of
future teachers, and even the latter should not expect that they will
be serviceable for the systematic exposition of a ready-made science,
but merely for the discovery of the science itself.

There are scholarly men, to whom the history of philosophy (both
ancient and modern) is philosophy itself; for these the present
Prolegomena are not written. They must wait till those who endeavor to
draw from the fountain of reason itself have completed their work; it
will then be the historian's turn to inform the world of what has been
done. Unfortunately, nothing can be said, which in their opinion has
not been said before, and truly the same prophecy applies to all
future time; for since the human reason has for many centuries
speculated upon innumerable objects in various ways, it is hardly to
be expected that we should not be able to discover analogies for every
new idea among the old sayings of past ages.

My object is to persuade all those who think Metaphysics worth
studying, that it is absolutely necessary to pause a moment, and,
neglecting all that has been done, to propose first the preliminary
question, ‘Whether such a thing as metaphysics be at all

If it be a science, how comes it that it cannot, like other sciences,
obtain universal and permanent recognition? If not, how can it
maintain its pretensions, and keep the human mind in suspense with
hopes, never ceasing, yet never fulfilled? Whether then we demonstrate
our knowledge or our ignorance in this field, we must come once for
all to a definite conclusion respecting the nature of this so-called
science, which cannot possibly remain on its present footing. It seems
almost ridiculous, while every other science is continually advancing,
that in this, which pretends to be Wisdom incarnate, for whose oracle
every one inquires, we should constantly move round the same spot,
without gaining a single step. And so its followers having melted
away, we do not find men confident of their ability to shine in other
sciences venturing their reputation here, where everybody, however
ignorant in other matters, may deliver a final verdict, as in this
domain there is as yet no standard weight and measure to distinguish
sound knowledge from shallow talk.

After all it is nothing extraordinary in the elaboration of a science,
when men begin to wonder how far it has advanced, that the question
should at last occur, whether and how such a science is possible?
Human reason so delights in constructions, that it has several times
built up a tower, and then razed it to examine the nature of the
foundation. It is never too late to become wise; but if the change
comes late, there is always more difficulty in starting a reform.

The question whether a science be possible, presupposes a doubt as to
its actuality. But such a doubt offends the men whose whole
possessions consist of this supposed jewel; hence he who raises the
doubt must expect opposition from all sides. Some, in the proud
consciousness of their possessions, which are ancient, and therefore
considered legitimate, will take their metaphysical compendia in their
hands, and look down on him with contempt; others, who never see
anything except it be identical with what they have seen before, will
not understand him, and everything will remain for a time, as if
nothing had happened to excite the concern, or the hope, for an
impending change.

Nevertheless, I venture to predict that the independent reader of
these Prolegomena will not only doubt his previous science, but
ultimately be fully persuaded, that it cannot exist unless the demands
here stated on which its possibility depends, be satisfied; and, as
this has never been done, that there is, as yet, no such thing as
Metaphysics. But as it can never cease to be in demand,{5}—since the
interests of common sense are intimately interwoven with it, he must
confess that a radical reform, or rather a new birth of the science
after an original plan, are unavoidable, however men may struggle
against it for a while.

{5} Says Horace:
"Rusticus expectat, dum defluat amnis, at ille
Labitur et labetur in omne volubilis aevum;"
"A rustic fellow waiteth on the shore
For the river to flow away,
But the river flows, and flows on as before,
And it flows forever and aye."

Since the Essays of Locke and Leibnitz, or rather since the origin of
metaphysics so far as we know its history, nothing has ever happened
which was more decisive to its fate than the attack made upon it by
David Hume. He threw no light on this species of knowledge, but he
certainly struck a spark from which light might have been obtained,
had it caught some inflammable substance and had its smouldering fire
been carefully nursed and developed.

Hume started from a single but important concept in Metaphysics, viz.,
that of Cause and Effect (including its derivatives force and action,
etc.). He challenges reason, which pretends to have given birth to
this idea from herself, to answer him by what right she thinks
anything to be so constituted, that if that thing be posited,
something else also must necessarily be posited; for this is the
meaning of the concept of cause. He demonstrated irrefutably that it
was perfectly impossible for reason to think a priori and by means of
concepts a combination involving necessity. We cannot at all see why,
in consequence of the existence of one thing, another must necessarily
exist, or how the concept of such a combination can arise a priori.
Hence he inferred, that reason was altogether deluded with reference
to this concept, which she erroneously considered as one of her
children, whereas in reality it was nothing but a bastard of
imagination, impregnated by experience, which subsumed certain
representations under the Law of Association, and mistook the
subjective necessity of habit for an objective necessity arising from
insight. Hence he inferred that reason had no power to think such
combinations, even generally, because her concepts would then be
purely fictitious, and all her pretended a priori cognitions nothing
but common experiences marked with a false stamp. In plain language
there is not, and cannot be, any such thing as metaphysics at all.{6}

{6} Nevertheless Hume called this very destructive science metaphysics
and attached to it great value. Metaphysics and morals [he declares in
the fourth part of his Essays] are the most important branches of
science; mathematics and physics are not nearly so important. But the
acute man merely regarded the negative use arising from the moderation
of extravagant claims of speculative reason, and the complete
settlement of the many endless and troublesome controversies that
mislead mankind. He overlooked the positive injury which results, if
reason be deprived of its most important prospects, which can alone
supply to the will the highest aim for all its endeavor.

However hasty and mistaken Hume's conclusion may appear, it was at
least founded upon investigation, and this investigation deserved the
concentrated attention of the brighter spirits of his day as well as
determined efforts on their part to discover, if possible, a happier
solution of the problem in the sense proposed by him, all of which
would have speedily resulted in a complete reform of the science.

But Hume suffered the usual misfortune of metaphysicians, of not being
understood. It is positively painful to see how utterly his opponents,
Reid, Oswald, Beattie, and lastly Priestley, missed the point of the
problem; for while they were ever taking for granted that which he
doubted, and demonstrating with zeal and often with impudence that
which he never thought of doubting, they so misconstrued his valuable
suggestion that everything remained in its old condition, as if
nothing had happened.

The question was not whether the concept of cause was right, useful,
and even indispensable for our knowledge of nature, for this Hume had
never doubted; but whether that concept could be thought by reason a
priori, and consequently whether it possessed an inner truth,
independent of all experience, implying a wider application than
merely to the objects of experience. This was Hume's problem. It was a
question concerning the origin, not concerning the indispensable need
of the concept. Were the former decided, the conditions of the use and
the sphere of its valid application would have been determined as a
matter of course.

But to satisfy the conditions of the problem, the opponents of the
great thinker should have penetrated very deeply into the nature of
reason, so far as it is concerned with pure thinking,—a task which
did not suit them. They found a more convenient method of being
defiant without any insight, viz., the appeal to common sense. It is
indeed a great gift of God, to possess right, or (as they now call it)
plain common sense. But this common sense must be shown practically,
by well-considered and reasonable thoughts and words, not by appealing
to it as an oracle, when no rational justification can be advanced. To
appeal to common sense, when insight and science fail, and no
sooner—this is one of the subtile discoveries of modern times, by
means of which the most superficial ranter can safely enter the lists
with the most thorough thinker, and hold his own. But as long as a
particle of insight remains, no one would think of having recourse to
this subterfuge. For what is it but an appeal to the opinion of the
multitude, of whose applause the philosopher is ashamed, while the
popular charlatan glories and confides in it? I should think that Hume
might fairly have laid as much claim to common sense as Beattie, and
in addition to a critical reason (such as the latter did not possess),
which keeps common sense in check and prevents it from speculating,
or, if speculations are under discussion, restrains the desire to
decide because it cannot satisfy itself concerning its own arguments.
By this means alone can common sense remain sound. Chisels and hammers
may suffice to work a piece of wood, but for steel-engraving we
require an engraver's needle. Thus common sense and speculative
understanding are each serviceable in their own way, the former in
judgments which apply immediately to experience, the latter when we
judge universally from mere concepts, as in metaphysics, where sound
common sense, so called in spite of the inapplicability of the word,
has no right to judge at all.

I openly confess, the suggestion of David Hume was the very thing,
which many years ago first interrupted my dogmatic slumber, and gave
my investigations in the field of speculative philosophy quite a new
direction. I was far from following him in the conclusions at which he
arrived by regarding, not the whole of his problem, but a part, which
by itself can give us no information. If we start from a well-founded,
but undeveloped, thought, which another has bequeathed to us, we may
well hope by continued reflection to advance farther than the acute
man, to whom we owe the first spark of light.

I therefore first tried whether Hume's objection could not be put into
a general form, and soon found that the concept of the connexion of
cause and effect was by no means the only idea by which the
understanding thinks the connexion of things a priori, but rather that
metaphysics consists altogether of such connexions. I sought to
ascertain their number, and when I had satisfactorily succeeded in
this by starting from a single principle, I proceeded to the deduction
of these concepts, which I was now certain were not deduced from
experience, as Hume had apprehended, but sprang from the pure
understanding. This deduction (which seemed impossible to my acute
predecessor, which had never even occurred to any one else, though no
one had hesitated to use the concepts without investigating the basis
of their objective validity) was the most difficult task ever
undertaken in the service of metaphysics; and the worst was that
metaphysics, such as it then existed, could not assist me in the
least, because this deduction alone can render metaphysics possible.
But as soon as I had succeeded in solving Hume's problem not merely in
a particular case, but with respect to the whole faculty of pure
reason, I could proceed safely, though slowly, to determine the whole
sphere of pure reason completely and from general principles, in its
circumference as well as in its contents. This was required for
metaphysics in order to construct its system according to a reliable

But I fear that the execution of Hume's problem in its widest extent
(viz., my Critique of the Pure Reason) will fare as the problem itself
fared, when first proposed. It will be misjudged because it is
misunderstood, and misunderstood because men choose to skim through
the book, and not to think through it—a disagreeable task, because
the work is dry, obscure, opposed to all ordinary notions, and
moreover long-winded. I confess, however, I did not expect to hear
from philosophers complaints of want of popularity, entertainment, and
facility, when the existence of a highly prized and indispensable
cognition is at stake, which cannot be established otherwise than by
the strictest rules of methodic precision. Popularity may follow, but
is inadmissible at the beginning. Yet as regards a certain obscurity,
arising partly from the diffuseness of the plan, owing to which the
principal points of the investigation are easily lost sight of, the
complaint is just, and I intend to remove it by the present

The first-mentioned work, which discusses the pure faculty of reason
in its whole compass and bounds, will remain the foundation, to which
the Prolegomena, as a preliminary exercise, refer; for our critique
must first be established as a complete and perfected science, before
we can think of letting Metaphysics appear on the scene, or even have
the most distant hope of attaining it.

We have been long accustomed to seeing antiquated knowledge produced
as new by taking it out of its former context, and reducing it to
system in a new suit of any fancy pattern under new titles. Most
readers will set out by expecting nothing else from the Critique; but
these Prolegomena may persuade him that it is a perfectly new science,
of which no one has ever even thought, the very idea of which was
unknown, and for which nothing hitherto accomplished can be of the
smallest use, except it be the suggestion of Hume's doubts. Yet ever,
he did not suspect such a formal science, but ran his ship ashore, for
safety's sake, landing on scepticism, there to let it lie and rot;
whereas my object is rather to give it a pilot, who, by means of safe
astronomical principles drawn from a knowledge of the globe, and
provided with a complete chart and compass, may steer the ship safely,
whither he listeth.

If in a new science, which is wholly isolated and unique in its kind,
we started with the prejudice that we can judge of things by means of
our previously acquired knowledge, which is precisely what has first
to be called in question, we should only fancy we saw everywhere what
we had already known, the expressions, having a similar sound, only
that all would appear utterly metamorphosed, senseless and
unintelligible, because we should have as a foundation our own
notions, made by long habit a second nature, instead of the author's.
But the longwindedness of the work, so far as it depends on the
subject, and not the exposition, its consequent unavoidable dryness
and its scholastic precision are qualities which can only benefit the
science, though they may discredit the book.

Few writers are gifted with the subtilty, and at the same time with
the grace, of David Hume, or with the depth, as well as the elegance,
of Moses Mendelssohn. Yet I flatter myself I might have made my own
exposition popular, had my object been merely to sketch out a plan and
leave its completion to others, instead of having my heart in the
welfare of the science, to which I had devoted myself so long; in
truth, it required no little constancy, and even self-denial, to
postpone the sweets of an immediate success to the prospect of a
slower, but more lasting, reputation.

Making plans is often the occupation of an opulent and boastful mind,
which thus obtains the reputation of a creative genius, by demanding
what it cannot itself supply; by censuring, what it cannot improve;
and by proposing, what it knows not where to find. And yet something
more should belong to a sound plan of a general critique of pure
reason than mere conjectures, if this plan is to be other than the
usual declamations of pious aspirations. But pure reason is a sphere
so separate and self-contained, that we cannot touch a part without
affecting all the rest. We can therefore do nothing without first
determining the position of each part, and its relation to the rest;
for, as our judgment cannot be corrected by anything without, the
validity and use of every part depends upon the relation in which it
stands to all the rest within the domain of reason.

So in the structure of an organized body, the end of each member can
only be deduced from the full conception of the whole. It may, then,
be said of such a critique that it is never trustworthy except it be
perfectly complete, down to the smallest elements of pure reason. In
the sphere of this faculty you can determine either everything or

But although a mere sketch, preceding the Critique of Pure Reason,
would be unintelligible, unreliable, and useless, it is all the more
useful as a sequel. For so we are able to grasp the whole, to examine
in detail the chief points of importance in the science, and to
improve in many respects our exposition, as compared with the first
execution of the work.

After the completion of the work I offer here such a plan which is
sketched out after an analytical method, while the work itself had to
be executed in the synthetical style, in order that the science may
present all its articulations, as the structure of a peculiar
cognitive faculty, in their natural combination. But should any reader
find this plan, which I publish as the Prolegomena to any future
Metaphysics, still obscure, let him consider that not every one is
bound to study Metaphysics, that many minds will succeed very well, in
the exact and even in deep sciences, more closely allied to practical
experience,{7} while they cannot succeed in investigations dealing
exclusively with abstract concepts. In such cases men should apply
their talents to other subjects. But he who undertakes to judge, or
still more, to construct, a system of Metaphysics, must satisfy the
demands here made, either by adopting my solution, or by thoroughly
refuting it, and substituting another. To evade it is impossible.

{7} The term Anschauung here used means sense-perception. It is that
which is given to the senses and apprehended immediately, as an object
is seen by merely looking at it. The translation intuition, though
etymologically correct, is misleading. In the present passage the term
is not used in its technical significance but means "practical

In conclusion, let it be remembered that this much-abused obscurity
(frequently serving as a mere pretext under which people hide their
own indolence or dullness) has its uses, since all who in other
sciences observe a judicious silence, speak authoritatively in
metaphysics and make bold decisions, because their ignorance is not
here contrasted with the knowledge of others. Yet it does contrast
with sound critical principles, which we may therefore commend in the
words of Virgil:

"Ignavum, fucos, pecus a praesepibus arcent."
"Bees are defending their hives against drones, those indolent



§ 1. Of the Sources of Metaphysics.

If it becomes desirable to formulate any cognition as science, it will
be necessary first to determine accurately those peculiar features
which no other science has in common with it, constituting its
characteristics; otherwise the boundaries of all sciences become
confused, and none of them can be treated thoroughly according to its

The characteristics of a science may consist of a simple difference of
object, or of the sources of cognition, or of the kind of cognition,
or perhaps of all three conjointly. On this, therefore, depends the
idea of a possible science and its territory.

First, as concerns the sources of metaphysical cognition, its very
concept implies that they cannot be empirical. Its principles
(including not only its maxims but its basic notions) must never be
derived from experience. It must not be physical but metaphysical
knowledge, viz., knowledge lying beyond experience. It can therefore
have for its basis neither external experience, which is the source of
physics proper, nor internal, which is the basis of empirical
psychology. It is therefore a priori knowledge, coming from pure
Understanding and pure Reason.

But so far Metaphysics would not be distinguish able from pure
Mathematics; it must therefore be called pure philosophical cognition;
and for the meaning of this term I refer to the Critique of the Pure
Reason (II. "Method of Transcendentalism," Chap. I., Sec. i), where
the distinction between these two employments of the reason is
sufficiently explained. So far concerning the sources of metaphysical

§ 2. Concerning the Kind of Cognition which can alone be called

a. Of the Distinction between Analytical and Synthetical Judgments in
general.—The peculiarity of its sources demands that metaphysical
cognition must consist of nothing but a priori judgments. But whatever
be their origin, or their logical form, there is a distinction in
judgments, as to their content, according to which they are either
merely explicative, adding nothing to the content of the cognition, or
expansive, increasing the given cognition: the former may be called
analytical, the latter synthetical, judgments.

Analytical judgments express nothing in the predicate but what has
been already actually thought in the concept of the subject, though
not so distinctly or with the same (full) consciousness. When I say:
All bodies are extended, I have not amplified in the least my concept
of body, but have only analysed it, as extension was really thought to
belong to that concept before the judgment was made, though it was not
expressed; this judgment is therefore analytical. On the contrary,
this judgment, All bodies have weight, contains in its predicate
something not actually thought in the general concept of the body; it
amplifies my knowledge by adding something to my concept, and must
therefore be called synthetical.

b. The Common Principle of all Analytical Judgments is the Law of
Contradiction.—All analytical judgments depend wholly on the law of
Contradiction, and are in their nature a priori cognitions, whether
the concepts that supply them with matter be empirical or not. For the
predicate of an affirmative analytical judgment is already contained
in the concept of the subject, of which it cannot be denied without
contradiction. In the same way its opposite is necessarily denied of
the subject in an analytical, but negative, judgment, by the same law
of contradiction. Such is the nature of the judgments: all bodies are
extended, and no bodies are unextended (i.e., simple).

For this very reason all analytical judgments are a priori even when
the concepts are empirical, as, for example, Gold is a yellow metal;
for to know this I require no experience beyond my concept of gold as
a yellow metal: it is, in fact, the very concept, and I need only
analyse it, without looking beyond it elsewhere.

c. Synthetical Judgments require a different Principle from the Law of
Contradiction.—There are synthetical a posteriori judgments of
empirical origin; but there are also others which are proved to be
certain a priori, and which spring from pure Understanding and Reason.
Yet they both agree in this, that they cannot possibly spring from the
principle of analysis, viz., the law of contradiction, alone; they
require a quite different principle, though, from whatever they may be
deduced, they must be subject to the law of contradiction, which must
never be violated, even though everything cannot be deduced from it. I
shall first classify synthetical judgments.

1. Empirical Judgments are always synthetical. For it would be absurd
to base an analytical judgment on experience, as our concept suffices
for the purpose without requiring any testimony from experience. That
body is extended, is a judgment established a priori, and not an
empirical judgment. For before appealing to experience, we already
have all the conditions of the judgment in the concept, from which we
have but to elicit the predicate according to the law of
contradiction, and thereby to become conscious of the necessity of the
judgment, which experience could not even teach us.

2. Mathematical Judgments are all synthetical. This fact seems
hitherto to have altogether escaped the observation of those who have
analysed human reason; it even seems directly opposed to all their
conjectures, though incontestably certain, and most important in its
consequences. For as it was found that the conclusions of
mathematicians all proceed according to the law of contradiction (as
is demanded by all apodeictic certainty), men persuaded themselves
that the fundamental principles were known from the same law. This was
a great mistake, for a synthetical proposition can indeed be
comprehended according to the law of contradiction, but only by
presupposing another synthetical proposition from which it follows,
but never in itself.

First of all, we must observe that all proper mathematical judgments
are a priori, and not empirical, because they carry with them
necessity, which cannot be obtained from experience. But if this be
not conceded to me, very good; I shall confine my assertion to pure
Mathematics, the very notion of which implies that it contains pure a
priori and not empirical cognitions.

It might at first be thought that the proposition 7 + 5 = 12 is a mere
analytical judgment, following from the concept of the sum of seven
and five, according to the law of contradiction. But on closer
examination it appears that the concept of the sum of 7 + 5 contains
merely their union in a single number, without its being at all
thought what the particular number is that unites them. The concept of
twelve is by no means thought by merely thinking of the combination of
seven and five; and analyse this possible sum as we may, we shall not
discover twelve in the concept. We must go beyond these concepts, by
calling to our aid some concrete image (Anschauung), i.e., either our
five fingers, or five points (as Segner has it in his Arithmetic), and
we must add successively the units of the five, given in some concrete
image (Anschauung), to the concept of seven. Hence our concept is
really amplified by the proposition 7 + 5 = 12, and we add to the
first a second, not thought in it. Arithmetical judgments are
therefore synthetical, and the more plainly according as we take
larger numbers; for in such cases it is clear that, however closely we
analyse our concepts without calling visual images (Anschauung) to our
aid, we can never find the sum by such mere dissection.

All principles of geometry are no less analytical. That a straight
line is the shortest path between two points, is a synthetical
proposition. For my concept of straight contains nothing of quantity,
but only a quality. The attribute of shortness is therefore altogether
additional, and cannot be obtained by any analysis of the concept.
Here, too, visualisation (Anschauung) must come to aid us. It alone
makes the synthesis possible.

Some other principles, assumed by geometers, are indeed actually
analytical, and depend on the law of contradiction; but they only
serve, as identical propositions, as a method of concatenation, and
not as principles, e.g., a = a, the whole is equal to itself, or a + b
> a, the whole is greater than its part. And yet even these, though
they are recognised as valid from mere concepts, are only admitted in
mathematics, because they can be represented in some visual form
(Anschauung). What usually makes us believe that the predicate of such
apodeictic{8} judgments is already contained in our concept, and that
the judgment is therefore analytical, is the duplicity of the
expression, requesting us to think a certain predicate as of necessity
implied in the thought of a given concept, which necessity attaches to
the concept. But the question is not what we are requested to join in
thought to the given concept, but what we actually think together with
and in it, though obscurely; and so it appears that the predicate
belongs to these concepts necessarily indeed, yet not directly but
indirectly by an added visualisation (Anschauung).

{8} The term apodeictic is borrowed by Kant from Aristotle who uses it
in the sense of "certain beyond dispute." The word is derived from
ἀποδείκνυμι (= I show) and is contrasted to dialectic
propositions, i.e., such statements as admit of controversy.—Ed.

§ 3. A Remark on the General Division of Judgments into Analytical
and Synthetical.

This division is indispensable, as concerns the Critique of human
understanding, and therefore deserves to be called classical, though
otherwise it is of little use, but this is the reason why dogmatic
philosophers, who always seek the sources of metaphysical judgments in
Metaphysics itself, and not apart from it, in the pure laws of reason
generally, altogether neglected this apparently obvious distinction.
Thus the celebrated Wolf, and his acute follower Baumgarten, came to
seek the proof of the principle of Sufficient Reason, which is clearly
synthetical, in the principle of Contradiction. In Locke's Essay,
however, I find an indication of my division. For in the fourth book
(chap. iii. § 9, seq.), having discussed the various connexions of
representations in judgments, and their sources, one of which he makes
"identity and contradiction" (analytical judgments), and another the
coexistence of representations in a subject, he confesses (§ 10) that
our a priori knowledge of the latter is very narrow, and almost
nothing. But in his remarks on this species of cognition, there is so
little of what is definite, and reduced to rules, that we cannot
wonder if no one, not even Hume, was led to make investigations
concerning this sort of judgments. For such general and yet definite
principles are not easily learned from other men, who have had them
obscurely in their minds. We must hit on them first by our own
reflexion, then we find them elsewhere, where we could not possibly
have found them at first, because the authors themselves did not know
that such an idea lay at the basis of their observations. Men who
never think independently have nevertheless the acuteness to discover
everything, after it has been once shown them, in what was said long
since, though no one ever saw it there before.

§ 4. The General Question of the Prolegomena.—Is Metaphysics at all

Were a metaphysics, which could maintain its place as a science,
really in existence; could we say, here is metaphysics, learn it, and
it will convince you irresistibly and irrevocably of its truth: this
question would be useless, and there would only remain that other
question (which would rather be a test of our acuteness, than a proof
of the existence of the thing itself), "How is the science possible,
and how does reason come to attain it?" But human reason has not been
so fortunate in this case. There is no single book to which you can
point as you do to Euclid, and say: This is Metaphysics; here you may
find the noblest objects of this science, the knowledge of a highest
Being, and of a future existence, proved from principles of pure
reason. We can be shown indeed many judgments, demonstrably certain,
and never questioned; but these are all analytical, and rather concern
the materials and the scaffolding for Metaphysics, than the extension
of knowledge, which is our proper object in studying it (§ 2). Even
supposing you produce synthetical judgments (such as the law of
Sufficient Reason, which you have never proved, as you ought to, from
pure reason a priori, though we gladly concede its truth), you lapse
when they come to be employed for your principal object, into such
doubtful assertions, that in all ages one Metaphysics has contradicted
another, either in its assertions, or their proofs, and thus has
itself destroyed its own claim to lasting assent. Nay, the very
attempts to set up such a science are the main cause of the early
appearance of scepticism, a mental attitude in which reason treats
itself with such violence that it could never have arisen save from
complete despair of ever satisfying our most important aspirations.
For long before men began to inquire into nature methodically, they
consulted abstract reason, which had to some extent been exercised by
means of ordinary experience; for reason is ever present, while laws
of nature must usually be discovered with labor. So Metaphysics
floated to the surface, like foam, which dissolved the moment it was
scooped off. But immediately there appeared a new supply on the
surface, to be ever eagerly gathered up by some, while others, instead
of seeking in the depths the cause of the phenomenon, thought they
showed their wisdom by ridiculing the idle labor of their neighbors.

The essential and distinguishing feature of pure mathematical
cognition among all other a priori cognitions is, that it cannot at
all proceed from concepts, but only by means of the construction of
concepts (see Critique II., Method of Transcendentalism, chap. I.,
sect. 1). As therefore in its judgments it must proceed beyond the
concept to that which its corresponding visualisation (Anschauung)
contains, these judgments neither can, nor ought to, arise
analytically, by dissecting the concept, but are all synthetical.

I cannot refrain from pointing out the disadvantage resulting to
philosophy from the neglect of this easy and apparently insignificant
observation. Hume being prompted (a task worthy of a philosopher) to
cast his eye over the whole field of a priori cognitions in which
human understanding claims such mighty possessions, heedlessly severed
from it a whole, and indeed its most valuable, province, viz., pure
mathematics; for he thought its nature, or, so to speak, the
state-constitution of this empire, depended on totally different
principles, namely, on the law of contradiction alone; and although he
did not divide Judgments in this manner formally and universally as I
have done here, what he said was equivalent to this: that mathematics
contains only analytical, but metaphysics synthetical, a priori
judgments. In this, however, he was greatly mistaken, and the mistake
had a decidedly injurious effect upon his whole conception. But for
this, he would have extended his question concerning the origin of our
synthetical judgments far beyond the metaphysical concept of
Causality, and included in it the possibility of mathematics a priori
also, for this latter he must have assumed to be equally synthetical.
And then he could not have based his metaphysical judgments on mere
experience without subjecting the axioms of mathematics equally to
experience, a thing which he was far too acute to do. The good company
into which metaphysics would thus have been brought, would have saved
it from the danger of a contemptuous ill-treatment, for the thrust
intended for it must have reached mathematics, which was not and could
not have been Hume's intention. Thus that acute man would have been
led into considerations which must needs be similar to those that now
occupy us, but which would have gained inestimably by his inimitably
elegant style.

Metaphysical judgments, properly so called, are all synthetical. We
must distinguish judgments pertaining to metaphysics from metaphysical
judgments properly so called. Many of the former are analytical, but
they only afford the means for metaphysical judgments, which are the
whole end of the science, and which are always synthetical. For if
there be concepts pertaining to metaphysics (as, for example, that of
substance), the judgments springing from simple analysis of them also
pertain to metaphysics, as, for example, substance is that which only
exists as subject; and by means of several such analytical judgments,
we seek to approach the definition of the concept. But as the analysis
of a pure concept of the understanding pertaining to metaphysics, does
not proceed in any different manner from the dissection of any other,
even empirical, concepts, not pertaining to metaphysics (such as: air
is an elastic fluid, the elasticity of which is not destroyed by any
known degree of cold), it follows that the concept indeed, but not the
analytical judgment, is properly metaphysical. This science has
something peculiar in the production of its a priori cognitions, which
must therefore be distinguished from the features it has in common
with other rational knowledge. Thus the judgment, that all the
substance in things is permanent, is a synthetical and properly
metaphysical judgment.

If the a priori principles, which constitute the materials of
metaphysics, have first been collected according to fixed principles,
then their analysis will be of great value; it might be taught as a
particular part (as a philosophia definitiva), containing nothing but
analytical judgments pertaining to metaphysics, and could be treated
separately from the synthetical which constitute metaphysics proper.
For indeed these analyses are not elsewhere of much value, except in
metaphysics, i.e., as regards the synthetical judgments, which are to
be generated by these previously analysed concepts.

The conclusion drawn in this section then is, that metaphysics is
properly concerned with synethetical propositions a priori, and these
alone constitute its end, for which it indeed requires various
dissections of its concepts, viz., of its analytical judgments, but
wherein the procedure is not different from that in every other kind
of knowledge, in which we merely seek to render our concepts distinct
by analysis. But the generation of a priori cognition by concrete
images as well as by concepts, in fine of synthetical propositions a
priori in philosophical cognition, constitutes the essential subject
of Metaphysics.

Weary therefore as well of dogmatism, which teaches us nothing, as of
scepticism, which does not even promise us anything, not even the
quiet state of a contented ignorance; disquieted by the importance of
knowledge so much needed; and lastly, rendered suspicious by long
experience of all knowledge which we believe we possess, or which
offers itself, under the title of pure reason: there remains but one
critical question on the answer to which our future procedure depends,
viz., Is Metaphysics at all possible? But this question must be
answered not by sceptical objections to the asseverations of some
actual system of metaphysics (for we do not as yet admit such a thing
to exist), but from the conception, as yet only problematical, of a
science of this sort.

In the Critique of Pure Reason I have treated this question
synthetically, by making inquiries into pure reason itself, and
endeavoring in this source to determine the elements as well as the
laws of its pure use according to principles. The task is difficult,
and requires a resolute reader to penetrate by degrees into a system,
based on no data except reason itself, and which therefore seeks,
without resting upon any fact, to unfold knowledge from its original
germs. Prolegomena, however, are designed for preparatory exercises;
they are intended rather to point out what we have to do in order if
possible to actualise a science, than to propound it. They must
therefore rest upon something already known as trustworthy, from which
we can set out with confidence, and ascend to sources as yet unknown,
the discovery of which will not only explain to us what we knew, but
exhibit a sphere of many cognitions which all spring from the same
sources. The method of Prolegomena, especially of those designed as a
preparation for future metaphysics, is consequently analytical.

But it happens fortunately, that though we cannot assume metaphysics
to be an actual science, we can say with confidence that certain pure
a priori synthetical cognitions, pure Mathematics and pure Physics are
actual and given; for both contain propositions, which are thoroughly
recognised as apodeictically certain, partly by mere reason, partly by
general consent arising from experience, and yet as independent of
experience. We have therefore some at least uncontested synthetical
knowledge a priori, and need not ask whether it be possible, for it is
actual, but how it is possible, in order that we may deduce from the
principle which makes the given cognitions possible the possibility of
all the rest.

The General Problem: How is Cognition from Pure Reason Possible?

§ 5. We have above learned the significant distinction between
analytical and synthetical judgments. The possibility of analytical
propositions was easily comprehended, being entirely founded on the
law of Contradiction. The possibility of synthetical a posteriori
judgments, of those which are gathered from experience, also requires
no particular explanation; for experience is nothing but a continual
synthesis of perceptions. There remain therefore only synthetical
propositions a priori, of which the possibility must be sought or
investigated, because they must depend upon other principles than the
law of contradiction.

But here we need not first establish the possibility of such
propositions so as to ask whether they are possible. For there are
enough of them which indeed are of undoubted certainty, and as our
present method is analytical, we shall start from the fact, that such
synthetical but purely rational cognition actually exists; but we must
now inquire into the reason of this possibility, and ask, how such
cognition is possible, in order that we may from the principles of its
possibility be enabled to determine the conditions of its use, its
sphere and its limits. The proper problem upon which all depends, when
expressed with scholastic precision, is therefore:

How are Synthetic Propositions a priori possible?

For the sake of popularity I have above expressed this problem
somewhat differently, as an inquiry into purely rational cognition,
which I could do for once without detriment to the desired
comprehension, because, as we have only to do here with metaphysics
and its sources, the reader will, I hope, after the fore going
remarks, keep in mind that when we speak of purely rational cognition,
we do not mean analytical, but synthetical cognition.{9}

{9} It is unavoidable that as knowledge advances, certain expressions
which have become classical, after having been used since the infancy
of science, will be found inadequate and unsuitable, and a newer and
more appropriate application of the terms will give rise to confusion.
[This is the case with the term "analytical."] The analytical method,
so far as it is opposed to the synthetical, is very different from
that which constitutes the essence of analytical propositions: it
signifies only that we start from what is sought, as if it were given,
and ascend to the only conditions under which it is possible. In this
method we often use nothing but synthetical propositions, as in
mathematical analysis, and it were better to term it the regressive
method, in contradistinction to the synthetic or progressive. A
principal part of Logic too is distinguished by the name of Analytics,
which here signifies the logic of truth in contrast to Dialectics,
without considering whether the cognitions belonging to it are
analytical or synthetical.

Metaphysics stands or falls with the solution of this problem: its
very existence depends upon it. Let any one make metaphysical
assertions with ever so much plausibility, let him overwhelm us with
conclusions, if he has not previously proved able to answer this
question satisfactorily, I have a right to say: this is all vain
baseless philosophy and false wisdom. You speak through pure reason,
and claim, as it were to create cognitions a priori by not only
dissecting given concepts, but also by asserting connexions which do
not rest upon the law of contradiction, and which you believe you
conceive quite independently of all experience; how do you arrive at
this, and how will you justify your pretensions? An appeal to the
consent of the common sense of mankind cannot be allowed; for that is
a witness whose authority depends merely upon rumor. Says Horace:

"Quodcunque ostendis mihi sic, incredulus odi."

"To all that which thou provest me thus, I refuse to give credence."

The answer to this question, though indispensable, is difficult; and
though the principal reason that it was not made long ago is, that the
possibility of the question never occurred to anybody, there is yet
another reason, which is this that a satisfactory answer to this one
question requires a much more persistent, profound, and painstaking
reflexion, than the most diffuse work on Metaphysics, which on its
first appearance promised immortality to its author. And every
intelligent reader, when he carefully reflects what this problem
requires, must at first be struck with its difficulty, and would
regard it as insoluble and even impossible, did there not actually
exist pure synthetical cognitions a priori. This actually happened to
David Hume, though he did not conceive the question in its entire
universality as is done here, and as must be done, should the answer
be decisive for all Metaphysics. For how is it possible, says that
acute man, that when a concept is given me, I can go beyond it and
connect with it another, which is not contained in it, in such a
manner as if the latter necessarily belonged to the former? Nothing
but experience can furnish us with such connexions (thus he concluded
from the difficulty which he took to be an impossibility), and all
that vaunted necessity, or, what is the same thing, all cognition
assumed to be a priori, is nothing but a long habit of accepting
something as true, and hence of mistaking subjective necessity for

Should my reader complain of the difficulty and the trouble which I
occasion him in the solution of this problem, he is at liberty to
solve it himself in an easier way. Perhaps he will then feel under
obligation to the person who has undertaken for him a labor of so
profound research, and will rather be surprised at the facility with
which, considering the nature of the subject, the solution has been
attained. Yet it has cost years of work to solve the problem in its
whole universality (using the term in the mathematical sense, viz.,
for that which is sufficient for all cases), and finally to exhibit it
in the analytical form, as the reader finds it here.

All metaphysicians are therefore solemnly and legally suspended from
their occupations till they shall have answered in a satisfactory
manner the question, "How are synthetic cognitions a priori possible?"
For the answer contains which they must show when they have anything
to offer in the name of pure reason. But if they do not possess these
credentials, they can expect nothing else of reasonable people, who
have been deceived so often, than to be dismissed without further ado.

If they on the other hand desire to carry on their business, not as a
science, but as an art of wholesome oratory suited to the common sense
of man, they cannot in justice be prevented. They will then speak the
modest language of a rational belief, they will grant that they are
not allowed even to conjecture, far less to know, anything which lies
beyond the bounds of all possible experience, but only to assume (not
for speculative use, which they must abandon, but for practical
purposes only) the existence of something that is possible and even
indispensable for the guidance of the understanding and of the will in
life. In this manner alone can they be called useful and wise men, and
the more so as they renounce the title of metaphysicians; for the
latter profess to be speculative philosophers, and since, when
judgments a priori are under discussion, poor probabilities cannot be
admitted (for what is declared to be known a priori is thereby
announced as necessary), such men cannot be permitted to play with
conjectures, but their assertions must be either science, or are worth
nothing at all.

It may be said, that the entire transcendental philosophy, which
necessarily precedes all metaphysics, is nothing but the complete
solution of the problem here propounded, in systematical order and
completeness, and hitherto we have never had any transcendental
philosophy; for what goes by its name is properly a part of
metaphysics, whereas the former science is intended first to
constitute the possibility of the latter, and must therefore precede
all metaphysics. And it is not surprising that when a whole science,
deprived of all help from other sciences, and consequently in itself
quite new, is required to answer a single question satisfactorily, we
should find the answer troublesome and difficult, nay even shrouded in

As we now proceed to this solution according to the analytical method,
in which we assume that such cognitions from pure reasons actually
exist, we can only appeal to two sciences of theoretical cognition
(which alone is under consideration here), pure mathematics and pure
natural science (physics). For these alone can exhibit to us objects
in a definite and actualisable form (in der Anschauung), and
consequently (if there should occur in them a cognition a priori) can
show the truth or conformity of the cognition to the object in
concreto, that is, its actuality, from which we could proceed to the
reason of its possibility by the analytic method. This facilitates our
work greatly for here universal considerations are not only applied to
facts, but even start from them, while in a synthetic procedure they
must strictly be derived in abstracto from concepts.

But, in order to rise from these actual and at the same time
well-grounded pure cognitions a priori to such a possible cognition of
the same as we are seeking, viz., to metaphysics as a science, we must
comprehend that which occasions it, I mean the mere natural, though in
spite of its truth not unsuspected, cognition a priori which lies at
the bottom of that science, the elaboration of which without any
critical investigation of its possibility is commonly called
metaphysics. In a word, we must comprehend the natural conditions of
such a science as a part of our inquiry, and thus the transcendental
problem will be gradually answered by a division into four questions:

1. How is pure mathematics possible?
2. How is pure natural science possible?
3. How is metaphysics in general possible?
4. How is metaphysics as a science possible?

It may be seen that the solution of these problems, though chiefly
designed to exhibit the essential matter of the Critique, has yet
something peculiar, which for itself alone deserves attention. This is
the search for the sources of given sciences in reason itself, so that
its faculty of knowing something a priori may by its own deeds be
investigated and measured. By this procedure these sciences gain, if
not with regard to their contents, yet as to their proper use, and
while they throw light on the higher question concerning their common
origin, they give, at the same time, an occasion better to explain
their own nature.



§ 6.

Here is a great and established branch of knowledge, encompassing even
now a wonderfully large domain and promising an unlimited extension in
the future. Yet it carries with it thoroughly apodeictical certainty,
i.e., absolute necessity, which therefore rests upon no empirical
grounds. Consequently it is a pure product of reason, and moreover is
thoroughly synthetical. [Here the question arises:]

"How then is it possible for human reason to produce a cognition of
this nature entirely a priori?"

Does not this faculty [which produces mathematics], as it neither is
nor can be based upon experience, presuppose some ground of cognition
a priori, which lies deeply hidden, but which might reveal itself by
these its effects, if their first beginnings were but diligently
ferreted out?

§ 7. But we find that all mathematical cognition has this
peculiarity: it must first exhibit its concept in a visual form
(Anschauung) and indeed a priori, therefore in a visual form which is
not empirical, but pure. Without this mathematics cannot take a single
step; hence its judgments are always visual, viz., "intuitive";
whereas philosophy must be satisfied with discursive judgments from
mere concepts, and though it may illustrate its doctrines through a
visual figure, can never derive them from it. This observation on the
nature of mathematics gives us a clue to the first and highest
condition of its possibility, which is, that some non-sensuous
visualisation (called pure intuition, or reine Anschauung) must form
its basis, in which all its concepts can be exhibited or constructed,
in concreto and yet a priori. If we can find out this pure intuition
and its possibility, we may thence easily explain how synthetical
propositions a priori are possible in pure mathematics, and
consequently how this science itself is possible. Empirical intuition
[viz., sense-perception] enables us without difficulty to enlarge the
concept which we frame of an object of intuition [or
sense-perception], by new predicates, which intuition [i.e.,
sense-perception] itself presents synthetically in experience. Pure
intuition [viz., the visualisation of forms in our imagination, from
which every thing sensual, i.e., every thought of material qualities,
is excluded] does so likewise, only with this difference, that in the
latter case the synthetical judgment is a priori certain and
apodeictical, in the former, only a posteriori and empirically
certain; because this latter contains only that which occurs in
contingent empirical intuition, but the former, that which must
necessarily be discovered in pure intuition. Here intuition, being an
intuition a priori, is before all experience, viz., before any
perception of particular objects, inseparably conjoined with its

§ 8. But with this step our perplexity seems rather to increase than
to lessen. For the question now is, "How is it possible to intuite [in
a visual form] anything a priori?" An intuition [viz., a visual
sense-perception] is such a representation as immediately depends upon
the presence of the object. Hence it seems impossible to intuite from
the outset a priori, because intuition would in that event take place
without either a former or a present object to refer to, and by
consequence could not be intuition. Concepts indeed are such, that we
can easily form some of them a priori, viz., such as contain nothing
but the thought of an object in general; and we need not find
ourselves in an immediate relation to the object. Take, for instance,
the concepts of Quantity, of Cause, etc. But even these require, in
order to make them under stood, a certain concrete use—that is, an
application to some sense-experience (Anschauung), by which an object
of them is given us. But how can the intuition of the object [its
visualisation] precede the object itself?

§ 9. If our intuition [i.e., our sense-experience] were perforce of
such a nature as to represent things as they are in themselves, there
would not be any intuition a priori, but intuition would be always
empirical. For I can only know what is contained in the object in
itself when it is present and given to me. It is indeed even then
incomprehensible how the visualising (Anschauung) of a present thing
should make me know this thing as it is in itself, as its properties
cannot migrate into my faculty of representation. But even granting
this possibility, a visualising of that sort would not take place a
priori, that is, before the object were presented to me; for without
this latter fact no reason of a relation between my representation and
the object can be imagined, unless it depend upon a direct

Therefore in one way only can my intuition (Anschauung) anticipate the
actuality of the object, and be a cognition a priori, viz.: if my
intuition contains nothing but the form of sensibility, antedating in
my subjectivity all the actual impressions through which I am affected
by objects.

For that objects of sense can only be intuited according to this form
of sensibility I can know a priori. Hence it follows: that
propositions, which concern this form of sensuous intuition only, are
possible and valid for objects of the senses; as also, conversely,
that intuitions which are possible a priori can never concern any
other things than objects of our senses.{10}

{10} This whole paragraph (§ 9) will be better understood when compared
with Remark I., following this section, appearing in the present
edition on page 40.—Ed.

§ 10. Accordingly, it is only the form of the sensuous intuition by
which we can intuite things a priori, but by which we can know objects
only as they appear to us (to our senses), not as they are in
themselves; and this assumption is absolutely necessary if synthetical
propositions a priori be granted as possible, or if, in case they
actually occur, their possibility is to be comprehended and determined

Now, the intuitions which pure mathematics lays at the foundation of
all its cognitions and judgments which appear at once apodeictic and
necessary are Space and Time. For mathematics must first have all its
concepts in intuition, and pure mathematics in pure intuition, that
is, it must construct them. If it proceeded in any other way, it would
be impossible to make any headway, for mathematics proceeds, not
analytically by dissection of concepts, but synthetically, and if pure
intuition be wanting, there is nothing in which the matter for
synthetical judgments a priori can be given. Geometry is based upon
the pure intuition of space. Arithmetic accomplishes its concept of
number by the successive addition of units in time; and pure mechanics
especially cannot attain its concepts of motion without employing the
representation of time. Both representations, however, are only
intuitions; for if we omit from the empirical intuitions of bodies and
their alterations (motion) everything empirical, or belonging to
sensation, space and time still remain, which are therefore pure
intuitions that lie a priori at the basis of the empirical. Hence they
can never be omitted, but at the same time, by their being pure
intuitions a priori, they prove that they are mere forms of our
sensibility, which must precede all empirical intuition, or perception
of actual objects, and conformably to which objects can be known a
priori, but only as they appear to us.

§ 11. The problem of the present section is therefore solved. Pure
mathematics, as synthetical cognition a priori, is only possible by
referring to no other objects than those of the senses. At the basis
of their empirical intuition lies a pure intuition (of space and of
time) which is a priori. This is possible, because the latter
intuition is nothing but the mere form of sensibility, which precedes
the actual appearance of the objects, in that it, in fact, makes them
possible. Yet this faculty of intuiting a priori affects not the
matter of the phenomenon (that is, the sense-element in it, for this
constitutes that which is empirical), but its form, viz., space and
time. Should any man venture to doubt that these are determinations
adhering not to things in themselves, but to their relation to our
sensibility, I should be glad to know how it can be possible to know
the constitution of things a priori, viz., before we have any
acquaintance with them and before they are presented to us. Such,
however, is the case with space and time. But this is quite
comprehensible as soon as both count for nothing more than formal
conditions of our sensibility, while the objects count merely as
phenomena; for then the form of the phenomenon, i.e., pure intuition,
can by all means be represented as proceeding from ourselves, that is,
a priori.

§ 12. In order to add something by way of illustration and
confirmation, we need only watch the ordinary and necessary procedure
of geometers. All proofs of the complete congruence of two given
figures (where the one can in every respect be substituted for the
other) come ultimately to this that they may be made to coincide;
which is evidently nothing else than a synthetical proposition resting
upon immediate intuition, and this intuition must be pure, or given a
priori, otherwise the proposition could not rank as apodeictically
certain, but would have empirical certainty only. In that case, it
could only be said that it is always found to be so, and holds good
only as far as our perception reaches. That everywhere space (which
[in its entirety] is itself no longer the boundary of another space)
has three dimensions, and that space cannot in any way have more, is
based on the proposition that not more than three lines can intersect
at right angles in one point; but this proposition cannot by any means
be shown from concepts, but rests immediately on intuition, and indeed
on pure and a priori intuition, because it is apodeictically certain.
That we can require a line to be drawn to infinity (in indefinitum),
or that a series of changes (for example, spaces traversed by motion)
shall be infinitely continued, presupposes a representation of space
and time, which can only attach to intuition, namely, so far as it in
itself is bounded by nothing, for from concepts it could never be
inferred. Consequently, the basis of mathematics actually are pure
intuitions, which make its synthetical and apodeictically valid
propositions possible. Hence our transcendental deduction of the
notions of space and of time explains at the same time the possibility
of pure mathematics. Without some such deduction its truth may be
granted, but its existence could by no means be understood, and we
must assume "that everything which can be given to our senses (to the
external senses in space, to the internal one in time) is intuited by
us as it appears to us, not as it is in itself."

§ 13. Those who cannot yet rid themselves of the notion that space
and time are actual qualities inhering in things in themselves, may
exercise their acumen on the following paradox. When they have in vain
attempted its solution, and are free from prejudices at least for a
few moments, they will suspect that the degradation of space and of
time to mere forms of our sensuous intuition may perhaps be well

If two things are quite equal in all respects as much as can be
ascertained by all means possible, quantitatively and qualitatively,
it must follow, that the one can in all cases and under all
circumstances replace the other, and this substitution would not
occasion the least perceptible difference. This in fact is true of
plane figures in geometry; but some spherical figures exhibit,
notwithstanding a complete internal agreement, such a contrast in
their external relation, that the one figure cannot possibly be put in
the place of the other. For instance, two spherical triangles on
opposite hemispheres, which have an arc of the equator as their common
base, may be quite equal, both as regards sides and angles, so that
nothing is to be found in either, if it be described for itself alone
and completed, that would not equally be applicable to both; and yet
the one cannot be put in the place of the other (being situated upon
the opposite hemisphere). Here then is an internal difference between
the two triangles, which difference our understanding cannot describe
as internal, and which only manifests itself by external relations in

But I shall adduce examples, taken from common life, that are more
obvious still.

What can be more similar in every respect and in every part more alike
to my hand and to my ear, than their images in a mirror? And yet I
cannot put such a hand as is seen in the glass in the place of its
archetype; for if this is a right hand, that in the glass is a left
one, and the image or reflexion of the right ear is a left one which
never can serve as a substitute for the other. There are in this case
no internal differences which our understanding could determine by
thinking alone. Yet the differences are internal as the senses teach,
for, notwithstanding their complete equality and similarity, the left
hand cannot be enclosed in the same bounds as the right one (they are
not congruent); the glove of one hand cannot be used for the other.
What is the solution? These objects are not representations of things
as they are in themselves, and as the pure understanding would cognise
them, but sensuous intuitions, that is, appearances, the possibility
of which rests upon the relation of certain things unknown in
themselves to something else, viz., to our sensibility. Space is the
form of the external intuition of this sensibility, and the internal
determination of every space is only possible by the determination of
its external relation to the whole space, of which it is a part (in
other words, by its relation to the external sense). That is to say,
the part is only possible through the whole, which is never the case
with things in themselves, as objects of the mere understanding, but
with appearances only. Hence the difference between similar and equal
things, which are yet not congruent (for instance, two symmetric
helices), cannot be made intelligible by any concept, but only by the
relation to the right and the left hands which immediately refers to

Remark I.

Pure Mathematics, and especially pure geometry, can only have
objective reality on condition that they refer to objects of sense.
But in regard to the latter the principle holds good, that our sense
representation is not a representation of things in themselves, but of
the way in which they appear to us. Hence it follows, that the
propositions of geometry are not the results of a mere creation of our
poetic imagination, and that therefore they cannot be referred with
assurance to actual objects; but rather that they are necessarily
valid of space, and consequently of all that may be found in space,
because space is nothing else than the form of all external
appearances, and it is this form alone in which objects of sense can
be given. Sensibility, the form of which is the basis of geometry, is
that upon which the possibility of external appearance depends.
Therefore these appearances can never contain anything but what
geometry prescribes to them.

It would be quite otherwise if the senses were so constituted as to
represent objects as they are in themselves. For then it would not by
any means follow from the conception of space, which with all its
properties serves to the geometer as an a priori foundation, together
with what is thence inferred, must be so in nature. The space of the
geometer would be considered a mere fiction, and it would not be
credited with objective validity, because we cannot see how things
must of necessity agree with an image of them, which we make
spontaneously and previous to our acquaintance with them. But if this
image, or rather this formal intuition, is the essential property of
our sensibility, by means of which alone objects are given to us, and
if this sensibility represents not things in themselves, but their
appearances: we shall easily comprehend, and at the same time
indisputably prove, that all external objects of our world of sense
must necessarily coincide in the most rigorous way with the
propositions of geometry; because sensibility by means of its form of
external intuition, viz., by space, the same with which the geometer
is occupied, makes those objects at all possible as mere appearances.

It will always remain a remarkable phenomenon in the history of
philosophy, that there was a time, when even mathematicians, who at
the same time were philosophers, began to doubt, not of the accuracy
of their geometrical propositions so far as they concerned space, but
of their objective validity and the applicability of this concept
itself, and of all its corollaries, to nature. They showed much
concern whether a line in nature might not consist of physical points,
and consequently that true space in the object might consist of simple
[discrete] parts, while the space which the geometer has in his mind
[being continuous] cannot be such. They did not recognise that this
mental space renders possible the physical space, i.e., the extension
of matter; that this pure space is not at all a quality of things in
themselves, but a form of our sensuous faculty of representation; and
that all objects in space are mere appearances, i.e., not things in
themselves but representations of our sensuous intuition. But such is
the case, for the space of the geometer is exactly the form of
sensuous intuition which we find a priori in us, and contains the
ground of the possibility of all external appearances (according to
their form), and the latter must necessarily and most rigidly agree
with the propositions of the geometer, which he draws not from any
fictitious concept, but from the subjective basis of all external
phenomena, which is sensibility itself. In this and no other way can
geometry be made secure as to the undoubted objective reality of its
propositions against all the intrigues of a shallow Metaphysics, which
is surprised at them [the geometrical propositions], because it has
not traced them to the sources of their concepts.

Remark II.

Whatever is given us as object, must be given us in intuition. All our
intuition however takes place by means of the senses only; the
understanding intuites nothing, but only reflects. And as we have just
shown that the senses never and in no manner enable us to know things
in themselves, but only their appearances, which are mere
representations of the sensibility, we conclude that 'all bodies,
together with the space in which they are, must be considered nothing
but mere representations in us, and exist nowhere but in our
thoughts.' You will say: Is not this manifest idealism?

Idealism consists in the assertion, that there are none but thinking
beings, all other things, which we think are perceived in intuition,
being nothing but representations in the thinking beings, to which no
object external to them corresponds in fact. Whereas I say, that
things as objects of our senses existing outside us are given, but we
know nothing of what they may be in themselves, knowing only their
appearances, i.e., the representations which they cause in us by
affecting our senses. Consequently I grant by all means that there are
bodies without us, that is, things which, though quite unknown to us
as to what they are in themselves, we yet know by the representations
which their influence on our sensibility procures us, and which we
call bodies, a term signifying merely the appearance of the thing
which is unknown to us, but not therefore less actual. Can this be
termed idealism? It is the very contrary.

Long before Locke's time, but assuredly since him, it has been
generally assumed and granted without detriment to the actual
existence of external things, that many of their predicates may be
said to belong not to the things in themselves, but to their
appearances, and to have no proper existence outside our
representation. Heat, color, and taste, for instance, are of this
kind. Now, if I go farther, and for weighty reasons rank as mere
appearances the remaining qualities of bodies also, which are called
primary, such as extension, place, and in general space, with all that
which belongs to it (impenetrability or materiality, space, etc.)—no
one in the least can adduce the reason of its being inadmissible. As
little as the man who admits colors not to be properties of the object
in itself, but only as modifications of the sense of sight, should on
that account be called an idealist, so little can my system be named
idealistic, merely because I find that more, nay,

All the properties which constitute the intuition of a body belong
merely to its appearance.

The existence of the thing that appears is thereby not destroyed, as
in genuine idealism, but it is only shown, that we cannot possibly
know it by the senses as it is in itself.

I should be glad to know what my assertions must be in order to avoid
all idealism. Undoubtedly, I should say, that the representation of
space is not only perfectly conformable to the relation which our
sensibility has to objects—that I have said—but that it is quite
similar to the object,—an assertion in which I can find as little
meaning as if I said that the sensation of red has a similarity to the
property of vermilion, which in me excites this sensation.

Remark III.

Hence we may at once dismiss an easily foreseen but futile objection,
"that by admitting the ideality of space and of time the whole
sensible world would be turned into mere sham." At first all
philosophical insight into the nature of sensuous cognition was
spoiled, by making the sensibility merely a confused mode of
representation, according to which we still know things as they are,
but without being able to reduce everything in this our representation
to a clear consciousness; whereas proof is offered by us that
sensibility consists, not in this logical distinction of clearness and
obscurity, but in the genetical one of the origin of cognition itself.
For sensuous perception represents things not at all as they are, but
only the mode in which they affect our senses, and consequently by
sensuous perception appearances only and not things themselves are
given to the understanding for reflexion. After this necessary
corrective, an objection rises from an unpardonable and almost
intentional misconception, as if my doctrine turned all the things of
the world of sense into mere illusion.

When an appearance is given us, we are still quite free as to how we
should judge the matter. The appearance depends upon the senses, but
the judgment upon the understanding, and the only question is, whether
in the determination of the object there is truth or not. But the
difference between truth and dreaming is not ascertained by the nature
of the representations, which are referred to objects (for they are
the same in both cases), but by their connexion according to those
rules, which determine the coherence of the representations in the
concept of an object, and by ascertaining whether they can subsist
together in experience or not. And it is not the fault of the
appearances if our cognition takes illusion for truth, i.e., if the
intuition, by which an object is given us, is considered a concept of
the thing or of its existence also, which the understanding can only
think. The senses represent to us the paths of the planets as now
progressive, now retrogressive, and herein is neither falsehood nor
truth, because as long as we hold this path to be nothing but
appearance, we do not judge of the objective nature of their motion.
But as a false judgment may easily arise when the understanding is not
on its guard against this subjective mode of representation being
considered objective, we say they appear to move backward; it is not
the senses however which must be charged with the illusion, but the
understanding, whose province alone it is to give an objective
judgment on appearances.

Thus, even if we did not at all reflect on the origin of our
representations, whenever we connect our intuitions of sense (whatever
they may contain), in space and in time, according to the rules of the
coherence of all cognition in experience, illusion or truth will arise
according as we are negligent or careful. It is merely a question of
the use of sensuous representations in the understanding, and not of
their origin. In the same way, if I consider all the representations
of the senses, together with their form, space and time, to be nothing
but appearances, and space and time to be a mere form of the
sensibility, which is not to be met with in objects out of it, and if
I make use of these representations in reference to possible
experience only, there is nothing in my regarding them as appearances
that can lead astray or cause illusion. For all that they can
correctly cohere according to rules of truth in experience. Thus all
the propositions of geometry hold good of space as well as of all the
objects of the senses, consequently of all possible experience,
whether I consider space as a mere form of the sensibility, or as
something cleaving to the things themselves. In the former case
however I comprehend how I can know a priori these propositions
concerning all the objects of external intuition. Otherwise,
everything else as regards all possible experience remains just as if
I had not departed from the vulgar view.

But if I venture to go beyond all possible experience with my notions
of space and time, which I cannot refrain from doing if I proclaim
them qualities inherent in things in themselves (for what should
prevent me from letting them hold good of the same things, even though
my senses might be different, and unsuited to them?), then a grave
error may arise due to illusion, for thus I would proclaim to be
universally valid what is merely a subjective condition of the
intuition of things and sure only for all objects of sense, viz., for
all possible experience; I would refer this condition to things in
themselves, and do not limit it to the conditions of experience.

My doctrine of the ideality of space and of time, therefore, far from
reducing the whole sensible world to mere illusion, is the only means
of securing the application of one of the most important cognitions
(that which mathematics propounds a priori) to actual objects, and of
preventing its being regarded as mere illusion. For without this
observation it would be quite impossible to make out whether the
intuitions of space and time, which we borrow from no experience, and
which yet lie in our representation a priori, are not mere phantasms
of our brain, to which objects do not correspond, at least not
adequately, and consequently, whether we have been able to show its
unquestionable validity with regard to all the objects of the sensible
world just because they are mere appearances.

Secondly, though these my principles make appearances of the
representations of the senses, they are so far from turning the truth
of experience into mere illusion, that they are rather the only means
of preventing the transcendental illusion, by which metaphysics has
hitherto been deceived, leading to the childish endeavor of catching
at bubbles, because appearances, which are mere representations, were
taken for things in themselves. Here originated the remarkable event
of the antimony of Reason which I shall mention by and by, and which
is destroyed by the single observation, that appearance, as long as it
is employed in experience, produces truth, but the moment it
transgresses the bounds of experience, and consequently becomes
transcendent, produces nothing but illusion.

Inasmuch, therefore, as I leave to things as we obtain them by the
senses their actuality, and only limit our sensuous intuition of these
things to this, that they represent in no respect, not even in the
pure intuitions of space and of time, anything more than mere
appearance of those things, but never their constitution in
themselves, this is not a sweeping illusion invented for nature by me.
My protestation too against all charges of idealism is so valid and
clear as even to seem superfluous, were there not incompetent judges,
who, while they would have an old name for every deviation from their
perverse though common opinion, and never judge of the spirit of
philosophic nomenclature, but cling to the letter only, are ready to
put their own conceits in the place of well-defined notions, and
thereby deform and distort them. I have myself given this my theory
the name of transcendental idealism, but that cannot authorise any one
to confound it either with the empirical idealism of Descartes,
(indeed, his was only an insoluble problem, owing to which he thought
every one at liberty to deny the existence of the corporeal world,
because it could never be proved satisfactorily), or with the mystical
and visionary idealism of Berkeley, against which and other similar
phantasms our Critique contains the proper antidote. My idealism
concerns not the existence of things (the doubting of which, however,
constitutes idealism in the ordinary sense), since it never came into
my head to doubt it, but it concerns the sensuous representation of
things, to which space and time especially belong. Of these [viz.,
space and time], consequently of all appearances in general, I have
only shown, that they are neither things (but mere modes of
representation), nor determinations belonging to things in themselves.
But the word "transcendental," which with me means a reference of our
cognition, i.e., not to things, but only to the cognitive faculty, was
meant to obviate this misconception. Yet rather than give further
occasion to it by this word, I now retract it, and desire this
idealism of mine to be called critical. But if it be really an
objectionable idealism to convert actual things (not appearances) into
mere representations, by what name shall we call him who conversely
changes mere representations to things? It may, I think, be called
"dreaming idealism," in contradistinction to the former, which may be
called "visionary," both of which are to be refuted by my
transcendental, or, better, critical idealism.



§ 14.

Nature is the existence of things, so far as it is determined
according to universal laws. Should nature signify the existence of
things in themselves, we could never cognise it either a priori or a
posteriori. Not a priori, for how can we know what belongs to things
in themselves, since this never can be done by the dissection of our
concepts (in analytical judgments)? We do not want to know what is
contained in our concept of a thing (for the [concept describes what]
belongs to its logical being), but what is in the actuality of the
thing superadded to our concept, and by what the thing itself is
determined in its existence outside the concept. Our understanding,
and the conditions on which alone it can connect the determinations of
things in their existence, do not prescribe any rule to things
themselves; these do not conform to our understanding, but it must
conform itself to them; they must therefore be first given us in order
to gather these determinations from them, wherefore they would not be
cognised a priori.

A cognition of the nature of things in themselves a posteriori would
be equally impossible. For, if experience is to teach us laws, to
which the existence of things is subject, these laws, if they regard
things in themselves, must belong to them of necessity even outside
our experience. But experience teaches us what exists and how it
exists, but never that it must necessarily exist so and not otherwise.
Experience therefore can never teach us the nature of things in

§ 15. We nevertheless actually possess a pure science of nature in
which are propounded, a priori and with all the necessity requisite to
apodeictical propositions, laws to which nature is subject. I need
only call to witness that propaedeutic of natural science which, under
the title of the universal Science of Nature, precedes all Physics
(which is founded upon empirical principles). In it we have
Mathematics applied to appearance, and also merely discursive
principles (or those derived from concepts), which constitute the
philosophical part of the pure cognition of nature. But there are
several things in it, which are not quite pure and independent of
empirical sources: such as the concept of motion, that of
impenetrability (upon which the empirical concept of matter rests),
that of inertia, and many others, which prevent its being called a
perfectly pure science of nature. Besides, it only refers to objects
of the external sense, and therefore does not give an example of a
universal science of nature, in the strict sense, for such a science
must reduce nature in general, whether it regards the object of the
external or that of the internal sense (the object of Physics as well
as Psychology), to universal laws. But among the principles of this
universal physics there are a few which actually have the required
universality; for instance, the propositions that "substance is
permanent," and that "every event is determined by a cause according
to constant laws," etc. These are actually universal laws of nature,
which subsist completely a priori. There is then in fact a pure
science of nature, and the question arises, How is it possible?

§ 16. The word "nature" assumes yet another meaning, which determines
the object, whereas in the former sense it only denotes the conformity
to law [Gesetzmässigkeit] of the determinations of the existence of
things generally. If we consider it materialiter (i.e., in the matter
that forms its objects) "nature is the complex of all the objects of
experience." And with this only are we now concerned, for besides,
things which can never be objects of experience, if they must be
cognised as to their nature, would oblige us to have recourse to
concepts whose meaning could never be given in concreto (by any
example of possible experience). Consequently we must form for
ourselves a list of concepts of their nature, the reality whereof
(i.e., whether they actually refer to objects, or are mere creations
of thought) could never be determined. The cognition of what cannot be
an object of experience would be hyperphysical, and with things
hyperphysical we are here not concerned, but only with the cognition
of nature, the actuality of which can be confirmed by experience,
though it [the cognition of nature] is possible a priori and precedes
all experience.

§ 17. The formal [aspect] of nature in this narrower sense is
therefore the conformity to law of all the objects of experience, and
so far as it is cognised a priori, their necessary conformity. But it
has just been shown that the laws of nature can never be cognised a
priori in objects so far as they are considered not in reference to
possible experience, but as things in themselves. And our inquiry here
extends not to things in themselves (the properties of which we pass
by), but to things as objects of possible experience, and the complex
of these is what we properly designate as nature. And now I ask, when
the possibility of a cognition of nature a priori is in question,
whether it is better to arrange the problem thus: How can we cognise a
priori that things as objects of experience necessarily conform to
law? or thus: How is it possible to cognise a priori the necessary
conformity to law of experience itself as regards all its objects

Closely considered, the solution of the problem, represented in either
way, amounts, with regard to the pure cognition of nature (which is
the point of the question at issue), entirely to the same thing. For
the subjective laws, under which alone an empirical cognition of
things is possible, hold good of these things, as Objects of possible
experience (not as things in themselves, which are not considered
here). Either of the following statements means quite the same:

A judgment of observation can never rank as experience, without the
law, that "whenever an event is observed, it is always referred to
some antecedent, which it follows according to a universal rule."

"Everything, of which experience teaches that it happens, must have a

It is, however, more commendable to choose the first formula. For we
can a priori and previous to all given objects have a cognition of
those conditions, on which alone experience is possible, but never of
the laws to which things may in themselves be subject, without
reference to possible experience. We cannot therefore study the nature
of things a priori otherwise than by investigating the conditions and
the universal (though subjective) laws, under which alone such a
cognition as experience (as to mere form) is possible, and we
determine accordingly the possibility of things, as objects of
experience. For if I should choose the second formula, and seek the
conditions a priori, on which nature as an object of experience is
possible, I might easily fall into error, and fancy that I was
speaking of nature as a thing in itself, and then move round in
endless circles, in a vain search for laws concerning things of which
nothing is given me.

Accordingly we shall here be concerned with experience only, and the
universal conditions of its possibility which are given a priori.
Thence we shall determine nature as the whole object of all possible
experience. I think it will be understood that I here do not mean the
rules of the observation of a nature that is already given, for these
already presuppose experience. I do not mean how (through experience)
we can study the laws of nature; for these would not then be laws a
priori, and would yield us no pure science of nature; but [I mean to
ask] how the conditions a priori of the possibility of experience are
at the same time the sources from which all the universal laws of
nature must be derived.

§ 18. In the first place we must state that, while all judgments of
experience (Erfahrungsurtheile) are empirical (i.e., have their ground
in immediate sense perception), vice versa, all empirical judgments
(empirische Urtheile) are not judgments of experience, but, besides
the empirical, and in general besides what is given to the sensuous
intuition, particular concepts must yet be superadded—concepts which
have their origin quite a priori in the pure understanding, and under
which every perception must be first of all subsumed and then by their
means changed into experience.{11}

{11} Empirical judgments (empirische Urtheile) are either mere
statements of fact, viz., records of a perception, or statements of a
natural law, implying a causal connexion between two facts. The former
Kant calls "judgments of perception" (Wahrnehmungsurtheile) the latter
"judgments of experience" (Erhfahrungsurtheile).—Ed.

Empirical judgments, so far as they have objective validity, are
judgments of experience; but those which are only subjectively valid,
I name mere judgments of perception. The latter require no pure
concept of the understanding, but only the logical connexion of
perception in a thinking subject. But the former always require,
besides the representation of the sensuous intuition, particular
concepts originally begotten in the understanding, which produce the
objective validity of the judgment of experience.

All our judgments are at first merely judgments of perception; they
hold good only for us (i.e., for our subject), and we do not till
afterwards give them a new reference (to an object), and desire that
they shall always hold good for us and in the same way for everybody
else; for when a judgment agrees with an object, all judgments
concerning the same object must likewise agree among themselves, and
thus the objective validity of the judgment of experience signifies
nothing else than its necessary universality of application. And
conversely when we have reason to consider a judgment necessarily
universal (which never depends upon perception, but upon the pure
concept of the understanding, under which the perception is subsumed),
we must consider it objective also, that is, that it expresses not
merely a reference of our perception to a subject, but a quality of
the object. For there would be no reason for the judgments of other
men necessarily agreeing with mine, if it were not the unity of the
object to which they all refer, and with which they accord; hence they
must all agree with one another.

§ 19. Therefore objective validity and necessary universality (for
everybody) are equivalent terms, and though we do not know the object
in itself, yet when we consider a judgment as universal, and also
necessary, we understand it to have objective validity. By this
judgment we cognise the object (though it remains unknown as it is in
itself) by the universal and necessary connexion of the given
perceptions. As this is the case with all objects of sense, judgments
of experience take their objective validity not from the immediate
cognition of the object (which is impossible), but from the condition
of universal validity in empirical judgments, which, as already said,
never rests upon empirical, or, in short, sensuous conditions, but
upon a pure concept of the understanding. The object always remains
unknown in itself; but when by the concept of the understanding the
connexion of the representations of the object, which are given to our
sensibility, is determined as universally valid, the object is
determined by this relation, and it is the judgment that is objective.

To illustrate the matter: When we say, "the room is warm, sugar sweet,
and wormwood bitter"{12}—we have only subjectively valid judgments. I
do not at all expect that I or any other person shall always find it
as I now do; each of these sentences only expresses a relation of two
sensations to the same subject, to myself, and that only in my present
state of perception; consequently they are not valid of the object.
Such are judgments of perception. Judgments of experience are of quite
a different nature. What experience teaches me under certain
circumstances, it must always teach me and everybody; and its validity
is not limited to the subject nor to its state at a particular time.
Hence I pronounce all such judgments as being objectively valid. For
instance, when I say the air is elastic, this judgment is as yet a
judgment of perception only—I do nothing but refer two of my
sensations to one another. But, if I would have it called a judgment
of experience, I require this connexion to stand under a condition,
which makes it universally valid. I desire therefore that I and
everybody else should always connect necessarily the same perceptions
under the same circumstances.

{12} I freely grant that these examples do not represent such judgments
of perception as ever could become judgments of experience, even
though a concept of the understanding were superadded, because they
refer merely to feeling, which everybody knows to be merely
subjective, and which of course can never be attributed to the object,
and consequently never become objective. I only wished to give here an
example of a judgment that is merely subjectively valid, containing no
ground for universal validity, and thereby for a relation to the
object. An example of the judgments of perception, which become
judgments of experience by superadded concepts of the understanding,
will be given in the next note.

§ 20. We must consequently analyse experience in order to see what is
contained in this product of the senses and of the understanding, and
how the judgment of experience itself is possible. The foundation is
the intuition of which I become conscious, i.e., perception
(perceptio), which pertains merely to the senses. But in the next
place, there are acts of judging (which belong only to the
understanding). But this judging may be twofold—first, I may merely
compare perceptions and connect them in a particular state of my
consciousness; or, secondly, I may connect them in consciousness
generally. The former judgment is merely a judgment of perception, and
of subjective validity only: it is merely a connexion of perceptions
in my mental state, without reference to the object. Hence it is not,
as is commonly imagined, enough for experience to compare perceptions
and to connect them in consciousness through judgment; there arises no
universality and necessity, for which alone judgments can become
objectively valid and be called experience.

Quite another judgment therefore is required before perception can
become experience. The given intuition must be subsumed under a
concept, which determines the form of judging in general relatively to
the intuition, connects its empirical consciousness in consciousness
generally, and thereby procures universal validity for empirical
judgments. A concept of this nature is a pure a priori concept of the
Understanding, which does nothing but determine for an intuition the
general way in which it can be used for judgments. Let the concept be
that of cause, then it determines the intuition which is subsumed
under it, e.g., that of air, relative to judgments in general, viz.,
the concept of air serves with regard to its expansion in the relation
of antecedent to consequent in a hypothetical judgment. The concept of
cause accordingly is a pure concept of the understanding, which is
totally disparate from all possible perception, and only serves to
determine the representation subsumed under it, relatively to
judgments in general, and so to make a universally valid judgment

Before, therefore, a judgment of perception can become a judgment of
experience, it is requisite that the perception should be subsumed
under some such a concept of the understanding; for instance, air
ranks under the concept of causes, which determines our judgment about
it in regard to its expansion as hypothetical.{13} Thereby the expansion
of the air is represented not as merely belonging to the perception of
the air in my present state or in several states of mine, or in the
state of perception of others, but as belonging to it necessarily. The
judgment, "the air is elastic," becomes universally valid, and a
judgment of experience, only by certain judgments preceding it, which
subsume the intuition of air under the concept of cause and effect:
and they thereby determine the perceptions not merely as regards one
another in me, but relatively to the form of judging in general, which
is here hypothetical, and in this way they render the empirical
judgment universally valid.

{13} As an easier example, we may take the following: "When the sun
shines on the stone, it grows warm." This judgment, however often I
and others may have perceived it, is a mere judgment of perception,
and contains no necessity; perceptions are only usually conjoined in
this manner. But if I say, "The sun warms the stone," I add to the
perception a concept of the understanding, viz., that of cause, which
connects with the concept of sunshine that of heat as a necessary
consequence, and the synthetical judgment becomes of necessity
universally valid, viz., objective, and is converted from a perception
into experience.

If all our synthetical judgments are analysed so far as they are
objectively valid, it will be found that they never consist of mere
intuitions connected only (as is commonly believed) by comparison into
a judgment; but that they would be impossible were not a pure concept
of the understanding superadded to the concepts abstracted from
intuition, under which concept these latter are subsumed, and in this
manner only combined into an objectively valid judgment. Even the
judgments of pure mathematics in their simplest axioms are not exempt
from this condition. The principle, "a straight line is the shortest
between two points," presupposes that the line is subsumed under the
concept of quantity, which certainly is no mere intuition, but has its
seat in the understanding alone, and serves to determine the intuition
(of the line) with regard to the judgments which may be made about it,
relatively to their quantity, that is, to plurality (as judicia
plurativa).{14} For under them it is understood that in a given
intuition there is contained a plurality of homogenous parts.

{14} This name seems preferable to the term particularia, which is used
for these judgments in logic. For the latter implies the idea that
they are not universal. But when I start from unity (in single
judgments) and so proceed to universality, I must not [even indirectly
and negatively] imply any reference to universality. I think plurality
merely without universality, and not the exception from universality.
This is necessary, if logical considerations shall form the basis of
the pure concepts of the understanding. However, there is no need of
making changes in logic.

§ 21. To prove, then, the possibility of experience so far as it
rests upon pure concepts of the understanding a priori, we must first
represent what belongs to judgments in general and the various
functions of the understanding, in a complete table. For the pure
concepts of the understanding must run parallel to these functions, as
such concepts are nothing more than concepts of intuitions in general,
so far as these are determined by one or other of these functions of
judging, in themselves, that is, necessarily and universally. Hereby
also the a priori principles of the possibility of all experience, as
of an objectively valid empirical cognition, will be precisely
determined. For they are nothing but propositions by which all
perception is (under certain universal conditions of intuition)
subsumed under those pure concepts of the understanding.

Logical Table of Judgments.

     1.                             2.
As to Quantity.               As to Quality.
  Universal.                    Affirmative.
  Particular.                   Negative.
  Singular.                     Infinite.

     3.                             4.
As to Relation.               As to Modality.
  Categorical.                  Problematical.
  Hypothetical.                 Assertorial.
  Disjunctive.                  Apodeictical.

Transcendental Table of the Pure Concepts of the Understanding.

     1.                             2.
As to Quantity.               As to Quality.
  Unity (the Measure)           Reality.
  Plurality (the Quantity)      Negation.
  Totality (the Whole)          Limitation.

     3.                             4.
As to Relation.               As to Modality.
  Substance.                    Possibility.
  Cause.                        Existence.
  Community.                    Necessity.

Pure Physiological Table of the Universal Principles of the Science of Nature.

        1.                                2.
Axioms of Intuition.        Anticipations of Perception.

        3.                                4.
Analogies of Experience.    Postulates of Empirical Thinking

§ 21a. In order to comprise the whole matter in one idea, it is first
necessary to remind the reader that we are discussing not the origin
of experience, but of that which lies in experience. The former
pertains to empirical psychology, and would even then never be
adequately explained without the latter, which belongs to the Critique
of cognition, and particularly of the understanding.

Experience consists of intuitions, which belong to the sensibility,
and of judgments, which are entirely a work of the understanding. But
the judgments, which the understanding forms alone from sensuous
intuitions, are far from being judgments of experience. For in the one
case the judgment connects only the perceptions as they are given in
the sensuous intuition, while in the other the judgments must express
what experience in general, and not what the mere perception (which
possesses only subjective validity) contains. The judgment of
experience must therefore add to the sensuous intuition and its
logical connexion in a judgment (after it has been rendered universal
by comparison) something that determines the synthetical judgment as
necessary and therefore as universally valid. This can be nothing else
than that concept which represents the intuition as determined in
itself with regard to one form of judgment rather than another, viz.,
a concept of that synthetical unity of intuitions which can only be
represented by a given logical function of judgments.

§ 22. The sum of the matter is this: the business of the senses is to
intuite—that of the understanding is to think. But thinking is
uniting representations in one consciousness. This union originates
either merely relative to the subject, and is accidental and
subjective, or is absolute, and is necessary or objective. The union
of representations in one consciousness is judgment. Thinking
therefore is the same as judging, or referring representations to
judgments in general. Hence judgments are either merely subjective,
when representations are referred to a consciousness in one subject
only, and united in it, or objective, when they are united in a
consciousness generally, that is, necessarily. The logical functions
of all judgments are but various modes of uniting representations in
consciousness. But if they serve for concepts, they are concepts of
their necessary union in a consciousness, and so principles of
objectively valid judgments. This union in a consciousness is either
analytical, by identity, or synthetical, by the combination and
addition of various representations one to another. Experience
consists in the synthetical connexion of phenomena (perceptions) in
consciousness, so far as this connexion is necessary. Hence the pure
concepts of the understanding are those under which all perceptions
must be subsumed ere they can serve for judgments of experience, in
which the synthetical unity of the perceptions is represented as
necessary and universally valid.{15}

{15} But how does this proposition, "that judgments of experience
contain necessity in the synthesis of perceptions," agree with my
statement so often before inculcated, that "experience as cognition a
posteriori can afford contingent judgments only?" When I say that
experience teaches me something, I mean only the perception that lies
in experience,—for example, that heat always follows the shining of
the sun on a stone; consequently the proposition of experience is
always so far accidental. That this heat necessarily follows the
shining of the sun is contained indeed in the judgment of experience
(by means of the concept of cause), yet is a fact not learned by
experience; for conversely, experience is first of all generated by
this addition of the concept of the understanding (of cause) to
perception. How perception attains this addition may be seen by
referring in the Critique itself to the section on the Transcendental
faculty of Judgment [viz., in the first edition, Von dem Schematismus
der reinen Verstandsbegriffe].

§ 23. Judgments, when considered merely as the condition of the
union of given representations in a consciousness, are rules. These
rules, so far as they represent the union as necessary, are rules a
priori, and so far as they cannot be deduced from higher rules, are
fundamental principles. But in regard to the possibility of all
experience, merely in relation to the form of thinking in it, no
conditions of judgments of experience are higher than those which
bring the phenomena, according to the various form of their intuition,
under pure concepts of the understanding, and render the empirical
judgment objectively valid. These concepts are therefore the a priori
principles of possible experience.

The principles of possible experience are then at the same time
universal laws of nature, which can be cognised a priori. And thus the
problem in our second question, "How is the pure Science of Nature
possible?" is solved. For the system which is required for the form of
a science is to be met with in perfection here, because, beyond the
above-mentioned formal conditions of all judgments in general offered
in logic, no others are possible, and these constitute a logical
system. The concepts grounded thereupon, which contain the a priori
conditions of all synthetical and necessary judgments, accordingly
constitute a transcendental system. Finally the principles, by means
of which all phenomena are subsumed under these concepts, constitute a
physical{16} system, that is, a system of nature, which precedes all
empirical cognition of nature, makes it even possible, and hence may
in strictness be denominated the universal and pure science of nature.

{16} [Kant uses the term physiological in its etymological meaning as
"pertaining to the science of physics," i.e., nature in general, not
as we use the term now as "pertaining to the functions of the living
body." Accordingly it has been translated "physical."—Ed.]

§ 24. The first one{17} of the physiological principles subsumes all
phenomena, as intuitions in space and time, under the concept of
Quantity, and is so far a principle of the application of Mathematics
to experience. The second one subsumes the empirical element, viz.,
sensation which denotes the real in intuitions, not indeed directly
under the concept of quantity, because sensation is not an intuition
that contains either space or time, though it places the respective
object into both. But still there is between reality
(sense-representation) and the zero, or total void of intuition in
time, a difference which has a quantity. For between every given
degree of light and of darkness, between every degree of heat and of
absolute cold, between every degree of weight and of absolute
lightness, between every degree of occupied space and of totally void
space, diminishing degrees can be conceived, in the same manner as
between consciousness and total unconsciousness (the darkness of a
psychological blank) ever diminishing degrees obtain. Hence there is
no perception that can prove an absolute absence of it; for instance,
no psychological darkness that cannot be considered as a kind of
consciousness. This occurs in all cases of sensation, and so the
understanding can anticipate even sensations, which constitute the
peculiar quality of empirical representations (appearances), by means
of the principle: "that they all have (consequently that what is real
in all phenomena has) a degree." Here is the second application of
mathematics (mathesis intensorum) to the science of nature.

{17} The three following paragraphs will hardly be understood unless
reference be made to what the Critique itself says on the subject of
the Principles; they will, however, be of service in giving a general
view of the Principles, and in fixing the attention on the main

§ 25. Anent the relation of appearances merely with a view to their
existence, the determination is not mathematical but dynamical, and
can never be objectively valid, consequently never fit for experience,
if it does not come under a priori principles by which the cognition
of experience relative to appearances becomes even possible. Hence
appearances must be subsumed under the concept of Substance, which is
the foundation of all determination of existence, as a concept of the
thing itself; or secondly—so far as, a succession is found among
phenomena, that is, an event—under the concept of an Effect with
reference to Cause; or lastly—so far as coexistence is to be known
objectively, that is, by a judgment of experience—under the concept
of Community (action and reaction).{18} Thus a priori principles form
the basis of objectively valid, though empirical judgments, that is,
of the possibility of experience so far as it must connect objects as
existing in nature. These principles are the proper laws of nature,
which may be termed dynamical.

{18} [Kant uses here the equivocal term Wechselwirkung.—Ed.]

Finally the cognition of the agreement and connexion not only of
appearances among themselves in experience, but of their relation to
experience in general, belongs to the judgments of experience. This
relation contains either their agreement with the formal conditions,
which the understanding cognises, or their coherence with the
materials of the senses and of perception, or combines both into one
concept. Consequently it contains Possibility, Actuality, and
Necessity according to universal laws of nature; and this constitutes
the physical doctrine of method, or the distinction of truth and of
hypotheses, and the bounds of the certainty of the latter.

§ 26. The third table of Principles drawn from the nature of the
understanding itself after the critical method, shows an inherent
perfection, which raises it far above every other table which has
hitherto though in vain been tried or may yet be tried by analysing
the objects themselves dogmatically. It exhibits all synthetical a
priori principles completely and according to one principle, viz., the
faculty of judging in general, constituting the essence of experience
as regards the understanding, so that we can be certain that there are
no more such principles, a satisfaction such as can never be attained
by the dogmatical method. Yet is this not all: there is a still
greater merit in it.

We must carefully bear in mind the proof which shows the possibility
of this cognition a priori, and at the same time limits all such
principles to a condition which must never be lost sight of, if we
desire it not to be misunderstood, and extended in use beyond the
original sense which the understanding attaches to it. This limit is
that they contain nothing but the conditions of possible experience in
general so far as it is subjected to laws a priori. Consequently I do
not say, that things in themselves possess a quantity, that their
actuality possesses a degree, their existence a connexion of accidents
in a substance, etc. This nobody can prove, because such a synthetical
connexion from mere concepts, without any reference to sensuous
intuition on the one side, or connexion of it in a possible experience
on the other, is absolutely impossible. The essential limitation of
the concepts in these principles then is: That all things stand
necessarily a priori under the afore-mentioned conditions, as objects
of experience only.

Hence there follows secondly a specifically peculiar mode of proof of
these principles: they are not directly referred to appearances and to
their relations, but to the possibility of experience, of which
appearances constitute the matter only, not the form. Thus they are
referred to objectively and universally valid synthetical
propositions, in which we distinguish judgments of experience from
those of perception. This takes place because appearances, as mere
intuitions, occupying a part of space and time, come under the concept
of Quantity, which unites their multiplicity a priori according to
rules synthetically. Again, so far as the perception contains, besides
intuition, sensibility, and between the latter and nothing (i.e., the
total disappearance of sensibility), there is an ever decreasing
transition, it is apparent that that which is in appearances must have
a degree, so far as it (viz., the perception) does not itself occupy
any part of space or of time.{19} Still the transition to actuality from
empty time or empty space is only possible in time; consequently
though sensibility, as the quality of empirical intuition, can never
be cognised a priori, by its specific difference from other
sensibilities, yet it can, in a possible experience in general, as a
quantity of perception be intensely distinguished from every other
similar perception. Hence the application of mathematics to nature, as
regards the sensuous intuition by which nature is given to us, becomes
possible and is thus determined.

{19} Heat and light are in a small space just as large as to degree as
in a large one; in like manner the internal representations, pain,
consciousness in general, whether they last a short or a long time,
need not vary as to the degree. Hence the quantity is here in a point
and in a moment just as great as in any space or time however great.
Degrees are therefore capable of increase, but not in intuition,
rather in mere sensation (or the quantity of the degree of an
intuition). Hence they can only be estimated quantitatively by the
relation of 1 to 0, viz., by their capability of decreasing by
infinite intermediate degrees to disappearance, or of increasing from
naught through infinite gradations to a determinate sensation in a
certain time. Quantitas qualitatis est gradus [i.e., the degrees of
quality must be measured by equality].

Above all, the reader must pay attention to the mode of proof of the
principles which occur under the title of Analogies of experience. For
these do not refer to the genesis of intuitions, as do the principles
of applied mathematics, but to the connexion of their existence in
experience; and this can be nothing but the determination of their
existence in time according to necessary laws, under which alone the
connexion is objectively valid, and thus becomes experience. The proof
therefore does not turn on the synthetical unity in the connexion of
things in themselves, but merely of perceptions, and of these not in
regard to their matter, but to the determination of time and of the
relation of their existence in it, according to universal laws. If the
empirical determination in relative time is indeed objectively valid
(i.e., experience), these universal laws contain the necessary
determination of existence in time generally (viz., according to a
rule of the understanding a priori).

In these Prolegomena I cannot further descant on the subject, but my
reader (who has probably been long accustomed to consider experience a
mere empirical synthesis of perceptions, and hence not considered that
it goes much beyond them, as it imparts to empirical judgments
universal validity, and for that purpose requires a pure and a priori
unity of the understanding) is recommended to pay special attention to
this distinction of experience from a mere aggregate of perceptions,
and to judge the mode of proof from this point of view.

§ 27. Now we are prepared to remove Hume's doubt. He justly
maintains, that we cannot comprehend by reason the possibility of
Causality, that is, of the reference of the existence of one thing to
the existence of another, which is necessitated by the former. I add,
that we comprehend just as little the concept of Subsistence, that is,
the necessity that at the foundation of the existence of things there
lies a subject which cannot itself be a predicate of any other thing;
nay, we cannot even form a notion of the possibility of such a thing
(though we can point out examples of its use in experience). The very
same in comprehensibility affects the Community of things, as we
cannot comprehend how from the state of one thing an inference to the
state of quite another thing beyond it, and vice versa, can be drawn,
and how substances which have each their own separate existence should
depend upon one another necessarily. But I am very far from holding
these concepts to be derived merely from experience, and the necessity
represented in them, to be imaginary and a mere illusion produced in
us by long habit. On the contrary, I have amply shown, that they and
the theorems derived from them are firmly established a priori, or
before all experience, and have their undoubted objective value,
though only with regard to experience.

§ 28. Though I have no notion of such a connexion of things in
themselves, that they can either exist as substances, or act as
causes, or stand in community with others (as parts of a real whole),
and I can just as little conceive such properties in appearances as
such (because those concepts contain nothing that lies in the
appearances, but only what the understanding alone must think): we
have yet a notion of such a connexion of representations in our
understanding, and in judgments generally; consisting in this that
representations appear in one sort of judgments as subject in relation
to predicates, in another as reason in relation to consequences, and
in a third as parts, which constitute together a total possible
cognition. Besides we cognise a priori that without considering the
representation of an object as determined in some of these respects,
we can have no valid cognition of the object, and, if we should occupy
ourselves about the object in itself, there is no possible attribute,
by which I could know that it is determined under any of these
aspects, that is, under the concept either of substance, or of cause,
or (in relation to other substances) of community, for I have no
notion of the possibility of such a connexion of existence. But the
question is not how things in themselves, but how the empirical
cognition of things is determined, as regards the above aspects of
judgments in general, that is, how things, as objects of experience,
can and shall be subsumed under these concepts of the understanding.
And then it is clear, that I completely comprehend not only the
possibility, but also the necessity of subsuming all phenomena under
these concepts, that is, of using them for principles of the
possibility of experience.

§ 29. When making an experiment with Hume's problematical concept
(his crux metaphysicorum), the concept of cause, we have, in the first
place, given a priori, by means of logic, the form of a conditional
judgment in general, i.e., we have one given cognition as antecedent
and another as consequence. But it is possible, that in perception we
may meet with a rule of relation, which runs thus: that a certain
phenomenon is constantly followed by another (though not conversely),
and this is a case for me to use the hypothetical judgment, and, for
instance, to say, it the sun shines long enough upon a body, it grows
warm. Here there is indeed as yet no necessity of connexion, or
concept of cause. But I proceed and say, that if this proposition,
which is merely a subjective connexion of perceptions, is to be a
judgment of experience, it must be considered as necessary and
universally valid. Such a proposition would be, "the sun is by its
light the cause of heat." The empirical rule is now considered as a
law, and as valid not merely of appearances but valid of them for the
purposes of a possible experience which requires universal and
therefore necessarily valid rules. I therefore easily comprehend the
concept of cause, as a concept necessarily belonging to the mere form
of experience, and its possibility as a synthetical union of
perceptions in consciousness generally; but I do not at all comprehend
the possibility of a thing generally as a cause, because the concept
of cause denotes a condition not at all belonging to things, but to
experience. It is nothing in fact but an objectively valid cognition
of appearances and of their succession, so far as the antecedent can
be conjoined with the consequent according to the rule of hypothetical

§ 30. Hence if the pure concepts of the understanding do not refer to
objects of experience but to things in themselves (noumena), they have
no signification whatever. They serve, as it were, only to decipher
appearances, that we may be able to read them as experience. The
principles which arise from their reference to the sensible world,
only serve our understanding for empirical use. Beyond this they are
arbitrary combinations, without objective reality, and we can neither
cognise their possibility a priori, nor verify their reference to
objects, let alone make it intelligible by any example; because
examples can only be borrowed from some possible experience,
consequently the objects of these concepts can be found nowhere but in
a possible experience.

This complete (though to its originator unexpected) solution of Hume's
problem rescues for the pure concepts of the understanding their a
priori origin, and for the universal laws of nature their validity, as
laws of the understanding, yet in such a way as to limit their use to
experience, because their possibility depends solely on the reference
of the understanding to experience, but with a completely reversed
mode of connexion which never occurred to Hume, not by deriving them
from experience, but by deriving experience from them.

This is therefore the result of all our foregoing inquiries: "All
synthetical principles a priori are nothing more than principles of
possible experience, and can never be referred to things in
themselves, but to appearances as objects of experience. And hence
pure mathematics as well as a pure science of nature can never be
referred to anything more than mere appearances, and can only
represent either that which makes experience generally possible, or
else that which, as it is derived from these principles, must always
be capable of being represented in some possible experience.

§ 31. And thus we have at last something definite, upon which to
depend in all metaphysical enterprises, which have hitherto, boldly
enough but always at random, attempted everything without
discrimination. That the aim of their exertions should be so near,
struck neither the dogmatical thinkers nor those who, confident in
their supposed sound common sense, started with concepts and
principles of pure reason (which were legitimate and natural, but
destined for mere empirical use) in quest of fields of knowledge, to
which they neither knew nor could know any determinate bounds, because
they had never reflected nor were able to reflect on the nature or
even on the possibility of such a pure understanding.

Many a naturalist of pure reason (by which I mean the man who believes
he can decide in matters of metaphysics without any science) may
pretend, that he long ago by the prophetic spirit of his sound sense,
not only suspected, but knew and comprehended, what is here propounded
with so much ado, or, if he likes, with prolix and pedantic pomp:
"that with all our reason we can never reach beyond the field of
experience." But when he is questioned about his rational principles
individually, he must grant, that there are many of them which he has
not taken from experience, and which are therefore independent of it
and valid a priori. How then and on what grounds will he restrain both
himself and the dogmatist, who makes use of these concepts and
principles beyond all possible experience, because they are recognised
to be independent of it? And even he, this adept in sound sense, in
spite of all his assumed and cheaply acquired wisdom, is not exempt
from wandering inadvertently beyond objects of experience into the
field of chimeras. He is often deeply enough involved in them, though
in announcing everything as mere probability, rational conjecture, or
analogy, he gives by his popular language a color to his groundless

§ 32. Since the oldest days of philosophy inquirers into pure reason
have conceived, besides the things of sense, or appearances
(phenomena), which make up the sensible world, certain creations of
the understanding (Verstandeswesen), called noumena, which should
constitute an intelligible world. And as appearance and illusion were
by those men identified (a thing which we may well excuse in an
undeveloped epoch), actuality was only conceded to the creations of

And we indeed, rightly considering objects of sense as mere
appearances, confess thereby that they are based upon a thing in
itself, though we know not this thing in its internal constitution,
but only know its appearances, viz., the way in which our senses are
affected by this unknown something. The understanding therefore, by
assuming appearances, grants the existence of things in themselves
also, and so far we may say, that the representation of such things as
form the basis of phenomena, consequently of mere creations of the
understanding, is not only admissible, but unavoidable.

Our critical deduction by no means excludes things of that sort
(noumena), but rather limits the principles of the Aesthetic (the
science of the sensibility) to this, that they shall not extend to all
things, as everything would then be turned into mere appearance, but
that they shall only hold good of objects of possible experience.
Hereby then objects of the understanding are granted, but with the
inculcation of this rule which admits of no exception: "that we
neither know nor can know anything at all definite of these pure
objects of the understanding, because our pure concepts of the
understanding as well as our pure intuitions extend to nothing but
objects of possible experience, consequently to mere things of sense,
and as soon as we leave this sphere these concepts retain no meaning

§ 33. There is indeed something seductive in our pure concepts of the
understanding, which tempts us to a transcendent use, —a use which
transcends all possible experience. Not only are our concepts of
substance, of power, of action, of reality, and others, quite
independent of experience, containing nothing of sense appearance, and
so apparently applicable to things in themselves (noumena), but, what
strengthens this conjecture, they contain a necessity of determination
in themselves, which experience never attains. The concept of cause
implies a rule, according to which one state follows another
necessarily; but experience can only show us, that one state of things
often, or at most, commonly, follows another, and therefore affords
neither strict universality, nor necessity.

Hence the Categories seem to have a deeper meaning and import than can
be exhausted by their empirical use, and so the understanding
inadvertently adds for itself to the house of experience a much more
extensive wing, which it fills with nothing but creatures of thought,
without ever observing that it has transgressed with its otherwise
lawful concepts the bounds of their use.

§ 34. Two important, and even indispensable, though very dry,
investigations had therefore become indispensable in the Critique of
Pure Reason,—viz., the two chapters "Vom Schematismus der reinen
Verstandsbegriffe," and "Vom Grunde der Unterscheidung aller
Verstandesbegriffe überhaupt in Phänomena und Noumena." In the
former it is shown, that the senses furnish not the pure concepts of
the understanding in concreto, but only the schedule for their use,
and that the object conformable to it occurs only in experience (as
the product of the understanding from materials of the sensibility).
In the latter it is shown, that, although our pure concepts of the
understanding and our principles are independent of experience, and
despite of the apparently greater sphere of their use, still nothing
whatever can be thought by them beyond the field of experience,
because they can do nothing but merely determine the logical form of
the judgment relatively to given intuitions. But as there is no
intuition at all beyond the field of the sensibility, these pure
concepts, as they cannot possibly be exhibited in concreto, are void
of all meaning; consequently all these noumena, together with their
complex, the intelligible world,{20} are nothing but representation of a
problem, of which the object in itself is possible, but the solution,
from the nature of our understanding, totally impossible. For our
understanding is not a faculty of intuition, but of the connexion of
given intuitions in experience. Experience must therefore contain all
the objects for our concepts; but beyond it no concepts have any
significance, as there is no intuition that might offer them a

{20} We speak of the "intelligible world," not (as the usual expression
is) "intellectual world." For cognitions are intellectual through the
understanding, and refer to our world of sense also; but objects, so
far as they can be represented merely by the understanding, and to
which none of our sensible intuitions can refer, are termed
"intelligible." But as some possible intuition must correspond to
every object, we would have to assume an understanding that intuites
things immediately; but of such we have not the least notion, nor have
we of the things of the understanding [Verstandeswesen], to which it
should be applied.

§ 35. The imagination may perhaps be forgiven for occasional
vagaries, and for not keeping carefully within the limits of
experience, since it gains life and vigor by such flights, and since
it is always easier to moderate its boldness, than to stimulate its
languor. But the understanding which ought to think can never be
forgiven for indulging in vagaries; for we depend upon it alone for
assistance to set bounds, when necessary, to the vagaries of the

But the understanding begins its aberrations very innocently and
modestly. It first elucidates the elementary cognitions, which inhere
in it prior to all experience, but yet must always have their
application in experience. It gradually drops these limits, and what
is there to prevent it, as it has quite freely derived its principles
from itself? And then it proceeds first to newly-imagined powers in
nature, then to beings, outside nature; in short to a world, for whose
construction the materials cannot be wanting, because fertile fiction
furnishes them abundantly, and though not confirmed, is never refuted,
by experience. This is the reason that young thinkers are so partial
to metaphysics of the truly dogmatical kind, and often sacrifice to it
their time and their talents, which might be otherwise better

But there is no use in trying to moderate these fruitless endeavors of
pure reason by all manner of cautions as to the difficulties of
solving questions so occult, by complaints of the limits of our
reason, and by degrading our assertions into mere conjectures. For if
their impossibility is not distinctly shown, and reason's cognition of
its own essence does not become a true science, in which the field of
its right use is distinguished, so to say, with mathematical certainty
from that of its worthless and idle use, these fruitless efforts will
never be abandoned for good.

§ 36. How is Nature itself possible?

This question—the highest point that transcendental philosophy can
ever reach, and to which, as its boundary and completion, it must
proceed—properly contains two questions.

First: How is nature at all possible in the material sense, by
intuition, considered as the totality of appearances; how are space,
time, and that which fills both—the object of sensation, in general
possible? The answer is: By means of the constitution of our
Sensibility, according to which it is specifically affected by
objects, which are in themselves unknown to it, and totally distinct
from those phenomena. This answer is given in the Critique itself in
the transcendental Aesthetic, and in these Prolegomena by the solution
of the first general problem.

Secondly: How is nature possible in the formal sense, as the totality
of the rules, under which all phenomena must come, in order to be
thought as connected in experience? The answer must be this: It is
only possible by means of the constitution of our Understanding,
according to which all the above representations of the sensibility
are necessarily referred to a consciousness, and by which the peculiar
way in which we think (viz., by rules), and hence experience also, are
possible, but must be clearly distinguished from an insight into the
objects in themselves. This answer is given in the Critique itself in
the transcendental Logic, and in these Prolegomena, in the course of
the solution of the second main problem.

But how this peculiar property of our sensibility itself is possible,
or that of our understanding and of the apperception which is
necessarily its basis and that of all thinking, cannot be further
analysed or answered, because it is of them that we are in need for
all our answers and for all our thinking about objects.

There are many laws of nature, which we can only know by means of
experience; but conformity to law in the connexion of appearances,
i.e., in nature in general, we cannot discover by any experience,
because experience itself requires laws which are a priori at the
basis of its possibility.

The possibility of experience in general is therefore at the same time
the universal law of nature, and the principles of the experience are
the very laws of nature. For we do not know nature but as the totality
of appearances, i.e., of representations in us, and hence we can only
derive the laws of its connexion from the principles of their
connexion in us, that is, from the conditions of their necessary union
in consciousness, which constitutes the possibility of experience.

Even the main proposition expounded throughout this section—that
universal laws of nature can be distinctly cognised a priori—leads
naturally to the proposition: that the highest legislation of nature
must lie in ourselves, i.e., in our understanding, and that we must
not seek the universal laws of nature in nature by means of
experience, but conversely must seek nature, as to its universal
conformity to law, in the conditions of the possibility of experience,
which lie in our sensibility and in our understanding. For how were it
otherwise possible to know a priori these laws, as they are not rules
of analytical cognition, but truly synthetical extensions of it?

Such a necessary agreement of the principles of possible experience
with the laws of the possibility of nature, can only proceed from one
of two reasons: either these laws are drawn from nature by means of
experience, or conversely nature is derived from the laws of the
possibility of experience in general, and is quite the same as the
mere universal conformity to law of the latter. The former is
self-contradictory, for the universal laws of nature can and must be
cognised a priori (that is, independent of all experience), and be the
foundation of all empirical use of the understanding; the latter
alternative therefore alone remains.{21}

{21} Crusius alone thought of a compromise: that a Spirit, who can
neither err nor deceive, implanted these laws in us originally. But
since false principles often intrude themselves, as indeed the very
system of this man shows in not a few examples, we are involved in
difficulties as to the use of such a principle in the absence of sure
criteria to distinguish the genuine origin from the spurious, as we
never can know certainly what the Spirit of truth or the father of
lies may have instilled into us.

But we must distinguish the empirical laws of nature, which always
presuppose particular perceptions, from the pure or universal laws of
nature, which, without being based on particular perceptions, contain
merely the conditions of their necessary union in experience. In
relation to the latter, nature and possible experience are quite the
same, and as the conformity to law here depends upon the necessary
connexion of appearances in experience (without which we cannot
cognise any object whatever in the sensible world), consequently upon
the original laws of the understanding, it seems at first strange, but
is not the less certain, to say:

The understanding does not derive its laws (a priori) from, but
prescribes them to, nature.

§ 37. We shall illustrate this seemingly bold proposition by an
example, which will show, that laws, which we discover in objects of
sensuous intuition (especially when these laws are cognised as
necessary), are commonly held by us to be such as have been placed
there by the understanding, in spite of their being similar in all
points to the laws of nature, which we ascribe to experience.

§ 38. If we consider the properties of the circle, by which this
figure combines so many arbitrary determinations of space in itself,
at once in a universal rule, we cannot avoid attributing a
constitution (eine Natur) to this geometrical thing. Two right lines,
for example, which intersect one another and the circle, howsoever
they may be drawn, are always divided so that the rectangle
constructed with the segments of the one is equal to that constructed
with the segments of the other. The question now is: Does this law lie
in the circle or in the understanding, that is, Does this figure,
independently of the understanding, contain in itself the ground of
the law, or does the understanding, having constructed according to
its concepts (according to the quality of the radii) the figure
itself, introduce into it this law of the chords cutting one another
in geometrical proportion? When we follow the proofs of this law, we
soon perceive, that it can only be derived from the condition on which
the understanding founds the construction of this figure, and which is
that of the equality of the radii. But, if we enlarge this concept, to
pursue further the unity of various properties of geometrical figures
under common laws, and consider the circle as a conic section, which
of course is subject to the same fundamental conditions of
construction as other conic sections, we shall find that all the
chords which intersect within the ellipse, parabola, and hyperbola,
always intersect so that the rectangles of their segments are not
indeed equal, but always bear a constant ratio to one another. If we
proceed still farther, to the fundamental laws of physical astronomy,
we find a physical law of reciprocal attraction diffused over all
material nature, the rule of which is: "that it decreases inversely as
the square of the distance from each attracting point, i.e., as the
spherical surfaces increase, over which this force spreads," which law
seems to be necessarily inherent in the very nature of things, and
hence is usually propounded as cognisable a priori. Simple as the
sources of this law are, merely resting upon the relation of spherical
surfaces of different radii, its consequences are so valuable with
regard to the variety of their agreement and its regularity, that not
only are all possible orbits of the celestial bodies conic sections,
but such a relation of these orbits to each other results, that no
other law of attraction, than that of the inverse square of the
distance, can be imagined as fit for a cosmical system.

Here accordingly is a nature that rests upon laws which the
understanding cognises a priori, and chiefly from the universal
principles of the determination of space. Now I ask:

Do the laws of nature lie in space, and does the understanding learn
them by merely endeavoring to find out the enormous wealth of meaning
that lies in space; or do they inhere in the understanding and in the
way in which it determines space according to the conditions of the
synthetical unity in which its concepts are all centred?

Space is something so uniform and as to all particular properties so
indeterminate, that we should certainly not seek a store of laws of
nature in it. Whereas that which determines space to assume the form
of a circle or the figures of a cone and a sphere, is the
understanding, so far as it contains the ground of the unity of their

The mere universal form of intuition, called space, must therefore be
the substratum of all intuitions determinable to particular objects,
and in it of course the condition of the possibility and of the
variety of these intuitions lies. But the unity of the objects is
entirely determined by the understanding, and on conditions which lie
in its own nature; and thus the understanding is the origin of the
universal order of nature, in that it comprehends all appearances
under its own laws, and thereby first constructs, a priori, experience
(as to its form), by means of which whatever is to be cognised only by
experience, is necessarily subjected to its laws. For we are not now
concerned with the nature of things in themselves, which is
independent of the conditions both of our sensibility and our
understanding, but with nature, as an object of possible experience,
and in this case the understanding, whilst it makes experience
possible, thereby insists that the sensuous world is either not an
object of experience at all, or must be nature [viz., an existence of
things, determined according to universal laws{22}].

{22} The definition of nature is given in the beginning of the Second
Part of the "Transcendental Problem," in § 14.


§ 39. Of the System of the Categories.

There can be nothing more desirable to a philosopher, than to be able
to derive the scattered multiplicity of the concepts or the
principles, which had occurred to him in concrete use, from a
principle a priori, and to unite everything in this way in one
cognition. He formerly only believed that those things, which remained
after a certain abstraction, and seemed by comparison among one
another to constitute a particular kind of cognitions, were completely
collected; but this was only an Aggregate. Now he knows, that just so
many, neither more nor less, can constitute the mode of cognition, and
perceives the necessity of his division, which constitutes
comprehension; and now only he has attained a System.

To search in our daily cognition for the concepts, which do not rest
upon particular experience, and yet occur in all cognition of
experience, where they as it were constitute the mere form of
connexion, presupposes neither greater reflexion nor deeper insight,
than to detect in a language the rules of the actual use of words
generally, and thus to collect elements for a grammar. In fact both
researches are very nearly related, even though we are not able to
give a reason why each language has just this and no other formal
constitution, and still less why an exact number of such formal
determinations in general are found in it.

Aristotle collected ten pure elementary concepts under the name of
Categories.{23} To these, which are also called predicaments, he found
himself obliged afterwards to add five post-predicaments,{24} some of
which however (prius, simul, and motus) are contained in the former;
but this random collection must be considered (and commended) as a
mere hint for future inquirers, not as a regularly developed idea, and
hence it has, in the present more advanced state of philosophy, been
rejected as quite useless.

{23} 1. Substantia. 2. Qualitas. 3. Quantitas. 4. Relatio, 5. Actio.
6. Passio. 7. Quando, 8. Ubi. 9. Situs. 10. Habitus.

{24} Oppositum. Prius. Simul. Motus. Habere.

After long reflexion on the pure elements of human knowledge (those
which contain nothing empirical), I at last succeeded in
distinguishing with certainty and in separating the pure elementary
notions of the Sensibility (space and time) from those of the
Understanding. Thus the 7th, 8th, and 9th Categories had to be
excluded from the old list. And the others were of no service to me;
because there was no principle [in them], on which the understanding
could be investigated, measured in its completion, and all the
functions, whence its pure concepts arise, determined exhaustively and
with precision.

But in order to discover such a principle, I looked about for an act
of the understanding which comprises all the rest, and is
distinguished only by various modifications or phases, in reducing the
multiplicity of representation to the unity of thinking in general: I
found this act of the understanding to consist in judging. Here then
the labors of the logicians were ready at hand, though not yet quite
free from defects, and with this help I was enabled to exhibit a
complete table of the pure functions of the understanding, which are
however undetermined in regard to any object. I finally referred these
functions of judging to objects in general, or rather to the condition
of determining judgments as objectively valid, and so there arose the
pure concepts of the understanding, concerning which I could make
certain, that these, and this exact number only, constitute our whole
cognition of things from pure understanding. I was justified in
calling them by their old name, Categories, while I reserved for
myself the liberty of adding, under the title of "Predicables," a
complete list of all the concepts deducible from them, by combinations
whether among themselves, or with the pure form of the appearance,
i.e., space or time, or with its matter, so far as it is not yet
empirically determined (viz., the object of sensation in general), as
soon as a system of transcendental philosophy should be completed with
the construction of which I am engaged in the Critique of Pure Reason

Now the essential point in this system of Categories, which
distinguishes it from the old rhapsodical collection without any
principle, and for which alone it deserves to be considered as
philosophy, consists in this: that by means of it the true
significance of the pure concepts of the understanding and the
condition of their use could be precisely determined. For here it
became obvious that they are themselves nothing but logical functions,
and as such do not produce the least concept of an object, but require
some sensuous intuition as a basis. They therefore only serve to
determine empirical judgments, which are otherwise undetermined and
indifferent as regards all functions of judging, relatively to these
functions, thereby procuring them universal validity, and by means of
them making judgments of experience in general possible.

Such an insight into the nature of the categories, which limits them
at the same time to the mere use of experience, never occurred either
to their first author, or to any of his successors; but without this
insight (which immediately depends upon their derivation or
deduction), they are quite useless and only a miserable list of names,
without explanation or rule for their use. Had the ancients ever
conceived such a notion, doubtless the whole study of the pure
rational knowledge, which under the name of metaphysics has for
centuries spoiled many a sound mind, would have reached us in quite
another shape, and would have enlightened the human understanding,
instead of actually exhausting it in obscure and vain speculations,
thereby rendering it unfit for true science.

This system of categories makes all treatment of every object of pure
reason itself systematic, and affords a direction or clue how and
through what points of inquiry every metaphysical consideration must
proceed, in order to be complete; for it exhausts all the possible
movements (momenta) of the understanding, among which every concept
must be classed. In like manner the table of Principles has been
formulated, the completeness of which we can only vouch for by the
system of the categories. Even in the division of the concepts,{25}
which must go beyond the physical application of the understanding, it
is always the very same clue, which, as it must always be determined a
priori by the same fixed points of the human understanding, always
forms a closed circle. There is no doubt that the object of a pure
conception either of the understanding or of reason, so far as it is
to be estimated philosophically and on a priori principles, can in
this way be completely cognised. I could not therefore omit to make
use of this clue with regard to one of the most abstract ontological
divisions, viz., the various distinctions of "the notions of something
and of nothing," and to construct accordingly (Critique, p. 207) a
regular and necessary table of their divisions.{26}

{25} See the two tables in the chapters Von den Paralogismen der reinen
Vernuuft and the first division of the Antinomy of Pure Reason, System
der kosmologischen Ideen.

{26} On the table of the categories many neat observations may be made,
for instance: (1) that the third arises from the first and the second
joined in one concept; (2) that in those of Quantity and of Quality
there is merely a progress from unity to totality or from something to
nothing (for this purpose the categories of Quality must stand thus:
reality, limitation, total negation), without correlata or opposita,
whereas those of Relation and of Modality have them; (3) that, as in
Logic categorical judgments are the basis of all others, so the
category of Substance is the basis of all concepts of actual things;
(4) that as Modality in the judgment is not a particular predicate, so
by the modal concepts a determination is not superadded to things,
etc., etc. Such observations are of great use. If we besides enumerate
all the predicables, which we can find pretty completely in any good
ontology (for example, Baumgarten's), and arrange them in classes
under the categories, in which operation we must not neglect to add as
complete a dissection of all these concepts as possible, there will
then arise a merely analytical part of metaphysics, which does not
contain a single synthetical proposition, which might precede the
second (the synthetical), and would by its precision and completeness
be not only useful, but, in virtue of its system, be even to some
extent elegant.

And this system, like every other true one founded on a universal
principle, shows its inestimable value in this, that it excludes all
foreign concepts, which might otherwise intrude among the pure
concepts of the understanding, and determines the place of every
cognition. Those concepts, which under the name of "concepts of
reflexion" have been likewise arranged in a table according to the
clue of the categories, intrude, without having any privilege or title
to be among the pure concepts of the understanding in Ontology. They
are concepts of connexion, and thereby of the objects themselves,
whereas the former are only concepts of a mere comparison of concepts
already given, hence of quite another nature and use. By my systematic
division{27} they are saved from this confusion. But the value of my
special table of the categories will be still more obvious, when we
separate the table of the transcendental concepts of Reason from the
concepts of the understanding. The latter being of quite another
nature and origin, they must have quite another form than the former.
This so necessary separation has never yet been made in any system of
metaphysics for, as a rule, these rational concepts all mixed up with
the categories, like children of one family, which confusion was
unavoidable in the absence of a definite system of categories.

{27} See Critique of Pure Reason, Von der Amphibolie der Reflexbegriffe.



§ 40.

Pure mathematics and pure science of nature had no occasion for such a
deduction, as we have made of both, for their own safety and
certainty. For the former rests upon its own evidence; and the latter
(though sprung from pure sources of the understanding) upon experience
and its thorough confirmation. Physics cannot altogether refuse and
dispense with the testimony of the latter; because with all its
certainty, it can never, as philosophy, rival mathematics. Both
sciences therefore stood in need of this inquiry, not for themselves,
but for the sake of another science, metaphysics.

Metaphysics has to do not only with concepts of nature, which always
find their application in experience, but also with pure rational
concepts, which never can be given in any possible experience.
Consequently the objective reality of these concepts (viz., that they
are not mere chimeras), and the truth or falsity of metaphysical
assertions, cannot be discovered or confirmed by any experience. This
part of metaphysics however is precisely what constitutes its
essential end, to which the rest is only a means, and thus this
science is in need of such a deduction for its own sake. The third
question now proposed relates therefore as it were to the root and
essential difference of metaphysics, i.e., the occupation of Reason
with itself, and the supposed knowledge of objects arising immediately
from this incubation of its own concepts, without requiring, or indeed
being able to reach that knowledge through, experience.{28}

{28} If we can say, that a science is actual at least in the ideas of
all men, as soon as it appears that the problems which lead to it are
proposed to everybody by the nature of human reason, and that
therefore many (though faulty) endeavors are unavoidably made in its
behalf, then we are bound to say that metaphysics is subjectively (and
indeed necessarily) actual, and therefore we justly ask, how is it
(objectively) possible.

Without solving this problem reason never is justified. The empirical
use to which reason limits the pure understanding, does not fully
satisfy the proper destination of the latter. Every single experience
is only a part of the whole sphere of its domain, but the absolute
totality of all possible experience is itself not experience. Yet it
is a necessary [concrete] problem for reason, the mere representation
of which requires concepts quite different from the categories, whose
use is only immanent, or refers to experience, so far as it can be
given. Whereas the concepts of reason aim at the completeness, i.e.,
the collective unity of all possible experience, and thereby transcend
every given experience. Thus they become transcendent.

As the understanding stands in need of categories for experience,
reason contains in itself the source of ideas, by which I mean
necessary concepts, whose object cannot be given in any experience.
The latter are inherent in the nature of reason, as the former are in
that of the understanding. While the former carry with them an
illusion likely to mislead, the illusion of the latter is inevitable,
though it certainly can be kept from misleading us.

Since all illusion consists in holding the subjective ground of our
judgments to be objective, a self-knowledge of pure reason in its
transcendent (exaggerated) use is the sole preservative from the
aberrations into which reason falls when it mistakes its destination,
and refers that to the object transcendently, which only regards its
own subject and its guidance in all immanent use.

§ 41. The distinction of ideas, that is, of pure concepts of reason,
from categories, or pure concepts of the understanding, as cognitions
of a quite distinct species, origin and use, is so important a point
in founding a science which is to contain the system of all these a
priori cognitions, that without this distinction metaphysics is
absolutely impossible, or is at best a random, bungling attempt to
build a castle in the air without a knowledge of the materials or of
their fitness for any purpose. Had the Critique of Pure Reason done
nothing but first point out this distinction, it had thereby
contributed more to clear up our conception of, and to guide our
inquiry in, the field of metaphysics, than all the vain efforts which
have hitherto been made to satisfy the transcendent problems of pure
reason, without ever surmising that we were in quite another field
than that of the understanding, and hence classing concepts of the
understanding and those of reason together, as if they were of the
same kind.

§ 42. All pure cognitions of the understanding have this feature,
that their concepts present themselves in experience, and their
principles can be confirmed by it; whereas the transcendent cognitions
of reason cannot, either as ideas, appear in experience, or as
propositions ever be confirmed or refuted by it. Hence whatever errors
may slip in unawares, can only be discovered by pure reason itself—a
discovery of much difficulty, because this very reason naturally
becomes dialectical by means of its ideas, and this unavoidable
illusion cannot be limited by any objective and dogmatical researches
into things, but by a subjective investigation of reason itself as a
source of ideas.

§ 43. In the Critique of Pure Reason it was always my greatest care
to endeavor not only carefully to distinguish the several species of
cognition, but to derive concepts belonging to each one of them from
their common source. I did this in order that by knowing whence they
originated, I might determine their use with safety, and also have the
unanticipated but invaluable advantage of knowing the completeness of
my enumeration, classification and specification of concepts a priori,
and therefore according to principles. Without this, metaphysics is
mere rhapsody, in which no one knows whether he has enough, or whether
and where something is still wanting. We can indeed have this
advantage only in pure philosophy, but of this philosophy it
constitutes the very essence.

As I had found the origin of the categories in the four logical
functions of all the judgments of the understanding, it was quite
natural to seek the origin of the ideas in the three functions of the
syllogisms of reason. For as soon as these pure concepts of reason
(the transcendental ideas) are given, they could hardly, except they
be held innate, be found anywhere else, than in the same activity of
reason, which, so far as it regards mere form, constitutes the logical
element of the syllogisms of reason; but, so far as it represents
judgments of the understanding with respect to the one or to the other
form a priori, constitutes transcendental concepts of pure reason.

The formal distinction of syllogisms renders their division into
categorical, hypothetical, and disjunctive necessary. The concepts of
reason founded on them contained therefore, first, the idea of the
complete subject (the substantial); secondly, the idea of the complete
series of conditions; thirdly, the determination of all concepts in
the idea of a complete complex of that which is possible.{29} The first
idea is psychological, the second cosmological, the third theological,
and, as all three give occasion to Dialectics, yet each in its own
way, the division of the whole Dialects of pure reason into its
Paralogism, its Antinomy, and its Ideal, was arranged accordingly.
Through this deduction we may feel assured that all the claims of pure
reason are completely represented, and that none can be wanting;
because the faculty of reason itself, whence they all take their
origin, is thereby completely surveyed.

{29} In disjunctive judgments we consider all possibility as divided in
respect to a particular concept. By the ontological principle of the
universal determination of a thing in general, I understand the
principle that either the one or the other of all possible
contradictory predicates must be assigned to any object. This is at
the same time the principle of all disjunctive judgments, constituting
the foundation of our conception of possibility, and in it the
possibility of every object in general is considered as determined.
This may serve as a slight explanation of the above proposition: that
the activity of reason in disjunctive syllogisms is formally the same
as that by which it fashions the idea of a universal conception of all
reality, containing in itself that which is positive in all
contradictory predicates.

§ 44. In these general considerations it is also remarkable that the
ideas of reason are unlike the categories, of no service to the use of
our understanding in experience, but quite dispensable, and become
even an impediment to the maxims of a rational cognition of nature.
Yet in another aspect still to be determined they are necessary.
Whether the soul is or is not a simple substance, is of no consequence
to us in the explanation of its phenomena. For we cannot render the
notion of a simple being intelligible by any possible experience that
is sensuous or concrete. The notion is therefore quite void as regards
all hoped-for insight into the cause of phenomena, and cannot at all
serve as a principle of the explanation of that which internal or
external experience supplies. So the cosmological ideas of the
beginning of the world or of its eternity (a parte ante) cannot be of
any greater service to us for the explanation of any event in the
world itself. And finally we must, according to a right maxim of the
philosophy of nature, refrain from all explanations of the design of
nature, drawn from the will of a Supreme Being; because this would not
be natural philosophy, but an acknowledgment that we have come to the
end of it. The use of these ideas, therefore, is quite different from
that of those categories by which (and by the principles built upon
which) experience itself first becomes possible. But our laborious
analytics of the understanding would be superfluous if we had nothing
else in view than the mere cognition of nature as it can be given in
experience; for reason does its work, both in mathematics and in the
science of nature, quite safely and well without any of this subtle
deduction. Therefore our Critique of the Understanding combines with
the ideas of pure reason for a purpose which lies beyond the empirical
use of the understanding; but this we have above declared to be in
this aspect totally inadmissible, and without any object or meaning.
Yet there must be a harmony between that of the nature of reason and
that of the understanding, and the former must contribute to the
perfection of the latter, and cannot possibly upset it.

The solution of this question is as follows: Pure reason does not in
its ideas point to particular objects, which lie beyond the field of
experience, but only requires completeness of the use of the
understanding in the system of experience. But this completeness can
be a completeness of principles only, not of intuitions (i.e.,
concrete atsights or Anschauungen) and of objects. In order however to
represent the ideas definitely, reason conceives them after the
fashion of the cognition of an object. The cognition is as far as
these rules are concerned completely determined, but the object is
only an idea invented for the purpose of bringing the cognition of the
understanding as near as possible to the completeness represented by
that idea.

Prefatory Remark to the Dialectics of Pure Reason.

§ 45. We have above shown in §§ 33 and 34 that the purity of the
categories from all admixture of sensuous determinations may mislead
reason into extending their use, quite beyond all experience, to
things in themselves; though as these categories themselves find no
intuition which can give them meaning or sense in concreto, they, as
mere logical functions, can represent a thing in general, but not give
by themselves alone a determinate concept of anything. Such
hyperbolical objects are distinguised by the appellation of Noümena,
or pure beings of the understanding (or better, beings of thought),
such as, for example, "substance," but conceived without permanence in
time, or "cause," but not acting in time, etc. Here predicates, that
only serve to make the conformity-to-law of experience possible, are
applied to these concepts, and yet they are deprived of all the
conditions of intuition, on which alone experience is possible, and so
these concepts lose all significance.

There is no danger, however, of the understanding spontaneously making
an excursion so very wantonly beyond its own bounds into the field of
the mere creatures of thought, without being impelled by foreign laws.
But when reason, which cannot be fully satisfied with any empirical
use of the rules of the understanding, as being always conditioned,
requires a completion of this chain of conditions, then the
understanding is forced out of its sphere. And then it partly
represents objects of experience in a series so extended that no
experience can grasp, partly even (with a view to complete the series)
it seeks entirely beyond it noumena, to which it can attach that
chain, and so, having at last escaped from the conditions of
experience, make its attitude as it were final. These are then the
transcendental ideas, which, though according to the true but hidden
ends of the natural determination of our reason, they may aim not at
extravagant concepts, but at an unbounded extension of their empirical
use, yet seduce the understanding by an unavoidable illusion to a
transcendent use, which, though deceitful, cannot be restrained within
the bounds of experience by any resolution, but only by scientific
instruction and with much difficulty.

I. The Psychological Idea.{30}

{30} See Critique of Pure Reason, Von den Paralogismen der reinen

§ 46. People have long since observed, that in all substances the
proper subject, that which remains after all the accidents (as
predicates) are abstracted, consequently that which forms the
substance of things remains unknown, and various complaints have been
made concerning these limits to our knowledge. But it will be well to
consider that the human understanding is not to be blamed for its
inability to know the substance of things, that is, to determine it by
itself, but rather for requiring to cognise it which is a mere idea
definitely as though it were a given object. Pure reason requires us
to seek for every predicate of a thing its proper subject, and for
this subject, which is itself necessarily nothing but a predicate, its
subject, and so on indefinitely (or as far as we can reach). But hence
it follows, that we must not hold anything, at which we can arrive, to
be an ultimate subject, and that substance itself never can be thought
by our understanding, however deep we may penetrate, even if all
nature were unveiled to us. For the specific nature of our
understanding consists in thinking everything discursively, that is,
representing it by concepts, and so by mere predicates, to which
therefore the absolute subject must always be wanting. Hence all the
real properties, by which we cognise bodies, are mere accidents, not
excepting impenetrability, which we can only represent to ourselves as
the effect of a power of which the subject is unknown to us.

Now we appear to have this substance in the consciousness of ourselves
(in the thinking subject), and indeed in an immediate intuition; for
all the predicates of an internal sense refer to the ego, as a
subject, and I cannot conceive myself as the predicate of any other
subject. Hence completeness in the reference of the given concepts as
predicates to a subject—not merely an idea, but an object—that is,
the absolute subject itself, seems to be given in experience. But this
expectation is disappointed. For the ego is not a concept,{31} but only
the indication of the object of the internal sense, so far as we
cognise it by no further predicate. Consequently it cannot be in
itself a predicate of any other thing; but just as little can it be a
determinate concept of an absolute subject, but is, as in all other
cases, only the reference of the internal phenomena to their unknown
subject. Yet this idea (which serves very well, as a regulative
principle, totally to destroy all materialistic explanations of the
internal phenomena of the soul) occasions by a very natural
misunderstanding a very specious argument, which, from this supposed
cognition of the substance of our thinking being, infers its nature,
so far as the knowledge of it falls quite without the complex of

{31} Were the representation of the apperception (the Ego) a concept, by
which anything could be thought, it could be used as a predicate of
other things or contain predicates in itself. But it is nothing more
than the feeling of an existence without the least definite conception
and is only the representation of that to which all thinking stands in
relation (relatione accidentis).

§ 47. But though we may call this thinking self (the soul) substance,
as being the ultimate subject of thinking which cannot be further
represented as the predicate of another thing; it remains quite empty
and without significance, if permanence—the quality which renders
the concept of substances in experience fruitful—cannot be proved of

But permanence can never be proved of the concept of a substance, as a
thing in itself, but for the purposes of experience only. This is
sufficiently shown by the first Analogy of Experience,{32} and who ever
will not yield to this proof may try for himself whether he can
succeed in proving, from the concept of a subject which does not exist
itself as the predicate of another thing, that its existence is
thoroughly permanent, and that it cannot either in itself or by any
natural cause originate or be annihilated. These synthetical a priori
propositions can never be proved in themselves, but only in reference
to things as objects of possible experience.

{32} Cf. Critique, Von den Analogien der Erfahrung.

§ 48. If therefore from the concept of the soul as a substance, we
would infer its permanence, this can hold good as regards possible
experience only, not [of the soul] as a thing in itself and beyond all
possible experience. But life is the subjective condition of all our
possible experience, consequently we can only infer the permanence of
the soul in life; for the death of man is the end of all experience
which concerns the soul as an object of experience, except the
contrary be proved, which is the very question in hand. The permanence
of the soul can therefore only be proved (and no one cares for that)
during the life of man, but not, as we desire to do, after death; and
for this general reason, that the concept of substance, so far as it
is to be considered necessarily combined with the concept of
permanence, can be so combined only according to the principles of
possible experience, and therefore for the purposes of experience

{33} It is indeed very remarkable how carelessly metaphysicians have
always passed over the principle of the permanence of substances
without ever attempting a proof of it; doubtless because they found
themselves abandoned by all proofs as soon as they began to deal with
the concept of substance. Common sense, which felt distinctly that
without this presupposition do union of perceptions in experience is
possible, supplied the want by a postulate. From experience itself it
never could derive such a principle, partly because substances cannot
be so traced in all their alterations and dissolutions, that the
matter can always be found undiminished, partly because the principle
contains necessity, which is always the sign of an a priori principle.
People then boldly applied this postulate to the concept of soul as a
substance, and concluded a necessary continuance of the soul after the
death of man (especially as the simplicity of this substance, which is
inferred from the indivisibility of consciousness, secured it from
destruction by dissolution). Had they found the genuine source of this
principle—a discovery which requires deeper researches than they
were ever inclined to make—they would have seen, that the law of the
permanence of substances has place for the purposes of experience
only, and hence can hold good of things so far as they are to be
cognised and conjoined with others in experience, but never
independently of all possible experience, and consequently cannot hold
good of the soul after death.

§ 49. That there is something real without us which not only
corresponds, but must correspond, to our external perceptions, can
likewise be proved to be not a connexion of things in themselves, but
for the sake of experience. This means that there is something
empirical, i.e., some phenomenon in space without us, that admits of a
satisfactory proof, for we have nothing to do with other objects than
those which belong to possible experience; because objects which
cannot be given us in any experience, do not exist for us. Empirically
without me is that which appears in space, and space, together with
all the phenomena which it contains, belongs to the representations,
whose connexion according to laws of experience proves their objective
truth, just as the connexion of the phenomena of the internal sense
proves the actuality of my soul (as an object of the internal sense).
By means of external experience I am conscious of the actuality of
bodies, as external phenomena in space, in the same manner as by means
of the internal experience I am conscious of the existence of my soul
in time, but this soul is only cognised as an object of the internal
sense by phenomena that constitute an internal state, and of which the
essence in itself, which forms the basis of these phenomena, is
unknown. Cartesian idealism therefore does nothing but distinguish
external experience from dreaming; and the conformity to law (as a
criterion of its truth) of the former, from the irregularity and the
false illusion of the latter. In both it presupposes space and time as
conditions of the existence of objects, and it only inquires whether
the objects of the external senses, which we when awake put in space,
are as actually to be found in it, as the object of the internal
sense, the soul, is in time; that is, whether experience carries with
it sure criteria to distinguish it from imagination. This doubt,
however, may be easily disposed of, and we always do so in common life
by investigating the connexion of phenomena in both space and time
according to universal laws of experience, and we cannot doubt, when
the representation of external things throughout agrees therewith,
that they constitute truthful experience. Material idealism, in which
phenomena are considered as such only according to their connexion in
experience, may accordingly be very easily refuted; and it is just as
sure an experience, that bodies exist without us (in space), as that I
myself exist according to the representation of the internal sense (in
time): for the notion without us, only signifies existence in space.
However as the Ego in the proposition, "I am," means not only the
object of internal intuition (in time), but the subject of
consciousness, just as body means not only external intuition (in
space), but the thing-in-itself, which is the basis of this
phenomenon; [as this is the case] the question, whether bodies (as
phenomena of the external sense) exist as bodies apart from my
thoughts, may without any hesitation be denied in nature. But the
question, whether I myself as a phenomenon of the internal sense (the
soul according to empirical psychology) exist apart from my faculty of
representation in time, is an exactly similar inquiry, and must
likewise be answered in the negative. And in this manner everything,
when it is reduced to its true meaning, is decided and certain. The
formal (which I have also called transcendental) actually abolishes
the material, or Cartesian, idealism. For if space be nothing but a
form of my sensibility, it is as a representation in me just as actual
as I myself am, and nothing but the empirical truth of the
representations in it remains for consideration. But, if this is not
the case, if space and the phenomena in it are something existing
without us, then all the criteria of experience beyond our perception
can never prove the actuality of these objects without us.

II. The Cosmological Idea.{34}

{34} Cf. Critique, Die Antinomie der reinen Vernunft.

§ 50. This product of pure reason in its transcendent use is its most
remarkable curiosity. It serves as a very powerful agent to rouse
philosophy from its dogmatic slumber, and to stimulate it to the
arduous task of undertaking a Critique of Reason itself.

I term this idea cosmological, because it always takes its object only
from the sensible world, and does not use any other than those whose
object is given to sense, consequently it remains in this respect in
its native home, it does not become transcendent, and is therefore so
far not mere idea; whereas, to conceive the soul as a simple
substance, already means to conceive such an object (the simple) as
cannot be presented to the senses. Yet the cosmological idea extends
the connexion of the conditioned with its condition (whether the
connexion is mathematical or dynamical) so far, that experience never
can keep up with it. It is therefore with regard to this point always
an idea, whose object never can be adequately given in any experience.

§ 51. In the first place, the use of a system of categories becomes
here so obvious and unmistakable, that even if there were not several
other proofs of it, this alone would sufficiently prove it
indispensable in the system of pure reason. There are only four such
transcendent ideas, as there are so many classes of categories; in
each of which, however, they refer only to the absolute completeness
of the series of the conditions for a given conditioned. In analogy to
these cosmological ideas there are only four kinds of dialectical
assertions of pure reason, which, as they are dialectical, thereby
prove, that to each of them, on equally specious principles of pure
reason, a contradictory assertion stands opposed. As all the
metaphysical art of the most subtile distinction cannot prevent this
opposition, it compels the philosopher to recur to the first sources
of pure reason itself. This Antinomy, not arbitrarily invented, but
founded in the nature of human reason, and hence unavoidable and never
ceasing, contains the following four theses together with their


    The World has, as to Time and Space, a Beginning (limit).

       The World is, as to Time and Space, infinite.


  Everything in the World consists of [elements that are] simple.

      There is nothing simple, but everything is composite.


      There are in the World Causes through Freedom.

          There is no Liberty, but all is Nature.


   In the Series of the World-Causes there is some necessary Being.

There is Nothing necessary in the World, but in this Series All is

§ 52.a. Here is the most singular phenomenon of human reason, no
other instance of which can be shown in any other use. If we, as is
commonly done, represent to ourselves the appearances of the sensible
world as things in themselves, if we assume the principles of their
combination as principles universally valid of things in themselves
and not merely of experience, as is usually, nay without our Critique,
unavoidably done, there arises an unexpected conflict, which never can
be removed in the common dogmatical way; because the thesis, as well
as the antithesis, can be shown by equally clear, evident, and
irresistible proofs—for I pledge myself as to the correctness of all
these proofs—and reason therefore perceives that it is divided with
itself, a state at which the sceptic rejoices, but which must make the
critical philosopher pause and feel ill at ease.

§ 52.b. We may blunder in various ways in metaphysics without any
fear of being detected in falsehood. For we never can be refuted by
experience if we but avoid self-contradiction, which in synthetical,
though purely fictitious propositions, may be done whenever the
concepts, which we connect, are mere ideas, that cannot be given (in
their whole content) in experience. For how can we make out by
experience, whether the world is from eternity or had a beginning,
whether matter is infinitely divisible or consists of simple parts?
Such concept cannot be given in any experience, be it ever so
extensive, and consequently the falsehood either of the positive or
the negative proposition cannot be discovered by this touch-stone.

The only possible way in which reason could have revealed
unintentionally its secret Dialectics, falsely announced as Dogmatics,
would be when it were made to ground an assertion upon a universally
admitted principle, and to deduce the exact contrary with the greatest
accuracy of inference from another which is equally granted. This is
actually here the case with regard to four natural ideas of reason,
whence four assertions on the one side, and as many counter-assertions
on the other arise, each consistently following from
universally-acknowledged principles. Thus they reveal by the use of
these principles the dialectical illusion of pure reason which would
otherwise forever remain concealed.

This is therefore a decisive experiment, which must necessarily expose
any error lying hidden in the assumptions of reason.{35} Contradictory
propositions cannot both be false, except the concept, which is the
subject of both, is self-contradictory; for example, the propositions,
"a square circle is round, and a square circle is not round," are both
false. For, as to the former it is false, that the circle is round,
because it is quadrangular; and it is likewise false, that it is not
round, that is, angular, because it is a circle. For the logical
criterion of the impossibility of a concept consists in this, that if
we presuppose it, two contradictory propositions both become false;
consequently, as no middle between them is conceivable, nothing at all
is thought by that concept.

{35} I therefore would be pleased to have the critical reader to devote
to this antinomy of pure reason his chief attention, because nature
itself seems to have established it with a view to stagger reason in
its daring pretentions, and to force it to self-examination. For every
proof, which I have given, as well of the thesis as of the antithesis,
I undertake to be responsible, and thereby to show the certainty of
the inevitable antinomy of reason. When the reader is brought by this
curious phenomenon to fall back upon the proof of the presumption upon
which it rests, he will feel himself obliged to investigate the
ultimate foundation of all the cognition of pure reason with me more

§ 52.c. The first two antinomies, which I call mathematical, because
they are concerned with the addition or division of the homogeneous,
are founded on such a self-contradictory concept; and hence I explain
how it happens, that both the Thesis and Antithesis of the two are

When I speak of objects in time and in space, it is not of things in
themselves, of which I know nothing, but of things in appearance, that
is, of experience, as the particular way of cognising objects which is
afforded to man. I must not say of what I think in time or in space,
that in itself, and independent of these my thoughts, it exists in
space and in time; for in that case I should contradict myself;
because space and time, together with the appearances in them, are
nothing existing in themselves and outside of my representations, but
are themselves only modes of representation, and it is palpably
contradictory to say, that a mere mode of representation exists
without our representation. Objects of the senses therefore exist only
in experience; whereas to give them a self-subsisting existence apart
from experience or before it, is merely to represent to ourselves that
experience actually exists apart from experience or before it.

Now if I inquire after the quantity of the world, as to space and
time, it is equally impossible, as regards all my notions, to declare
it infinite or to declare it finite. For neither assertion can be
contained in experience, because experience either of an infinite
space, or of an infinite time elapsed, or again, of the boundary of
the world by a void space, or by an antecedent void time, is
impossible; these are mere ideas. This quantity of the world, which is
determined in either way, should therefore exist in the world itself
apart from all experience. This contradicts the notion of a world of
sense, which is merely a complex of the appearances whose existence
and connexion occur only in our representations, that is, in
experience, since this latter is not an object in itself, but a mere
mode of representation. Hence it follows, that as the concept of an
absolutely existing world of sense is self-contradictory, the solution
of the problem concerning its quantity, whether attempted
affirmatively or negatively, is always false.

The same holds good of the second antinomy, which relates to the
division of phenomena. For these are mere representations, and the
parts exist merely in their representation, consequently in the
division, or in a possible experience where they are given, and the
division reaches only as far as this latter reaches. To assume that an
appearance, e.g., that of body, contains in itself before all
experience all the parts, which any possible experience can ever
reach, is to impute to a mere appearance, which can exist only in
experience, an existence previous to experience. In other words, it
would mean that mere representations exist before they can be found in
our faculty of representation. Such an assertion is
self-contradictory, as also every solution of our misunderstood
problem, whether we maintain, that bodies in themselves consist of an
infinite number of parts, or of a finite number of simple parts.

§ 53. In the first (the mathematical) class of antinomies the
falsehood of the assumption consists in representing in one concept
something self-contradictory as if it were compatible (i.e., an
appearance as an object in itself). But, as to the second (the
dynamical) class of antinomies, the falsehood of the representation
consists in representing as contradictory what is compatible; so that,
as in the former case, the opposed assertions are both false, in this
case, on the other hand, where they are opposed to one another by mere
misunderstanding, they may both be true.

Any mathematical connexion necessarily presupposes homogeneity of what
is connected (in the concept of magnitude), while the dynamical one by
no means requires the same. When we have to deal with extended
magnitudes, all the parts must be homogeneous with one another and
with the whole; whereas, in the connexion of cause and effect,
homogeneity may indeed likewise be found, but is not necessary; for
the concept of causality (by means of which something is posited
through something else quite different from it), at all events, does
not require it.

If the objects of the world of sense are taken for things in
themselves, and the above laws of nature for the laws of things in
themselves, the contradiction would be unavoidable. So also, if the
subject of freedom were, like other objects, represented as mere
appearance, the contradiction would be just as unavoidable, for the
same predicate would at once be affirmed and denied of the same kind
of object in the same sense. But if natural necessity is referred
merely to appearances, and freedom merely to things in themselves, no
contradiction arises, if we at once assume, or admit both kinds of
causality, however difficult or impossible it may be to make the
latter kind conceivable.

As appearance every effect is an event, or something that happens in
time; it must, according to the universal law of nature, be preceded
by a determination of the causality of its cause (a state), which
follows according to a constant law. But this determination of the
cause as causality must likewise be something that takes place or
happens; the cause must have begun to act, otherwise no succession
between it and the effect could be conceived. Otherwise the effect, as
well as the causality of the cause, would have always existed.
Therefore the determination of the cause to act must also have
originated among appearances, and must consequently, as well as its
effect, be an event, which must again have its cause, and so on; hence
natural necessity must be the condition, on which effective causes are
determined. Whereas if freedom is to be a property of certain causes
of appearances, it must, as regards these, which are events, be a
faculty of starting them spontaneously, that is, without the causality
of the cause itself, and hence without requiring any other ground to
determine its start. But then the cause, as to its causality, must not
rank under time-determinations of its state, that is, it cannot be an
appearance, and must be considered a thing in itself, while its
effects would be only appearances.{36} If without contradiction we can
think of the beings of understanding [Verstandeswesen] as exercising
such an influence on appearances, then natural necessity will attach
to all connexions of cause and effect in the sensuous world, though on
the other hand, freedom can be granted to such cause, as is itself not
an appearance (but the foundation of appearance). Nature therefore and
freedom can without contradiction be attributed to the very same
thing, but in different relations—on one side as a phenomenon, on
the other as a thing in itself.

{36} The idea of freedom occurs only in the relation of the
intellectual, as cause, to the appearance, as effect. Hence we cannot
attribute freedom to matter in regard to the incessant action by which
it fills its space, though this action takes place from an internal
principle. We can likewise find no notion of freedom suitable to
purely rational beings, for instance, to God, so far as his action is
immanent. For his action, though independent of external determining
causes, is determined in his eternal reason, that is, in the divine
nature. It is only, if something is to start by an action, and so the
effect occurs in the sequence of time, or in the world of sense (e.g.,
the beginning of the world), that we can put the question, whether the
causality of the cause must in its turn have been started, or whether
the cause can originate an effect without its causality itself
beginning. In the former case the concept of this causality is a
concept of natural necessity, in the latter, that of freedom. From
this the reader will see, that, as I explained freedom to be the
faculty of starting an event spontaneously, I have exactly hit the
notion which is the problem of metaphysics.

We have in us a faculty, which not only stands in connexion with its
subjective determining grounds that are the natural causes of its
actions, and is so far the faculty of a being that itself belongs to
appearances, but is also referred to objective grounds, that are only
ideas, so far as they can determine this faculty, a connexion which is
expressed by the word ought. This faculty is called reason, and, so
far as we consider a being (man) entirely according to this
objectively determinable reason, he cannot be considered as a being of
sense, but this property is that of a thing in itself, of which we
cannot comprehend the possibility—I mean how the ought (which
however has never yet taken place) should determine its activity, and
can become the cause of actions, whose effect is an appearance in the
sensible world. Yet the causality of reason would be freedom with
regard to the effects in the sensuous world, so far as we can consider
objective grounds, which are themselves ideas, as their determinants.
For its action in that case would not depend upon subjective
conditions, consequently not upon those of time, and of course not
upon the law of nature, which serves to determine them, because
grounds of reason give to actions the rule universally, according to
principles, without the influence of the circumstances of either time
or place.

What I adduce here is merely meant as an example to make the thing
intelligible, and does not necessarily belong to our problem, which
must be decided from mere concepts, independently of the properties
which we meet in the actual world.

Now I may say without contradiction: that all the actions of rational
beings, so far as they are appearances (occurring in any experience),
are subject to the necessity of nature; but the same actions, as
regards merely the rational subject and its faculty of acting
according to mere reason, are free. For what is required for the
necessity of nature? Nothing more than the determinability of every
event in the world of sense according to constant laws, that is, a
reference to cause in the appearance; in this process the thing in
itself at its foundation and its causality remain unknown. But I say,
that the law of nature remains, whether the rational being is the
cause of the effects in the sensuous world from reason, that is,
through freedom, or whether it does not determine them on grounds of
reason. For, if the former is the case, the action is performed
according to maxims, the effect of which as appearance is always
conform able to constant laws; if the latter is the case, and the
action not performed on principles of reason, it is subjected to the
empirical laws of the sensibility, and in both cases the effects are
connected according to constant laws; more than this we do not require
or know concerning natural necessity. But in the former case reason is
the cause of these laws of nature, and therefore free; in the latter
the effects follow according to mere natural laws of sensibility,
because reason does not influence it; but reason itself is not
determined on that account by the sensibility, and is therefore free
in this case too. Freedom is therefore no hindrance to natural law in
appearance, neither does this law abrogate the freedom of the
practical use of reason, which is connected with things in themselves,
as determining grounds.

Thus practical freedom, viz., the freedom in which reason possesses
causality according to objectively determining grounds, is rescued and
yet natural necessity is not in the least curtailed with regard to the
very same effects, as appearances. The same remarks will serve to
explain what we had to say concerning transcendental freedom and its
compatibility with natural necessity (in the same subject, but not
taken in the same reference). For, as to this, every beginning of the
action of a being from objective causes regarded as determining
grounds, is always a first start, though the same action is in the
series of appearances only a subordinate start, which must be preceded
by a state of the cause, which determines it, and is itself determined
in the same manner by another immediately preceding. Thus we are able,
in rational beings, or in beings generally, so far as their causality
is determined in them as things in themselves, to imagine a faculty of
beginning from itself a series of states, without falling into
contradiction with the laws of nature. For the relation of the action
to objective grounds of reason is not a time-relation; in this case
that which determines the causality does not precede in time the
action, because such determining grounds represent not a reference to
objects of sense, e.g., to causes in the appearances, but to
determining causes, as things in themselves, which do not rank under
conditions of time. And in this way the action, with regard to the
causality of reason, can be considered as a first start in respect to
the series of appearances, and yet also as a merely subordinate
beginning. We may therefore without contradiction consider it in the
former aspect as free, but in the latter (in so far as it is merely
appearance) as subject to natural necessity.

As to the fourth Antinomy, it is solved in the same way as the
conflict of reason with itself in the third. For, provided the cause
in the appearance is distinguished from the cause of the appearance
(so far as it can be thought as a thing in itself), both propositions
are perfectly reconcilable: the one, that there is nowhere in the
sensuous world a cause (according to similar laws of causality), whose
existence is absolutely necessary; the other, that this world is
nevertheless connected with a Necessary Being as its cause (but of
another kind and according to another law). The incompatibility of
these propositions entirely rests upon the mistake of extending what
is valid merely of appearances to things in themselves, and in general
confusing both in one concept.

§ 54. This then is the proposition and this the solution of the whole
antinomy, in which reason finds itself involved in the application of
its principles to the sensible world. The former alone (the mere
proposition) would be a considerable service in the cause of our
knowledge of human reason, even though the solution might fail to
fully satisfy the reader, who has here to combat a natural illusion,
which has been but recently exposed to him, and which he had hitherto
always regarded as genuine. For one result at least is unavoidable. As
it is quite impossible to prevent this conflict of reason with
itself—so long as the objects of the sensible world are taken for
things in themselves, and not for mere appearances, which they are in
fact—the reader is thereby compelled to examine over again the
deduction of all our a priori cognition and the proof which I have
given of my deduction in order to come to a decision on the question.
This is all I require at present; for when in this occupation he shall
have thought himself deep enough into the nature of pure reason, those
concepts by which alone the solution of the conflict of reason is
possible, will become sufficiently familiar to him. Without this
preparation I cannot expect an unreserved assent even from the most
attentive reader.

III. The Theological Idea.{37}

{37} Cf. Critique, the chapter on "Transcendental Ideals."

§ 55. The third transcendental Idea, which affords matter for the
most important, but, if pursued only speculatively, transcendent and
thereby dialectical use of reason, is the ideal of pure reason. Reason
in this case does not, as with the psychological and the cosmological
Ideas, begin from experience, and err by exaggerating its grounds, in
striving to attain, if possible, the absolute completeness of their
series. It rather totally breaks with experience, and from mere
concepts of what constitutes the absolute completeness of a thing in
general, consequently by means of the idea of a most perfect primal
Being, it proceeds to determine the possibility and therefore the
actuality of all other things. And so the mere presupposition of a
Being, who is conceived not in the series of experience, yet for the
purposes of experience—for the sake of comprehending its connexion,
order, and unity—i.e., the idea [the notion of it], is more easily
distinguished from the concept of the understanding here, than in the
former cases. Hence we can easily expose the dialectical illusion
which arises from our making the subjective conditions of our thinking
objective conditions of objects themselves, and an hypothesis
necessary for the satisfaction of our reason, a dogma. As the
observations of the Critique on the pretensions of transcendental
theology are intelligible, clear, and decisive, I have nothing more to
add on the subject.

General Remark on the Transcendental Ideas.

§ 56. The objects, which are given us by experience, are in many
respects incomprehensible, and many questions, to which the law of
nature leads us, when carried beyond a certain point (though quite
conformably to the laws of nature), admit of no answer; as for example
the question: why substances attract one another? But if we entirely
quit nature, or in pursuing its combinations, exceed all possible
experience, and so enter the realm of mere ideas, we cannot then say
that the object is incomprehensible, and that the nature of things
proposes to us insoluble problems. For we are not then concerned with
nature or in general with given objects, but with concepts, which have
their origin merely in our reason, and with mere creations of thought;
and all the problems that arise from our notions of them must be
solved, because of course reason can and must give a full account of
its own procedure.{38} As the psychological, cosmological, and
theological Ideas are nothing but pure concepts of reason, which
cannot be given in any experience, the questions which reason asks us
about them are put to us not by the objects, but by mere maxims of our
reason for the sake of its own satisfaction. They must all be capable
of satisfactory answers, which is done by showing that they are
principles which bring our use of the understanding into thorough
agreement, completeness, and synthetical unity, and that they so far
hold good of experience only, but of experience as a whole.

{38} Herr Platner in his Aphorisms acutely says (§§ 728, 729), "If
reason be a criterion, no concept, which is incomprehensible to human
reason, can be possible. Incomprehensibility has place in what is
actual only. Here in comprehensibility arises from the insufficiency
of the acquired ideas." It sounds paradoxical, but is otherwise not
strange to say, that in nature there is much incomprehensible (e.g.,
the faculty of generation) but if we mount still higher, and even go
beyond nature, everything again becomes comprehensible; for we then
quit entirely the objects, which can be given us, and occupy ourselves
merely about ideas, in which occupation we can easily comprehend the
law that reason prescribes by them to the understanding for its use in
experience, because the law is the reason's own production.

Although an absolute whole of experience is impossible, the idea of a
whole of cognition according to principles must impart to our
knowledge a peculiar kind of unity, that of a system, without which it
is nothing but piecework, and cannot be used for proving the existence
of a highest purpose (which can only be the general system of all
purposes), I do not here refer only to the practical, but also to the
highest purpose of the speculative use of reason.

The transcendental Ideas therefore express the peculiar application of
reason as a principle of systematic unity in the use of the
understanding. Yet if we assume this unity of the mode of cognition to
be attached to the object of cognition, if we regard that which is
merely regulative to be constitutive, and if we persuade ourselves
that we can by means of these Ideas enlarge our cognition
transcendently, or far beyond all possible experience, while it only
serves to render experience within itself as nearly complete as
possible, i.e., to limit its progress by nothing that cannot belong to
experience: we suffer from a mere misunderstanding in our estimate of
the proper application of our reason and of its principles, and from a
Dialectic, which both confuses the empirical use of reason, and also
sets reason at variance with itself.


On the Determination of the Bounds of Pure Reason.

§ 57. Having adduced the clearest arguments, it would be absurd for
us to hope that we can know more of any object, than belongs to the
possible experience of it, or lay claim to the least atom of knowledge
about anything not assumed to be an object of possible experience,
which would determine it according to the constitution it has in
itself. For how could we determine anything in this way, since time,
space, and the categories, and still more all the concepts formed by
empirical experience or perception in the sensible world (Anschauung),
have and can have no other use, than to make experience possible. And
if this condition is omitted from the pure concepts of the
understanding, they do not determine any object, and have no meaning

But it would be on the other hand a still greater absurdity if we
conceded no things in themselves, or set up our experience for the
only possible mode of knowing things, our way of beholding
(Anschauung) them in space and in time for the only possible way, and
our discursive understanding for the archetype of every possible
understanding; in fact if we wished to have the principles of the
possibility of experience considered universal conditions of things in

Our principles, which limit the use of reason to possible experience,
might in this way become transcendent, and the limits of our reason be
set up as limits of the possibility of things in themselves (as Hume's
dialogues may illustrate), if a careful critique did not guard the
bounds of our reason with respect to its empirical use, and set a
limit to its pretensions. Scepticism originally arose from metaphysics
and its licentious dialectics. At first it might, merely to favor the
empirical use of reason, announce everything that transcends this use
as worthless and deceitful; but by and by, when it was perceived that
the very same principles that are used in experience, insensibly, and
apparently with the same right, led still further than experience
extends, then men began to doubt even the propositions of experience.
But here there is no danger; for common sense will doubtless always
assert its rights. A certain confusion, however, arose in science
which cannot determine how far reason is to be trusted, and why only
so far and no further, and this confusion can only be cleared up and
all future relapses obviated by a formal determination, on principle,
of the boundary of the use of our reason.

We cannot indeed, beyond all possible experience, form a definite
notion of what things in themselves may be. Yet we are not at liberty
to abstain entirely from inquiring into them; for experience never
satisfies reason fully, but in answering questions, refers us further
and further back, and leaves us dissatisfied with regard to their
complete solution. This any one may gather from the Dialectics of pure
reason, which therefore has its good subjective grounds. Having
acquired, as regards the nature of our soul, a clear conception of the
subject, and having come to the conviction, that its manifestations
cannot be explained materialistically, who can refrain from asking
what the soul really is, and, if no concept of experience suffices for
the purpose, from accounting for it by a concept of reason (that of a
simple immaterial being), though we cannot by any means prove its
objective reality? Who can satisfy himself with mere empirical
knowledge in all the cosmological questions of the duration and of the
quantity of the world, of freedom or of natural necessity, since every
answer given on principles of experience begets a fresh question,
which likewise requires its answer and thereby clearly shows the
insufficiency of all physical modes of explanation to satisfy reason?
Finally, who does not see in the thorough-going contingency and
dependence of all his thoughts and assumptions on mere principles of
experience, the impossibility of stopping there? And who does not feel
himself compelled, notwithstanding all interdictions against losing
himself in transcendent ideas, to seek rest and contentment beyond all
the concepts which he can vindicate by experience, in the concept of a
Being, the possibility of which we cannot conceive, but at the same
time cannot be refuted, because it relates to a mere being of the
understanding, and without it reason must needs remain forever

Bounds (in extended beings) always presuppose a space existing outside
a certain definite place, and in closing it; limits do not require
this, but are mere negations, which affect a quantity, so far as it is
not absolutely complete. But our reason, as it were, sees in its
surroundings a space for the cognition of things in themselves, though
we can never have definite notions of them, and are limited to
appearances only.

As long as the cognition of reason is homogeneous, definite bounds to
it are inconceivable. In mathematics and in natural philosophy human
reason admits of limits, but not of bounds, viz., that something
indeed lies without it, at which it can never arrive, but not that it
will at any point find completion in its internal progress. The
enlarging of our views in mathematics, and the possibility of new
discoveries, are infinite; and the same is the case with the discovery
of new properties of nature, of new powers and laws, by continued
experience and its rational combination. But limits cannot be mistaken
here, for mathematics refers to appearances only, and what cannot be
an object of sensuous contemplation, such as the concepts of
metaphysics and of morals, lies entirely without its sphere, and it
can never lead to them; neither does it require them. It is therefore
not a continual progress and an approximation towards these sciences,
and there is not, as it were, any point or line of contact. Natural
science will never reveal to us the internal constitution of things,
which though not appearance, yet can serve as the ultimate ground of
explaining appearance. Nor does that science require this for its
physical explanations. Nay even if such grounds should be offered from
other sources (for instance, the influence of immaterial beings), they
must be rejected and not used in the progress of its explanations. For
these explanations must only be grounded upon that which as an object
of sense can belong to experience, and be brought into connexion with
our actual perceptions and empirical laws.

But metaphysics leads us towards bounds in the dialectical attempts of
pure reason (not undertaken arbitrarily or wantonly, but stimulated
thereto by the nature of reason itself). And the transcendental Ideas,
as they do not admit of evasion, and are never capable of realisation,
serve to point out to us actually not only the bounds of the pure use
of reason, but also the way to determine them. Such is the end and the
use of this natural predisposition of our reason, which has brought
forth metaphysics as its favorite child, whose generation, like every
other in the world, is not to be ascribed to blind chance, but to an
original germ, wisely organised for great ends. For metaphysics, in
its fundamental features, perhaps more than any other science, is
placed in us by nature itself, and cannot be considered the production
of an arbitrary choice or a casual enlargement in the progress of
experience from which it is quite disparate.

Reason with all its concepts and laws of the understanding, which
suffice for empirical use, i.e., within the sensible world, finds in
itself no satisfaction because ever-recurring questions deprive us of
all hope of their complete solution. The transcendental ideas, which
have that completion in view, are such problems of reason. But it sees
clearly, that the sensuous world cannot contain this completion,
neither consequently can all the concepts, which serve merely for
understanding the world of sense, such as space and time, and whatever
we have adduced under the name of pure concepts of the understanding.
The sensuous world is nothing but a chain of appearances connected
according to universal laws; it has therefore no subsistence by
itself; it is not the thing in itself, and consequently must point to
that which contains the basis of this experience, to beings which
cannot be cognised merely as phenomena, but as things in themselves.
In the cognition of them alone reason can hope to satisfy its desire
of completeness in proceeding from the conditioned to its conditions.

We have above (§§ 33, 34) indicated the limits of reason with regard
to all cognition of mere creations of thought. Now, since the
transcendental ideas have urged us to approach them, and thus have led
us, as it were, to the spot where the occupied space (viz.,
experience) touches the void (that of which we can know nothing, viz.,
noumena), we can determine the bounds of pure reason. For in all
bounds there is something positive (e.g., a surface is the boundary of
corporeal space, and is therefore itself a space, a line is a space,
which is the boundary of the surface, a point the boundary of the
line, but yet always a place in space), whereas limits contain mere
negations. The limits pointed out in those paragraphs are not enough
after we have discovered that beyond them there still lies something
(though we can never cognise what it is in itself). For the question
now is, What is the attitude of our reason in this connexion of what
we know with what we do not, and never shall, know? This is an actual
connexion of a known thing with one quite unknown (and which will
always remain so), and though what is unknown should not become the
least more known—which we cannot even hope—yet the notion of this
connexion must be definite, and capable of being rendered distinct.

We must therefore accept an immaterial being, a world of
understanding, and a Supreme Being (all mere noumena), because in them
only, as things in themselves, reason finds that completion and
satisfaction, which it can never hope for in the derivation of
appearances from their homogeneous grounds, and because these actually
have reference to something distinct from them (and totally
heterogeneous), as appearances always presuppose an object in itself,
and therefore suggest its existence whether we can know more of it or

But as we can never cognise these beings of understanding as they are
in themselves, that is, definitely, yet must assume them as regards
the sensible world, and connect them with it by reason, we are at
least able to think this connexion by means of such concepts as
express their relation to the world of sense. Yet if we represent to
ourselves a being of the understanding by nothing but pure concepts of
the understanding, we then indeed represent nothing definite to
ourselves, consequently our concept has no significance; but if we
think it by properties borrowed from the sensuous world, it is no
longer a being of understanding, but is conceived as an appearance,
and belongs to the sensible world. Let us take an instance from the
notion of the Supreme Being.

Our deistic conception is quite a pure concept of reason, but
represents only a thing containing all realities, without being able
to determine any one of them; because for that purpose an example must
be taken from the world of sense, in which case we should have an
object of sense only, not something quite heterogeneous, which can
never be an object of sense. Suppose I attribute to the Supreme Being
understanding, for instance; I have no concept of an understanding
other than my own, one that must receive its perceptions (Anschauung)
by the senses, and which is occupied in bringing them under rules of
the unity of consciousness. Then the elements of my concept would
always lie in the appearance; I should however by the insufficiency of
the appearance be necessitated to go beyond them to the concept of a
being which neither depends upon appearance, nor is bound up with them
as conditions of its determination. But if I separate understanding
from sensibility to obtain a pure understanding, then nothing remains
but the mere form of thinking without perception (Anschauung), by
which form alone I can cognise nothing definite, and consequently no
object. For that purpose I should conceive another understanding, such
as would directly perceive its objects,{39} but of which I have not the
least notion; because the human understanding is discursive, and can
[not directly perceive, it can] only cognise by means of general
concepts. And the very same difficulties arise if we attribute a will
to the Supreme Being; for we have this concept only by drawing it from
our internal experience, and therefore from our dependence for
satisfaction upon objects whose existence we require; and so the
notion rests upon sensibility, which is absolutely incompatible with
the pure concept of the Supreme Being.

{39} Der die Gegenstände anschaute.

Hume's objections to deism are weak, and affect only the proofs, and
not the deistic assertion itself. But as regards theism, which depends
on a stricter determination of the concept of the Supreme Being which
in deism is merely transcendent, they are very strong, and as this
concept is formed, in certain (in fact in all common) cases
irrefutable. Hume always insists, that by the mere concept of an
original being, to which we apply only ontological predicates
(eternity, omnipresence, omnipotence), we think nothing definite, and
that properties which can yield a concept in concreto must be
superadded; that it is not enough to say, it is Cause, but we must
explain the nature of its causality, for example, that of an
understanding and of a will. He then begins his attacks on the
essential point itself, i.e., theism, as he had previously directed
his battery only against the proofs of deism, an attack which is not
very dangerous to it in its consequences. All his dangerous arguments
refer to anthropomorphism, which he holds to be inseparable from
theism, and to make it absurd in itself; but if the former be
abandoned, the latter must vanish with it, and nothing remain but
deism, of which nothing can come, which is of no value, and which
cannot serve as any foundation to religion or morals. If this
anthropomorphism were really unavoidable, no proofs whatever of the
existence of a Supreme Being, even were they all granted, could
determine for us the concept of this Being without involving us in

If we connect with the command to avoid all transcendent judgments of
pure reason, the command (which apparently conflicts with it) to
proceed to concepts that lie beyond the field of its immanent
(empirical) use, we discover that both can subsist together, but only
at the boundary of all lawful use of reason. For this boundary belongs
as well to the field of experience, as to that of the creations of
thought, and we are thereby taught, as well, how these so remarkable
ideas serve merely for marking the bounds of human reason. On the one
hand they give warning not boundlessly to extend cognition of
experience, as if nothing but world{40} remained for us to cognise, and
yet, on the other hand, not to transgress the bounds of experience,
and to think of judging about things beyond them, as things in

{40} The use of the word "world" without article, though odd, seems to
be the correct reading, but it may be a mere misprint.— Ed.

But we stop at this boundary if we limit our judgment merely to the
relation which the world may have to a Being whose very concept lies
beyond all the knowledge which we can attain within the world. For we
then do not attribute to the Supreme Being any of the properties in
themselves, by which we represent objects of experience, and thereby
avoid dogmatic anthropomorphism; but we attribute them to his relation
to the world, and allow ourselves a symbolical anthropomorphism, which
in fact concerns language only, and not the object itself.

If I say that we are compelled to consider the world, as if it were
the work of a Supreme Understanding and Will, I really say nothing
more, than that a watch, a ship, a regiment, bears the same relation
to the watchmaker, the shipbuilder, the commanding officer, as the
world of sense (or whatever constitutes the substratum of this complex
of appearances) does to the Unknown, which I do not hereby cognise as
it is in itself, but as it is for me or in relation to the world, of
which I am a part.

§ 58. Such a cognition is one of analogy, and does not signify (as is
commonly understood) an imperfect similarity of two things, but a
perfect similarity of relations between two quite dissimilar things.{41}
By means of this analogy, however, there remains a concept of the
Supreme Being sufficiently determined for us, though we have left out
everything that could deter mine it absolutely or in itself; for we
determine it as regards the world and as regards ourselves, and more
do we not require. The attacks which Hume makes upon those who would
determine this concept absolutely, by taking the materials for so
doing from themselves and the world, do not affect us; and he cannot
object to us, that we have nothing left if we give up the objective
anthropomorphism of the concept of the Supreme Being.

{41} There is, e.g., an analogy between the juridical relation of human
actions and the mechanical relation of motive powers. I never can do
anything to another man without giving him a right to do the same to
me on the same conditions; just as no mass can act with its motive
power on another mass without thereby occasioning the other to react
equally against it. Here right and motive power are quite dissimilar
things, but in their relation there is complete similarity. By means
of such an analogy I can obtain a notion of the relation of things
which absolutely are unknown to me. For instance, as the promotion of
the welfare of children (= a) is to the love of parents (= b), so the
welfare of the human species (= c) is to that unknown [quantity which
is] in God (= x), which we call love; not as if it had the least
similarity to any human inclination, but because we can suppose its
relation to the world to be similar to that which things of the world
bear one another. But the concept of relation in this case is a mere
category, viz., the concept of cause, which has nothing to do with

For let us assume at the outset (as Hume in his dialogues makes Philo
grant Cleanthes), as a necessary hypothesis, the deistical concept of
the First Being, in which this Being is thought by the mere
ontological predicates of substance, of cause, etc. This must be done,
because reason, actuated in the sensible world by mere conditions,
which are themselves always conditional, cannot otherwise have any
satisfaction, and it therefore can be done without falling into
anthropomorphism (which transfers predicates from the world of sense
to a Being quite distinct from the world), because those predicates
are mere categories, which, though they do not give a determinate
concept of God, yet give a concept not limited to any conditions of
sensibility. Thus nothing can prevent our predicating of this Being a
causality through reason with regard to the world, and thus passing to
theism, without being obliged to attribute to God in himself this kind
of reason, as a property inhering in him. For as to the former, the
only possible way of prosecuting the use of reason (as regards all
possible experience, in complete harmony with itself) in the world of
sense to the highest point, is to assume a supreme reason as a cause
of all the connexions in the world. Such a principle must be quite
advantageous to reason and can hurt it nowhere in its application to
nature. As to the latter, reason is thereby not transferred as a
property to the First Being in himself, but only to his relation to
the world of sense, and so anthropomorphism is entirely avoided. For
nothing is considered here but the cause of the form of reason which
is perceived everywhere in the world, and reason is attributed to the
Supreme Being, so far as it contains the ground of this form of reason
in the world, but according to analogy only, that is, so far as this
expression shows merely the relation, which the Supreme Cause unknown
to us has to the world, in order to determine everything in it
conformably to reason in the highest degree. We are thereby kept from
using reason as an attribute for the purpose of conceiving God, but
instead of conceiving the world in such a manner as is necessary to
have the greatest possible use of reason according to principle. We
thereby acknowledge that the Supreme Being is quite inscrutable and
even unthinkable in any definite way as to what he is in himself. We
are thereby kept, on the one hand, from making a transcendent use of
the concepts which we have of reason as an efficient cause (by means
of the will), in order to determine the Divine Nature by properties,
which are only borrowed from human nature, and from losing ourselves
in gross and extravagant notions, and on the other hand from deluging
the contemplation of the world with hyperphysical modes of explanation
according to our notions of human reason, which we transfer to God,
and so losing for this contemplation its proper application, according
to which it should be a rational study of mere nature, and not a
presumptuous derivation of its appearances from a Supreme Reason. The
expression suited to our feeble notions is, that we conceive the world
as if it came, as to its existence and internal plan, from a Supreme
Reason, by which notion we both cognise the constitution, which
belongs to the world itself, yet without pretending to determine the
nature of its cause in itself, and on the other hand, we transfer the
ground of this constitution (of the form of reason in the world) upon
the relation of the Supreme Cause to the world, without finding the
world sufficient by itself for that purpose.{42}

{42} I may say, that the causality of the Supreme Cause holds the same
place with regard to the world that human reason does with regard to
its works of art. Here the nature of the Supreme Cause itself remains
unknown to me: I only compare its effects (the order of the world)
which I know, and their conformity to reason, to the effects of human
reason which I also know; and hence I term the former reason, without
attributing to it on that account what I understand in man by this
term, or attaching to it anything else known to me, as its property.

Thus the difficulties which seem to oppose theism disappear by
combining with Hume's principle—"not to carry the use of reason
dogmatically beyond the field of all possible experience"—this other
principle, which he quite overlooked: "not to consider the field of
experience as one which bounds itself in the eye of our reason." The
Critique of Pure Reason here points out the true mean between
dogmatism, which Hume combats, and skepticism, which he would
substitute for it—a mean which is not like other means that we find
advisable to determine for ourselves as it were mechanically (by
adopting something from one side and something from the other), and by
which nobody is taught a better way, but such a one as can be
accurately determined on principles.

§ 59. At the beginning of this annotation I made use of the metaphor
of a boundary, in order to establish the limits of reason in regard to
its suitable use. The world of sense contains merely appearances,
which are not things in themselves, but the understanding must assume
these latter ones, viz., noumena. In our reason both are comprised,
and the question is, How does reason proceed to set boundaries to the
understanding as regards both these fields? Experience, which contains
all that belongs to the sensuous world, does not bound itself; it only
proceeds in every case from the conditioned to some other equally
conditioned object. Its boundary must lie quite without it, and this
field is that of the pure beings of the understanding. But this field,
so far as the determination of the nature of these beings is
concerned, is an empty space for us, and if dogmatically-determined
concepts alone are in question, we cannot pass out of the field of
possible experience. But as a boundary itself is something positive,
which belongs as well to that which lies within, as to the space that
lies without the given complex, it is still an actual positive
cognition, which reason only acquires by enlarging itself to this
boundary, yet without attempting to pass it; because it there finds
itself in the presence of an empty space, in which it can conceive
forms of things, but not things themselves. But the setting of a
boundary to the field of the understanding by something, which is
otherwise unknown to it, is still a cognition which belongs to reason
even at this standpoint, and by which it is neither confined within
the sensible, nor straying without it, but only refers, as befits the
knowledge of a boundary, to the relation between that which lies
without it, and that which is contained within it.

Natural theology is such a concept at the boundary of human reason,
being constrained to look beyond this boundary to the Idea of a
Supreme Being (and, for practical purposes to that of an intelligible
world also), not in order to determine anything relatively to this
pure creation of the understanding, which lies beyond the world of
sense, but in order to guide the use of reason within it according to
principles of the greatest possible (theoretical as well as practical)
unity. For this purpose we make use of the reference of the world of
sense to an independent reason, as the cause of all its connexions.
Thereby we do not purely invent a being, but, as beyond the sensible
world there must be something that can only be thought by the pure
understanding, we determine that something in this particular way,
though only of course according to analogy.

And thus there remains our original proposition, which is the résumé
of the whole Critique: "that reason by all its a priori principles
never teaches us anything more than objects of possible experience,
and even of these nothing more than can be cognised in experience."
But this limitation does not prevent reason leading us to the
objective boundary of experience, viz., to the reference to something
which is not itself an object of experience, but is the ground of all
experience. Reason does not however teach us anything concerning the
thing in itself: it only instructs us as regards its own complete and
highest use in the field of possible experience. But this is all that
can be reasonably desired in the present case, and with which we have
cause to be satisfied.

§ 60. Thus we have fully exhibited metaphysics as it is actually
given in the natural predisposition of human reason, and in that which
constitutes the essential end of its pursuit, according to its
subjective possibility. Though we have found, that this merely natural
use of such a predisposition of our reason, if no discipline arising
only from a scientific critique bridles and sets limits to it,
involves us in transcendent, either apparently or really conflicting,
dialectical syllogisms; and this fallacious metaphysics is not only
unnecessary as regards the promotion of our knowledge of nature, but
even disadvantageous to it: there yet remains a problem worthy of
solution, which is to find out the natural ends intended by this
disposition to transcendent concepts in our reason, because everything
that lies in nature must be originally intended for some useful

Such an inquiry is of a doubtful nature; and I acknowledge, that what
I can say about it is conjecture only, like every speculation about
the first ends of nature. The question does not concern the objective
validity of metaphysical judgments, but our natural predisposition to
them, and therefore does not belong to the system of metaphysics but
to anthropology.

When I compare all the transcendental Ideas, the totality of which
constitutes the particular problem of natural pure reason, compelling
it to quit the mere contemplation of nature, to transcend all possible
experience, and in this endeavor to produce the thing (be it knowledge
or fiction) called metaphysics, I think I perceive that the aim of
this natural tendency is, to free our notions from the fetters of
experience and from the limits of the mere contemplation of nature so
far as at least to open to us a field containing mere objects for the
pure understanding, which no sensibility can reach, not indeed for the
purpose of speculatively occupying ourselves with them (for there we
can find no ground to stand on), but because practical principles,
which, without finding some such scope for their necessary expectation
and hope, could not expand to the universality which reason
unavoidably requires from a moral point of view.

So I find that the Psychological Idea (however little it may reveal to
me the nature of the human soul, which is higher than all concepts of
experience), shows the insufficiency of these concepts plainly enough,
and thereby deters me from materialism, the psychological notion of
which is unfit for any explanation of nature, and besides confines
reason in practical respects. The Cosmological Ideas, by the obvious
insufficiency of all possible cognition of nature to satisfy reason in
its lawful inquiry, serve in the same manner to keep us from
naturalism, which asserts nature to be sufficient for itself. Finally,
all natural necessity in the sensible world is conditional, as it
always presupposes the dependence of things upon others, and
unconditional necessity must be sought only in the unity of a cause
different from the world of sense. But as the causality of this cause,
in its turn, were it merely nature, could never render the existence
of the contingent (as its consequent) comprehensible, reason frees
itself by means of the Theological Idea from fatalism, (both as a
blind natural necessity in the coherence of nature itself, without a
first principle, and as a blind causality of this principle itself),
and leads to the concept of a cause possessing freedom, or of a
Supreme Intelligence. Thus the transcendental Ideas serve, if not to
instruct us positively, at least to destroy the rash assertions of
Materialism, of Naturalism, and of Fatalism, and thus to afford scope
for the moral Ideas beyond the field of speculation. These
considerations, I should think, explain in some measure the natural
predisposition of which I spoke.

The practical value, which a merely speculative science may have, lies
without the bounds of this science, and can therefore be considered as
a scholion merely, and like all scholia does not form part of the
science itself. This application however surely lies within the bounds
of philosophy, especially of philosophy drawn from the pure sources of
reason, where its speculative use in metaphysics must necessarily be
at unity with its practical use in morals. Hence the unavoidable
dialectics of pure reason, considered in metaphysics, as a natural
tendency, deserves to be explained not as an illusion merely, which is
to be removed, but also, if possible, as a natural provision as
regards its end, though this duty, a work of supererogation, cannot
justly be assigned to metaphysics proper.

The solutions of these questions which are treated in the chapter on
the Regulative Use of the Ideas of Pure Reason{43} should be considered
a second scholion which however has a greater affinity with the
subject of metaphysics. For there certain rational principles are
expounded which determine a priori the order of nature or rather of
the understanding, which seeks nature's laws through experience. They
seem to be constitutive and legislative with regard to experience,
though they spring from pure reason, which cannot be considered, like
the understanding, as a principle of possible experience. Now whether
or not this harmony rests upon the fact, that just as nature does not
inhere in appearances or in their source (the sensibility) itself, but
only in so far as the latter is in relation to the understanding, as
also a systematic unity in applying the understanding to bring about
an entirety of all possible experience can only belong to the
understanding when in relation to reason; and whether or not
experience is in this way mediately subordinate to the legislation of
reason: may be discussed by those who desire to trace the nature of
reason even beyond its use in metaphysics, into the general principles
of a history of nature; I have represented this task as important, but
not attempted its solution, in the book itself.{44}

{43} Critique of Pure Reason, II., chap. III., section 7.

{44} Throughout in the Critique I never lost sight of the plan not to
neglect anything, were it ever so recondite, that could render the
inquiry into the nature of pure reason complete. Everybody may
afterwards carry his researches as far as he pleases, when he has been
merely shown what yet remains to be done. It is this a duty which must
reasonably be expected of him who has made it his business to survey
the whole field, in order to consign it to others for future
cultivation and allotment. And to this branch both the scholia belong,
which will hardly recommend themselves by their dryness to amateurs,
and hence are added here for connoisseurs only.

And thus I conclude the analytical solution of the main question which
I had proposed: How is metaphysics in general possible? by ascending
from the data of its actual use in its consequences, to the grounds of
its possibility.



Metaphysics, as a natural disposition of reason, is actual, but if
considered by itself alone (as the analytical solution of the third
principal question showed), dialectical and illusory. If we think of
taking principles from it, and in using them follow the natural, but
on that account not less false, illusion, we can never produce
science, but only a vain dialectical art, in which one school may
outdo another, but none can ever acquire a just and lasting

In order that as a science metaphysics may be entitled to claim not
mere fallacious plausibility, but in sight and conviction, a Critique
of Reason must itself exhibit the whole stock of a priori concepts,
their division according to their various sources (Sensibility,
Understanding, and Reason), together with a complete table of them,
the analysis of all these concepts, with all their consequences,
especially by means of the deduction of these concepts, the
possibility of synthetical cognition a priori, the principles of its
application and finally its bounds, all in a complete system.
Critique, therefore, and critique alone, contains in itself the whole
well-proved and well-tested plan, and even all the means required to
accomplish metaphysics, as a science; by other ways and means it is
impossible. The question here therefore is not so much how this
performance is possible, as how to set it going, and induce men of
clear heads to quit their hitherto perverted and fruitless cultivation
for one that will not deceive, and how such a union for the common end
may best be directed.

This much is certain, that whoever has once tasted Critique will be
ever after disgusted with all dogmatical twaddle which he formerly put
up with, because his reason must have something, and could find
nothing better for its support.

Critique stands in the same relation to the common metaphysics of the
schools, as chemistry does to alchemy, or as astronomy to the
astrology of the fortune-teller. I pledge myself that nobody who has
read through and through, and grasped the principles of, the Critique
even in these Prolegomena only, will ever return to that old and
sophistical pseudo-science; but will rather with a certain delight
look forward to metaphysics which is now indeed in his power,
requiring no more preparatory discoveries, and now at last affording
permanent satisfaction to reason. For here is an advantage upon which,
of all possible sciences, metaphysics alone can with certainty reckon:
that it can be brought to such completion and fixity as to be
incapable of further change, or of any augmentation by new
discoveries; because here reason has the sources of its knowledge in
itself, not in objects and their observation (Anschauung), by which
latter its stock of knowledge cannot be further increased. When
therefore it has exhibited the fundamental laws of its faculty
completely and so definitely as to avoid all misunderstanding, there
remains nothing for pure reason to cognise a priori, nay, there is
even no ground to raise further questions. The sure prospect of
knowledge so definite and so compact has a peculiar charm, even though
we should set aside all its advantages, of which I shall hereafter

All false art, all vain wisdom, lasts its time, but finally destroys
itself, and its highest culture is also the epoch of its decay. That
this time is come for metaphysics appears from the state into which it
has fallen among all learned nations, despite of all the zeal with
which other sciences of every kind are prosecuted. The old arrangement
of our university studies still preserves its shadow; now and then an
Academy of Science tempts men by offering prizes to write essays on
it, but it is no longer numbered among thorough sciences; and let any
one judge for himself how a man of genius, if he were called a great
metaphysician, would receive the compliment, which may be well-meant,
but is scarce envied by anybody.

Yet, though the period of the downfall of all dogmatical metaphysics
has undoubtedly arrived, we are yet far from being able to say that
the period of its regeneration is come by means of a thorough and
complete Critique of Reason. All transitions from a tendency to its
contrary pass through the stage of indifference, and this moment is
the most dangerous for an author, but, in my opinion, the most
favorable for the science. For, when party spirit has died out by a
total dissolution of former connexions, minds are in the best state to
listen to several proposals for an organisation according to a new

When I say, that I hope these Prolegomena will excite investigation in
the field of critique and afford a new and promising object to sustain
the general spirit of philosophy, which seems on its speculative side
to want sustenance, I can imagine beforehand, that every one, whom the
thorny paths of my Critique have tired and put out of humor, will ask
me, upon what I found this hope. My answer is, upon the irresistible
law of necessity.

That the human mind will ever give up metaphysical researches is as
little to be expected as that we should prefer to give up breathing
altogether, to avoid inhaling impure air. There will therefore always
be metaphysics in the world; nay, every one, especially every man of
reflexion, will have it, and for want of a recognised standard, will
shape it for himself after his own pattern. What has hitherto been
called metaphysics, cannot satisfy any critical mind, but to forego it
entirely is impossible; therefore a Critique of Pure Reason itself
must now be attempted or, if one exists, investigated, and brought to
the full test, because there is no other means of supplying this
pressing want, which is something more than mere thirst for knowledge.

Ever since I have come to know critique, whenever I finish reading a
book of metaphysical contents, which, by the preciseness of its
notions, by variety, order, and an easy style, was not only
entertaining but also helpful, I cannot help asking, "Has this author
indeed advanced metaphysics a single step?" The learned men, whose
works have been useful to me in other respects and always contributed
to the culture of my mental powers, will, I hope, forgive me for
saying, that I have never been able to find either their essays or my
own less important ones (though self-love may recommend them to me) to
have advanced the science of metaphysics in the least, and why?

Here is the very obvious reason: metaphysics did not then exist as a
science, nor can it be gathered piecemeal, but its germ must be fully
preformed in the Critique. But in order to prevent all misconception,
we must remember what has been already said, that by the analytical
treatment of our concepts the understanding gains indeed a great deal,
but the science (of metaphysics) is thereby not in the least advanced,
because these dissections of concepts are nothing but the materials
from which the intention is to carpenter our science. Let the concepts
of substance and of accident be ever so well dissected and determined,
all this is very well as a preparation for some future use. But if we
cannot prove, that in all which exists the substance endures, and only
the accidents vary, our science is not the least advanced by all our

Metaphysics has hitherto never been able to prove a priori either this
proposition, or that of sufficient reason, still, less any more
complex theorem, such as belongs to psychology or cosmology, or indeed
any synthetical proposition. By all its analysing therefore nothing is
affected, nothing obtained or forwarded, and the science, after all
this bustle and noise, still remains as it was in the days of
Aristotle, though far better preparations were made for it than of
old, if the clue to synthetical cognitions had only been discovered.

If any one thinks himself offended, he is at liberty to refute my
charge by producing a single synthetical proposition belonging to
metaphysics, which he would prove dogmatically a priori, for until he
has actually performed this feat, I shall not grant that he has truly
advanced the science; even should this proposition be sufficiently
confirmed by common experience. No demand can be more moderate or more
equitable, and in the (inevitably certain) event of its
non-performance, no assertion more just, than that hitherto
metaphysics has never existed as a science.

But there are two things which, in case the challenge be accepted, I
must deprecate: first, trifling about probability and conjecture,
which are suited as little to metaphysics, as to geometry; and
secondly, a decision by means of the magic wand of common sense, which
does not convince every one, but which accommodates itself to personal

For as to the former, nothing can be more absurd, than in metaphysics,
a philosophy from pure reason to think of grounding our judgments upon
probability and conjecture. Everything that is to be cognised a
priori, is thereby announced as apodeictically certain, and must
therefore be proved in this way. We might as well think of grounding
geometry or arithmetic upon conjectures. As to the doctrine of chances
in the latter, it does not contain probable, but perfectly certain,
judgments concerning the degree of the probability of certain cases,
under given uniform conditions, which, in the sum of all possible
cases, infallibly happen according to the rule, though it is not
sufficiently determined in respect to every single chance. Conjectures
(by means of induction and of analogy) can be suffered in an empirical
science of nature only, yet even there the possibility at least of
what we assume must be quite certain.

The appeal to common sense is even more absurd, when concept and
principles are announced as valid, not in so far as they hold with
regard to experience, but even beyond the conditions of experience.
For what is common sense? It is normal good sense, so far it judges
right. But what is normal good sense? It is the faculty of the
knowledge and use of rules in concreto, as distinguished from the
speculative understanding, which is a faculty of knowing rules in
abstracto. Common sense can hardly understand the rule, "that every
event is determined by means of its cause," and can never comprehend
it thus generally. It therefore demands an example from experience,
and when it hears that this rule means nothing but what it always
thought when a pane was broken or a kitchen-utensil missing, it then
understands the principle and grants it. Common sense therefore is
only of use so far as it can see its rules (though they actually are a
priori) confirmed by experience; consequently to comprehend them a
priori, or independently of experience, belongs to the speculative
understanding, and lies quite beyond the horizon of common sense. But
the province of metaphysics is entirely confined to the latter kind of
knowledge, and it is certainly a bad index of common sense to appeal
to it as a witness, for it cannot here form any opinion whatever, and
men look down upon it with contempt until they are in difficulties,
and can find in their speculation neither in nor out.

It is a common subterfuge of those false friends of common sense (who
occasionally prize it highly, but usually despise it) to say, that
there must surely be at all events some propositions which are
immediately certain, and of which there is no occasion to give any
proof, or even any account at all, because we otherwise could never
stop inquiring into the grounds of our judgments. But if we except the
principle of contradiction, which is not sufficient to show the truth
of synthetical judgments, they can never adduce, in proof of this
privilege, anything else indubitable, which they can immediately
ascribe to common sense, except mathematical propositions, such as
twice two make four, between two points there is but one straight
line, etc. But these judgments are radically different from those of
metaphysics. For in mathematics I myself can by thinking construct
whatever I represent to myself as possible by a concept: I add to the
first two the other two, one by one, and myself make the number four,
or I draw in thought from one point to another all manner of lines,
equal as well as unequal; yet I can draw one only, which is like
itself in all its parts. But I cannot, by all my power of thinking,
extract from the concept of a thing the concept of something else,
whose existence is necessarily connected with the former, but I must
call in experience. And though my understanding furnishes me a priori
(yet only in reference to possible experience) with the concept of
such a connexion (i.e., causation), I cannot exhibit it, like the
concepts of mathematics, by (Anschauung) visualising them, a priori,
and so show its possibility a priori. This concept, together with the
principles of its application, always requires, if it shall hold a
priori—as is requisite in metaphysics—a justification and
deduction of its possibility, because we cannot otherwise know how far
it holds good, and whether it can be used in experience only or beyond
it also.

Therefore in metaphysics, as a speculative science of pure reason, we
can never appeal to common sense, but may do so only when we are
forced to surrender it, and to renounce all purely speculative
cognition, which must always be knowledge, and consequently when we
forego metaphysics itself and its instruction, for the sake of
adopting a rational faith which alone may be possible for us, and
sufficient to our wants, perhaps even more salutary than knowledge
itself. For in this case the attitude of the question is quite
altered. Metaphysics must be science, not only as a whole, but in all
its parts, otherwise it is nothing; because, as a speculation of pure
reason, it finds a hold only on general opinions. Beyond its field,
however, probability and common sense may be used with advantage and
justly, but on quite special principles, of which the importance
always depends on the reference to practical life.

This is what I hold myself justified in requiring for the possibility
of metaphysics as a science.



Since all the ways heretofore taken have failed to attain the goal,
and since without a preceding critique of pure reason it is not likely
ever to be attained, the present essay now before the public has a
fair title to an accurate and careful investigation, except it be
thought more advisable to give up all pretensions to metaphysics, to
which, if men but would consistently adhere to their purpose, no
objection can be made.

If we take the course of things as it is, not as it ought to be, there
are two sorts of judgments: (1) one a judgment which precedes
investigation (in our case one in which the reader from his own
metaphysics pronounces judgment on the Critique of Pure Reason which
was intended to discuss the very possibility of metaphysics); (2) the
other a judgment subsequent to investigation. In the latter the reader
is enabled to waive for awhile the consequences of the critical
researches that may be repugnant to his formerly adopted metaphysics,
and first examines the grounds whence those consequences are derived.
If what common metaphysics propounds were demonstrably certain, as for
instance the theorems of geometry, the former way of judging would
hold good. For if the consequences of certain principles are repugnant
to established truths, these principles are false and without further
inquiry to be repudiated. But if metaphysics does not possess a stock
of indisputably certain (synthetical) propositions, and should it even
be the case that there are a number of them, which, though among the
most specious, are by their consequences in mutual collision, and if
no sure criterion of the truth of peculiarly metaphysical
(synthetical) propositions is to be met with in it, then the former
way of judging is not admissible, but the investigation of the
principles of the critique must precede all judgments as to its value.


This judgment is to be found in the Göttingischen gelehrten Anzeigen,
in the supplement to the third division, of January 19, 1782,
pages 40 et seq.

When an author who is familiar with the subject of his work and
endeavors to present his independent reflexions in its elaboration,
falls into the hands of a reviewer who, in his turn, is keen enough to
discern the points on which the worth or worthlessness of the book
rests, who does not cling to words, but goes to the heart of the
subject, sifting and testing more than the mere principles which the
author takes as his point of departure, the severity of the judgment
may indeed displease the latter, but the public does not care, as it
gains thereby; and the author himself may be contented, as an
opportunity of correcting or explaining his positions is afforded to
him at an early date by the examination of a competent judge, in such
a manner, that if he believes himself fundamentally right, he can
remove in time any stone of offence that might hurt the success of his

I find myself, with my reviewer, in quite another position. He seems
not to see at all the real matter of the investigation with which
(successfully or unsuccessfully) I have been occupied. It is either
impatience at thinking out a lengthy work, or vexation at a threatened
reform of a science in which he believed he had brought everything to
perfection long ago, or, what I am unwilling to imagine, real
narrowmindedness, that prevents him from ever carrying his thoughts
beyond his school-metaphysics. In short, he passes impatiently in
review a long series of propositions, by which, without knowing their
premises, we can think nothing, intersperses here and there his
censure, the reason of which the reader understands just as little as
the propositions against which it is directed; and hence [his report]
can neither serve the public nor damage me, in the judgment of
experts. I should, for these reasons, have passed over this judgment
altogether, were it not that it may afford me occasion for some
explanations which may in some cases save the readers of these
Prolegomena from a misconception.

In order to take a position from which my reviewer could most easily
set the whole work in a most unfavorable light, without venturing to
trouble himself with any special investigation, he begins and ends by

"This work is a system of transcendent (or, as he translates it, of
higher) Idealism."{45}

{45} By no means "higher." High towers, and metaphysically-great men
resembling them, round both of which there is commonly much wind, are
not for me. My place is the fruitful bathos, the bottom-land, of
experience; and the word transcendental, the meaning of which is so
often explained by me, but not once grasped by my reviewer (so
carelessly has he regarded everything), does not signify something
passing beyond all experience, but something that indeed precedes it a
priori, but that is intended simply to make cognition of experience
possible. If these conceptions overstep experience, their employment
is termed transcendent, a word which must be distinguished from
transcendental, the latter being limited to the immanent use, that is,
to experience. All misunderstandings of this kind have been
sufficiently guarded against in the work itself, but my reviewer found
his advantage in misunderstanding me.

A glance at this line soon showed me the sort of criticism that I had
to expect, much as though the reviewer were one who had never seen or
heard of geometry, having found a Euclid, and coming upon various
figures in turning over its leaves, were to say, on being asked his
opinion of it: "The work is a text-book of drawing; the author
introduces a peculiar terminology, in order to give dark,
incomprehensible directions, which in the end teach nothing more than
what every one can effect by a fair natural accuracy of eye, etc."

Let us see, in the meantime, what sort of an idealism it is that goes
through my whole work, although it does not by a long way constitute
the soul of the system.

The dictum of all genuine idealists from the Eleatic school to Bishop
Berkeley, is contained in this formula: "All cognition through the
senses and experience is nothing but sheer illusion, and only, in the
ideas of the pure understanding and reason there is truth."

The principle that throughout dominates and determines my Idealism, is
on the contrary: "All cognition of things merely from pure
understanding or pure reason is nothing but sheer illusion, and only
in experience is there truth."

But this is directly contrary to idealism proper. How came I then to
use this expression for quite an opposite purpose, and how came my
reviewer to see it everywhere?

The solution of this difficulty rests on something that could have
been very easily understood from the general bearing of the work, if
the reader had only desired to do so. Space and time, together with
all that they contain, are not things nor qualities in themselves, but
belong merely to the appearances of the latter: up to this point I am
one in confession with the above idealists. But these, and amongst
them more particularly Berkeley, regarded space as a mere empirical
presentation that, like the phenomenon it contains, is only known to
us by means of experience or perception, together with its
determinations. I, on the contrary, prove in the first place, that
space (and also time, which Berkeley did not consider) and all its
determinations a priori, can be cognised by us, because, no less than
time, it inheres in our sensibility as a pure form before all
perception or experience and makes all intuition of the same, and
therefore all its phenomena, possible. It follows from this, that as
truth rests on universal and necessary laws as its criteria,
experience, according to Berkeley, can have no criteria of truth,
because its phenomena (according to him) have nothing a priori at
their foundation; whence it follows, that they are nothing but sheer
illusion; whereas with us, space and time (in conjunction with the
pure conceptions of the understanding) prescribe their law to all
possible experience a priori, and at the same time afford the certain
criterion for distinguishing truth from illusion therein.{46}

{46} Idealism proper always has a mystical tendency, and can have no
other, but mine is solely designed for the purpose of comprehending
the possibility of our cognition a priori as to objects of experience,
which is a problem never hitherto solved or even suggested. In this
way all mystical idealism falls to the ground, for (as may be seen
already in Plato) it inferred from our cognitions a priori (even from
those of geometry) another intuition different from that of the senses
(namely, an intellectual intuition), because it never occurred to any
one that the senses themselves might intuite a priori.

My so-called (properly critical) Idealism is of quite a special
character, in that it subverts the ordinary idealism, and that through
it all cognition a priori, even that of geometry, first receives
objective reality, which, without my demonstrated ideality of space
and time, could not be maintained by the most zealous realists. This
being the state of the case, I could have wished, in order to avoid
all misunderstanding, to have named this conception of mine otherwise,
but to alter it altogether was impossible. It may be permitted me
however, in future, as has been above intimated, to term it the
formal, or better still, the critical Idealism, to distinguish it from
the dogmatic Idealism of Berkeley, and from the sceptical Idealism of

Beyond this, I find nothing further remarkable in the judgment of my
book. The reviewer criticises here and there, makes sweeping
criticisms, a mode prudently chosen, since it does not betray one's
own knowledge or ignorance; a single thorough criticism in detail, had
it touched the main question, as is only fair, would have exposed, it
may be my error, or it may be my reviewer's measure of insight into
this species of research. It was, moreover, not a badly conceived
plan, in order at once to take from readers (who are accustomed to
form their conceptions of books from newspaper reports) the desire to
read the book itself, to pour out in one breath a number of passages
in succession, torn from their connexion, and their grounds of proof
and explanations, and which must necessarily sound senseless,
especially considering how antipathetic they are to all
school-metaphysics; to exhaust the reader's patience ad nauseam, and
then, after having made me acquainted with the sensible proposition
that persistent illusion is truth, to conclude with the crude paternal
moralisation: to what end, then, the quarrel with accepted language,
to what end, and whence, the idealistic distinction? A judgment which
seeks all that is characteristic of my book, first supposed to be
metaphysically heterodox, in a mere innovation of the nomenclature,
proves clearly that my would-be judge has understood nothing of the
subject, and in addition, has not understood himself.{47}

{47} The reviewer often fights with his own shadow. When I oppose the
truth of experience to dream, he never thinks that I am here speaking
simply of the well-known somnio objective sumto of the Wolffian
philosophy, which is merely formal, and with which the distinction
between sleeping and waking is in no way concerned, and in a
transcendental philosophy indeed can have no place. For the rest, he
calls my deduction of the categories and table of the principles of
the understanding, "common well-known axioms of logic and ontology,
expressed in an idealistic manner." The reader need only consult these
Prolegomena upon this point, to convince himself that a more miserable
and historically incorrect, judgment, could hardly be made.

My reviewer speaks like a man who is conscious of important and
superior insight which he keeps hidden; for I am aware of nothing
recent with respect to metaphysics that could justify his tone. But he
should not withhold his discoveries from the world, for there are
doubtless many who, like myself, have not been able to find in all the
fine things that have for long past been written in this department,
anything that has advanced the science by so much as a fingerbreadth;
we find indeed the giving a new point to definitions, the supplying of
lame proofs with new crutches, the adding to the crazy-quilt of
metaphysics fresh patches or changing its pattern; but all this is not
what the world requires. The world is tired of metaphysical
assertions; it wants the possibility of the science, the sources from
which certainty therein can be derived, and certain criteria by which
it may distinguish the dialectical illusion of pure reason from truth.
To this the critic seems to possess a key, otherwise he would never
have spoken out in such a high tone.

But I am inclined to suspect that no such requirement of the science
has ever entered his thoughts, for in that case he would have directed
his judgment to this point, and even a mistaken attempt in such an
important matter, would have won his respect. If that be the case, we
are once more good friends. He may penetrate as deeply as he likes
into metaphysics, without any one hindering him; only as concerns that
which lies outside metaphysics, its sources, which are to be found in
reason, he cannot form a judgment. That my suspicion is not without
foundation, is proved by the fact that he does not mention a word
about the possibility of synthetic knowledge a priori, the special
problem upon the solution of which the fate of metaphysics wholly
rests, and upon which my Critique (as well as the present Prolegomena)
entirely hinges. The Idealism he encountered, and which he hung upon,
was only taken up in the doctrine as the sole means of solving the
above problem (although it received its confirmation on other
grounds), and hence he must have shown either that the above problem
does not possess the importance I attribute to it (even in these
Prolegomena), or that by my conception of appearances, it is either
not solved at all, or can be better solved in another way; but I do
not find a word of this in the criticism. The reviewer, then,
understands nothing of my work, and possibly also nothing of the
spirit and essential nature of metaphysics itself; and it is not, what
I would rather assume, the hurry of a man incensed at the labor of
plodding through so many obstacles, that threw an unfavorable shadow
over the work lying before him, and made its fundamental features

There is a good deal to be done before a learned journal, it matters
not with what care its writers may be selected, can maintain its
otherwise well-merited reputation, in the field of metaphysics as
elsewhere. Other sciences and branches of knowledge have their
standard. Mathematics has it, in itself; history and theology, in
profane or sacred books; natural science and the art of medicine, in
mathematics and experience; jurisprudence, in law books; and even
matters of taste in the examples of the ancients. But for the judgment
of the thing called metaphysics, the standard has yet to be found. I
have made an attempt to determine it, as well as its use. What is to
be done, then, until it be found, when works of this kind have to be
judged of? If they are of a dogmatic character, one may do what one
likes; no one will play the master over others here for long, before
someone else appears to deal with him in the same manner. If, however,
they are critical in their character, not indeed with reference to
other works, but to reason itself, so that the standard of judgment
cannot be assumed but has first of all to be sought for, then, though
objection and blame may indeed be permitted, yet a certain degree of
leniency is indispensable, since the need is common to us all, and the
lack of the necessary insight makes the high-handed attitude of judge

In order, however, to connect my defence with the interest of the
philosophical commonwealth, I propose a test, which must be decisive
as to the mode, whereby all metaphysical investigations may be
directed to their common purpose. This is nothing more than what
formerly mathematicians have done, in establishing the advantage of
their methods by competition. I challenge my critic to demonstrate, as
is only just, on a priori grounds, in his way, a single really
metaphysical principle asserted by him. Being metaphysical it must be
synthetic and cognised a priori from conceptions, but it may also be
any one of the most indispensable principles, as for instance, the
principle of the persistence of substance, or of the necessary
determination of events in the world by their causes. If he cannot do
this (silence however is confession), he must admit, that as
metaphysics without apodeictic certainty of propositions of this kind
is nothing at all, its possibility or impossibility must before all
things be established in a critique of the pure reason. Thus he is
bound either to confess that my principles in the Critique are
correct, or he must prove their invalidity. But as I can already
foresee, that, confidently as he has hitherto relied on the certainty
of his principles, when it comes to a strict test he will not find a
single one in the whole range of metaphysics he can bring forward, I
will concede to him an advantageous condition, which can only be
expected in such a competition, and will relieve him of the onus
probandi by laying it on myself.

He finds in these Prolegomena and in my Critique (chapter on the
"Theses and Antitheses of the Four Antinomies") eight propositions, of
which two and two contradict one another, but each of which
necessarily belongs to metaphysics, by which it must either be
accepted or rejected (although there is not one that has not in this
time been held by some philosopher). Now he has the liberty of
selecting any one of these eight propositions at his pleasure, and
accepting it without any proof, of which I shall make him a present,
but only one (for waste of time will be just as little serviceable to
him as to me), and then of attacking my proof of the opposite
proposition. If I can save this one, and at the same time show, that
according to principles which every dogmatic metaphysics must
necessarily recognise, the opposite of the proposition adopted by him
can be just as clearly proved, it is thereby established that
metaphysics has an hereditary failing, not to be explained, much less
set aside, until we ascend to its birth-place, pure reason itself, and
thus my Critique must either be accepted or a better one take its
place; it must at least be studied, which is the only thing I now
require. If, on the other hand, I cannot save my demonstration, then a
synthetic proposition a priori from dogmatic principles is to be
reckoned to the score of my opponent, then also I will deem my
impeachment of ordinary metaphysics as unjust, and pledge myself to
recognise his stricture on my Critique as justified (although this
would not be the consequence by a long way). To this end it would be
necessary, it seems to me, that he should step out of his incognito.
Otherwise I do not see how it could be avoided, that instead of
dealing with one, I should be honored by several problems coming from
anonymous and unqualified opponents.


I feel obliged to the honored public even for the silence with which
it for a long time favored my Critique, for this proves at least a
postponement of judgment, and some supposition that in a work, leaving
all beaten tracks and striking out on a new path, in which one cannot
at once perhaps so easily find one's way, something may perchance lie,
from which an important but at present dead branch of human knowledge
may derive new life and productiveness. Hence may have originated a
solicitude for the as yet tender shoot, lest it be destroyed by a
hasty judgment. A test of a judgment, delayed for the above reasons,
is now before my eye in the Gothaischen gelehrten Zeitung, the
thoroughness of which every reader will himself perceive, from the
clear and unperverted presentation of a fragment of one of the first
principles of my work, without taking into consideration my own
suspicious praise.

And now I propose, since an extensive structure cannot be judged of as
a whole from a hurried glance, to test it piece by piece from its
foundations, so thereby the present Prolegomena may fitly be used as a
general outline with which the work itself may occasionally be
compared. This notion, if it were founded on nothing more than my
conceit of importance, such as vanity commonly attributes to one's own
productions, would be immodest and would deserve to be repudiated with
disgust. But now, the interests of speculative philosophy have arrived
at the point of total extinction, while human reason hangs upon them
with inextinguishable affection, and only after having been
ceaselessly deceived does it vainly attempt to change this into

In our thinking age it is not to be supposed but that many deserving
men would use any good opportunity of working for the common interest
of the more and more enlightened reason, if there were only some hope
of attaining the goal. Mathematics, natural science, laws, arts, even
morality, etc., do not completely fill the soul; there is always a
space left over, reserved for pure and speculative reason, the vacuity
of which prompts us to seek in vagaries, buffooneries, and myticism
for what seems to be employment and entertainment, but what actually
is mere pastime; in order to deaden the troublesome voice of reason,
which in accordance with its nature requires something that can
satisfy it, and not merely subserve other ends or the interests of our
inclinations. A consideration, therefore, which is concerned only with
reason as it exists for it itself, has as I may reasonably suppose a
great fascination for every one who has attempted thus to extend his
conceptions, and I may even say a greater than any other theoretical
branch of knowledge, for which he would not willingly exchange it,
because here all other cognitions, and even purposes, must meet and
unite themselves in a whole.

I offer, therefore, these Prolegomena as a sketch and text-book for
this investigation, and not the work itself. Although I am even now
perfectly satisfied with the latter as far as contents, order, and
mode of presentation, and the care that I have expended in weighing
and testing every sentence before writing it down, are concerned (for
it has taken me years to satisfy myself fully, not only as regards the
whole, but in some cases even as to the sources of one particular
proposition); yet I am not quite satisfied with my exposition in some
sections of the doctrine of elements, as for instance in the deduction
of the conceptions of the Understanding, or in that on the paralogisms
of pure reason, because a certain diffuseness takes away from their
clearness, and in place of them, what is here said in the Prolegomena
respecting these sections, may be made the basis of the test.

It is the boast of the Germans that where steady and continuous
industry are requisite, they can carry things farther than other
nations. If this opinion be well founded, an opportunity, a business,
presents itself, the successful issue of which we can scarcely doubt,
and in which all thinking men can equally take part, though they have
hitherto been unsuccessful in accomplishing it and in thus confirming
the above good opinion. But this is chiefly because the science in
question is of so peculiar a kind, that it can be at once brought to
completion and to that enduring state that it will never be able to be
brought in the least degree farther or increased by later discoveries,
or even changed (leaving here out of account adornment by greater
clearness in some places, or additional uses), and this is an
advantage no other science has or can have, because there is none so
fully isolated and independent of others, and which is concerned with
the faculty of cognition pure and simple. And the present moment
seems, moreover, not to be unfavorable to my expectation, for just
now, in Germany, no one seems to know wherewith to occupy himself,
apart from the so-called useful sciences, so as to pursue not mere
play, but a business possessing an enduring purpose.

To discover the means how the endeavors of the learned may be united
in such a purpose, I must leave to others. In the meantime, it is my
intention to persuade any one merely to follow my propositions, or
even to flatter me with the hope that he will do so; but attacks,
repetitions, limitations, or confirmation, completion, and extension,
as the case may be, should be appended. If the matter be but
investigated from its foundation, it cannot fail that a system, albeit
not my own, shall be erected, that shall be a possession for future
generations for which they may have reason to be grateful.

It would lead us too far here to show what kind of metaphysics may be
expected, when only the principles of criticism have been perfected,
and how, because the old false feathers have been pulled out, she need
by no means appear poor and reduced to an insignificant figure, but
may be in other respects richly and respectably adorned. But other and
great uses which would result from such a reform, strike one
immediately. The ordinary metaphysics had its uses, in that it sought
out the elementary conceptions of the pure understanding in order to
make them clear through analysis, and definite by explanation. In this
way it was a training for reason, in whatever direction it might be
turned; but this was all the good it did; service was subsequently
effaced when it favored conceit by venturesome assertions, sophistry
by subtle distinctions and adornment, and shallowness by the ease with
which it decided the most difficult problems by means of a little
school-wisdom, which is only the more seductive the more it has the
choice, on the one hand, of taking something from the language of
science, and on the other from that of popular discourse, thus being
everything to everybody, but in reality nothing at all. By criticism,
however, a standard is given to our judgment, whereby knowledge may be
with certainty distinguished from pseudo-science, and firmly founded,
being brought into full operation in metaphysics; a mode of thought
extending by degrees its beneficial influence over every other use of
reason, at once infusing into it the true philosophical spirit. But
the service also that metaphysics performs for theology, by making it
independent of the judgment of dogmatic speculation, thereby assuring
it completely against the attacks of all such opponents, is certainly
not to be valued lightly. For ordinary metaphysics, although it
promised the latter much advantage, could not keep this promise, and
moreover, by summoning speculative dogmatics to its assistance, did
nothing but arm enemies against itself. Mysticism, which can prosper
in a rationalistic age only when it hides itself behind a system of
school-metaphysics, under the protection of which it may venture to
rave with a semblance of rationality, is driven from this, its last
hiding-place, by critical philosophy. Last, but not least, it cannot
be otherwise than important to a teacher of metaphysics, to be able to
say with universal assent, that what he expounds is Science, and that
thereby genuine services will be rendered to the commonweal.

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