Title: Selections from the Principles of Philosophy
Author: Descartes, René
Language: English
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SELECTIONS FROM THE PRINCIPLES OF PHILOSOPHY

OF

RENE DESCARTES
(1596-1650)

TRANSLATED BY
JOHN VEITCH, LL. D.
LATE PROFESSOR OF LOGIC AND RHETORIC IN THE UNIVERSITY OF GLASGOW



From the Publisher's Preface.

The present volume contains a reprint of the preface and the first
part of the Principles of Philosophy, together with selections from
the second, third and fourth parts of that work, corresponding to
the extracts in the French edition of Gamier, are also given, as
well as an appendix containing part of Descartes' reply to the
Second Objections (viz., his formal demonstrations of the existence
of Deity). The translation is based on the original Latin edition of
the Principles, published in 1644.

The work had been translated into French during Descartes' lifetime,
and personally revised and corrected by him, the French text is
evidently deserving of the same consideration as the Latin
originals, and consequently, the additions and variations of the
French version have also been given--the additions being put in
square brackets in the text and the variations in the footnotes.

A copy of the title-page of the original edition, as given in Dr. C.
Guttler's work (Munich: C. H. Beck. 1901), are also reproduced in
the present volume.



SELECTIONS FROM THE PRINCIPLES OF PHILOSOPHY

OF DESCARTES

TRANSLATED FROM THE LATIN AND COLLATED WITH THE FRENCH



LETTER OF THE AUTHOR

TO THE FRENCH TRANSLATOR OF THE PRINCIPLES OF PHILOSOPHY SERVING FOR
A PREFACE.

Sir,--The version of my principles which you have been at pains to
make, is so elegant and finished as to lead me to expect that the
work will be more generally read in French than in Latin, and better
understood. The only apprehension I entertain is lest the title
should deter some who have not been brought up to letters, or with
whom philosophy is in bad repute, because the kind they were taught
has proved unsatisfactory; and this makes me think that it will be
useful to add a preface to it for the purpose of showing what the
MATTER of the work is, what END I had in view in writing it, and
what UTILITY may be derived from it. But although it might be my
part to write a preface of this nature, seeing I ought to know those
particulars better than any other person, I cannot nevertheless
prevail upon myself to do anything more than merely to give a
summary of the chief points that fall, as I think, to be discussed
in it: and I leave it to your discretion to present to the public
such part of them as you shall judge proper.

I should have desired, in the first place, to explain in it what
philosophy is, by commencing with the most common matters, as, for
example, that the word PHILOSOPHY signifies the study of wisdom, and
that by wisdom is to be understood not merely prudence in the
management of affairs, but a perfect knowledge of all that man can
know, as well for the conduct of his life as for the preservation of
his health and the discovery of all the arts, and that knowledge to
subserve these ends must necessarily be deduced from first causes;
so that in order to study the acquisition of it (which is properly
called philosophizing), we must commence with the investigation of
those first causes which are called PRINCIPLES. Now these principles
must possess TWO CONDITIONS: in the first place, they must be so
clear and evident that the human mind, when it attentively considers
them, cannot doubt of their truth; in the second place, the
knowledge of other things must be so dependent on them as that
though the principles themselves may indeed be known apart from what
depends on them, the latter cannot nevertheless be known apart from
the former. It will accordingly be necessary thereafter to endeavour
so to deduce from those principles the knowledge of the things that
depend on them, as that there may be nothing in the whole series of
deductions which is not perfectly manifest. God is in truth the only
being who is absolutely wise, that is, who possesses a perfect
knowledge of all things; but we may say that men are more or less
wise as their knowledge of the most important truths is greater or
less. And I am confident that there is nothing, in what I have now
said, in which all the learned do not concur.

I should, in the next place, have proposed to consider the utility
of philosophy, and at the same time have shown that, since it
embraces all that the human mind can know, we ought to believe that
it is by it we are distinguished from savages and barbarians, and
that the civilisation and culture of a nation is regulated by the
degree in which true philosophy nourishes in it, and, accordingly,
that to contain true philosophers is the highest privilege a state
can enjoy. Besides this, I should have shown that, as regards
individuals, it is not only useful for each man to have intercourse
with those who apply themselves to this study, but that it is
incomparably better he should himself direct his attention to it;
just as it is doubtless to be preferred that a man should make use
of his own eyes to direct his steps, and enjoy by means of the same
the beauties of colour and light, than that he should blindly follow
the guidance of another; though the latter course is certainly
better than to have the eyes closed with no guide except one's self.
But to live without philosophizing is in truth the same as keeping
the eyes closed without attempting to open them; and the pleasure of
seeing all that sight discloses is not to be compared with the
satisfaction afforded by the discoveries of philosophy. And,
finally, this study is more imperatively requisite for the
regulation of our manners, and for conducting us through life, than
is the use of our eyes for directing our steps. The brutes, which
have only their bodies to conserve, are continually occupied in
seeking sources of nourishment; but men, of whom the chief part is
the mind, ought to make the search after wisdom their principal
care, for wisdom is the true nourishment of the mind; and I feel
assured, moreover, that there are very many who would not fail in
the search, if they would but hope for success in it, and knew the
degree of their capabilities for it. There is no mind, how ignoble
soever it be, which remains so firmly bound up in the objects of the
senses, as not sometime or other to turn itself away from them in
the aspiration after some higher good, although not knowing
frequently wherein that good consists. The greatest favourites of
fortune--those who have health, honours, and riches in abundance--
are not more exempt from aspirations of this nature than others;
nay, I am persuaded that these are the persons who sigh the most
deeply after another good greater and more perfect still than any
they already possess. But the supreme good, considered by natural
reason without the light of faith, is nothing more than the
knowledge of truth through its first causes, in other words, the
wisdom of which philosophy is the study. And, as all these
particulars are indisputably true, all that is required to gain
assent to their truth is that they be well stated.

But as one is restrained from assenting to these doctrines by
experience, which shows that they who make pretensions to philosophy
are often less wise and reasonable than others who never applied
themselves to the study, I should have here shortly explained
wherein consists all the science we now possess, and what are the
degrees of wisdom at which we have arrived. The first degree
contains only notions so clear of themselves that they can be
acquired without meditation; the second comprehends all that the
experience of the senses dictates; the third, that which the
conversation of other men teaches us; to which may be added as the
fourth, the reading, not of all books, but especially of such as
have been written by persons capable of conveying proper
instruction, for it is a species of conversation we hold with their
authors. And it seems to me that all the wisdom we in ordinary
possess is acquired only in these four ways; for I do not class
divine revelation among them, because it does not conduct us by
degrees, but elevates us at once to an infallible faith.

There have been, indeed, in all ages great minds who endeavoured to
find a fifth road to wisdom, incomparably more sure and elevated
than the other four. The path they essayed was the search of first
causes and true principles, from which might be deduced the reasons
of all that can be known by man; and it is to them the appellation
of philosophers has been more especially accorded. I am not aware
that there is any one of them up to the present who has succeeded in
this enterprise. The first and chief whose writings we possess are
Plato and Aristotle, between whom there was no difference, except
that the former, following in the footsteps of his master, Socrates,
ingenuously confessed that he had never yet been able to find
anything certain, and that he was contented to write what seemed to
him probable, imagining, for this end, certain principles by which
he endeavoured to account for the other things. Aristotle, on the
other hand, characterised by less candour, although for twenty years
the disciple of Plato, and with no principles beyond those of his
master, completely reversed his mode of putting them, and proposed
as true and certain what it is probable he himself never esteemed as
such. But these two men had acquired much judgment and wisdom by the
four preceding means, qualities which raised their authority very
high, so much so that those who succeeded them were willing rather
to acquiesce in their opinions, than to seek better for themselves.
The chief question among their disciples, however, was as to whether
we ought to doubt of all things or hold some as certain,--a dispute
which led them on both sides into extravagant errors; for a part of
those who were for doubt, extended it even to the actions of life,
to the neglect of the most ordinary rules required for its conduct;
those, on the other hand, who maintained the doctrine of certainty,
supposing that it must depend upon the senses, trusted entirely to
them. To such an extent was this carried by Epicurus, that it is
said he ventured to affirm, contrary to all the reasonings of the
astronomers, that the sun is no larger than it appears.

It is a fault we may remark in most disputes, that, as truth is the
mean between the two opinions that are upheld, each disputant
departs from it in proportion to the degree in which he possesses
the spirit of contradiction. But the error of those who leant too
much to the side of doubt, was not followed for any length of time,
and that of the opposite party has been to some extent corrected by
the doctrine that the senses are deceitful in many instances.
Nevertheless, I do not know that this error was wholly removed by
showing that certitude is not in the senses, but in the
understanding alone when it has clear perceptions; and that while we
only possess the knowledge which is acquired in the first four
grades of wisdom, we ought not to doubt of the things that appear to
be true in what regards the conduct of life, nor esteem them as so
certain that we cannot change our opinions regarding them, even
though constrained by the evidence of reason.

From ignorance of this truth, or, if there was any one to whom it
was known, from neglect of it, the majority of those who in these
later ages aspired to be philosophers, blindly followed Aristotle,
so that they frequently corrupted the sense of his writings, and
attributed to him various opinions which he would not recognise as
his own were he now to return to the world; and those who did not
follow him, among whom are to be found many of the greatest minds,
did yet not escape being imbued with his opinions in their youth, as
these form the staple of instruction in the schools; and thus their
minds were so preoccupied that they could not rise to the knowledge
of true principles. And though I hold all the philosophers in
esteem, and am unwilling to incur odium by my censure, I can adduce
a proof of my assertion, which I do not think any of them will
gainsay, which is, that they all laid down as a principle what they
did not perfectly know. For example, I know none of them who did not
suppose that there was gravity in terrestrial bodies; but although
experience shows us very clearly that bodies we call heavy descend
towards the center of the earth, we do not, therefore, know the
nature of gravity, that is, the cause or principle in virtue of
which bodies descend, and we must derive our knowledge of it from
some other source. The same may be said of a vacuum and atoms, of
heat and cold, of dryness and humidity, and of salt, sulphur, and
mercury, and the other things of this sort which some have adopted
as their principles. But no conclusion deduced from a principle
which is not clear can be evident, even although the deduction be
formally valid; and hence it follows that no reasonings based on
such principles could lead them to the certain knowledge of any one
thing, nor consequently advance them one step in the search after
wisdom. And if they did discover any truth, this was due to one or
other of the four means above mentioned. Notwithstanding this, I am
in no degree desirous to lessen the honour which each of them can
justly claim; I am only constrained to say, for the consolation of
those who have not given their attention to study, that just as in
travelling, when we turn our back upon the place to which we were
going, we recede the farther from it in proportion as we proceed in
the new direction for a greater length of time and with greater
speed, so that, though we may be afterwards brought back to the
right way, we cannot nevertheless arrive at the destined place as
soon as if we had not moved backwards at all; so in philosophy, when
we make use of false principles, we depart the farther from the
knowledge of truth and wisdom exactly in proportion to the care with
which we cultivate them, and apply ourselves to the deduction of
diverse consequences from them, thinking that we are philosophizing
well, while we are only departing the farther from the truth; from
which it must be inferred that they who have learned the least of
all that has been hitherto distinguished by the name of philosophy
are the most fitted for the apprehension of truth.

After making those matters clear, I should, in the next place, have
desired to set forth the grounds for holding that the true
principles by which we may reach that highest degree of wisdom
wherein consists the sovereign good of human life, are those I have
proposed in this work; and two considerations alone are sufficient
to establish this--the first of which is, that these principles are
very clear, and the second, that we can deduce all other truths from
them; for it is only these two conditions that are required in true
principles. But I easily prove that they are very clear; firstly, by
a reference to the manner in which I found them, namely, by
rejecting all propositions that were in the least doubtful, for it
is certain that such as could not be rejected by this test when they
were attentively considered, are the most evident and clear which
the human mind can know. Thus by considering that he who strives to
doubt of all is unable nevertheless to doubt that he is while he
doubts, and that what reasons thus, in not being able to doubt of
itself and doubting nevertheless of everything else, is not that
which we call our body, but what we name our mind or thought, I have
taken the existence of this thought for the first principle, from
which I very clearly deduced the following truths, namely, that
there is a God who is the author of all that is in the world, and
who, being the source of all truth, cannot have created our
understanding of such a nature as to be deceived in the judgments it
forms of the things of which it possesses a very clear and distinct
perception. Those are all the principles of which I avail myself
touching immaterial or metaphysical objects, from which I most
clearly deduce these other principles of physical or corporeal
things, namely, that there are bodies extended in length, breadth,
and depth, which are of diverse figures and are moved in a variety
of ways. Such are in sum the principles from which I deduce all
other truths. The second circumstance that proves the clearness of
these principles is, that they have been known in all ages, and even
received as true and indubitable by all men, with the exception only
of the existence of God, which has been doubted by some, because
they attributed too much to the perceptions of the senses, and God
can neither be seen nor touched.

But, though all the truths which I class among my principles were
known at all times, and by all men, nevertheless, there has been no
one up to the present, who, so far as I know, has adopted them as
principles of philosophy: in other words, as such that we can deduce
from them the knowledge of whatever else is in the world. It
accordingly now remains for me to prove that they are such; and it
appears to me that I cannot better establish this than by the test
of experience: in other words, by inviting readers to peruse the
following work. For, though I have not treated in it of all matters-
-that being impossible--I think I have so explained all of which I
had occasion to treat, that they who read it attentively will have
ground for the persuasion that it is unnecessary to seek for any
other principles than those I have given, in order to arrive at the
most exalted knowledge of which the mind of man is capable;
especially if, after the perusal of my writings, they take the
trouble to consider how many diverse questions are therein discussed
and explained, and, referring to the writings of others, they see
how little probability there is in the reasons that are adduced in
explanation of the same questions by principles different from mine.
And that they may the more easily undertake this, I might have said
that those imbued with my doctrines have much less difficulty in
comprehending the writings of others, and estimating their true
value, than those who have not been so imbued; and this is precisely
the opposite of what I before said of such as commenced with the
ancient philosophy, namely, that the more they have studied it the
less fit are they for rightly apprehending the truth.

I should also have added a word of advice regarding the manner of
reading this work, which is, that I should wish the reader at first
to go over the whole of it, as he would a romance, without greatly
straining his attention, or tarrying at the difficulties he may
perhaps meet with in it, with the view simply of knowing in general
the matters of which I treat; and that afterwards, if they seem to
him to merit a more careful examination, and he feel a desire to
know their causes, he may read it a second time, in order to observe
the connection of my reasonings; but that he must not then give it
up in despair, although he may not everywhere sufficiently discover
the connection of the proof, or understand all the reasonings--it
being only necessary to mark with a pen the places where the
difficulties occur, and continue to read without interruption to the
end; then, if he does not grudge to take up the book a third time, I
am confident he will find in a fresh perusal the solution of most of
the difficulties he will have marked before; and that, if any still
remain, their solution will in the end be found in another reading.

I have observed, on examining the natural constitutions of different
minds, that there are hardly any so dull or slow of understanding as
to be incapable of apprehending good opinions, or even of acquiring
all the highest sciences, if they be but conducted along the right
road. And this can also be proved by reason; for, as the principles
are clear, and as nothing ought to be deduced from them, unless most
manifest inferences, no one is so devoid of intelligence as to be
unable to comprehend the conclusions that flow from them. But,
besides the entanglement of prejudices, from which no one is
entirely exempt, although it is they who have been the most ardent
students of the false sciences that receive the greatest detriment
from them, it happens very generally that people of ordinary
capacity neglect to study from a conviction that they want ability,
and that others, who are more ardent, press on too rapidly: whence
it comes to pass that they frequently admit principles far from
evident, and draw doubtful inferences from them. For this reason, I
should wish to assure those who are too distrustful of their own
ability that there is nothing in my writings which they may not
entirely understand, if they only take the trouble to examine them;
and I should wish, at the same time, to warn those of an opposite
tendency that even the most superior minds will have need of much
time and attention to remark all I designed to embrace therein.

After this, that I might lead men to understand the real design I
had in publishing them, I should have wished here to explain the
order which it seems to me one ought to follow with the view of
instructing himself. In the first place, a man who has merely the
vulgar and imperfect knowledge which can be acquired by the four
means above explained, ought, before all else, to endeavour to form
for himself a code of morals, sufficient to regulate the actions of
his life, as well for the reason that this does not admit of delay
as because it ought to be our first care to live well. In the next
place, he ought to study Logic, not that of the schools, for it is
only, properly speaking, a dialectic which teaches the mode of
expounding to others what we already know, or even of speaking much,
without judgment, of what we do not know, by which means it corrupts
rather than increases good sense--but the logic which teaches the
right conduct of the reason with the view of discovering the truths
of which we are ignorant; and, because it greatly depends on usage,
it is desirable he should exercise himself for a length of time in
practising its rules on easy and simple questions, as those of the
mathematics. Then, when he has acquired some skill in discovering
the truth in these questions, he should commence to apply himself in
earnest to true philosophy, of which the first part is Metaphysics,
containing the principles of knowledge, among which is the
explication of the principal attributes of God, of the immateriality
of the soul, and of all the clear and simple notions that are in us;
the second is Physics, in which, after finding the true principles
of material things, we examine, in general, how the whole universe
has been framed; in the next place, we consider, in particular, the
nature of the earth, and of all the bodies that are most generally
found upon it, as air, water, fire, the loadstone and other
minerals. In the next place it is necessary also to examine singly
the nature of plants, of animals, and above all of man, in order
that we may thereafter be able to discover the other sciences that
are useful to us. Thus, all Philosophy is like a tree, of which
Metaphysics is the root, Physics the trunk, and all the other
sciences the branches that grow out of this trunk, which are reduced
to three principal, namely, Medicine, Mechanics, and Ethics. By the
science of Morals, I understand the highest and most perfect which,
presupposing an entire knowledge of the other sciences, is the last
degree of wisdom.

But as it is not from the roots or the trunks of trees that we
gather the fruit, but only from the extremities of their branches,
so the principal utility of philosophy depends on the separate uses
of its parts, which we can only learn last of all. But, though I am
ignorant of almost all these, the zeal I have always felt in
endeavouring to be of service to the public, was the reason why I
published, some ten or twelve years ago, certain Essays on the
doctrines I thought I had acquired. The first part of these Essays
was a "Discourse on the Method of rightly conducting the Reason, and
seeking Truth in the Sciences," in which I gave a summary of the
principal rules of logic, and also of an imperfect ethic, which a
person may follow provisionally so long as he does not know any
better. The other parts were three treatises: the first of
Dioptrics, the second of Meteors, and the third of Geometry. In the
Dioptrics, I designed to show that we might proceed far enough in
philosophy as to arrive, by its means, at the knowledge of the arts
that are useful to life, because the invention of the telescope, of
which I there gave an explanation, is one of the most difficult that
has ever been made. In the treatise of Meteors, I desired to exhibit
the difference that subsists between the philosophy I cultivate and
that taught in the schools, in which the same matters are usually
discussed. In fine, in the Geometry, I professed to demonstrate that
I had discovered many things that were before unknown, and thus
afford ground for believing that we may still discover many others,
with the view of thus stimulating all to the investigation of truth.
Since that period, anticipating the difficulty which many would
experience in apprehending the foundations of the Metaphysics, I
endeavoured to explain the chief points of them in a book of
Meditations, which is not in itself large, but the size of which has
been increased, and the matter greatly illustrated, by the
Objections which several very learned persons sent to me on occasion
of it, and by the Replies which I made to them. At length, after it
appeared to me that those preceding treatises had sufficiently
prepared the minds of my readers for the Principles of Philosophy, I
also published it; and I have divided this work into four parts, the
first of which contains the principles of human knowledge, and which
may be called the First Philosophy, or Metaphysics. That this part,
accordingly, may be properly understood, it will be necessary to
read beforehand the book of Meditations I wrote on the same subject.
The other three parts contain all that is most general in Physics,
namely, the explication of the first laws or principles of nature,
and the way in which the heavens, the fixed stars, the planets,
comets, and generally the whole universe, were composed; in the next
place, the explication, in particular, of the nature of this earth,
the air, water, fire, the magnet, which are the bodies we most
commonly find everywhere around it, and of all the qualities we
observe in these bodies, as light, heat, gravity, and the like. In
this way, it seems to me, I have commenced the orderly explanation
of the whole of philosophy, without omitting any of the matters that
ought to precede the last which I discussed. But to bring this
undertaking to its conclusion, I ought hereafter to explain, in the
same manner, the nature of the other more particular bodies that are
on the earth, namely, minerals, plants, animals, and especially man;
finally, to treat thereafter with accuracy of Medicine, Ethics, and
Mechanics. I should require to do this in order to give to the world
a complete body of philosophy; and I do not yet feel myself so old,-
-I do not so much distrust my strength, nor do I find myself so far
removed from the knowledge of what remains, as that I should not
dare to undertake to complete this design, provided I were in a
position to make all the experiments which I should require for the
basis and verification of my reasonings. But seeing that would
demand a great expenditure, to which the resources of a private
individual like myself would not be adequate, unless aided by the
public, and as I have no ground to expect this aid, I believe that I
ought for the future to content myself with studying for my own
instruction, and posterity will excuse me if I fail hereafter to
labour for them.

Meanwhile, that it may be seen wherein I think I have already
promoted the general good, I will here mention the fruits that may
be gathered from my Principles. The first is the satisfaction which
the mind will experience on finding in the work many truths before
unknown; for although frequently truth does not so greatly affect
our imagination as falsity and fiction, because it seems less
wonderful and is more simple, yet the gratification it affords is
always more durable and solid. The second fruit is, that in studying
these principles we will become accustomed by degrees to judge
better of all the things we come in contact with, and thus be made
wiser, in which respect the effect will be quite the opposite of the
common philosophy, for we may easily remark in those we call pedants
that it renders them less capable of rightly exercising their reason
than they would have been if they had never known it. The third is,
that the truths which they contain, being highly clear and certain,
will take away all ground of dispute, and thus dispose men's minds
to gentleness and concord; whereas the contrary is the effect of the
controversies of the schools, which, as they insensibly render those
who are exercised in them more wrangling and opinionative, are
perhaps the prime cause of the heresies and dissensions that now
harass the world. The last and chief fruit of these Principles is,
that one will be able, by cultivating them, to discover many truths
I myself have not unfolded, and thus passing by degrees from one to
another, to acquire in course of time a perfect knowledge of the
whole of philosophy, and to rise to the highest degree of wisdom.
For just as all the arts, though in their beginnings they are rude
and imperfect, are yet gradually perfected by practice, from their
containing at first something true, and whose effect experience
evinces; so in philosophy, when we have true principles, we cannot
fail by following them to meet sometimes with other truths; and we
could not better prove the falsity of those of Aristotle, than by
saying that men made no progress in knowledge by their means during
the many ages they prosecuted them.

I well know that there are some men so precipitate and accustomed to
use so little circumspection in what they do, that, even with the
most solid foundations, they could not rear a firm superstructure;
and as it is usually those who are the readiest to make books, they
would in a short time mar all that I have done, and introduce
uncertainty and doubt into my manner of philosophizing, from which I
have carefully endeavoured to banish them, if people were to receive
their writings as mine, or as representing my opinions. I had, not
long ago, some experience of this in one of those who were believed
desirous of following me the most closely, [Footnote: Regius; see La
Vie de M. Descartes, reduite en abrege (Baillet). Liv. vii., chap.
vii.--T.] and one too of whom I had somewhere said that I had such
confidence in his genius as to believe that he adhered to no
opinions which I should not be ready to avow as mine; for he last
year published a book entitled "Fundamental Physics," in which,
although he seems to have written nothing on the subject of Physics
and Medicine which he did not take from my writings, as well from
those I have published as from another still imperfect on the nature
of animals, which fell into his hands; nevertheless, because he has
copied them badly, and changed the order, and denied certain
metaphysical truths upon which all Physics ought to be based, I am
obliged wholly to disavow his work, and here to request readers not
to attribute to me any opinion unless they find it expressly stated
in my own writings, and to receive no opinion as true, whether in my
writings or elsewhere, unless they see that it is very clearly
deduced from true principles. I well know, likewise, that many ages
may elapse ere all the truths deducible from these principles are
evolved out of them, as well because the greater number of such as
remain to be discovered depend on certain particular experiments
that never occur by chance, but which require to be investigated
with care and expense by men of the highest intelligence, as because
it will hardly happen that the same persons who have the sagacity to
make a right use of them, will possess also the means of making
them, and also because the majority of the best minds have formed so
low an estimate of philosophy in general, from the imperfections
they have remarked in the kind in vogue up to the present time, that
they cannot apply themselves to the search after truth.

But, in conclusion, if the difference discernible between the
principles in question and those of every other system, and the
great array of truths deducible from them, lead them to discern the
importance of continuing the search after these truths, and to
observe the degree of wisdom, the perfection and felicity of life,
to which they are fitted to conduct us, I venture to believe that
there will not be found one who is not ready to labour hard in so
profitable a study, or at least to favour and aid with all his might
those who shall devote themselves to it with success.

The height of my wishes is, that posterity may sometime behold the
happy issue of it, etc.



TO THE MOST SERENE PRINCESS,

ELIZABETH, ELDEST DAUGHTER OF FREDERICK, KING OF BOHEMIA, COUNT
PALATINE, AND ELECTOR OF THE SACRED ROMAN EMPIRE.

MADAM,--The greatest advantage I have derived from the writings
which I have already published, has arisen from my having, through
means of them, become known to your Highness, and thus been
privileged to hold occasional converse with one in whom so many rare
and estimable qualities are united, as to lead me to believe I
should do service to the public by proposing them as an example to
posterity. It would ill become me to flatter, or to give expression
to anything of which I had no certain knowledge, especially in the
first pages of a work in which I aim at laying down the principles
of truth. And the generous modesty that is conspicuous in all your
actions, assures me that the frank and simple judgment of a man who
only writes what he believes will be more agreeable to you than the
ornate laudations of those who have studied the art of compliment.
For this reason, I will give insertion to nothing in this letter for
which I have not the certainty both of experience and reason; and in
the exordium, as in the rest of the work, I will write only as
becomes a philosopher. There is a vast difference between real and
apparent virtues; and there is also a great discrepancy between
those real virtues that proceed from an accurate knowledge of the
truth, and such as are accompanied with ignorance or error. The
virtues I call apparent are only, properly speaking, vices, which,
as they are less frequent than the vices that are opposed to them,
and are farther removed from them than the intermediate virtues, are
usually held in higher esteem than those virtues. Thus, because
those who fear dangers too much are more numerous than they who fear
them too little, temerity is frequently opposed to the vice of
timidity, and taken for a virtue, and is commonly more highly
esteemed than true fortitude. Thus, also, the prodigal are in
ordinary more praised than the liberal; and none more easily acquire
a great reputation for piety than the superstitious and
hypocritical. With regard to true virtues, these do not all proceed
from true knowledge, for there are some that likewise spring from
defect or error; thus, simplicity is frequently the source of
goodness, fear of devotion, and despair of courage. The virtues that
are thus accompanied with some imperfections differ from each other,
and have received diverse appellations. But those pure and perfect
virtues that arise from the knowledge of good alone are all of the
same nature, and may be comprised under the single term wisdom. For,
whoever owns the firm and constant resolution of always using his
reason as well as lies in his power, and in all his actions of doing
what he judges to be best, is truly wise, as far as his nature
permits; and by this alone he is just, courageous, temperate, and
possesses all the other virtues, but so well balanced as that none
of them appears more prominent than another: and for this reason,
although they are much more perfect than the virtues that blaze
forth through the mixture of some defect, yet, because the crowd
thus observes them less, they are not usually extolled so highly.
Besides, of the two things that are requisite for the wisdom thus
described, namely, the perception of the understanding and the
disposition of the will, it is only that which lies in the will
which all men can possess equally, inasmuch as the understanding of
some is inferior to that of others. But although those who have only
an inferior understanding may be as perfectly wise as their nature
permits, and may render themselves highly acceptable to God by their
virtue, provided they preserve always a firm and constant resolution
to do all that they shall judge to be right, and to omit nothing
that may lead them to the knowledge of the duties of which they are
ignorant; nevertheless, those who preserve a constant resolution of
performing the right, and are especially careful in instructing
themselves, and who possess also a highly perspicacious intellect,
arrive doubtless at a higher degree of wisdom than others; and I see
that these three particulars are found in great perfection in your
Highness. For, in the first place, your desire of self-instruction
is manifest, from the circumstance that neither the amusements of
the court, nor the accustomed mode of educating ladies, which
ordinarily condemns them to ignorance, have been sufficient to
prevent you from studying with much care all that is best in the
arts and sciences; and the incomparable perspicacity of your
intellect is evinced by this, that you penetrated the secrets of the
sciences and acquired an accurate knowledge of them in a very short
period. But of the vigour of your intellect I have a still stronger
proof, and one peculiar to myself, in that I have never yet met any
one who understood so generally and so well as yourself all that is
contained in my writings. For there are several, even among men of
the highest intellect and learning, who find them very obscure. And
I remark, in almost all those who are versant in Metaphysics, that
they are wholly disinclined from Geometry; and, on the other hand,
that the cultivators of Geometry have no ability for the
investigations of the First Philosophy: insomuch that I can say with
truth I know but one mind, and that is your own, to which both
studies are alike congenial, and which I therefore, with propriety,
designate incomparable. But what most of all enhances my admiration
is, that so accurate and varied an acquaintance with the whole
circle of the sciences is not found in some aged doctor who has
employed many years in contemplation, but in a Princess still young,
and whose countenance and years would more fitly represent one of
the Graces than a Muse or the sage Minerva. In conclusion, I not
only remark in your Highness all that is requisite on the part of
the mind to perfect and sublime wisdom, but also all that can be
required on the part of the will or the manners, in which benignity
and gentleness are so conjoined with majesty that, though fortune
has attacked you with continued injustice, it has failed either to
irritate or crush you. And this constrains me to such veneration
that I not only think this work due to you, since it treats of
philosophy which is the study of wisdom, but likewise feel not more
zeal for my reputation as a philosopher than pleasure in subscribing
myself,--

Of your most Serene Highness, The most devoted servant,

DESCARTES.


OF THE PRINCIPLES OF HUMAN KNOWLEDGE.

 I. THAT in order to seek truth, it is necessary once in the course
of our life, to doubt, as far as possible, of all things.

As we were at one time children, and as we formed various judgments
regarding the objects presented to our senses, when as yet we had
not the entire use of our reason, numerous prejudices stand in the
way of our arriving at the knowledge of truth; and of these it seems
impossible for us to rid ourselves, unless we undertake, once in our
lifetime, to doubt of all those things in which we may discover even
the smallest suspicion of uncertainty.

 II. That we ought also to consider as false all that is doubtful.

Moreover, it will be useful likewise to esteem as false the things
of which we shall be able to doubt, that we may with greater
clearness discover what possesses most certainty and is the easiest
to know.

 III. That we ought not meanwhile to make use of doubt in the
conduct of life.

In the meantime, it is to be observed that we are to avail ourselves
of this general doubt only while engaged in the contemplation of
truth. For, as far as concerns the conduct of life, we are very
frequently obliged to follow opinions merely probable, or even
sometimes, though of two courses of action we may not perceive more
probability in the one than in the other, to choose one or other,
seeing the opportunity of acting would not unfrequently pass away
before we could free ourselves from our doubts.

 IV. Why we may doubt of sensible things.

Accordingly, since we now only design to apply ourselves to the
investigation of truth, we will doubt, first, whether of all the
things that have ever fallen under our senses, or which we have ever
imagined, any one really exist; in the first place, because we know
by experience that the senses sometimes err, and it would be
imprudent to trust too much to what has even once deceived us;
secondly, because in dreams we perpetually seem to perceive or
imagine innumerable objects which have no existence. And to one who
has thus resolved upon a general doubt, there appear no marks by
which he can with certainty distinguish sleep from the waking state.

 V. Why we may also doubt of mathematical demonstrations.

We will also doubt of the other things we have before held as most
certain, even of the demonstrations of mathematics, and of their
principles which we have hitherto deemed self-evident; in the first
place, because we have sometimes seen men fall into error in such
matters, and admit as absolutely certain and self evident what to us
appeared false, but chiefly because we have learnt that God who
created us is all-powerful; for we do not yet know whether perhaps
it was his will to create us so that we are always deceived, even in
the things we think we know best: since this does not appear more
impossible than our being occasionally deceived, which, however, as
observation teaches us, is the case. And if we suppose that an all-
powerful God is not the author of our being, and that we exist of
ourselves or by some other means, still, the less powerful we
suppose our author to be, the greater reason will we have for
believing that we are not so perfect as that we may not be
continually deceived.

 VI. That we possess a free-will, by which we can withhold our
assent from what is doubtful, and thus avoid error.

But meanwhile, whoever in the end may be the author of our being,
and however powerful and deceitful he may be, we are nevertheless
conscious of a freedom, by which we can refrain from admitting to a
place in our belief aught that is not manifestly certain and
undoubted, and thus guard against ever being deceived.

 VII. That we cannot doubt of our existence while we doubt, and that
this is the first knowledge we acquire when we philosophize in
order.

While we thus reject all of which we can entertain the smallest
doubt, and even imagine that it is false, we easily indeed suppose
that there is neither God, nor sky, nor bodies, and that we
ourselves even have neither hands nor feet, nor, finally, a body;
but we cannot in the same way suppose that we are not while we doubt
of the truth of these things; for there is a repugnance in
conceiving that what thinks does not exist at the very time when it
thinks. Accordingly, the knowledge, _I_ THINK, THEREFORE _I_ AM, is
the first and most certain that occurs to one who philosophizes
orderly.

 VIII. That we hence discover the distinction between the mind and
the body, or between a thinking and corporeal thing.

And this is the best mode of discovering the nature of the mind, and
its distinctness from the body: for examining what we are, while
supposing, as we now do, that there is nothing really existing apart
from our thought, we clearly perceive that neither extension, nor
figure, nor local motion,[Footnote: Instead of "local motion," the
French has "existence in any place."] nor anything similar that can
be attributed to body, pertains to our nature, and nothing save
thought alone; and, consequently, that the notion we have of our
mind precedes that of any corporeal thing, and is more certain,
seeing we still doubt whether there is any body in existence, while
we already perceive that we think.

 IX. What thought (COGITATIO) is.

By the word thought, I understand all that which so takes place in
us that we of ourselves are immediately conscious of it; and,
accordingly, not only to understand (INTELLIGERE, ENTENDRE), to will
(VELLE), to imagine (IMAGINARI), but even to perceive (SENTIRE,
SENTIR), are here the same as to think (COGITARE, PENSER). For if I
say, I see, or, I walk, therefore I am; and if I understand by
vision or walking the act of my eyes or of my limbs, which is the
work of the body, the conclusion is not absolutely certain, because,
as is often the case in dreams, I may think that I see or walk,
although I do not open my eyes or move from my place, and even,
perhaps, although I have no body: but, if I mean the sensation
itself, or consciousness of seeing or walking, the knowledge is
manifestly certain, because it is then referred to the mind, which
alone perceives or is conscious that it sees or walks. [Footnote: In
the French, "which alone has the power of perceiving, or of being
conscious in any other way whatever."]

 X. That the notions which are simplest and self-evident, are
obscured by logical definitions; and that such are not to be
reckoned among the cognitions acquired by study, [but as born with
us].

I do not here explain several other terms which I have used, or
design to use in the sequel, because their meaning seems to me
sufficiently self-evident. And I frequently remarked that
philosophers erred in attempting to explain, by logical definitions,
such truths as are most simple and self-evident; for they thus only
rendered them more obscure. And when I said that the proposition,
_I_ THINK, THEREFORE _I_ AM, is of all others the first and most
certain which occurs to one philosophizing orderly, I did not
therefore deny that it was necessary to know what thought,
existence, and certitude are, and the truth that, in order to think
it is necessary to be, and the like; but, because these are the most
simple notions, and such as of themselves afford the knowledge of
nothing existing, I did not judge it proper there to enumerate them.

 XI. How we can know our mind more clearly than our body.

But now that it may be discerned how the knowledge we have of the
mind not only precedes, and has greater certainty, but is even
clearer, than that we have of the body, it must be remarked, as a
matter that is highly manifest by the natural light, that to nothing
no affections or qualities belong; and, accordingly, that where we
observe certain affections, there a thing or substance to which
these pertain, is necessarily found. The same light also shows us
that we know a thing or substance more clearly in proportion as we
discover in it a greater number of qualities. Now, it is manifest
that we remark a greater number of qualities in our mind than in any
other thing; for there is no occasion on which we know anything
whatever when we are not at the same time led with much greater
certainty to the knowledge of our own mind. For example, if I judge
that there is an earth because I touch or see it, on the same
ground, and with still greater reason, I must be persuaded that my
mind exists; for it may be, perhaps, that I think I touch the earth
while there is one in existence; but it is not possible that I
should so judge, and my mind which thus judges not exist; and the
same holds good of whatever object is presented to our mind.

 XII. How it happens that every one does not come equally to know
this.

Those who have not philosophized in order have had other opinions on
this subject, because they never distinguished with sufficient care
the mind from the body. For, although they had no difficulty in
believing that they themselves existed, and that they had a higher
assurance of this than of any other thing, nevertheless, as they did
not observe that by THEMSELVES, they ought here to understand their
MINDS alone [when the question related to metaphysical certainty];
and since, on the contrary, they rather meant their bodies which
they saw with their eyes, touched with their hands, and to which
they erroneously attributed the faculty of perception, they were
prevented from distinctly apprehending the nature of the mind.

 XIII. In what sense the knowledge of other things depends upon the
knowledge of God.

But when the mind, which thus knows itself but is still in doubt as
to all other things, looks around on all sides, with a view to the
farther extension of its knowledge, it first of all discovers within
itself the ideas of many things; and while it simply contemplates
them, and neither affirms nor denies that there is anything beyond
itself corresponding to them, it is in no danger of erring. The mind
also discovers certain common notions out of which it frames various
demonstrations that carry conviction to such a degree as to render
doubt of their truth impossible, so long as we give attention to
them. For example, the mind has within itself ideas of numbers and
figures, and it has likewise among its common notions the principle
THAT IF EQUALS BE ADDED TO EQUALS THE WHOLES WILL BE EQUAL and the
like; from which it is easy to demonstrate that the three angles of
a triangle are equal to two right angles, etc. Now, so long as we
attend to the premises from which this conclusion and others similar
to it were deduced, we feel assured of their truth; but, as the mind
cannot always think of these with attention, when it has the
remembrance of a conclusion without recollecting the order of its
deduction, and is uncertain whether the author of its being has
created it of a nature that is liable to be deceived, even in what
appears most evident, it perceives that there is just ground to
distrust the truth of such conclusions, and that it cannot possess
any certain knowledge until it has discovered its author.

 XIV. That we may validly infer the existence of God from necessary
existence being comprised in the concept we have of him.

When the mind afterwards reviews the different ideas that are in it,
it discovers what is by far the chief among them--that of a Being
omniscient, all-powerful, and absolutely perfect; and it observes
that in this idea there is contained not only possible and
contingent existence, as in the ideas of all other things which it
clearly perceives, but existence absolutely necessary and eternal.
And just as because, for example, the equality of its three angles
to two right angles is necessarily comprised in the idea of a
triangle, the mind is firmly persuaded that the three angles of a
triangle are equal to two right angles; so, from its perceiving
necessary and eternal existence to be comprised in the idea which it
has of an all-perfect Being, it ought manifestly to conclude that
this all-perfect Being exists.

 XV. That necessary existence is not in the same way comprised in
the notions which we have of other things, but merely contingent
existence.

The mind will be still more certain of the truth of this conclusion,
if it consider that it has no idea of any other thing in which it
can discover that necessary existence is contained; for, from this
circumstance alone, it will discern that the idea of an all-perfect
Being has not been framed by itself, and that it does not represent
a chimera, but a true and immutable nature, which must exist since
it can only be conceived as necessarily existing.

 XVI. That prejudices hinder many from clearly knowing the necessity
of the existence of God.

Our mind would have no difficulty in assenting to this truth, if it
were, first of all, wholly free from prejudices; but as we have been
accustomed to distinguish, in all other things, essence from
existence, and to imagine at will many ideas of things which neither
are nor have been, it easily happens, when we do not steadily fix
our thoughts on the contemplation of the all-perfect Being, that a
doubt arises as to whether the idea we have of him is not one of
those which we frame at pleasure, or at least of that class to whose
essence existence does not pertain.

 XVII. That the greater objective (representative) perfection there
is in our idea of a thing, the greater also must be the perfection
of its cause.

When we further reflect on the various ideas that are in us, it is
easy to perceive that there is not much difference among them, when
we consider them simply as certain modes of thinking, but that they
are widely different, considered in reference to the objects they
represent; and that their causes must be so much the more perfect
according to the degree of objective perfection contained in them.
[Footnote: "as what they represent of their object has more
perfection."--FRENCH.] For there is no difference between this and
the case of a person who has the idea of a machine, in the
construction of which great skill is displayed, in which
circumstances we have a right to inquire how he came by this idea,
whether, for example, he somewhere saw such a machine constructed by
another, or whether he was so accurately taught the mechanical
sciences, or is endowed with such force of genius, that he was able
of himself to invent it, without having elsewhere seen anything like
it; for all the ingenuity which is contained in the idea objectively
only, or as it were in a picture, must exist at least in its first
and chief cause, whatever that may be, not only objectively or
representatively, but in truth formally or eminently.

 XVIII. That the existence of God may be again inferred from the
above.

Thus, because we discover in our minds the idea of God, or of an
all-perfect Being, we have a right to inquire into the source whence
we derive it; and we will discover that the perfections it
represents are so immense as to render it quite certain that we
could only derive it from an all-perfect Being; that is, from a God
really existing. For it is not only manifest by the natural light
that nothing cannot be the cause of anything whatever, and that the
more perfect cannot arise from the less perfect, so as to be thereby
produced as by its efficient and total cause, but also that it is
impossible we can have the idea or representation of anything
whatever, unless there be somewhere, either in us or out of us, an
original which comprises, in reality, all the perfections that are
thus represented to us; but, as we do not in any way find in
ourselves those absolute perfections of which we have the idea, we
must conclude that they exist in some nature different from ours,
that is, in God, or at least that they were once in him; and it most
manifestly follows [from their infinity] that they are still there.

 XIX. That, although we may not comprehend the nature of God, there
is yet nothing which we know so clearly as his perfections.

This will appear sufficiently certain and manifest to those who have
been accustomed to contemplate the idea of God, and to turn their
thoughts to his infinite perfections; for, although we may not
comprehend them, because it is of the nature of the infinite not to
be comprehended by what is finite, we nevertheless conceive them
more clearly and distinctly than material objects, for this reason,
that, being simple, and unobscured by limits,[Footnote: After
LIMITS, "what of them we do conceive is much less confused. There
is, besides, no speculation more calculated to aid in perfecting our
understanding, and which is more important than this, inasmuch as
the consideration of an object that has no limits to its perfections
fills us with satisfaction and assurance."-FRENCH.] they occupy our
mind more fully.

 XX. That we are not the cause of ourselves, but that this is God,
and consequently that there is a God.

But, because every one has not observed this, and because, when we
have an idea of any machine in which great skill is displayed, we
usually know with sufficient accuracy the manner in which we
obtained it, and as we cannot even recollect when the idea we have
of a God was communicated to us by him, seeing it was always in our
minds, it is still necessary that we should continue our review, and
make inquiry after our author, possessing, as we do, the idea of the
infinite perfections of a God: for it is in the highest degree
evident by the natural light, that that which knows something more
perfect than itself, is not the source of its own being, since it
would thus have given to itself all the perfections which it knows;
and that, consequently, it could draw its origin from no other being
than from him who possesses in himself all those perfections, that
is, from God.

 XXI. That the duration alone of our life is sufficient to
demonstrate the existence of God.

The truth of this demonstration will clearly appear, provided we
consider the nature of time, or the duration of things; for this is
of such a kind that its parts are not mutually dependent, and never
co-existent; and, accordingly, from the fact that we now are, it
does not necessarily follow that we shall be a moment afterwards,
unless some cause, viz., that which first produced us, shall, as it
were, continually reproduce us, that is, conserve us. For we easily
understand that there is no power in us by which we can conserve
ourselves, and that the being who has so much power as to conserve
us out of himself, must also by so much the greater reason conserve
himself, or rather stand in need of being conserved by no one
whatever, and, in fine, be God.

 XXII. That in knowing the existence of God, in the manner here
explained, we likewise know all his attributes, as far as they can
be known by the natural light alone.

There is the great advantage in proving the existence of God in this
way, viz., by his idea, that we at the same time know what he is, as
far as the weakness of our nature allows; for, reflecting on the
idea we have of him which is born with us, we perceive that he is
eternal, omniscient, omnipotent, the source of all goodness and
truth, creator of all things, and that, in fine, he has in himself
all that in which we can clearly discover any infinite perfection or
good that is not limited by any imperfection.

 XXIII. That God is not corporeal, and does not perceive by means of
senses as we do, or will the evil of sin.

For there are indeed many things in the world that are to a certain
extent imperfect or limited, though possessing also some perfection;
and it is accordingly impossible that any such can be in God. Thus,
looking to corporeal nature,[Footnote: In the French, "since
extension constitutes the nature of body."] since divisibility is
included in local extension, and this indicates imperfection, it is
certain that God is not body. And although in men it is to some
degree a perfection to be capable of perceiving by means of the
senses, nevertheless since in every sense there is passivity
[Footnote: In the French, "because our perceptions arise from
impressions made upon us from another source," i.e., than
ourselves.] which indicates dependency, we must conclude that God is
in no manner possessed of senses, and that he only understands and
wills, not, however, like us, by acts in any way distinct, but
always by an act that is one, identical, and the simplest possible,
understands, wills, and operates all, that is, all things that in
reality exist; for he does not will the evil of sin, seeing this is
but the negation of being.

 XXIV. That in passing from the knowledge of God to the knowledge of
the creatures, it is necessary to remember that our understanding is
finite, and the power of God infinite.

But as we know that God alone is the true cause of all that is or
can be, we will doubtless follow the best way of philosophizing, if,
from the knowledge we have of God himself, we pass to the
explication of the things which he has created, and essay to deduce
it from the notions that are naturally in our minds, for we will
thus obtain the most perfect science, that is, the knowledge of
effects through their causes. But that we may be able to make this
attempt with sufficient security from error, we must use the
precaution to bear in mind as much as possible that God, who is the
author of things, is infinite, while we are wholly finite.

 XXV. That we must believe all that God has revealed, although it
may surpass the reach of our faculties.

Thus, if perhaps God reveal to us or others, matters concerning
himself which surpass the natural powers of our mind, such as the
mysteries of the incarnation and of the trinity, we will not refuse
to believe them, although we may not clearly understand them; nor
will we be in any way surprised to find in the immensity of his
nature, or even in what he has created, many things that exceed our
comprehension.

 XXVI. That it is not needful to enter into disputes [Footnote: "to
essay to comprehend the infinite."--FRENCH.] regarding the infinite,
but merely to hold all that in which we can find no limits as
indefinite, such as the extension of the world, the divisibility of
the parts of matter, the number of the stars, etc.

We will thus never embarrass ourselves by disputes about the
infinite, seeing it would be absurd for us who are finite to
undertake to determine anything regarding it, and thus as it were to
limit it by endeavouring to comprehend it. We will accordingly give
ourselves no concern to reply to those who demand whether the half
of an infinite line is also infinite, and whether an infinite number
is even or odd, and the like, because it is only such as imagine
their minds to be infinite who seem bound to entertain questions of
this sort. And, for our part, looking to all those things in which
in certain senses, we discover no limits, we will not, therefore,
affirm that they are infinite, but will regard them simply as
indefinite. Thus, because we cannot imagine extension so great that
we cannot still conceive greater, we will say that the magnitude of
possible things is indefinite, and because a body cannot be divided
into parts so small that each of these may not be conceived as again
divided into others still smaller, let us regard quantity as
divisible into parts whose number is indefinite; and as we cannot
imagine so many stars that it would seem impossible for God to
create more, let us suppose that their number is indefinite, and so
in other instances.

 XXVII. What difference there is between the indefinite and the
infinite.

And we will call those things indefinite rather than infinite, with
the view of reserving to God alone the appellation of infinite; in
the first place, because not only do we discover in him alone no
limits on any side, but also because we positively conceive that he
admits of none; and in the second place, because we do not in the
same way positively conceive that other things are in every part
unlimited, but merely negatively admit that their limits, if they
have any, cannot be discovered by us.

 XXVIII. That we must examine, not the final, but the efficient,
causes of created things.

Likewise, finally, we will not seek reasons of natural things from
the end which God or nature proposed to himself in their creation
(i. e., final causes), [Footnote: "We will not stop to consider the
ends which God proposed to himself in the creation of the world, and
we will entirely reject from our philosophy the search of final
causes!"--French.] for we ought not to presume so far as to think
that we are sharers in the counsels of Deity, but, considering him
as the efficient cause of all things, let us endeavour to discover
by the natural light [Footnote: "Faculty of reasoning."--FRENCH.]
which he has planted in us, applied to those of his attributes of
which he has been willing we should have some knowledge, what must
be concluded regarding those effects we perceive by our senses;
bearing in mind, however, what has been already said, that we must
only confide in this natural light so long as nothing contrary to
its dictates is revealed by God himself. [Footnote: The last clause,
beginning "bearing in mind." is omitted in the French.]

 XXIX. That God is not the cause of our errors.

The first attribute of God which here falls to be considered, is
that he is absolutely veracious and the source of all light, so that
it is plainly repugnant for him to deceive us, or to be properly and
positively the cause of the errors to which we are consciously
subject; for although the address to deceive seems to be some mark
of subtlety of mind among men, yet without doubt the will to deceive
only proceeds from malice or from fear and weakness, and
consequently cannot be attributed to God.

 XXX. That consequently all which we clearly perceive is true, and
that we are thus delivered from the doubts above proposed.

Whence it follows, that the light of nature, or faculty of knowledge
given us by God, can never compass any object which is not true, in
as far as it attains to a knowledge of it, that is, in as far as the
object is clearly and distinctly apprehended. For God would have
merited the appellation of a deceiver if he had given us this
faculty perverted, and such as might lead us to take falsity for
truth [when we used it aright]. Thus the highest doubt is removed,
which arose from our ignorance on the point as to whether perhaps
our nature was such that we might be deceived even in those things
that appear to us the most evident. The same principle ought also to
be of avail against all the other grounds of doubting that have been
already enumerated. For mathematical truths ought now to be above
suspicion, since these are of the clearest. And if we perceive
anything by our senses, whether while awake or asleep, we will
easily discover the truth provided we separate what there is of
clear and distinct in the knowledge from what is obscure and
confused. There is no need that I should here say more on this
subject, since it has already received ample treatment in the
metaphysical Meditations; and what follows will serve to explain it
still more accurately.

 XXXI. That our errors are, in respect of God, merely negations,
but, in respect of ourselves, privations.

But as it happens that we frequently fall into error, although God
is no deceiver, if we desire to inquire into the origin and cause of
our errors, with a view to guard against them, it is necessary to
observe that they depend less on our understanding than on our will,
and that they have no need of the actual concourse of God, in order
to their production; so that, when considered in reference to God,
they are merely negations, but in reference to ourselves,
privations.

 XXXII. That there are only two modes of thinking in us, viz., the
perception of the understanding and the action of the will.

For all the modes of thinking of which we are conscious may be
referred to two general classes, the one of which is the perception
or operation of the understanding, and the other the volition or
operation of the will. Thus, to perceive by the senses (SENTIRE), to
imagine, and to conceive things purely intelligible, are only
different modes of perceiving (PERCIP IENDI); but to desire, to be
averse from, to affirm, to deny, to doubt, are different modes of
willing.

 XXXIII. That we never err unless when we judge of something which
we do not sufficiently apprehend.

When we apprehend anything we are in no danger of error, if we
refrain from judging of it in any way; and even when we have formed
a judgment regarding it, we would never fall into error, provided we
gave our assent only to what we clearly and distinctly perceived;
but the reason why we are usually deceived, is that we judge without
possessing an exact knowledge of that of which we judge.

 XXXIV. That the will as well as the understanding is required for
judging.

I admit that the understanding is necessary for judging, there being
no room to suppose that we can judge of that which we in no way
apprehend; but the will also is required in order to our assenting
to what we have in any degree perceived. It is not necessary,
however, at least to form any judgment whatever, that we have an
entire and perfect apprehension of a thing; for we may assent to
many things of which we have only a very obscure and confused
knowledge.

 XXXV. That the will is of greater extension than the understanding,
and is thus the source of our errors.

Further, the perception of the intellect extends only to the few
things that are presented to it, and is always very limited: the
will, on the other hand, may, in a certain sense, be said to be
infinite, because we observe nothing that can be the object of the
will of any other, even of the unlimited will of God, to which ours
cannot also extend, so that we easily carry it beyond the objects we
clearly perceive; and when we do this, it is not wonderful that we
happen to be deceived.

 XXXVI. That our errors cannot be imputed to God.

But although God has not given us an omniscient understanding, he is
not on this account to be considered in any wise the author of our
errors, for it is of the nature of created intellect to be finite,
and of finite intellect not to embrace all things.

 XXXVII. That the chief perfection of man is his being able to act
freely or by will, and that it is this which renders him worthy of
praise or blame.

That the will should be the more extensive is in harmony with its
nature: and it is a high perfection in man to be able to act by
means of it, that is, freely; and thus in a peculiar way to be the
master of his own actions, and merit praise or blame. For self-
acting machines are not commended because they perform with
exactness all the movements for which they were adapted, seeing
their motions are carried on necessarily; but the maker of them is
praised on account of the exactness with which they were framed,
because he did not act of necessity, but freely; and, on the same
principle, we must attribute to ourselves something more on this
account, that when we embrace truth, we do so not of necessity, but
freely.

 XXXVIII. That error is a defect in our mode of acting, not in our
nature; and that the faults of their subjects may be frequently
attributed to other masters, but never to God.

It is true, that as often as we err, there is some defect in our
mode of action or in the use of our liberty, but not in our nature,
because this is always the same, whether our judgments be true or
false. And although God could have given to us such perspicacity of
intellect that we should never have erred, we have, notwithstanding,
no right to demand this of him; for, although with us he who was
able to prevent evil and did not is held guilty of it, God is not in
the same way to be reckoned responsible for our errors because he
had the power to prevent them, inasmuch as the dominion which some
men possess over others has been instituted for the purpose of
enabling them to hinder those under them from doing evil, whereas
the dominion which God exercises over the universe is perfectly
absolute and free. For this reason we ought to thank him for the
goods he has given us, and not complain that he has not blessed us
with all which we know it was in his power to impart.

 XXXIX. That the liberty of our will is self-evident.

Finally, it is so manifest that we possess a free will, capable of
giving or withholding its assent, that this truth must be reckoned
among the first and most common notions which are born with us.
This, indeed, has already very clearly appeared, for when essaying
to doubt of all things, we went so far as to suppose even that he
who created us employed his limitless power in deceiving us in every
way, we were conscious nevertheless of being free to abstain from
believing what was not in every respect certain and undoubted. Bat
that of which we are unable to doubt at such a time is as self-
evident and clear as any thing we can ever know.

 XL. That it is likewise certain that God has fore-ordained all
things.

But because what we have already discovered of God, gives us the
assurance that his power is so immense that we would sin in thinking
ourselves capable of ever doing anything which he had not ordained
beforehand, we should soon be embarrassed in great difficulties if
we undertook to harmonise the pre-ordination of God with the freedom
of our will, and endeavoured to comprehend both truths at once.

 XLI. How the freedom of our will may be reconciled with the Divine
pre-ordination.

But, in place of this, we will be free from these embarrassments if
we recollect that our mind is limited, while the power of God, by
which he not only knew from all eternity what is or can be, but also
willed and pre-ordained it, is infinite. It thus happens that we
possess sufficient intelligence to know clearly and distinctly that
this power is in God, but not enough to comprehend how he leaves the
free actions of men indeterminate} and, on the other hand, we have
such consciousness of the liberty and indifference which exists in
ourselves, that there is nothing we more clearly or perfectly
comprehend: [so that the omnipotence of God ought not to keep us
from believing it]. For it would be absurd to doubt of that of which
we are fully conscious, and which we experience as existing in
ourselves, because we do not comprehend another matter which, from
its very nature, we know to be incomprehensible.

 XLII. How, although we never will to err, it is nevertheless by our
will that we do err.

But now since we know that all our errors depend upon our will, and
as no one wishes to deceive himself, it may seem wonderful that
there is any error in our judgments at all. It is necessary to
remark, however, that there is a great difference between willing to
be deceived, and willing to yield assent to opinions in which it
happens that error is found. For though there is no one who
expressly wishes to fall into error, we will yet hardly find any one
who is not ready to assent to things in which, unknown to himself,
error lurks; and it even frequently happens that it is the desire
itself of following after truth that leads those not fully aware of
the order in which it ought to be sought for, to pass judgment on
matters of which they have no adequate knowledge, and thus to fall
into error.

 XLIII. That we shall never err if we give our assent only to what
we clearly and distinctly perceive.

But it is certain we will never admit falsity for truth, so long as
we judge only of that which we clearly and distinctly perceive;
because, as God is no deceiver, the faculty of knowledge which he
has given us cannot be fallacious, nor, for the same reason, the
faculty of will, when we do not extend it beyond the objects we
clearly know. And even although this truth could not be established
by reasoning, the minds of all have been so impressed by nature as
spontaneously to assent to whatever is clearly perceived, and to
experience an impossibility to doubt of its truth.

 XLIV. That we uniformly judge improperly when we assent to what we
do not clearly perceive, although our judgment may chance to be
true; and that it is frequently our memory which deceives us by
leading us to believe that certain things were formerly sufficiently
understood by us.

It is likewise certain that, when we approve of any reason which we
do not apprehend, we are either deceived, or, if we stumble on the
truth, it is only by chance, and thus we can never possess the
assurance that we are not in error. I confess it seldom happens that
we judge of a thing when we have observed we do not apprehend it,
because it is a dictate of the natural light never to judge of what
we do not know. But we most frequently err in this, that we presume
upon a past knowledge of much to which we give our assent, as to
something treasured up in the memory, and perfectly known to us;
whereas, in truth, we have no such knowledge.

 XLV. What constitutes clear and distinct perception.

There are indeed a great many persons who, through their whole
lifetime, never perceive anything in a way necessary for judging of
it properly; for the knowledge upon which we can establish a certain
and indubitable judgment must be not only clear, but also, distinct.
I call that clear which is present and manifest to the mind giving
attention to it, just as we are said clearly to see objects when,
being present to the eye looking on, they stimulate it with
sufficient force. and it is disposed to regard them; but the
distinct is that which is so precise and different from all other
objects as to comprehend in itself only what is clear. [Footnote:
"what appears manifestly to him who considers it as he ought."--
FRENCH.]

 XLVI. It is shown, from the example of pain, that a perception may
be clear without being distinct, but that it cannot be distinct
unless it is clear.

For example, when any one feels intense pain, the knowledge which he
has of this pain is very clear, but it is not always distinct; for
men usually confound it with the obscure judgment they form
regarding its nature, and think that there is in the suffering part
something similar to the sensation of pain of which they are alone
conscious. And thus perception may be clear without being distinct,
but it can never be distinct without likewise being clear.

 XLVII. That, to correct the prejudices of our early years, we must
consider what is clear in each of our simple [Footnote: "first."--
FRENCH.] notions.

And, indeed, in our early years, the mind was so immersed in the
body, that, although it perceived many things with sufficient
clearness, it yet knew nothing distinctly; and since even at that
time we exercised our judgment in many matters, numerous prejudices
were thus contracted, which, by the majority, are never afterwards
laid aside. But that we may now be in a position to get rid of
these, I will here briefly enumerate all the simple notions of which
our thoughts are composed, and distinguish in each what is clear
from what is obscure, or fitted to lead into error.

 XLVIII. That all the objects of our knowledge are to be regarded
either (1) as things or the affections of things: or (2) as eternal
truths; with the enumeration of things.

Whatever objects fall under our knowledge we consider either as
things or the affections of things,[Footnote: Things and the
affections of things are (in the French) equivalent to "what has
some (i.e., a REAL) existence," as opposed to the class of "eternal
truths," which have merely an IDEAL existence.] or as eternal truths
possessing no existence beyond our thought. Of the first class the
most general are substance, duration, order, number, and perhaps
also some others, which notions apply to all the kinds of things. I
do not, however, recognise more than two highest kinds (SUMMA
GENERA) of things; the first of intellectual things, or such as have
the power of thinking, including mind or thinking substance and its
properties; the second, of material things, embracing extended
substance, or body and its properties. Perception, volition, and all
modes as well of knowing as of willing, are related to thinking
substance; on the other hand, to extended substance we refer
magnitude, or extension in length, breadth, and depth, figure,
motion, situation, divisibility of parts themselves, and the like.
There are, however, besides these, certain things of which we have
an internal experience that ought not to be referred either to the
mind of itself, or to the body alone, but to the close and intimate
union between them, as will hereafter be shown in its place. Of this
class are the appetites of hunger and thirst, etc., and also the
emotions or passions of the mind which are not exclusively mental
affections, as the emotions of anger, joy, sadness, love, etc.; and,
finally, all the sensations, as of pain, titillation, light and
colours, sounds, smells, tastes, heat, hardness, and the other
tactile qualities.

 XLIX. That the eternal truths cannot be thus enumerated, but that
this is not necessary.

What I have already enumerated we are to regard as things, or the
qualities or modes of things. We now come to speak of eternal
truths. When we apprehend that it is impossible a thing can arise
from nothing, this proposition, EX NIHILO NIHIL FIT, is not
considered as somewhat existing, or as the mode of a thing, but as
an eternal truth having its seat in our mind, and is called a common
notion or axiom. Of this class are the following:--It is impossible
the same thing can at once be and not be; what is done cannot be
undone; he who thinks must exist while he thinks; and innumerable
others, the whole of which it is indeed difficult to enumerate, but
this is not necessary, since, if blinded by no prejudices, we cannot
fail to know them when the occasion of thinking them occurs.

 L. That these truths are clearly perceived, but not equally by all
men, on account of prejudices.

And, indeed, with regard to these common notions, it is not to be
doubted that they can be clearly and distinctly known, for otherwise
they would not merit this appellation: as, in truth, some of them
are not, with respect to all men, equally deserving of the name,
because they are not equally admitted by all: not, however, from
this reason, as I think, that the faculty of knowledge of one man
extends farther than that of another, but rather because these
common notions are opposed to the prejudices of some, who, on this
account, are not able readily to embrace them, even although others,
who are free from those prejudices, apprehend them with the greatest
clearness.

 LI. What substance is, and that the term is not applicable to God
and the creatures in the same sense.

But with regard to what we consider as things or the modes of
things, it is worth while to examine each of them by itself. By
substance we can conceive nothing else than a thing which exists in
such a way as to stand in need of nothing beyond itself in order to
its existence. And, in truth, there can be conceived but one
substance which is absolutely independent, and that is God. We
perceive that all other things can exist only by help of the
concourse of God. And, accordingly, the term substance does not
apply to God and the creatures UNIVOCALLY, to adopt a term familiar
in the schools; that is, no signification of this word can be
distinctly understood which is common to God and them.

 LII. That the term is applicable univocally to the mind and the
body, and how substance itself is known.

Created substances, however, whether corporeal or thinking, may be
conceived under this common concept; for these are things which, in
order to their existence, stand in need of nothing but the concourse
of God. But yet substance cannot be first discovered merely from its
being a thing which exists independently, for existence by itself is
not observed by us. We easily, however, discover substance itself
from any attribute of it, by this common notion, that of nothing
there are no attributes, properties, or qualities: for, from
perceiving that some attribute is present, we infer that some
existing thing or substance to which it may be attributed is also of
necessity present.

 LIII. That of every substance there is one principal attribute, as
thinking of the mind, extension of the body.

But, although any attribute is sufficient to lead us to the
knowledge of substance, there is, however, one principal property of
every substance, which constitutes its nature or essence, and upon
which all the others depend. Thus, extension in length, breadth, and
depth, constitutes the nature of corporeal substance; and thought
the nature of thinking substance. For every other thing that can be
attributed to body, presupposes extension, and is only some mode of
an extended thing; as all the properties we discover in the mind are
only diverse modes of thinking. Thus, for example, we cannot
conceive figure unless in something extended, nor motion unless in
extended space, nor imagination, sensation, or will, unless in a
thinking thing. But, on the other hand, we can conceive extension
without figure or motion, and thought without imagination or
sensation, and so of the others; as is clear to any one who attends
to these matters.

 LIV. How we may have clear and distinct notions of the substance
which thinks, of that which is corporeal, and of God.

And thus we may easily have two clear and distinct notions or ideas,
the one of created substance, which thinks, the other of corporeal
substance, provided we carefully distinguish all the attributes of
thought from those of extension. We may also have a clear and
distinct idea of an uncreated and independent thinking substance,
that is, of God, provided we do not suppose that this idea
adequately represents to us all that is in God, and do not mix up
with it anything fictitious, but attend simply to the characters
that are comprised in the notion we have of him, and which we
clearly know to belong to the nature of an absolutely perfect Being.
For no one can deny that there is in us such an idea of God, without
groundlessly supposing that there is no knowledge of God at all in
the human mind.

 LV. How duration, order, and number may be also distinctly
conceived.

We will also have most distinct conceptions of duration, order, and
number, if, in place of mixing up with our notions of them that
which properly belongs to the concept of substance, we merely think
that the duration of a thing is a mode under which we conceive this
thing, in so far as it continues to exist; and, in like manner, that
order and number are not in reality different from things disposed
in order and numbered, but only modes under which we diversely
consider these things.

 LVI. What are modes, qualities, attributes.

And, indeed, we here understand by modes the same with what we
elsewhere designate attributes or qualities. But when we consider
substance as affected or varied by them, we use the term modes; when
from this variation it may be denominated of such a kind, we adopt
the term qualities [to designate the different modes which cause it
to be so named]; and, finally, when we simply regard these modes as
in the substance, we call them attributes. Accordingly, since God
must be conceived as superior to change, it is not proper to say
that there are modes or qualities in him, but simply attributes; and
even in created things that which is found in them always in the
same mode, as existence and duration in the thing which exists and
endures, ought to be called attribute and not mode or quality.

 LVII. That some attributes exist in the things to which they are
attributed, and others only in our thought; and what duration and
time are.

Of these attributes or modes there are some which exist in the
things themselves, and others that have only an existence in our
thought; thus, for example, time, which we distinguish from duration
taken in its generality, and call the measure of motion, is only a
certain mode under which we think duration itself, for we do not
indeed conceive the duration of things that are moved to be
different from the duration of things that are not moved: as is
evident from this, that if two bodies are in motion for an hour, the
one moving quickly and the other slowly, we do not reckon more time
in the one than in the other, although there may be much more motion
in the one of the bodies than in the other. But that we may
comprehend the duration of all things under a common measure, we
compare their duration with that of the greatest and most regular
motions that give rise to years and days, and which we call time;
hence what is so designated is nothing superadded to duration, taken
in its generality, but a mode of thinking.

 LVIII. That number and all universals are only modes of thought.

In the same way number, when it is not considered as in created
things, but merely in the abstract or in general, is only a mode of
thinking; and the same is true of all those general ideas we call
universals.

 LIX. How universals are formed; and what are the five common, viz.,
genus, species, difference, property, and accident.

Universals arise merely from our making use of one and the same idea
in thinking of all individual objects between which there subsists a
certain likeness; and when we comprehend all the objects represented
by this idea under one name, this term likewise becomes universal.
For example, when we see two stones, and do not regard their nature
farther than to remark that there are two of them, we form the idea
of a certain number, which we call the binary; and when we
afterwards see two birds or two trees, and merely take notice of
them so far as to observe that there are two of them, we again take
up the same idea as before, which is, accordingly, universal; and we
likewise give to this number the same universal appellation of
binary. In the same way, when we consider a figure of three sides,
we form a certain idea, which we call the idea of a triangle, and we
afterwards make use of it as the universal to represent to our mind
all other figures of three sides. But when we remark more
particularly that of figures of three sides, some have a right angle
and others not, we form the universal idea of a right-angled
triangle, which being related to the preceding as more general, may
be called species; and the right angle the universal difference by
which right-angled triangles are distinguished from all others; and
farther, because the square of the side which sustains the right
angle is equal to the squares of the other two sides, and because
this property belongs only to this species of triangles, we may call
it the universal property of the species. Finally, if we suppose
that of these triangles some are moved and others not, this will be
their universal accident; and, accordingly, we commonly reckon five
universals, viz., genus, species, difference, property, accident.

 LX. Of distinctions; and first of the real.

But number in things themselves arises from the distinction there is
between them: and distinction is threefold, viz., real, modal, and
of reason. The real properly subsists between two or more
substances; and it is sufficient to assure us that two substances
are really mutually distinct, if only we are able clearly and
distinctly to conceive the one of them without the other. For the
knowledge we have of God renders it certain that he can effect all
that of which we have a distinct idea: wherefore, since we have now,
for example, the idea of an extended and corporeal substance, though
we as yet do not know with certainty whether any such thing is
really existent, nevertheless, merely because we have the idea of
it, we may be assured that such may exist; and, if it really exists,
that every part which we can determine by thought must be really
distinct from the other parts of the same substance. In the same
way, since every one is conscious that he thinks, and that he in
thought can exclude from himself every other substance, whether
thinking or extended, it is certain that each of us thus considered
is really distinct from every other thinking and corporeal
substance. And although we suppose that God united a body to a soul
so closely that it was impossible to form a more intimate union, and
thus made a composite whole, the two substances would remain really
distinct, notwithstanding this union; for with whatever tie God
connected them, he was not able to rid himself of the power he
possessed of separating them, or of conserving the one apart from
the other, and the things which God can separate or conserve
separately are really distinct.

 LXI. Of the modal distinction.

There are two kinds of modal distinctions, viz., that between the
mode properly so-called and the substance of which it is a mode, and
that between two modes of the same substance. Of the former we have
an example in this, that we can clearly apprehend substance apart
from the mode which we say differs from it; while, on the other
hand, we cannot conceive this mode without conceiving the substance
itself. There is, for example, a modal distinction between figure or
motion and corporeal substance in which both exist; there is a
similar distinction between affirmation or recollection and the
mind. Of the latter kind we have an illustration in our ability to
recognise the one of two modes apart from the other, as figure apart
from motion, and motion apart from figure; though we cannot think of
either the one or the other without thinking of the common substance
in which they adhere. If, for example, a stone is moved, and is
withal square, we can, indeed, conceive its square figure without
its motion, and reciprocally its motion without its square figure;
but we can conceive neither this motion nor this figure apart from
the substance of the stone. As for the distinction according to
which the mode of one substance is different from another substance,
or from the mode of another substance, as the motion of one body is
different from another body or from the mind, or as motion is
different from doubt, it seems to me that it should be called real
rather than modal, because these modes cannot be clearly conceived
apart from the really distinct substances of which they are the
modes.

 LXII. Of the distinction of reason (logical distinction).

Finally, the distinction of reason is that between a substance and
some one of its attributes, without which it is impossible, however,
we can have a distinct conception of the substance itself; or
between two such attributes of a common substance, the one of which
we essay to think without the other. This distinction is manifest
from our inability to form a clear and distinct idea of such
substance, if we separate from it such attribute; or to have a clear
perception of the one of two such attributes if we separate it from
the other. For example, because any substance which ceases to endure
ceases also to exist, duration is not distinct from substance except
in thought (RATIONE); and in general all the modes of thinking which
we consider as in objects differ only in thought, as well from the
objects of which they are thought as from each other in a common
object.[Footnote: "and generally all the attributes that lead us to
entertain different thoughts of the same thing, such as, for
example, the extension of body and its property of divisibility, do
not differ from the body which is to us the object of them, or from
each other, unless as we sometimes confusedly think the one without
thinking the other."--FRENCH.] It occurs, indeed, to me that I have
elsewhere classed this kind of distinction with the modal (viz.,
towards the end of the Reply to the First Objections to the
Meditations on the First Philosophy); but there it was only
necessary to treat of these distinctions generally, and it was
sufficient for my purpose at that time simply to distinguish both of
them from the real.

 LXIII. How thought and extension may be distinctly known, as
constituting, the one the nature of mind, the other that of body.

Thought and extension may be regarded as constituting the natures of
intelligent and corporeal substance; and then they must not be
otherwise conceived than as the thinking and extended substances
themselves, that is, as mind and body, which in this way are
conceived with the greatest clearness and distinctness. Moreover, we
more easily conceive extended or thinking substance than substance
by itself, or with the omission of its thinking or extension. For
there is some difficulty in abstracting the notion of substance from
the notions of thinking and extension, which, in truth, are only
diverse in thought itself (i.e., logically different); and a concept
is not more distinct because it comprehends fewer properties, but
because we accurately distinguish what is comprehended in it from
all other notions.

 LXIV. How these may likewise be distinctly conceived as modes of
substance.

Thought and extension may be also considered as modes of substance;
in as far, namely, as the same mind may have many different
thoughts, and the same body, with its size unchanged, may be
extended in several diverse ways, at one time more in length and
less in breadth or depth, and at another time more in breadth and
less in length; and then they are modally distinguished from
substance, and can be conceived not less clearly and distinctly,
provided they be not regarded as substances or things separated from
others, but simply as modes of things. For by regarding them as in
the substances of which they are the modes, we distinguish them from
these substances, and take them for what in truth they are: whereas,
on the other hand, if we wish to consider them apart from the
substances in which they are, we should by this itself regard them
as self-subsisting things, and thus confound the ideas of mode and
substance.

 LXV. How we may likewise know their modes.

In the same way we will best apprehend the diverse modes of thought,
as intellection, imagination, recollection, volition, etc., and also
the diverse modes of extension, or those that belong to extension,
as all figures, the situation of parts and their motions, provided
we consider them simply as modes of the things in which they are;
and motion as far as it is concerned, provided we think merely of
locomotion, without seeking to know the force that produces it, and
which nevertheless I will essay to explain in its own place.

 LXVI. How our sensations, affections, and appetites may be clearly
known, although we are frequently wrong in our judgments regarding
them.

There remain our sensations, affections, and appetites, of which we
may also have a clear knowledge, if we take care to comprehend in
the judgments we form of them only that which is precisely contained
in our perception of them, and of which we are immediately
conscious. There is, however, great difficulty in observing this, at
least in respect of sensations; because we have all, without
exception, from our youth judged that all the things we perceived by
our senses had an existence beyond our thought, and that they were
entirely similar to the sensations, that is, perceptions, we ad of
them. Thus when, for example, we saw a certain colour, we thought we
saw something occupying a place out of us, and which was entirely
similar to that idea of colour we were then conscious of; and from
the habit of judging in this way, we seemed to see this so clearly
and distinctly that we esteemed it (i.e., the externality of the
colour) certain and indubitable.

 LXVII. That we are frequently deceived in our judgments regarding
pain itself.

The same prejudice has place in all our other sensations, even in
those of titillation and pain. For though we are not in the habit of
believing that there exist out of us objects that resemble
titillation and pain, we do not nevertheless consider these
sensations as in the mind alone, or in our perception, but as in the
hand, or foot, or some other part of our body. There is no reason,
however, to constrain us to believe that the pain, for example,
which we feel, as it were, in the foot is something out of the mind
existing in the foot, or that the light which we see, as it were, in
the sun exists in the sun as it is in us. Both these beliefs are
prejudices of our early years, as will clearly appear in the sequel.

 LXVIII. How in these things what we clearly conceive is to be
distinguished from that in which we may be deceived.

But that we may distinguish what is clear in our sensations from
what is obscure, we ought most carefully to observe that we possess
a clear and distinct knowledge of pain, colour, and other things of
this sort, when we consider them simply as sensations or thoughts;
but that, when they are judged to be certain things subsisting
beyond our mind, we are wholly unable to form any conception of
them. Indeed, when any one tells us that he sees colour in a body or
feels pain in one of his limbs, this is exactly the same as if he
said that he there saw or felt something of the nature of which he
was entirely ignorant, or that he did not know what he saw or felt.
For although, when less attentively examining his thoughts, a person
may easily persuade himself that he has some knowledge of it, since
he supposes that there is something resembling that sensation of
colour or of pain of which he is conscious; yet, if he reflects on
what the sensation of colour or pain represents to him as existing
in a coloured body or in a wounded member, he will find that of such
he has absolutely no knowledge.

 LXIX. That magnitude, figure, etc., are known far differently from
colour, pain, etc.

What we have said above will be more manifest; especially if we
consider that size in the body perceived, figure, motion (at least
local, for philosophers by fancying other kinds of motion have
rendered its nature less intelligible to themselves), the situation
of parts, duration, number, and those other properties which, as we
have already said, we clearly perceive in all bodies, are known by
us in a way altogether different from that in which we know what
colour is in the same body, or pain, smell, taste, or any other of
those properties which I have said above must be referred to the
senses. For although when we see a body we are not less assured of
its existence from its appearing figured than from its appearing
coloured,[Footnote: "by the colour we perceive on occasion of it."--
FRENCH.] we yet know with far greater clearness its property of
figure than its colour.

 LXX. That we may judge of sensible things in two ways, by the one
of which we avoid error, by the other fall into it.

It is thus manifest that to say we perceive colours in objects is in
reality equivalent to saying we perceive something in objects and
are yet ignorant of what it is, except as that which determines in
us a certain highly vivid and clear sensation, which we call the
sensation of colours. There is, however, very great diversity in the
manner of judging: for so long as we simply judge that there is an
unknown something in objects (that is, in things such as they are,
from which the sensation reached us), so far are we from falling
into error that, on the contrary, we thus rather provide against it,
for we are less apt to judge rashly of a thing which we observe we
do not know. But when we think we perceive colours in objects,
although we are in reality ignorant of what we then denominate
colour, and are unable to conceive any resemblance between the
colour we suppose to be in objects, and that of which we are
conscious in sensation, yet because we do not observe this, or
because there are in objects several properties, as size, figure,
number, etc., which, as we clearly know, exist, or may exist in them
as they are perceived by our senses or conceived by our
understanding, we easily glide into the error of holding that what
is called colour in objects is something entirely resembling the
colour we perceive, and thereafter of supposing that we have a clear
perception of what is in no way perceived by us.

 LXXI. That the chief cause of our errors is to be found in the
prejudices of our childhood.

And here we may notice the first and chief cause of our errors. In
early life the mind was so closely bound to the body that it
attended to nothing beyond the thoughts by which it perceived the
objects that made impression on the body; nor as yet did it refer
these thoughts to anything existing beyond itself, but simply felt
pain when the body was hurt, or pleasure when anything beneficial to
the body occurred, or if the body was so highly affected that it was
neither greatly benefited nor hurt, the mind experienced the
sensations we call tastes, smells, sounds, heat, cold, light,
colours, and the like, which in truth are representative of nothing
existing out of our mind, and which vary according to the
diversities of the parts and modes in which the body is affected.
[Footnote: "which vary according to the diversities of the movements
that pass from all parts of our body to the part of the brain to
which it (the mind) is closely joined and united."--FRENCH.] The
mind at the same time also perceived magnitudes, figures, motions,
and the like, which were not presented to it as sensations but as
things or the modes of things existing, or at least capable of
existing out of thought, although it did not yet observe this
difference between these two kinds of perceptions. And afterwards
when the machine of the body, which has been so fabricated by nature
that it can of its own inherent power move itself in various ways,
by turning itself at random on every side, followed after what was
useful and avoided what was detrimental; the mind, which was closely
connected with it, reflecting on the objects it pursued or avoided,
remarked, for the first time, that they existed out of itself, and
not only attributed to them magnitudes, figures, motions, and the
like, which it apprehended either as things or as the modes of
things, but, in addition, attributed to them tastes, odours, and the
other ideas of that sort, the sensations of which were caused by
itself; [Footnote: "which it perceived on occasion of them" (i.e.,
of external objects).--FRENCH.] and as it only considered other
objects in so far as they were useful to the body, in which it was
immersed, it judged that there was greater or less reality in each
object, according as the impressions it caused on the body were more
or less powerful. Hence arose the belief that there was more
substance or body in rocks and metals than in air or water, because
the mind perceived in them more hardness and weight. Moreover, the
air was thought to be merely nothing so long as we experienced no
agitation of it by the wind, or did not feel it hot or cold. And
because the stars gave hardly more light than the slender flames of
candles, we supposed that each star was but of this size. Again,
since the mind did not observe that the earth moved on its axis, or
that its superficies was curved like that of a globe, it was on that
account more ready to judge the earth immovable and its surface
flat. And our mind has been imbued from our infancy with a thousand
other prejudices of the same sort which afterwards in our youth we
forgot we had accepted without sufficient examination, and admitted
as possessed of the highest truth and clearness, as if they had been
known by means of our senses, or implanted in us by nature.

 LXXII. That the second cause of our errors is that we cannot forget
these prejudices.

And although now in our mature years, when the mind, being no longer
wholly subject to the body, is not in the habit of referring all
things to it, but also seeks to discover the truth of things
considered in themselves, we observe the falsehood of a great many
of the judgments we had before formed; yet we experience a
difficulty in expunging them from our memory, and, so long as they
remain there, they give rise to various errors. Thus, for example,
since from our earliest years we imagined the stars to be of very
small size, we find it highly difficult to rid ourselves of this
imagination, although assured by plain astronomical reasons that
they are of the greatest,--so prevailing is the power of
preconceived opinion.

 LXXIII. The third cause is, that we become fatigued by attending to
those objects which are not present to the senses; and that we are
thus accustomed to judge of these not from present perception but
from pre-conceived opinion.

Besides, our mind cannot attend to any object without at length
experiencing some pain and fatigue; and of all objects it has the
greatest difficulty in attending to those which are present neither
to the senses nor to the imagination: whether for the reason that
this is natural to it from its union with the body, or because in
our early years, being occupied merely with perceptions and
imaginations, it has become more familiar with, and acquired greater
facility in thinking in those modes than in any other. Hence it also
happens that many are unable to conceive any substance except what
is imaginable and corporeal, and even sensible. For they are
ignorant of the circumstance, that those objects alone are
imaginable which consist in extension, motion, and figure, while
there are many others besides these that are intelligible; and they
persuade themselves that nothing can subsist but body, and, finally,
that there is no body which is not sensible. And since in truth we
perceive no object such as it is by sense alone [but only by our
reason exercised upon sensible objects], as will hereafter be
clearly shown, it thus happens that the majority during life
perceive nothing unless in a confused way.

 LXXIV. The fourth source of our errors is, that we attach our
thoughts to words which do not express them with accuracy.

Finally, since for the use of speech we attach all our conceptions
to words by which to express them, and commit to memory our thoughts
in connection with these terms, and as we afterwards find it more
easy to recall the words than the things signified by them, we can
scarcely conceive anything with such distinctness as to separate
entirely what we conceive from the words that were selected to
express it. On this account the majority attend to words rather than
to things; and thus very frequently assent to terms without
attaching to them any meaning, either because they think they once
understood them, or imagine they received them from others by whom
they were correctly understood. This, however, is not the place to
treat of this matter in detail, seeing the nature of the human body
has not yet been expounded, nor the existence even of body
established; enough, nevertheless, appears to have been said to
enable one to distinguish such of our conceptions as are clear and
distinct from those that are obscure and confused.

 LXXV. Summary of what must be observed in order to philosophize
correctly.

Wherefore if we would philosophize in earnest, and give ourselves to
the search after all the truths we are capable of knowing, we must,
in the first place, lay aside our prejudices; in other words, we
must take care scrupulously to withhold our assent from the opinions
we have formerly admitted, until upon new examination we discover
that they are true. We must, in the next place, make an orderly
review of the notions we have in our minds, and hold as true all and
only those which we will clearly and distinctly apprehend. In this
way we will observe, first of all, that we exist in so far as it is
our nature to think, and at the same time that there is a God upon
whom we depend; and after considering his attributes we will be able
to investigate the truth of all other things, since God is the cause
of them. Besides the notions we have of God and of our mind, we will
likewise find that we possess the knowledge of many propositions
which are eternally true, as, for example, that nothing cannot be
the cause of anything, etc. We will farther discover in our minds
the knowledge of a corporeal or extended nature that may be moved,
divided, etc., and also of certain sensations that affect us, as of
pain, colours, tastes, etc., although we do not yet know the cause
of our being so affected; and, comparing what we have now learne'd,
by examining those things in their order, with our former confused
knowledge of them, we will acquire the habit of forming clear and
distinct conceptions of all the objects we are capable of knowing.
In these few precepts seem to me to be comprised the most general
and important principles of human knowledge.

 LXXVI. That we ought to prefer the Divine authority to our
perception; [Footnote: "reasonings."--FRENCH]. but that, apart from
things revealed, we ought to assent to nothing that we do not
clearly apprehend.

Above all, we must impress on our memory the infallible rule, that
what God has revealed is incomparably more certain than anything
else; and that, we ought to submit our belief to the Divine
authority rather than to our own judgment, even although perhaps the
light of reason should, with the greatest clearness and evidence,
appear to suggest to us something contrary to what is revealed. But
in things regarding which there is no revelation, it is by no means
consistent with the character of a philosopher to accept as true
what he has not ascertained to be such, and to trust more to the
senses, in other words, to the inconsiderate judgments of childhood
than to the dictates of mature reason.

 PART II.

OF THE PRINCIPLES OF MATERIAL THINGS.

I. The grounds on which the existence of material things may be
known with certainty.

Although we are all sufficiently persuaded of the existence of
material things, yet, since this was before called in question by
us, and since we reckoned the persuasion of their existence as among
the prejudices of our childhood, it is now necessary for us to
investigate the grounds on which this truth may be known with
certainty. In the first place, then, it cannot be doubted that every
perception we have comes to us from some object different from our
mind; for it is not in our power to cause ourselves to experience
one perception rather than another, the perception being entirely
dependent on the object which affects our senses. It may, indeed, be
matter of inquiry whether that object be God, or something different
from God; but because we perceive, or rather, stimulated by sense,
clearly and distinctly apprehend, certain matter extended in length,
breadth, and thickness, the various parts of which have different
figures and motions, and give rise to the sensation we have of
colours, smells, pain, etc., God would, without question, deserve to
be regarded as a deceiver, if he directly and of himself presented
to our mind the idea of this extended matter, or merely caused it to
be presented to us by some object which possessed neither extension,
figure, nor motion. For we clearly conceive this matter as entirely
distinct from God, and from ourselves, or our mind; and appear even
clearly to discern that the idea of it is formed in us on occasion
of objects existing out of our minds, to which it is in every
respect similar. But since God cannot deceive us, for this is
repugnant to his nature, as has been already remarked, we must
unhesitatingly conclude that there exists a certain object extended
in length, breadth, and thickness, and possessing all those
properties which we clearly apprehend to belong to what is extended.
And this extended substance is what we call body or matter.

 II. How we likewise know that the human body is closely connected
with the mind.

We ought also to conclude that a certain body is more closely united
to our mind than any other, because we clearly observe that pain and
other sensations affect us without our foreseeing them; and these,
the mind is conscious, do not arise from itself alone, nor pertain
to it, in so far as it is a thing which thinks, but only in so far
as it is united to another thing extended and movable, which is
called the human body. But this is not the place to treat in detail
of this matter.

 III. That the perceptions of the senses do not teach us what is in
reality in things, but what is beneficial of hurtful to the
composite whole of mind and body.

It will be sufficient to remark that the perceptions of the senses
are merely to be referred to this intimate union of the human body
and mind, and that they usually make us aware of what, in external
objects, may be useful or adverse to this union, but do not present
to us these objects as they are in themselves, unless occasionally
and by accident. For, after this observation, we will without
difficulty lay aside the prejudices of the senses, and will have
recourse to our understanding alone on this question by reflecting
carefully on the ideas implanted in it by nature.

 IV. That the nature of body consists not in weight hardness, colour
and the like, but in extension alone.

In this way we will discern that the nature of matter or body,
considered in general, does not consist in its being hard, or
ponderous, or coloured, or that which affects our senses in any
other way, but simply in its being a substance extended in length,
breadth, and depth. For with respect to hardness, we know nothing of
it by sense farther than that the parts of hard bodies resist the
motion of our hands on coming into contact with them; but if every
time our hands moved towards any part, all the bodies in that place
receded as quickly as our hands approached, we should never feel
hardness; and yet we have no reason to believe that bodies which
might thus recede would on this account lose that which makes them
bodies. The nature of body does not, therefore, consist in hardness.
In the same way, it may be shown that weight, colour, and all the
other qualities of this sort, which are perceived in corporeal
matter, may be taken from it, itself meanwhile remaining entire: it
thus follows that the nature of body depends on none of these.

 V. That the truth regarding the nature of body is obscured by the
opinions respecting rarefaction and a vacuum with which we are pre-
occupied.

There still remain two causes to prevent its being fully admitted
that the true nature of body consists in extension alone. The first
is the prevalent opinion, that most bodies admit of being so
rarefied and condensed that, when rarefied, they have greater
extension than when condensed; and some even have subtilized to such
a degree as to make a distinction between the substance of body and
its quantity, and between quantity itself and extension. The second
cause is this, that where we conceive only extension in length,
breadth, and depth, we are not in the habit of saying that body is
there, but only space and further void space, which the generality
believe to be a mere negation.

 VI. In what way rarefaction takes place.

But with regard to rarefaction and condensation, whoever gives his
attention to his own thoughts, and admits nothing of which he is not
clearly conscious, will not suppose that there is anything in those
processes further than a change of figure in the body rarefied or
condensed: so that, in other words, rare bodies are those between
the parts of which there are numerous distances filled with other
bodies; and dense bodies, on the other hand, those whose parts
approaching each other, either diminish these distances or take them
wholly away, in the latter of which cases the body is rendered
absolutely dense. The body, however, when condensed, has not,
therefore, less extension than when the parts embrace a greater
space, owing to their removal from each other, and their dispersion
into branches. For we ought not to attribute to it the extension of
the pores or distances which its parts do not occupy when it is
rarefied, but to the other bodies that fill these interstices; just
as when we see a sponge full of water or any other liquid, we do not
suppose that each part of the sponge has on this account greater
extension than when compressed and dry, but only that its pores are
wider, and therefore that the body is diffused over a larger space.

 VII. That rarefaction cannot be intelligibly explained unless in
the way here proposed.

And indeed I am unable to discover the force of the reasons which
have induced some to say that rarefaction is the result of the
augmentation of the quantity of body, rather than to explain it on
the principle exemplified in the case of a sponge. For although when
air or water is rarefied we do not see any of the pores that are
rendered large, or the new body that is added to occupy them, it is
yet less agreeable to reason to suppose something that is
unintelligible for the purpose of giving a verbal and merely
apparent explanation of the rarefaction of bodies, than to conclude,
because of their rarefaction, that there are pores or distances
between the parts which are increased in size, and filled with some
new body. Nor ought we to refrain from assenting to this
explanation, because we perceive this new body by none of our
senses, for there is no reason which obliges us to believe that we
should perceive by our senses all the bodies in existence. And we
see that it is very easy to explain rarefaction in this manner, but
impossible in any other; for, in fine, there would be, as appears to
me, a manifest contradiction in supposing that any body was
increased by a quantity or extension which it had not before,
without the addition to it of a new extended substance, in other
words, of another body, because it is impossible to conceive any
addition of extension or quantity to a thing without supposing the
addition of a substance having quantity or extension, as will more
clearly appear from what follows.

 VIII. That quantity and number differ only in thought (RATIONE)
from that which has quantity and is numbered.

For quantity differs from extended substance, and number from what
is numbered, not in reality but merely in our thought; so that, for
example, we may consider the whole nature of a corporeal substance
which is comprised in a space of ten feet, although we do not attend
to this measure of ten feet, for the obvious reason that the thing
conceived is of the same nature in any part of that space as in the
whole; and, on the other hand, we can conceive the number ten, as
also a continuous quantity of ten feet, without thinking of this
determinate substance, because the concept of the number ten is
manifestly the same whether we consider a number of ten feet or ten
of anything else; and we can conceive a continuous quantity of ten
feet without thinking of this or that determinate substance,
although we cannot conceive it without some extended substance of
which it is the quantity. It is in reality, however, impossible that
any, even the least part, of such quantity or extension, can be
taken away, without the retrenchment at the same time of as much of
the substance, nor, on the other hand, can we lessen the substance,
without at the same time taking as much from the quantity or
extension.

 IX. That corporeal substance, when distinguished from its quantity,
is confusedly conceived as something incorporeal.

Although perhaps some express themselves otherwise on this matter, I
am nevertheless convinced that they do not think differently from
what I have now said: for when they distinguish (corporeal)
substance from extension or quantity, they either mean nothing by
the word (corporeal) substance, or they form in their minds merely a
confused idea of incorporeal substance, which they falsely attribute
to corporeal, and leave to extension the true idea of this corporeal
substance; which extension they call an accident, but with such
impropriety as to make it easy to discover that their words are not
in harmony with their thoughts.

 X. What space or internal place is.

Space or internal place, and the corporeal substance which is
comprised in it, are not different in reality, but merely in the
mode in which they are wont to be conceived by us. For, in truth,
the same extension in length, breadth, and depth, which constitutes
space, constitutes body; and the difference between them lies only
in this, that in body we consider extension as particular, and
conceive it to change with the body; whereas in space we attribute
to extension a generic unity, so that after taking from a certain
space the body which occupied it, we do not suppose that we have at
the same time removed the extension of the space, because it appears
to us that the same extension remains there so long as it is of the
same magnitude and figure, and preserves the same situation in
respect to certain bodies around it, by means of which we determine
this space.

 XI. How space is not in reality different from corporeal substance.

And indeed it will be easy to discern that it is the same extension
which constitutes the nature of body as of space, and that these two
things are mutually diverse only as the nature of the genus and
species differs from that of the individual, provided we reflect on
the idea we have of any body, taking a stone for example, and reject
all that is not essential to the nature of body. In the first place,
then, hardness may be rejected, because if the stone were liquefied
or reduced to powder, it would no longer possess hardness, and yet
would not cease to be a body; colour also may be thrown out of
account, because we have frequently seen stones so transparent as to
have no colour; again, we may reject weight, because we have the
case of fire, which, though very light, is still a body; and,
finally, we may reject cold, heat, and all the other qualities of
this sort, either because they are not considered as in the stone,
or because, with the change of these qualities, the stone is not
supposed to have lost the nature of body. After this examination we
will find that nothing remains in the idea of body, except that it
is something extended in length, breadth, and depth; and this
something is comprised in our idea of space, not only of that which
is full of body, but even of what is called void space.

 XII. How space differs from body in our mode of conceiving it.

There is, however, some difference between them in the mode of
conception; for if we remove a stone from the space or place in
which it was, we conceive that its extension also is taken away,
because we regard this as particular, and inseparable from the stone
itself: but meanwhile we suppose that the same extension of place in
which this stone was remains, although the place of the stone be
occupied by wood, water, air, or by any other body, or be even
supposed vacant, because we now consider extension in general, and
think that the same is common to stones, wood, water, air, and other
bodies, and even to a vacuum itself, if there is any such thing,
provided it be of the same magnitude and figure as before, and
preserve the same situation among the external bodies which
determine this space.

 XIII. What external place is.

The reason of which is, that the words place and space signify
nothing really different from body which is said to be in place, but
merely designate its magnitude, figure, and situation among other
bodies. For it is necessary, in order to determine this situation,
to regard certain other bodies which we consider as immovable; and,
according as we look to different bodies, we may see that the same
thing at the same time does and does not change place. For example,
when a vessel is being carried out to sea, a person sitting at the
stern may be said to remain always in one place, if we look to the
parts of the vessel, since with respect to these he preserves the
same situation; and on the other hand, if regard be had to the
neighbouring shores, the same person will seem to be perpetually
changing place, seeing he is constantly receding from one shore and
approaching another. And besides, if we suppose that the earth
moves, and that it makes precisely as much way from west to east as
the vessel from east to west, we will again say that the person at
the stern does not change his place, because this place will be
determined by certain immovable points which we imagine to be in the
heavens. But if at length we are persuaded that there are no points
really immovable in the universe, as will hereafter be shown to be
probable, we will thence conclude that nothing has a permanent place
unless in so far as it is fixed by our thought.

 XIV. Wherein place and space differ.

The terms place and space, however, differ in signification, because
place more expressly designates situation than magnitude or figure,
while, on the other hand, we think of the latter when we speak of
space. For we frequently say that a thing succeeds to the place of
another, although it be not exactly of the same magnitude or figure;
but we do not therefore admit that it occupies the same space as the
other; and when the situation is changed we say that the place also
is changed, although there are the same magnitude and figure as
before: so that when we say that a thing is in a particular place,
we mean merely that it is situated in a determinate way in respect
of certain other objects; and when we add that it occupies such a
space or place, we understand besides that it is of such determinate
magnitude and figure as exactly to fill this space.

 XV. How external place is rightly taken for the superficies of the
surrounding body.

And thus we never indeed distinguish space from extension in length,
breadth, and depth; we sometimes, however, consider place as in the
thing placed, and at other times as out of it. Internal place indeed
differs in no way from space; but external place may be taken for
the superficies that immediately surrounds the thing placed. It
ought to be remarked that by superficies we do not here understand
any part of the surrounding body, but only the boundary between the
surrounding and surrounded bodies, which is nothing more than a
mode; or at least that we speak of superficies in general which is
no part of one body rather than another, but is always considered
the same, provided it retain the same magnitude and figure. For
although the whole surrounding body with its superficies were
changed, it would not be supposed that the body which was surrounded
by it had therefore changed its place, if it meanwhile preserved the
same situation with respect to the other bodies that are regarded as
immovable. Thus, if we suppose that a boat is carried in one
direction by the current of a stream, and impelled by the wind in
the opposite with an equal force, so that its situation with respect
to the banks is not changed, we will readily admit that it remains
in the same place, although the whole superficies which surrounds it
is incessantly changing.

 XVI. That a vacuum or space in which there is absolutely no body is
repugnant to reason.

With regard to a vacuum, in the philosophical sense of the term,
that is, a space in which there is no substance, it is evident that
such does not exist, seeing the extension of space or internal place
is not different from that of body. For since from this alone, that
a body has extension in length, breadth, and depth, we have reason
to conclude that it is a substance, it being absolutely
contradictory that nothing should possess extension, we ought to
form a similar inference regarding the space which is supposed void,
viz., that since there is extension in it there is necessarily also
substance.

 XVII. That a vacuum in the ordinary use of the term does not
exclude all body.

And, in truth, by the term vacuum in its common use, we do not mean
a place or space in which there is absolutely nothing, but only a
place in which there is none of those things we presume ought to be
there. Thus, because a pitcher is made to hold water, it is said to
be empty when it is merely filled with air; or if there are no fish
in a fish-pond, we say there is nothing in it, although it be full
of water; thus a vessel is said to be empty, when, in place of the
merchandise which it was designed to carry, it is loaded with sand
only, to enable it to resist the violence of the wind; and, finally,
it is in the same sense that we say space is void when it contains
nothing sensible, although it contain created and self-subsisting
matter; for we are not in the habit of considering the bodies near
us, unless in so far as they cause in our organs of sense,
impressions strong enough to enable us to perceive them. And if, in
place of keeping in mind what ought to be understood by these terms
a vacuum and nothing, we afterwards suppose that in the space we
called a vacuum, there is not only no sensible object, but no object
at all, we will fall into the same error as if, because a pitcher in
which there is nothing but air, is, in common speech, said to be
empty, we were therefore to judge that the air contained in it is
not a substance (RES SUBSISTENS).

 XVIII. How the prejudice of an absolute vacuum is to be corrected.

We have almost all fallen into this error from the earliest age,
for, observing that there is no necessary connection between a
vessel and the body it contains, we thought that God at least could
take from a vessel the body which occupied it, without it being
necessary that any other should be put in the place of the one
removed. But that we may be able now to correct this false opinion,
it is necessary to remark that there is in truth no connection
between the vessel and the particular body which it contains, but
that there is an absolutely necessary connection between the concave
figure of the vessel and the extension considered generally which
must be comprised in this cavity; so that it is not more
contradictory to conceive a mountain without a valley than such a
cavity without the extension it contains, or this extension apart
from an extended substance, for, as we have often said, of nothing
there can be no extension. And accordingly, if it be asked what
would happen were God to remove from a vessel all the body contained
in it, without permitting another body to occupy its place, the
answer must be that the sides of the vessel would thus come into
proximity with each other. For two bodies must touch each other when
there is nothing between them, and it is manifestly contradictory
for two bodies to be apart, in other words, that there should be a
distance between them, and this distance yet be nothing; for all
distance is a mode of extension, and cannot therefore exist without
an extended substance.

 XIX. That this confirms what was said of rarefaction.

After we have thus remarked that the nature of corporeal substance
consists only in its being an extended thing, and that its extension
is not different from that which we attribute to space, however
empty, it is easy to discover the impossibility of any one of its
parts in any way whatsoever occupying more space at one time than at
another, and thus of being otherwise rarefied than in the way
explained above; and it is easy to perceive also that there cannot
be more matter or body in a vessel when it is filled with lead or
gold, or any other body however heavy and hard, than when it but
contains air and is supposed to be empty: for the quantity of the
parts of which a body is composed does not depend on their weight or
hardness, but only on the extension, which is always equal in the
same vase.

 XX. That from this the non-existence of atoms may likewise be
demonstrated.

We likewise discover that there cannot exist any atoms or parts of
matter that are of their own nature indivisible. For however small
we suppose these parts to be, yet because they are necessarily
extended, we are always able in thought to divide any one of them
into two or more smaller parts, and may accordingly admit their
divisibility. For there is nothing we can divide in thought which we
do not thereby recognize to be divisible; and, therefore, were we to
judge it indivisible our judgment would not be in harmony with the
knowledge we have of the thing; and although we should even suppose
that God had reduced any particle of matter to a smallness so
extreme that it did not admit of being further divided, it would
nevertheless be improperly styled indivisible, for though God had
rendered the particle so small that it was not in the power of any
creature to divide it, he could not however deprive himself of the
ability to do so, since it is absolutely impossible for him to
lessen his own omnipotence, as was before observed. Wherefore,
absolutely speaking, the smallest extended particle is always
divisible, since it is such of its very nature.

 XXI. It is thus also demonstrated that the extension of the world
is indefinite.

We further discover that this world or the whole (universitas) of
corporeal substance, is extended without limit, for wherever we fix
a limit, we still not only imagine beyond it spaces indefinitely
extended, but perceive these to be truly imaginable, in other words,
to be in reality such as we imagine them; so that they contain in
them corporeal substance indefinitely extended, for, as has been
already shown at length, the idea of extension which we conceive in
any space whatever is plainly identical with the idea of corporeal
substance.

 XXII. It also follows that the matter of the heavens and earth is
the same, and that there cannot be a plurality of worlds.

And it may also be easily inferred from all this that the earth and
heavens are made of the same matter; and that even although there
were an infinity of worlds, they would all be composed of this
matter; from which it follows that a plurality of worlds is
impossible, because we clearly conceive that the matter whose nature
consists only in its being an extended substance, already wholly
occupies all the imaginable spaces where these other worlds could
alone be, and we cannot find in ourselves the idea of any other
matter.

 XXIII. That all the variety of matter, or the diversity of its
forms, depends on motion.

There is therefore but one kind of matter in the whole universe, and
this we know only by its being extended. All the properties we
distinctly perceive to belong to it are reducible to its capacity of
being divided and moved according to its parts; and accordingly it
is capable of all those affections which we perceive can arise from
the motion of its parts. For the partition of matter in thought
makes no change in it; but all variation of it, or diversity of
form, depends on motion. The philosophers even seem universally to
have observed this, for they said that nature was the principle of
motion and rest, and by nature they understood that by which all
corporeal things become such as they are found in experience.

 XXIV. What motion is, taking the term in its common use.

But motion (viz., local, for I can conceive no other kind of motion,
and therefore I do not think we ought to suppose there is any other
in nature), in the ordinary sense of the term, is nothing more than
the action by which a body passes from one place to another. And
just as we have remarked above that the same thing may be said to
change and not to change place at the same time, so also we may say
that the same thing is at the same time moved and not moved. Thus,
for example, a person seated in a vessel which is setting sail,
thinks he is in motion if he look to the shore that he has left, and
consider it as fixed; but not if he regard the ship itself, among
the parts of which he preserves always the same situation. Moreover,
because we are accustomed to suppose that there is no motion without
action, and that in rest there is the cessation of action, the
person thus seated is more properly said to be at rest than in
motion, seeing he is not conscious of being in action.

 XXV. What motion is properly so called.

But if, instead of occupying ourselves with that which has no
foundation, unless in ordinary usage, we desire to know what ought
to be understood by motion according to the truth of the thing, we
may say, in order to give it a determinate nature, that it is THE
TRANSPORTING OF ONE PART OF MATTER OR OF ONE BODY FROM THE VICINITY
OF THOSE BODIES THAT ARE IN IMMEDIATE CONTACT WITH IT, OR WHICH WE
REGARD AS AT REST, to the vicinity of other bodies. By a body as a
part of matter, I understand all that which is transferred together,
although it be perhaps composed of several parts, which in
themselves have other motions; and I say that it is the transporting
and not the force or action which transports, with the view of
showing that motion is always in the movable thing, not in that
which moves; for it seems to me that we are not accustomed to
distinguish these two things with sufficient accuracy. Farther, I
understand that it is a mode of the movable thing, and not a
substance, just as figure is a property of the thing figured, and
repose of that which is at rest.



PART III.

OF THE VISIBLE WORLD.

 I. That we cannot think too highly of the works of God.

Having now ascertained certain principles of material things, which
were sought, not by the prejudices of the senses, but by the light
of reason, and which thus possess so great evidence that we cannot
doubt of their truth, it remains for us to consider whether from
these alone we can deduce the explication of all the phenomena of
nature. We will commence with those phenomena that are of the
greatest generality, and upon which the others depend, as, for
example, with the general structure of this whole visible world. But
in order to our philosophizing aright regarding this, two things are
first of all to be observed. The first is, that we should ever bear
in mind the infinity of the power and goodness of God, that we may
not fear falling into error by imagining his works to be too great,
beautiful, and perfect, but that we may, on the contrary, take care
lest, by supposing limits to them of which we have no certain
knowledge, we appear to think less highly than we ought of the power
of God.

 II. That we ought to beware lest, in our presumption, we imagine
that the ends which God proposed to himself in the creation of the
world are understood by us.

The second is, that we should beware of presuming too highly of
ourselves, as it seems we should do if we supposed certain limits to
the world, without being assured of their existence either by
natural reasons or by divine revelation, as if the power of our
thought extended beyond what God has in reality made; but likewise
still more if we persuaded ourselves that all things were created by
God for us only, or if we merely supposed that we could comprehend
by the power of our intellect the ends which God proposed to himself
in creating the universe.

 III. In what sense it may be said that all things were created for
the sake of man.

For although, as far as regards morals, it may be a pious thought to
believe that God made all things for us, seeing we may thus be
incited to greater gratitude and love toward him; and although it is
even in some sense true, because there is no created thing of which
we cannot make some use, if it be only that of exercising our mind
in considering it, and honouring God on account of it, it is yet by
no means probable that all things were created for us in this way
that God had no other end in their creation; and this supposition
would be plainly ridiculous and inept in physical reasoning, for we
do not doubt but that many things exist, or formerly existed and
have now ceased to be, which were never seen or known by man, and
were never of use to him.



PART IV.

OF THE EARTH.

 CLXXXVIII. Of what is to be borrowed from disquisitions on animals
and man to advance the knowledge of material objects.

I should add nothing farther to this the Fourth Part of the
Principles of Philosophy, did I purpose carrying out my original
design of writing a Fifth and Sixth Part, the one treating of things
possessed of life, that is, animals and plants, and the other of
man. But because I have not yet acquired sufficient knowledge of all
the matters of which I should desire to treat in these two last
parts, and do not know whether I shall ever have sufficient leisure
to finish them, I will here subjoin a few things regarding the
objects of our senses, that I may not, for the sake of the latter,
delay too long the publication of the former parts, or of what may
be desiderated in them, which I might have reserved for explanation
in those others: for I have hitherto described this earth, and
generally the whole visible world, as if it were merely a machine in
which there was nothing at all to consider except the figures and
motions of its parts, whereas our senses present to us many other
things, for example colours, smells, sounds, and the like, of which,
if I did not speak at all, it would be thought I had omitted the
explication of the majority of the objects that are in nature.

 CLXXXIX. What perception (SENSUS) is, and how we perceive.

We must know, therefore, that although the human soul is united to
the whole body, it has, nevertheless, its principal seat in the
brain, where alone it not only understands and imagines, but also
perceives; and this by the medium of the nerves, which are extended
like threads from the brain to all the other members, with which
they are so connected that we can hardly touch any one of them
without moving the extremities of some of the nerves spread over it;
and this motion passes to the other extremities of those nerves
which are collected in the brain round the seat of the soul,
[Footnote: *** FOOTNOTE NOT VISIBLE IN PAGE IMAGE (#98, Text p 195)]
as I have already explained with sufficient minuteness in the fourth
chapter of the Dioptrics. But the movements which are thus excited
in the brain by the nerves variously affect the soul or mind, which
is intimately conjoined with the brain, according to the diversity
of the motions themselves. And the diverse affections of the mind or
thoughts that immediately arise from these motions, are called
perceptions of the senses (SENSUUM PERCEPTIONES), or, as we commonly
speak, sensations (SENSUS).

 CXC. Of the distinction of the senses; and, first, of the internal,
that is, of the affections of the mind (passions), and the natural
appetites.

The varieties of these sensations depend, firstly, on the diversity
of the nerves themselves, and, secondly, of the movements that are
made in each nerve. We have not, however, as many different senses
as there are nerves. We can distinguish but seven principal classes
of nerves, of which two belong to the internal, and the other five
to the external senses. The nerves which extend to the stomach, the
oesophagus, the fauces, and the other internal parts that are
subservient to our natural wants, constitute one of our internal
senses. This is called the natural appetite (APPETITUS NATURALIS).
The other internal sense, which embraces all the emotions
(COMMOTIONES) of the mind or passions, and affections, as joy,
sadness, love, hate, and the like, depends upon the nerves which
extend to the heart and the parts about the heart, and are
exceedingly small; for, by way of example, when the blood happens to
be pure and well tempered, so that it dilates in the heart more
readily and strongly than usual, this so enlarges and moves the
small nerves scattered around the orifices, that there is thence a
corresponding movement in the brain, which affects the mind with a
certain natural feeling of joy; and as often as these same nerves
are moved in the same way, although this is by other causes, they
excite in our mind the same feeling (sensus, sentiment). Thus, the
imagination of the enjoyment of a good does not contain in itself
the feeling of joy, but it causes the animal spirits to pass from
the brain to the muscles in which these nerves are inserted; and
thus dilating the orifices of the heart, it also causes these small
nerves to move in the way appointed by nature to afford the
sensation of joy. Thus, when we receive news, the mind first of all
judges of it, and if the news be good, it rejoices with that
intellectual joy (GAUDIUM INTELLECTUALE) which is independent of any
emotion (COMMOTIO) of the body, and which the Stoics did not deny to
their wise man [although they supposed him exempt from all passion].
But as soon as this joy passes from the understanding to the
imagination, the spirits flow from the brain to the muscles that are
about the heart, and there excite the motion of the small nerves, by
means of which another motion is caused in the brain, which affects
the mind with the sensation of animal joy (LAETITIA ANIMALIS). On
the same principle, when the blood is so thick that it flows but
sparingly into the ventricles of the heart, and is not there
sufficiently dilated, it excites in the same nerves a motion quite
different from the preceding, which, communicated to the brain,
gives to the mind the sensation of sadness, although the mind itself
is perhaps ignorant of the cause of its sadness. And all the other
causes which move these nerves in the same way may also give to the
mind the same sensation. But the other movements of the same nerves
produce other effects, as the feelings of love, hate, fear, anger,
etc., as far as they are merely affections or passions of the mind;
in other words, as far as they are confused thoughts which the mind
has not from itself alone, but from its being closely joined to the
body, from which it receives impressions; for there is the widest
difference between these passions and the distinct thoughts which we
have of what ought to be loved, or chosen, or shunned, etc.,
[although these are often enough found together]. The natural
appetites, as hunger, thirst, and the others, are likewise
sensations excited in the mind by means of the nerves of the
stomach, fauces, and other parts, and are entirely different from
the will which we have to eat, drink, [and to do all that which we
think proper for the conservation of our body]; but, because this
will or appetition almost always accompanies them, they are
therefore named appetites.

 CXCI. Of the external senses; and first of touch.

We commonly reckon the external senses five in number, because there
are as many different kinds of objects which move the nerves and
their organs, and an equal number of kinds of confused thoughts
excited in the soul by these emotions. In the first place, the
nerves terminating in the skin of the whole body can be touched
through this medium by any terrene objects whatever, and moved by
these wholes, in one way by their hardness, in another by their
gravity, in a third by their heat, in a fourth by their humidity,
etc.--and in as many diverse modes as they are either moved or
hindered from their ordinary motion, to that extent are diverse
sensations excited in the mind, from which a corresponding number of
tactile qualities derive their appellations. Besides this, when
these nerves are moved a little more powerfully than usual, but not
nevertheless to the degree by which our body is in any way hurt,
there thus arises a sensation of titillation, which is naturally
agreeable to the mind, because it testifies to it of the powers of
the body with which it is joined, [in that the latter can suffer the
action causing this titillation, without being hurt]. But if this
action be strong enough to hurt our body in any way, this gives to
our mind the sensation of pain. And we thus see why corporeal
pleasure and pain, although sensations of quite an opposite
character, arise nevertheless from causes nearly alike.

 CXCII. Of taste.

In the second place, the other nerves scattered over the tongue and
the parts in its vicinity are diversely moved by the particles of
the same bodies, separated from each other and floating in the
saliva in the mouth, and thus cause sensations of diverse tastes
according to the diversity of figure in these particles. [Footnote:
In the French this section begins, "Taste, after touch the grossest
of the senses," etc.]

 CXCIII. Of smell.

Thirdly, two nerves also or appendages of the brain, for they do not
go beyond the limits of the skull, are moved by the particles of
terrestrial bodies, separated and flying in the air, not indeed by
all particles indifferently, but by those only that are sufficiently
subtle and penetrating to enter the pores of the bone we call the
spongy, when drawn into the nostrils, and thus to reach the nerves.
From the different motions of these particles arise the sensations
of the different smells.

 CXCIV. Of hearing.

Fourthly, there are two nerves within the ears, so attached to three
small bones that are mutually sustaining, and the first of which
rests on the small membrane that covers the cavity we call the
tympanum of the ear, that all the diverse vibrations which the
surrounding air communicates to this membrane are transmitted to the
mind by these nerves, and these vibrations give rise, according to
their diversity, to the sensations of the different sounds.

 CXCV. Of sight.

Finally, the extremities of the optic nerves, composing the coat in
the eyes called the retina, are not moved by the air nor by any
terrestrial object, but only by the globules of the second element,
whence we have the sense of light and colours: as I have already at
sufficient length explained in the Dioptrics and treatise of
Meteors. [Footnote: In the French this section begins, "Finally,
sight is the most subtle of all the senses," etc.]

 CXCVI. That the soul perceives only in so far as it is in the
brain.

It is clearly established, however, that the soul does not perceive
in so far as it is in each member of the body, but only in so far as
it is in the brain, where the nerves by their movements convey to it
the diverse actions of the external objects that touch the parts of
the body in which they are inserted. For, in the first place, there
are various maladies, which, though they affect the brain alone, yet
bring disorder upon, or deprive us altogether of the use of, our
senses, just as sleep, which affects the brain only, and yet takes
from us daily during a great part of our time the faculty of
perception, which afterwards in our waking state is restored to us.
The second proof is, that though there be no disease in the brain,
[or in the members in which the organs of the external senses are],
it is nevertheless sufficient to take away sensation from the part
of the body where the nerves terminate, if only the movement of one
of the nerves that extend from the brain to these members be
obstructed in any part of the distance that is between the two. And
the last proof is, that we sometimes feel pain as if in certain of
our members, the cause of which, however, is not in these members
where it is felt, but somewhere nearer the brain, through which the
nerves pass that give to the mind the sensation of it. I could
establish this fact by innumerable experiments; I will here,
however, merely refer to one of them. A girl suffering from a bad
ulcer in the hand, had her eyes bandaged whenever the surgeon came
to visit her, not being able to bear the sight of the dressing of
the sore; and, the gangrene having spread, after the expiry of a few
days the arm was amputated from the elbow [without the girl's
knowledge]; linen cloths tied one above the other were substituted
in place of the part amputated, so that she remained for some time
without knowing that the operation had been performed, and meanwhile
she complained of feeling various pains, sometimes in one finger of
the hand that was cut off, and sometimes in another. The only
explanation of this is, that the nerves which before stretched
downwards from the brain to the hand, and then terminated in the arm
close to the elbow, were there moved in the same way as they
required to be moved before in the hand for the purpose of
impressing on the mind residing in the brain the sensation of pain
in this or that finger. [And this clearly shows that the pain of the
hand is not felt by the mind in so far as it is in the hand, but in
so far as it is in the brain.]

 CXCVII. That the nature of the mind is such that from the motion
alone of body the various sensations can be excited in it.

In the next place, it can be proved that our mind is of such a
nature that the motions of the body alone are sufficient to excite
in it all sorts of thoughts, without it being necessary that these
should in any way resemble the motions which give rise to them, and
especially that these motions can excite in it those confused
thoughts called sensations (SENSUS, SENSATIONES). For we see that
words, whether uttered by the voice or merely written, excite in our
minds all kinds of thoughts and emotions. On the same paper, with
the same pen and ink, by merely moving the point of the pen over the
paper in a particular way, we can trace letters that will raise in
the minds of our readers the thoughts of combats, tempests, or the
furies, and the passions of indignation and sorrow; in place of
which, if the pen be moved in another way hardly different from the
former, this slight change will cause thoughts widely different from
the above, such as those of repose, peace, pleasantness, and the
quite opposite passions of love and joy. Some one will perhaps
object that writing and speech do not immediately excite in the mind
any passions, or imaginations of things different from the letters
and sounds, but afford simply the knowledge of these, on occasion of
which the mind, understanding the signification of the words,
afterwards excites in itself the imaginations and passions that
correspond to the words. But what will be said of the sensations of
pain and titillation? The motion merely of a sword cutting a part of
our skin causes pain, [but does not on that account make us aware of
the motion or figure of the sword]. And it is certain that this
sensation of pain is not less different from the motion that causes
it, or from that of the part of our body which the sword cuts, than
are the sensations we have of colour, sound, odour, or taste. On
this ground we may conclude that our mind is of such a nature that
the motions alone of certain bodies can also easily excite in it all
the other sensations, as the motion of a sword excites in it the
sensation of pain.

 CXCVIII. That by our senses we know nothing of external objects
beyond their figure [or situation], magnitude, and motion.

Besides, we observe no such difference between the nerves as to lead
us to judge that one set of them convey to the brain from the organs
of the external senses anything different from another, or that
anything at all reaches the brain besides the local motion of the
nerves themselves. And we see that local motion alone causes in us
not only the sensation of titillation and of pain, but also of light
and sounds. For if we receive a blow on the eye of sufficient force
to cause the vibration of the stroke to reach the retina, we see
numerous sparks of fire, which, nevertheless, are not out of our
eye; and when we stop our ear with our finger, we hear a humming
sound, the cause of which can only proceed from the agitation of the
air that is shut up within it. Finally, we frequently observe that
heat [hardness, weight], and the other sensible qualities, as far as
they are in objects, and also the forms of those bodies that are
purely material, as, for example, the forms of fire, are produced in
them by the motion of certain other bodies, and that these in their
turn likewise produce other motions in other bodies. And we can
easily conceive how the motion of one body may be caused by that of
another, and diversified by the size, figure, and situation of its
parts, but we are wholly unable to conceive how these same things
(viz., size, figure, and motion), can produce something else of a
nature entirely different from themselves, as, for example, those
substantial forms and real qualities which many philosophers suppose
to be in bodies; nor likewise can we conceive how these qualities or
forms possess force to cause motions in other bodies. But since we
know, from the nature of our soul, that the diverse motions of body
are sufficient to produce in it all the sensations which it has, and
since we learn from experience that several of its sensations are in
reality caused by such motions, while we do not discover that
anything besides these motions ever passes from the organs of the
external senses to the brain, we have reason to conclude that we in
no way likewise apprehend that in external objects, which we call
light, colour, smell, taste, sound, heat or cold, and the other
tactile qualities, or that which we call their substantial forms,
unless as the various dispositions of these objects which have the
power of moving our nerves in various ways. [Footnote: "the diverse
figures, situations, magnitudes, and motions of their parts."--
French.]

 CXCIX. That there is no phenomenon of nature whose explanation has
been omitted in this treatise.

And thus it may be gathered, from an enumeration that is easily
made, that there is no phenomenon of nature whose explanation has
been omitted in this treatise; for beyond what is perceived by the
senses, there is nothing that can be considered a phenomenon of
nature. But leaving out of account motion, magnitude, figure, [and
the situation of the parts of each body], which I have explained as
they exist in body, we perceive nothing out of us by our senses
except light, colours, smells, tastes, sounds, and the tactile
qualities; and these I have recently shown to be nothing more, at
least so far as they are known to us, than certain dispositions of
the objects, consisting in magnitude, figure, and motion.

 CC. That this treatise contains no principles which are not
universally received; and that this philosophy is not new, but of
all others the most ancient and common.

But I am desirous also that it should be observed that, though I
have here endeavoured to give an explanation of the whole nature of
material things, I have nevertheless made use of no principle which
was not received and approved by Aristotle, and by the other
philosophers of all ages; so that this philosophy, so far from being
new, is of all others the most ancient and common: for I have in
truth merely considered the figure, motion, and magnitude of bodies,
and examined what must follow from their mutual concourse on the
principles of mechanics, which are confirmed by certain and daily
experience. But no one ever doubted that bodies are moved, and that
they are of various sizes and figures, according to the diversity of
which their motions also vary, and that from mutual collision those
somewhat greater than others are divided into many smaller, and thus
change figure. We have experience of the truth of this, not merely
by a single sense, but by several, as touch, sight, and hearing: we
also distinctly imagine and understand it. This cannot be said of
any of the other things that fall under our senses, as colours,
sounds, and the like; for each of these affects but one of our
senses, and merely impresses upon our imagination a confused image
of itself, affording our understanding no distinct knowledge of what
it is.

 CCI. That sensible bodies are composed of insensible particles.

But I allow many particles in each body that are perceived by none
of our senses, and this will not perhaps be approved of by those who
take the senses for the measure of the knowable. [We greatly wrong
human reason, however, as appears to me, if we suppose that it does
not go beyond the eye-sight]; for no one can doubt that there are
bodies so small as not to be perceptible by any of our senses,
provided he only consider what is each moment added to those bodies
that are being increased little by little, and what is taken from
those that are diminished in the same way. A tree increases daily,
and it is impossible to conceive how it becomes greater than it was
before, unless we at the same time conceive that some body is added
to it. But who ever observed by the senses those small bodies that
are in one day added to a tree while growing? Among the philosophers
at least, those who hold that quantity is indefinitely divisible,
ought to admit that in the division the parts may become so small as
to be wholly imperceptible. And indeed it ought not to be a matter
of surprise, that we are unable to perceive very minute bodies; for
the nerves that must be moved by objects to cause perception are not
themselves very minute, but are like small cords, being composed of
a quantity of smaller fibres, and thus the most minute bodies are
not capable of moving them. Nor do I think that any one who makes
use of his reason will deny that we philosophize with much greater
truth when we judge of what takes place in those small bodies which
are imperceptible from their minuteness only, after the analogy of
what we see occurring in those we do perceive, [and in this way
explain all that is in nature, as I have essayed to do in this
treatise], than when we give an explanation of the same things by
inventing I know not what novelties, that have no relation to the
things we actually perceive, [as first matter, substantial forms,
and all that grand array of qualities which many are in the habit of
supposing, each of which is more difficult to comprehend than all
that is professed to be explained by means of them].

 CCII. That the philosophy of Democritus is not less different from
ours than from the common. [Footnote: "that of Aristotle or the
others."--French.]

But it may be said that Democritus also supposed certain corpuscles
that were of various figures, sizes, and motions, from the heaping
together and mutual concourse of which all sensible bodies arose;
and, nevertheless, his mode of philosophizing is commonly rejected
by all. To this I reply that the philosophy of Democritus was never
rejected by any one, because he allowed the existence of bodies
smaller than those we perceive, and attributed to them diverse
sizes, figures, and motions, for no one can doubt that there are in
reality such, as we have already shown; but it was rejected, in the
first place, because he supposed that these corpuscles were
indivisible, on which ground I also reject it; in the second place,
because he imagined there was a vacuum about them, which I show to
be impossible; thirdly, because he attributed gravity to these
bodies, of which I deny the existence in any body, in so far as a
body is considered by itself, because it is a quality that depends
on the relations of situation and motion which several bodies bear
to each other; and, finally, because he has not explained in
particular how all things arose from the concourse of corpuscles
alone, or, if he gave this explanation with regard to a few of them,
his whole reasoning was far from being coherent, [or such as would
warrant us in extending the same explanation to the whole of
nature]. This, at least, is the verdict we must give regarding his
philosophy, if we may judge of his opinions from what has been
handed down to us in writing. I leave it to others to determine
whether the philosophy I profess possesses a valid coherency, [and
whether on its principles we can make the requisite number of
deductions; and, inasmuch as the consideration of figure, magnitude,
and motion has been admitted by Aristotle and by all the others, as
well as by Democritus, and since I reject all that the latter has
supposed, with this single exception, while I reject generally all
that has been supposed by the others, it is plain that this mode of
philosophizing has no more affinity with that of Democritus than of
any other particular sect].

 CCIII. How we may arrive at the knowledge of the figures,
[magnitudes], and motions of the insensible particles of bodies.

But, since I assign determinate figures, magnitudes, and motions to
the insensible particles of bodies, as if I had seen them, whereas I
admit that they do not fall under the senses, some one will perhaps
demand how I have come by my knowledge of them. [To this I reply,
that I first considered in general all the clear and distinct
notions of material things that are to be found in our
understanding, and that, finding no others except those of figures,
magnitudes, and motions, and of the rules according to which these
three things can be diversified by each other, which rules are the
principles of geometry and mechanics, I judged that all the
knowledge man can have of nature must of necessity be drawn from
this source; because all the other notions we have of sensible
things, as confused and obscure, can be of no avail in affording us
the knowledge of anything out of ourselves, but must serve rather to
impede it]. Thereupon, taking as my ground of inference the simplest
and best known of the principles that have been implanted in our
minds by nature, I considered the chief differences that could
possibly subsist between the magnitudes, and figures, and situations
of bodies insensible on account of their smallness alone, and what
sensible effects could be produced by their various modes of coming
into contact; and afterwards, when I found like effects in the
bodies that we perceive by our senses, I judged that they could have
been thus produced, especially since no other mode of explaining
them could be devised. And in this matter the example of several
bodies made by art was of great service to me: for I recognize no
difference between these and natural bodies beyond this, that the
effects of machines depend for the most part on the agency of
certain instruments, which, as they must bear some proportion to the
hands of those who make them, are always so large that their figures
and motions can be seen; in place of which, the effects of natural
bodies almost always depend upon certain organs so minute as to
escape our senses. And it is certain that all the rules of mechanics
belong also to physics, of which it is a part or species, [so that
all that is artificial is withal natural]: for it is not less
natural for a clock, made of the requisite number of wheels, to mark
the hours, than for a tree, which has sprung from this or that seed,
to produce the fruit peculiar to it. Accordingly, just as those who
are familiar with automata, when they are informed of the use of a
machine, and see some of its parts, easily infer from these the way
in which the others, that are not seen by them, are made; so from
considering the sensible effects and parts of natural bodies, I have
essayed to determine the character of their causes and insensible
parts.

 CCIV. That, touching the things which our senses do not perceive,
it is sufficient to explain how they can be, [and that this is all
that Aristotle has essayed].

But here some one will perhaps reply, that although I have supposed
causes which could produce all natural objects, we ought not on this
account to conclude that they were produced by these causes; for,
just as the same artisan can make two clocks, which, though they
both equally well indicate the time, and are not different in
outward appearance, have nevertheless nothing resembling in the
composition of their wheels; so doubtless the Supreme Maker of
things has an infinity of diverse means at his disposal, by each of
which he could have made all the things of this world to appear as
we see them, without it being possible for the human mind to know
which of all these means he chose to employ. I most freely concede
this; and I believe that I have done all that was required, if the
causes I have assigned are such that their effects accurately
correspond to all the phenomena of nature, without determining
whether it is by these or by others that they are actually produced.
And it will be sufficient for the use of life to know the causes
thus imagined, for medicine, mechanics, and in general all the arts
to which the knowledge of physics is of service, have for their end
only those effects that are sensible, and that are accordingly to be
reckoned among the phenomena of nature. [Footnote: "have for their
end only to apply certain sensible bodies to each other in such a
way that, in the course of natural causes, certain sensible effects
may be produced; and we will be able to accomplish this quite as
well by considering the series of certain causes thus imagined,
although false, as if they were the true, since this series is
supposed similar as far as regards sensible effects."-French.]

And lest it should be supposed that Aristotle did, or professed to
do, anything more than this, it ought to be remembered that he
himself expressly says, at the commencement of the seventh chapter
of the first book of the Meteorologies, that, with regard to things
which are not manifest to the senses, he thinks to adduce sufficient
reasons and demonstrations of them, if he only shows that they may
be such as he explains them. [Footnote: words in Greek]

 CCV. That nevertheless there is a moral certainty that all the
things of this world are such as has been here shown they may be.

But nevertheless, that I may not wrong the truth by supposing it
less certain than it is, I will here distinguish two kinds of
certitude. The first is called moral, that is, a certainty
sufficient for the conduct of life, though, if we look to the
absolute power of God, what is morally certain may be false. [Thus,
those who never visited Rome do not doubt that it is a city of
Italy, though it might be that all from whom they got their
information were deceived]. Again, if any one, wishing to decipher a
letter written in Latin characters that are not placed in regular
order, bethinks himself of reading a B wherever an A is found, and a
C wherever there is a B, and thus of substituting in place of each
letter the one which follows it in the order of the alphabet, and if
by this means he finds that there are certain Latin words composed
of these, he will not doubt that the true meaning of the writing is
contained in these words, although he may discover this only by
conjecture, and although it is possible that the writer of it did
not arrange the letters on this principle of alphabetical order, but
on some other, and thus concealed another meaning in it: for this is
so improbable [especially when the cipher contains a number of
words] as to seem incredible. But they who observe how many things
regarding the magnet, fire, and the fabric of the whole world, are
here deduced from a very small number of principles, though they
deemed that I had taken them up at random and without grounds, will
yet perhaps acknowledge that it could hardly happen that so many
things should cohere if these principles were false.

 CCVI. That we possess even more than a moral certainty of it.

Besides, there are some, even among natural, things which we judge
to be absolutely certain. [Absolute certainty arises when we judge
that it is impossible a thing can be otherwise than as we think it].
This certainty is founded on the metaphysical ground, that, as God
is supremely good and the source of all truth, the faculty of
distinguishing truth from error which he gave us, cannot be
fallacious so long as we use it aright, and distinctly perceive
anything by it. Of this character are the demonstrations of
mathematics, the knowledge that material things exist, and the clear
reasonings that are formed regarding them. The results I have given
in this treatise will perhaps be admitted to a place in the class of
truths that are absolutely certain, if it be considered that they
are deduced in a continuous series from the first and most
elementary principles of human knowledge; especially if it be
sufficiently understood that we can perceive no external objects
unless some local motion be caused by them in our nerves, and that
such motion cannot be caused by the fixed stars, owing to their
great distance from us, unless a motion be also produced in them and
in the whole heavens lying between them and us: for these points
being admitted, all the others, at least the more general doctrines
which I have advanced regarding the world or earth [e. g., the
fluidity of the heavens, Part III., Section XLVI.], will appear to
be almost the only possible explanations of the phenomena they
present.

 CCVII. That, however, I submit all my opinions to the authority of
the church.

Nevertheless, lest I should presume too far, I affirm nothing, but
submit all these my opinions to the authority of the church and the
judgment of the more sage; and I desire no one to believe anything I
may have said, unless he is constrained to admit it by the force and
evidence of reason.





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