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Title: Discourse on the Method of Rightly Conducting One's Reason and of Seeking Truth in the Sciences
Author: Descartes, René, 1596-1650
Language: English
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                           by Rene Descartes


If this Discourse appear too long to be read at once, it may be divided
into six Parts:  and, in the first, will be found various
considerations touching the Sciences; in the second, the principal
rules of the Method which the Author has discovered, in the third,
certain of the rules of Morals which he has deduced from this Method;
in the fourth, the reasonings by which he establishes the existence of
God and of the Human Soul, which are the foundations of his Metaphysic;
in the fifth, the order of the Physical questions which he has
investigated, and, in particular, the explication of the motion of the
heart and of some other difficulties pertaining to Medicine, as also
the difference between the soul of man and that of the brutes; and, in
the last, what the Author believes to be required in order to greater
advancement in the investigation of Nature than has yet been made, with
the reasons that have induced him to write.


Good sense is, of all things among men, the most equally distributed;
for every one thinks himself so abundantly provided with it, that those
even who are the most difficult to satisfy in everything else, do not
usually desire a larger measure of this quality than they already
possess.  And in this it is not likely that all are mistaken the
conviction is rather to be held as testifying that the power of judging
aright and of distinguishing truth from error, which is properly what
is called  good sense or reason, is by nature equal in all men; and
that the diversity of our opinions, consequently, does not arise from
some being endowed with a larger share of reason than others, but
solely from this, that we conduct our thoughts along different ways,
and do not fix our attention on the same objects.  For to be possessed
of a vigorous mind is not enough; the prime requisite is rightly to
apply it.  The greatest minds, as they are capable of the highest
excellences, are open likewise to the greatest aberrations; and those
who travel very slowly may yet make far greater progress, provided they
keep always to the straight road, than those who, while they run,
forsake it.

For myself, I have never fancied my mind to be in any respect more
perfect than those of the generality; on the contrary, I have often
wished that I were equal to some others in promptitude of thought, or
in clearness and distinctness of imagination, or in fullness and
readiness of memory.  And besides these, I know of no other qualities
that contribute to the perfection of the mind; for as to the reason or
sense, inasmuch as it is that alone which constitutes us men, and
distinguishes us from the brutes, I am disposed to believe that it is
to be found complete in each individual; and on this point to adopt the
common opinion of philosophers, who say that the difference of greater
and less holds only among the accidents, and not among the forms or
natures of individuals of the same species.

I will not hesitate, however, to avow my belief that it has been my
singular good  fortune to have very early in life fallen in with
certain tracks which have conducted me to considerations and maxims, of
which I have formed a method that gives me the means, as I think, of
gradually augmenting my knowledge, and of raising it by little and
little to the highest point which the mediocrity of my talents and the
brief duration of my life will permit me to reach.  For I have already
reaped from it such fruits that, although I have been accustomed to
think lowly enough of myself, and although when I look with the eye of
a philosopher at the varied courses and pursuits of mankind at large, I
find scarcely one which does not appear in vain and useless, I
nevertheless derive the highest satisfaction from the progress I
conceive myself to have already made in the search after truth, and
cannot help entertaining such expectations of the future as to believe
that if, among the occupations of men as men, there is any one really
excellent and important, it is that which I have chosen.

After all, it is possible I may be mistaken; and it is but a little
copper and glass, perhaps, that I take for gold and diamonds.  I know
how very liable we are to delusion in what relates to ourselves, and
also how much the judgments of our friends are to be suspected when
given in our favor.  But I shall endeavor in this discourse to describe
the paths I have followed, and to delineate my life as in a picture, in
order that each one may also be able to judge of them for himself, and
that in the general opinion entertained of them, as gathered from
current report, I myself may have a new help towards instruction to be
added to those I have been in the habit of employing.

My present design, then, is not to teach the method which each ought to
follow for the right conduct of his reason, but solely to describe the
way in which I have endeavored to conduct my own.  They who set
themselves to give precepts must of course regard themselves as
possessed of greater skill than those to whom they prescribe; and if
they err in the slightest particular, they subject themselves to
censure.  But as this tract is put forth merely as a history, or, if
you will, as a tale, in which, amid some examples worthy of imitation,
there will be found, perhaps, as many more which it were advisable not
to follow, I hope it will prove useful to some without being hurtful to
any, and that my openness will find some favor with all.

From my childhood, I have been familiar with letters; and as I was
given to believe that by their help a clear and certain knowledge of
all that is useful in life might be acquired, I was ardently desirous
of instruction.  But as soon as I had finished the entire course of
study, at the close of which it is customary to be admitted into the
order of the learned, I completely changed my opinion.  For I found
myself involved in so many doubts and errors, that I was convinced I
had advanced no farther in all my attempts at learning, than the
discovery at every turn of my own ignorance.  And yet I was studying in
one of the most celebrated schools in Europe, in which I thought there
must be learned men,  if such were anywhere to be found.  I had been
taught all that others learned there; and not contented with the
sciences actually taught us, I had, in addition, read all the books
that had fallen into my hands, treating of such branches as are
esteemed the most curious and rare.  I knew the judgment which others
had formed of me; and I did not find that I was considered inferior to
my fellows, although there were among them some who were already marked
out to fill the places of our instructors.  And, in fine, our age
appeared to me as flourishing, and as fertile in powerful minds as any
preceding one.  I was thus led to take the liberty of judging of all
other men by myself, and of concluding that there was no science in
existence that was of such a nature as I had previously been given to

I still continued, however, to hold in esteem the studies of the
schools.  I was aware that the languages taught in them are necessary
to the understanding of the writings of the ancients; that the grace of
fable stirs the mind; that the memorable deeds of history elevate it;
and, if read with discretion, aid in forming the judgment; that the
perusal of all excellent books is,  as it were, to interview with the
noblest men of past ages, who have written them, and even a studied
interview, in which are discovered to us only their choicest thoughts;
that eloquence has incomparable force and beauty; that poesy has its
ravishing graces and delights; that in the mathematics there are many
refined discoveries eminently suited to gratify the inquisitive, as
well as further all the arts an lessen the labour of man; that numerous
highly useful precepts and exhortations to virtue are contained in
treatises on morals; that theology points out the path to heaven; that
philosophy affords the means of discoursing with an appearance of truth
on all matters, and commands the admiration of the more simple; that
jurisprudence, medicine, and the other sciences, secure for their
cultivators honors and riches; and, in fine, that it is useful to
bestow some attention upon all, even upon those abounding the most in
superstition and error, that we may be in a position to determine their
real value, and guard against being deceived.

But I believed that I had already given sufficient time to languages,
and likewise to the reading of the writings of the ancients, to their
histories and fables.   For to hold converse with those of other ages
and to travel, are almost the same thing.  It is useful to know
something of the manners of different nations, that we may be enabled
to form a more correct judgment regarding our own, and be prevented
from thinking that everything contrary to our customs is ridiculous and
irrational, a conclusion usually come to by those whose experience has
been limited to their own country.  On the other hand, when too much
time is occupied in traveling, we become strangers to our native
country; and the over curious in the customs of the past are generally
ignorant of those of the present.  Besides, fictitious narratives lead
us to imagine the possibility of many events that are impossible; and
even the most faithful histories, if they do not wholly misrepresent
matters, or exaggerate their importance to render the account of them
more worthy of perusal, omit, at least, almost always the meanest and
least striking of the attendant circumstances; hence it happens that
the remainder does not represent the truth, and that such as regulate
their conduct by examples drawn from this source, are apt to fall into
the extravagances of the knight-errants of romance, and to entertain
projects that exceed their powers.

I esteemed eloquence highly, and was in raptures with poesy; but I
thought that both were gifts of nature rather than fruits of study.
Those in whom the faculty of reason is predominant, and who most
skillfully dispose their thoughts with a view to render them clear and
intelligible, are always the best able to persuade others of the truth
of what they lay down, though they should speak only in the language of
Lower Brittany, and be wholly ignorant of the rules of rhetoric; and
those whose minds are stored with the most agreeable fancies, and who
can give expression to them with the greatest embellishment and
harmony, are still the best poets, though unacquainted with the art of

I was especially delighted with the mathematics, on account of the
certitude and evidence of their reasonings;  but I had not as yet a
precise knowledge of their true use; and thinking that they but
contributed to the advancement of the mechanical arts, I was astonished
that foundations, so strong and solid, should have had no loftier
superstructure reared on them.  On the other hand, I compared the
disquisitions of the ancient moralists to very towering and magnificent
palaces with no better foundation than sand and mud:  they laud the
virtues very highly, and exhibit them as estimable far above anything
on earth; but they give us no adequate criterion of virtue, and
frequently that which they designate with so fine a name is but apathy,
or pride, or despair, or parricide.

I revered our theology, and aspired as much as any one to reach heaven:
but being given assuredly to understand that the way is not less open
to the most ignorant than to the most learned, and that the revealed
truths which lead to heaven are above our comprehension, I did not
presume to subject them to the impotency of my reason; and I thought
that in order competently to undertake their examination, there was
need of some special help from heaven, and of being more than man.

Of philosophy I will say nothing, except that when I saw that it had
been cultivated for many ages by the most distinguished men, and that
yet there is not a single matter within its sphere which is not still
in dispute, and nothing, therefore, which is above doubt, I did not
presume to anticipate that my success would be greater in it than that
of others; and further, when I considered the number of conflicting
opinions touching a single matter that may be upheld by learned men,
while there can be but one true, I reckoned as well-nigh false all that
was only probable.

As to the other sciences, inasmuch as these borrow their principles
from philosophy, I judged that no solid superstructures could be reared
on foundations so infirm; and neither the honor nor the gain held out
by them was sufficient to determine me to their cultivation:  for I was
not, thank Heaven, in a condition which compelled me to make
merchandise of science for the bettering of my fortune; and though I
might not profess to scorn glory as a cynic, I yet made very slight
account of that honor which I hoped to acquire only through fictitious
titles.  And, in fine, of false sciences I thought I knew the worth
sufficiently to escape being deceived by the professions of an
alchemist, the predictions of an astrologer, the impostures of a
magician, or by the artifices and boasting of any of those who profess
to know things of which they are ignorant.

For these reasons, as soon as my age permitted me to pass from under
the control of my instructors, I entirely abandoned the study of
letters, and resolved no longer to seek any other science than the
knowledge of myself, or of the great book of the world.  I spent the
remainder of my youth in traveling, in visiting courts and armies, in
holding intercourse with men of different dispositions and ranks, in
collecting varied experience, in proving myself in the different
situations into which fortune threw me, and, above all, in making such
reflection on the matter of my experience as to secure my improvement.
For it occurred to me that I should find much more truth in the
reasonings of each individual with reference to the affairs in which he
is personally interested, and the issue of which must presently punish
him if he has judged amiss, than in those conducted by a man of letters
in his study, regarding speculative matters that are of no practical
moment, and followed by no consequences to himself, farther, perhaps,
than that they foster his vanity the better the more remote they are
from common sense; requiring, as they must in this case, the exercise
of greater ingenuity and art to render them probable.  In addition, I
had always a most earnest desire to know how to distinguish the true
from the false, in order that I might be able clearly to discriminate
the right path in life, and proceed in it with confidence.

It is true that, while busied only in considering the manners of other
men, I found here, too, scarce any ground for settled conviction, and
remarked hardly less contradiction among them than in the opinions of
the philosophers.  So that the greatest advantage I derived from the
study consisted in this, that, observing many things which, however
extravagant and ridiculous to our apprehension, are yet by common
consent received and approved by other great nations, I learned to
entertain too decided a belief in regard to nothing of the truth of
which I had been persuaded merely by example and custom; and thus I
gradually extricated myself from many errors powerful enough to darken
our natural intelligence, and incapacitate us in great measure from
listening to reason.  But after I had been occupied several years in
thus studying the book of the world, and in essaying to gather some
experience, I at length resolved to make myself an object of study, and
to employ all the powers of my mind in choosing the paths I ought to
follow, an undertaking which was accompanied with greater success than
it would have been had I never quitted my country or my books.


I was then in Germany, attracted thither by the wars in that country,
which have not yet been brought to a termination; and as I was
returning to the army from the coronation of the emperor, the setting
in of winter arrested me in a locality where, as I found no society to
interest me, and was besides fortunately undisturbed by any cares or
passions, I remained the whole day in seclusion, with full opportunity
to occupy my attention with my own thoughts.  Of these one of the very
first that occurred to me was, that there is seldom so much perfection
in works composed of many separate parts, upon which different hands
had been employed, as in those completed by a single master.   Thus it
is observable that the buildings which a single architect has planned
and executed, are generally more elegant and commodious than those
which several have attempted to improve, by making old walls serve for
purposes for which they were not originally built.  Thus also, those
ancient cities which, from being at first only villages, have become,
in course of time, large towns, are usually but ill laid out compared
with the regularity constructed towns which a professional architect
has freely planned on an open plain; so that although the several
buildings of the former may often equal or surpass in beauty those of
the latter, yet when one observes their indiscriminate juxtaposition,
there a large one and here a small, and the consequent crookedness and
irregularity of the streets, one is disposed to allege that chance
rather than any human will guided by reason must have led to such an
arrangement.  And if we consider that nevertheless there have been at
all times certain officers whose duty it was to see that private
buildings contributed to public ornament, the difficulty of reaching
high perfection with but the materials of others to operate on, will be
readily acknowledged.  In the same way I fancied that those nations
which, starting from a semi-barbarous state and advancing to
civilization by slow degrees, have had their laws successively
determined, and, as it were, forced upon them simply by experience of
the hurtfulness of particular crimes and disputes, would by this
process come to be possessed of less perfect institutions than those
which, from the commencement of their association as communities, have
followed the appointments of some wise legislator.  It is thus quite
certain that the constitution of the true religion, the ordinances of
which are derived from God, must be incomparably superior to that of
every other.  And, to speak of human affairs, I believe that the
pre-eminence of Sparta was due not to the goodness of each of its laws
in particular, for many of these were very strange, and even opposed to
good morals, but to the circumstance that, originated by a single
individual, they all tended to a single end.  In the same way I thought
that the sciences contained in books (such of them at least as are made
up of probable reasonings, without demonstrations), composed as they
are of the opinions of many different individuals massed together, are
farther removed from truth than the simple inferences which a man of
good sense using his natural and unprejudiced judgment draws respecting
the matters of his experience.  And because we have all to pass through
a state of infancy to manhood, and have been of necessity, for a length
of time, governed by our desires and preceptors (whose dictates were
frequently conflicting, while neither perhaps always counseled us for
the best), I farther concluded that it is almost impossible that our
judgments can be so correct or solid as they would have been, had our
reason been mature from the moment of our birth, and had we always been
guided by it alone.

It is true, however, that it is not customary to pull down all the
houses of a town with the single design of rebuilding them differently,
and thereby rendering the streets more handsome; but it often happens
that a private individual takes down his own with the view of erecting
it anew, and that people are even sometimes constrained to this when
their houses are in danger of falling from age, or when the foundations
are insecure.  With this before me by way of example, I was persuaded
that it would indeed be preposterous for a private individual to think
of reforming a state by fundamentally changing it throughout, and
overturning it in order to set it up amended; and the same I thought
was true of any similar project for reforming the body of the sciences,
or the order of teaching them established in the schools:  but as for
the opinions which up to that time I had embraced, I thought that I
could not do better than resolve at once to sweep them wholly away,
that I might afterwards be in a position to admit either others more
correct, or even perhaps the same when they had undergone the scrutiny
of reason.  I firmly believed that in this way I should much better
succeed in the conduct of my life, than if I built only upon old
foundations, and leaned upon principles which, in my youth, I had taken
upon trust.  For although I recognized various difficulties in this
undertaking, these were not, however, without remedy, nor once to be
compared with such as attend the slightest reformation in public
affairs.  Large bodies, if once overthrown, are with great difficulty
set up again, or even kept erect when once seriously shaken, and the
fall of such is always disastrous.  Then if there are any imperfections
in the constitutions of states (and that many such exist the diversity
of constitutions is alone sufficient to assure us), custom has without
doubt materially smoothed their inconveniences, and has even managed to
steer altogether clear of, or insensibly corrected a number which
sagacity could not have provided against with equal effect; and, in
fine, the defects are almost always more tolerable than the change
necessary for their removal; in the same manner that highways which
wind among mountains, by being much frequented, become gradually so
smooth and commodious, that it is much better to follow them than to
seek a straighter path by climbing over the tops of rocks and
descending to the bottoms of precipices.

Hence it is that I cannot in any degree approve of those restless and
busy meddlers who, called neither by birth nor fortune to take part in
the management of public affairs, are yet always projecting reforms;
and if I thought that this tract contained aught which might justify
the suspicion that I was a victim of such folly, I would by no means
permit its publication.  I have never contemplated anything higher than
the reformation of my own opinions, and basing them on a foundation
wholly my own.  And although my own satisfaction with my work has led
me to present here a draft of it, I do not by any means therefore
recommend to every one else to make a similar attempt.  Those whom God
has endowed with a larger measure of genius will entertain, perhaps,
designs still more exalted; but for the many I am much afraid lest even
the present undertaking be more than they can safely venture to
imitate.  The single design to strip one's self of all past beliefs is
one that ought not to be taken by every one.  The majority of men is
composed of two classes, for neither of which would this be at all a
befitting resolution:  in the first place, of those who with more than
a due confidence in their own powers, are precipitate in their
judgments and want the patience requisite for orderly and circumspect
thinking; whence it happens, that if men of this class once take the
liberty to doubt of their accustomed opinions, and quit the beaten
highway, they will never be able to thread the byway that would lead
them by a shorter course, and will lose themselves and continue to
wander for life; in the second place, of those who, possessed of
sufficient sense or modesty to determine that there are others who
excel them in the power of discriminating between truth and error, and
by whom they may be instructed, ought rather to content themselves with
the opinions of such than trust for more correct to their own reason.

For my own part, I should doubtless have belonged to the latter class,
had I received instruction from but one master, or had I never known
the diversities of opinion that from time immemorial have prevailed
among men of the greatest learning.  But I had become aware, even so
early as during my college life, that no opinion, however absurd and
incredible, can be imagined, which has not been maintained by some on
of the philosophers; and afterwards in the course of my travels I
remarked that all those whose opinions are decidedly repugnant to ours
are not in that account barbarians and savages, but on the contrary
that many of these nations make an equally good, if not better, use of
their reason than we do.  I took into account also the very different
character which a person brought up from infancy in France or Germany
exhibits, from that which, with the same mind originally, this
individual would have possessed had he lived always among the Chinese
or with savages, and the circumstance that in dress itself the fashion
which pleased us ten years ago, and which may again, perhaps, be
received into favor before ten years have gone, appears to us at this
moment extravagant and ridiculous.  I was thus led to infer that the
ground of our opinions is far more custom and example than any certain
knowledge.  And, finally, although such be the ground of our opinions,
I remarked that a plurality of suffrages is no guarantee of truth where
it is at all of difficult discovery, as in such cases it is much more
likely that it will be found by one than by many.  I could, however,
select from the crowd no one whose opinions seemed worthy of
preference, and thus I found myself constrained, as it were, to use my
own reason in the conduct of my life.

But like one walking alone and in the dark, I resolved to proceed so
slowly and with such circumspection, that if I did not advance far, I
would at least guard against falling.  I did not even choose to dismiss
summarily any of the opinions that had crept into my belief without
having been introduced by reason, but first of all took sufficient time
carefully to satisfy myself of the general nature of the task I was
setting myself, and ascertain the true method by which to arrive at the
knowledge of whatever lay within the compass of my powers.

Among the branches of philosophy, I had, at an earlier period, given
some attention to logic, and among those of the mathematics to
geometrical analysis and algebra,--three arts or sciences which ought,
as I conceived, to contribute something to my design.  But, on
examination, I found that, as for logic, its syllogisms and the
majority of its other precepts are of avail--rather in the
communication of what we already know, or even as the art of Lully, in
speaking without judgment of things of which we are ignorant, than in
the investigation of the unknown; and although this science contains
indeed a number of correct and very excellent precepts, there are,
nevertheless, so many others, and these either injurious or
superfluous, mingled with the former, that it is almost quite as
difficult to effect a severance of the true from the false as it is to
extract a Diana or a Minerva from a rough block of marble.  Then as to
the analysis of the ancients and the algebra of the moderns, besides
that they embrace only matters highly abstract, and, to appearance, of
no use, the former is so exclusively restricted to the consideration of
figures, that it can exercise the understanding only on condition of
greatly fatiguing the imagination; and, in the latter, there is so
complete a subjection to certain rules and formulas, that there results
an art full of confusion and obscurity calculated to embarrass, instead
of a science fitted to cultivate the mind.  By these considerations I
was induced to seek some other method which would comprise the
advantages of the three and be exempt from their defects.  And as a
multitude of laws often only hampers justice, so that a state is best
governed when, with few laws, these are rigidly administered; in like
manner, instead of the great number of precepts of which logic is
composed, I believed that the four following would prove perfectly
sufficient for me, provided I took the firm and unwavering resolution
never in a single instance to fail in observing them.

The first was never to accept anything for true which I did not clearly
know to be such; that is to say, carefully to avoid precipitancy and
prejudice, and to comprise nothing more in my judgement than what was
presented to my mind so clearly and distinctly as to exclude all ground
of doubt.

The second, to divide each of the difficulties under examination into
as many parts as possible, and as might be necessary for its adequate

The third, to conduct my thoughts in such order that, by commencing
with objects the simplest and easiest to know, I might ascend by little
and little, and, as it were, step by step, to the knowledge of the more
complex; assigning in thought a certain order even to those objects
which in their own nature do not stand in a relation of antecedence and

And the last, in every case to make enumerations so complete, and
reviews so general, that I might be assured that nothing was omitted.

The long chains of simple and easy reasonings by means of which
geometers are accustomed to reach the conclusions of their most
difficult demonstrations, had led me to imagine that all things, to the
knowledge of which man is competent, are mutually connected in the same
way, and that there is nothing so far removed from us as to be beyond
our reach, or so hidden that we cannot discover it, provided only we
abstain from accepting the false for the true, and always preserve in
our thoughts the order necessary for the deduction of one truth from
another.  And I had little difficulty in determining the objects with
which it was necessary to commence, for I was already persuaded that it
must be with the simplest and easiest to know, and, considering that of
all those who have hitherto sought truth in the sciences, the
mathematicians alone have been able to find any demonstrations, that
is, any certain and evident reasons, I did not doubt but that such must
have been the rule of their investigations.  I resolved to commence,
therefore, with the examination of the simplest objects, not
anticipating, however, from this any other advantage than that to be
found in accustoming my mind to the love and nourishment of truth, and
to a distaste for all such reasonings as were unsound.  But I had no
intention on that account of attempting to master all the particular
sciences commonly denominated mathematics:  but observing that, however
different their objects, they all agree in considering only the various
relations or proportions subsisting among those objects, I thought it
best for my purpose to consider these proportions in the most general
form possible, without referring them to any objects in particular,
except such as would most facilitate the knowledge of them, and without
by any means restricting them to these, that afterwards I might thus be
the better able to apply them to every other class of objects to which
they are legitimately applicable.  Perceiving further, that in order to
understand these relations I should sometimes have to consider them one
by one and sometimes only to bear them in mind, or embrace them in the
aggregate, I thought that, in order the better to consider them
individually, I should view them as subsisting between straight lines,
than which I could find no objects more simple, or capable of being
more distinctly represented to my imagination and senses; and on the
other hand, that in order to retain them in the memory or embrace an
aggregate of many, I should express them by certain characters the
briefest possible.  In this way I believed that I could borrow all that
was best both in geometrical analysis and in algebra, and correct all
the defects of the one by help of the other.

And, in point of fact, the accurate observance of these few precepts
gave me, I take the liberty of saying, such ease in unraveling all the
questions embraced in these two sciences, that in the two or three
months I devoted to their examination, not only did I reach solutions
of questions I had formerly deemed exceedingly difficult but even as
regards questions of the solution of which I continued ignorant, I was
enabled, as it appeared to me, to determine the means whereby, and the
extent to which a solution was possible; results attributable to the
circumstance that I commenced with the simplest and most general
truths, and that thus each truth discovered was a rule available in the
discovery of subsequent ones Nor in this perhaps shall I appear too
vain, if it be considered that, as the truth on any particular point is
one whoever apprehends the truth, knows all that on that  point can be
known.  The child, for example, who has been instructed in the elements
of arithmetic, and has made a particular addition, according to rule,
may be assured that he has found, with respect to the sum of the
numbers before him, and that in this instance is within the reach of
human genius.  Now, in conclusion, the method which teaches adherence
to the true order, and an exact enumeration of all the conditions of
the thing sought includes all that gives certitude to the rules of

But the chief ground of my satisfaction with thus method, was the
assurance I had of thereby exercising my reason in all matters, if not
with absolute perfection, at least with the greatest attainable by me:
besides, I was conscious that by its use my mind was becoming gradually
habituated to clearer and more distinct conceptions of its objects; and
I hoped also, from not having restricted this method to any particular
matter, to apply it to the difficulties of the other sciences, with not
less success than to those of algebra.  I should not, however, on this
account have ventured at once on the examination of all the
difficulties of the sciences which presented themselves to me, for this
would have been contrary to the order prescribed in the method, but
observing that the knowledge of such is dependent on principles
borrowed from philosophy, in which I found nothing certain, I thought
it necessary first of all to endeavor to establish its principles.  And
because I observed, besides, that an inquiry of this kind was of all
others of the greatest moment, and one in which precipitancy and
anticipation in judgment were most to be dreaded, I thought that I
ought not to approach it till I had reached a more mature age (being at
that time but twenty-three), and had first of all employed much of my
time in preparation for the work, as well by eradicating from my mind
all the erroneous opinions I had up to that moment accepted, as by
amassing variety of experience to afford materials for my reasonings,
and by continually exercising myself in my chosen method with a view to
increased skill in its application.


And finally, as it is not enough, before commencing to rebuild the
house in which we live, that it be pulled down, and materials and
builders provided, or that we engage in the work ourselves, according
to a plan which we have beforehand carefully drawn out, but as it is
likewise necessary that we be furnished with some other house in which
we may live commodiously during the operations, so that I might not
remain irresolute in my actions, while my reason compelled me to
suspend my judgement, and that I might not be prevented from living
thenceforward in the greatest possible felicity, I formed a provisory
code of morals, composed of three or four maxims, with which I am
desirous to make you acquainted.

The first was to obey the laws and customs of my country, adhering
firmly to the faith in which, by the grace of God, I had been educated
from my childhood and regulating my conduct in every other matter
according to the most moderate opinions, and the farthest removed from
extremes, which should happen to be adopted in practice with general
consent of the most judicious of those among whom I might be living.
For as I had from that time begun to hold my own opinions for nought
because I wished to subject them all to examination, I was convinced
that I could not do better than follow in the meantime the opinions of
the most judicious; and although there are some perhaps among the
Persians and Chinese as judicious as among ourselves, expediency seemed
to dictate that I should regulate my practice conformably to the
opinions of those with whom I should have to live; and it appeared to
me that, in order to ascertain the real opinions of such, I ought
rather to take cognizance of what they practised than of what they
said, not only because, in the corruption of our manners, there are few
disposed to speak exactly as they believe, but also because very many
are not aware of what it is that they really believe; for, as the act
of mind by which a thing is believed is different from that by which we
know that we believe it, the one act is often found without the other.
Also, amid many opinions held in equal repute, I chose always the most
moderate, as much for the reason that these are always the most
convenient for practice, and probably the best (for all excess is
generally vicious), as that, in the event of my falling into error, I
might be at less distance from the truth than if, having chosen one of
the extremes, it should turn out to be the other which I ought to have
adopted.  And I placed in the class of extremes especially all promises
by which somewhat of our freedom is abridged; not that I disapproved of
the laws which, to provide against the instability of men of feeble
resolution, when what is sought to be accomplished is some good, permit
engagements by vows and contracts binding the parties to persevere in
it, or even, for the security of commerce, sanction similar engagements
where the purpose sought to be realized is indifferent:  but because I
did not find anything on earth which was wholly superior to change, and
because, for myself in particular, I hoped gradually to perfect my
judgments, and not to suffer them to deteriorate, I would have deemed
it a grave sin against good sense, if, for the reason that I approved
of something at a particular time, I therefore bound myself to hold it
for good at a subsequent time, when perhaps it had ceased to be so, or
I had ceased to esteem it such.

My second maxim was to be as firm and resolute in my actions as I was
able, and not to adhere less steadfastly to the most doubtful opinions,
when once adopted, than if they had been highly certain; imitating in
this the example of travelers who, when they have lost their way in a
forest, ought not to wander from side to side, far less remain in one
place, but proceed constantly towards the same side in as straight a
line as possible, without changing their direction for slight reasons,
although perhaps it might be chance alone which at first determined the
selection; for in this way, if they do not exactly reach the point they
desire, they will come at least in the end to some place that will
probably be preferable to the middle of a forest.  In the same way,
since in action it frequently happens that no delay is permissible, it
is very certain that, when it is not in our power to determine what is
true, we ought to act according to what is most probable; and even
although we should not remark a greater probability in one opinion than
in another, we ought notwithstanding to choose one or the other, and
afterwards consider it, in so far as it relates to practice, as no
longer dubious, but manifestly true and certain,  since the reason by
which our choice has been determined  is itself possessed of these
qualities.  This principle was sufficient thenceforward to rid me of
all those repentings and pangs of remorse that usually disturb the
consciences of such feeble and uncertain minds as, destitute of any
clear and determinate principle of choice, allow themselves one day to
adopt a course of action as the best, which they abandon the next, as
the opposite.

My third maxim was to endeavor always to conquer myself rather than
fortune, and change my desires rather than the order of the world, and
in general, accustom  myself to the persuasion that, except our own
thoughts, there is nothing absolutely in our power; so that when we
have done our best in things external to us, all wherein we fail of
success is to be held, as regards us, absolutely impossible:  and this
single principle seemed to me sufficient to prevent me from desiring
for the future anything which I could not obtain, and thus render me
contented; for since our will naturally seeks those objects alone which
the understanding represents as in some way possible of attainment, it
is plain, that if we consider all external goods as equally beyond our
power, we shall no more regret the absence of such goods as seem due to
our birth, when deprived of them without any fault of ours,  than our
not possessing the kingdoms of China or Mexico, and thus making, so to
speak, a virtue of necessity, we shall no more desire health in
disease, or freedom in imprisonment, than we now do bodies
incorruptible as diamonds, or the wings of birds to fly with.  But I
confess there is need of prolonged discipline and frequently repeated
meditation to accustom the mind to view all objects in this light; and
I believe that in this chiefly consisted the secret of the power of
such philosophers as in former times were enabled to rise superior to
the influence of fortune, and, amid suffering and poverty, enjoy a
happiness which their gods might have envied.  For, occupied
incessantly with the consideration of the limits prescribed to their
power by nature, they became so entirely convinced that nothing was at
their disposal except their own thoughts, that this conviction was of
itself sufficient to prevent their entertaining any desire of other
objects; and over their thoughts they acquired a sway so absolute, that
they had some ground on this account for esteeming themselves more rich
and more powerful, more free and more happy, than other men who,
whatever be the favors heaped on them by nature and fortune, if
destitute of this philosophy, can never command the realization of all
their desires.

In fine, to conclude this code of morals, I thought of reviewing the
different occupations of men in this life, with the view of making
choice of the best.  And, without wishing to offer any remarks on the
employments of others, I may state that it was my conviction that I
could not do better than continue in that in which I was engaged, viz.,
in devoting my whole life to the culture of my reason, and in making
the greatest progress I was able in the knowledge of truth, on the
principles of the method which I had prescribed to myself.  This
method, from the time I had begun to apply it, had been to me the
source of satisfaction so intense as to lead me to, believe that more
perfect or more innocent could not be enjoyed in this life; and as by
its means I daily discovered truths that appeared to me of some
importance, and of which other men were generally ignorant, the
gratification thence arising so occupied my mind that I was wholly
indifferent to every other object.  Besides, the three preceding maxims
were founded singly on the design of continuing the work of
self-instruction.  For since God has endowed each of us with some light
of reason by which to distinguish truth from error, I could not have
believed that I ought for a single moment to rest satisfied with the
opinions of another, unless I had resolved to exercise my own judgment
in examining these whenever I should be duly qualified for the task.
Nor could I have proceeded on such opinions without scruple, had I
supposed that I should thereby forfeit any advantage for attaining
still more accurate, should such exist.  And, in fine, I could not have
restrained my desires, nor remained satisfied had I not followed a path
in which I thought myself certain of attaining all the knowledge to the
acquisition of which I was competent, as well as the largest amount of
what is truly good which I could ever hope to secure Inasmuch as we
neither seek nor shun any object except in so far as our understanding
represents it as good or bad, all that is necessary to right action is
right judgment, and to the best action the most correct judgment, that
is, to the acquisition of all the virtues with all else that is truly
valuable and within our reach; and the assurance of such an acquisition
cannot fail to render us contented.

Having thus provided myself with these maxims, and having placed them
in reserve along with the truths of  faith, which have ever occupied
the first place in my  belief, I came to the conclusion that I might
with freedom set about ridding myself of what remained of my opinions.
And, inasmuch as I hoped to be better able successfully to accomplish
this work by holding intercourse with mankind, than by remaining longer
shut up in the retirement where these thoughts had occurred to me, I
betook me again to traveling before the winter was well ended.  And,
during the nine subsequent years, I did nothing but roam from one place
to another, desirous of being a  spectator rather than an actor in the
plays exhibited on the theater of the world; and, as I made it my
business in each matter to reflect particularly upon what might fairly
be doubted and prove a source of error, I gradually rooted out from my
mind all the errors which had hitherto crept into it.  Not that in this
I imitated the sceptics who doubt only that they may doubt, and seek
nothing beyond uncertainty itself; for, on the contrary, my design  was
singly to find ground of assurance, and cast aside the  loose earth and
sand, that I might reach the rock or the clay.  In this, as appears to
me, I was successful enough; for, since I endeavored to discover the
falsehood or incertitude of the propositions I examined, not by feeble
conjectures, but by clear and certain reasonings, I met with nothing so
doubtful as not to yield some conclusion of adequate certainty,
although this were merely the inference, that the matter in question
contained nothing certain.  And, just as in pulling down an old house,
we usually reserve the ruins to contribute towards the erection, so, in
destroying such of my opinions as I judged to be Ill-founded, I made a
variety of observations and acquired an amount of experience of which I
availed myself in the establishment of more certain.  And further, I
continued to exercise myself in the method I had prescribed; for,
besides taking care in general to conduct all my thoughts according to
its rules, I reserved some hours from time to time which I expressly
devoted to the employment of the method in the solution of mathematical
difficulties, or even in the solution likewise of some questions
belonging to other sciences, but which, by my having detached them from
such principles of these sciences as were of inadequate certainty, were
rendered almost mathematical:  the truth of this will be manifest from
the numerous examples contained in this volume.  And thus, without in
appearance living otherwise than those who, with no other occupation
than that of spending their lives agreeably and innocently, study to
sever pleasure from vice, and who, that they may enjoy their leisure
without ennui, have recourse to such pursuits as are honorable, I was
nevertheless prosecuting my design, and making greater progress in the
knowledge of truth, than I might, perhaps, have made had I been engaged
in the perusal of books merely, or in holding converse with men of

These nine years passed away, however, before I had come to any
determinate judgment respecting the difficulties which form matter of
dispute among the learned, or had commenced to seek the principles of
any philosophy more certain than the vulgar.  And the examples of many
men of the highest genius, who had, in former times, engaged in this
inquiry, but, as appeared to me, without success, led me to imagine it
to be a work of so much difficulty, that I would not perhaps have
ventured on it so soon had I not heard it currently  rumored that I had
already completed the inquiry.  I know not what were the grounds of
this opinion; and, if my conversation contributed in any measure to its
rise, this must have happened rather from my having confessed my
Ignorance with greater freedom than those are accustomed to do who have
studied a little, and expounded perhaps, the reasons that led me to
doubt of many of those things that by others are esteemed certain, than
from my having boasted of any system of philosophy.  But, as I am of a
disposition that makes me unwilling to be esteemed different from what
I really am, I thought it necessary to endeavor by all means to render
myself worthy of the reputation accorded to me; and it is now exactly
eight years since this desire constrained me to remove from all those
places where interruption from any of my acquaintances was possible,
and betake myself to this country, in which the long duration of the
war has led to the establishment of such discipline, that the armies
maintained seem to be of use only in enabling the inhabitants to enjoy
more securely the blessings of peace and where, in the midst of a great
crowd actively engaged in business, and more careful of their own
affairs than curious about those of others, I have been enabled to live
without being deprived of any of the conveniences to be had in the most
populous cities, and yet as solitary and as retired as in the midst of
the most remote deserts.


I am in doubt as to the propriety of making my first meditations in the
place above mentioned matter of discourse; for these are so
metaphysical, and so uncommon, as not, perhaps, to be acceptable to
every one.  And yet, that it may be determined whether the foundations
that I have laid are sufficiently secure, I find myself in a measure
constrained to advert to them.  I had long before remarked that, in
relation to practice, it is sometimes necessary to adopt, as if above
doubt, opinions which we discern to be highly uncertain, as has been
already said; but as I then desired to give my attention solely to the
search after truth, I thought that a procedure exactly the opposite was
called for, and that I ought to reject as absolutely false all opinions
in regard to which I could suppose the least ground for doubt, in order
to ascertain whether after that there remained aught in my belief that
was wholly indubitable.  Accordingly, seeing that our senses sometimes
deceive us, I was willing to suppose that there existed nothing really
such as they presented to us; and because some men err in reasoning,
and fall into paralogisms, even on the simplest matters of geometry, I,
convinced that I was as open to error as any other, rejected as false
all the reasonings I had hitherto taken for demonstrations; and
finally, when I considered that the very same thoughts (presentations)
which we experience when awake may also be experienced when we are
asleep, while there is at that time not one of them true, I supposed
that all the objects (presentations) that had ever entered into my mind
when awake, had in them no more truth than the illusions of my dreams.
But immediately upon this I observed that, whilst I thus wished to
think that all was false, it was absolutely necessary that I, who thus
thought, should be somewhat; and as I observed that this truth, I
think, therefore I am (COGITO ERGO SUM), was so certain and of such
evidence that no ground of doubt, however extravagant, could be alleged
by the sceptics capable of shaking it, I concluded that I might,
without scruple, accept it as the first principle of the philosophy of
which I was in search.

In the next place, I attentively examined what I was and as I observed
that I could suppose that I had no body, and that there was no world
nor any place in which I might be; but that I could not therefore
suppose that I was not; and that, on the contrary, from the very
circumstance that I thought to doubt of the truth of other things, it
most clearly and certainly followed that I was; while, on the other
hand, if I had only ceased to think, although all the other objects
which I had ever imagined had been in reality existent, I would have
had no reason to believe that I existed; I thence concluded that I was
a substance whose whole essence or nature consists only in thinking,
and which, that it may exist, has need of no place, nor is dependent on
any material thing; so that "I," that is to say, the mind by which I am
what I am, is wholly distinct from the body, and is  even more easily
known than the latter, and is such, that although the latter were not,
it would still continue to be all that it is.

After this I inquired in general into what is essential I to the truth
and certainty of a proposition; for since I had discovered one which I
knew to be true, I thought that I must likewise be able to discover the
ground of this certitude.  And as I observed that in the words I think,
therefore I am, there is nothing at all which gives me assurance of
their truth beyond this, that I see very clearly that in order to think
it is necessary to exist, I concluded that I might take, as a general
rule, the principle, that all the things which we very clearly and
distinctly conceive are true, only observing, however, that there is
some difficulty in rightly determining the objects which we distinctly

In the next place, from reflecting on the circumstance that I doubted,
and that consequently my being was not wholly perfect (for I clearly
saw that it was a greater perfection to know than to doubt), I was led
to inquire whence I had learned to think of something more perfect than
myself; and I clearly recognized that I must hold this notion from some
nature which in reality was more perfect.  As for the thoughts of many
other objects external to me, as of the sky, the earth, light, heat,
and a thousand more, I was less at a loss to know whence these came;
for since I remarked in them nothing which seemed to render them
superior to myself, I could believe that, if these were true, they were
dependencies on my own nature, in so far as it possessed a certain
perfection, and, if they were false, that I held them from nothing,
that is to say, that they were in me because of a certain imperfection
of my nature.  But this could not be the case with-the idea of a nature
more perfect than myself; for to receive it from nothing was a thing
manifestly impossible; and, because it is not less repugnant that the
more perfect should be an effect of, and dependence on the less
perfect, than that something should proceed from nothing, it was
equally impossible that I could hold it from myself: accordingly, it
but remained that it had been placed in me by a nature which was in
reality more perfect than mine, and which even possessed within itself
all the perfections of which I could form any idea; that is to say, in
a single word, which was God.  And to this I added that, since I knew
some perfections which I did not possess, I was not the only being in
existence (I will here, with your permission, freely use the terms of
the schools); but, on the contrary, that there was of necessity some
other more perfect Being upon whom I was dependent, and from whom I had
received all that I possessed; for if I had existed alone, and
independently of every other being, so as to have had from myself all
the perfection, however little, which I actually possessed, I should
have been able, for the same reason, to have had from myself the whole
remainder of perfection, of the want of which I was conscious, and thus
could of myself have become infinite, eternal, immutable, omniscient,
all-powerful, and, in fine, have possessed all the perfections which I
could recognize in God.  For in order to know the nature of God (whose
existence has been established by the preceding reasonings), as far as
my own nature permitted, I had only to consider in reference to all the
properties of which I found in my  mind some idea, whether their
possession was a mark of perfection; and I was assured that no one
which indicated any imperfection was in him, and that none of the rest
was awanting.  Thus I perceived that doubt, inconstancy,  sadness, and
such like, could not be found in God, since I myself would have been
happy to be free from them.  Besides, I had ideas of many sensible and
corporeal things; for although I might suppose that I was dreaming, and
that all which I saw or imagined was false, I could not, nevertheless,
deny that the ideas were in reality in my thoughts.  But, because I had
already very clearly recognized in myself that the intelligent nature
is distinct from the corporeal, and as I observed that all composition
is an evidence of dependency, and that a state of dependency is
manifestly a state of imperfection, I therefore determined that it
could not be a perfection in God to be compounded of these two natures
and that consequently he was not so compounded; but that if there were
any bodies in the world, or even any intelligences, or other natures
that were not wholly perfect, their existence depended on his power in
such a way that they could not subsist without him for a single moment.

I was disposed straightway to search for other truths and when I had
represented to myself the object of the geometers, which I conceived to
be a continuous body or a space indefinitely extended in length,
breadth, and height or depth, divisible into divers parts which admit
of different figures and sizes, and of being moved or transposed in all
manner of ways (for all this the geometers suppose to be in the object
they contemplate), I went over some of their simplest demonstrations.
And, in the first place, I observed, that the great certitude which by
common consent is accorded to these demonstrations, is founded solely
upon this, that they are clearly conceived in accordance with the rules
I have already laid down In the next place, I perceived that there was
nothing at all in these demonstrations which could assure me of the
existence of their object: thus, for example, supposing a triangle to
be given, I distinctly perceived that its three angles were necessarily
equal to two right angles, but I did not on that account perceive
anything which could assure me that any triangle existed:  while, on
the contrary, recurring to the examination of the idea of a Perfect
Being, I found that the existence of the Being was comprised in the
idea in the same way that the equality of its three angles to two right
angles is comprised in the idea of a triangle, or as in the idea of a
sphere, the equidistance of all points on its surface from the center,
or even still more clearly; and that consequently it is at least as
certain that God, who is this Perfect Being, is, or exists, as any
demonstration of geometry can be.

But the reason which leads many to persuade them selves that there is a
difficulty in knowing this truth, and even also in knowing what their
mind really is, is that they never raise their thoughts above sensible
objects, and are so accustomed to consider nothing except by way of
imagination, which is a mode of thinking limited to material objects,
that all that is not imaginable seems to them not intelligible.  The
truth of this is sufficiently manifest from the single circumstance,
that the philosophers of the schools accept as a maxim that there is
nothing in the understanding which was not previously in the senses, in
which however it is certain that the ideas of God and of the soul have
never been; and it appears to me that they who make use of their
imagination to comprehend these ideas do exactly the some thing as if,
in order to hear sounds or smell odors, they strove to avail themselves
of their eyes; unless indeed that there is this difference, that the
sense of sight does not afford us an inferior assurance to those of
smell or hearing; in place of which, neither our imagination nor our
senses can give us assurance of anything unless our understanding

Finally, if there be still persons who are not sufficiently persuaded
of the existence of God and of the soul, by the reasons I have adduced,
I am desirous that they should know that all the other propositions, of
the truth of which they deem themselves perhaps more assured, as that
we have a body, and that there exist stars and an earth, and such like,
are less certain; for, although we have a moral assurance of these
things, which is so strong that there is an appearance of extravagance
in doubting of their existence, yet at the same time no one, unless his
intellect is impaired, can deny, when the question relates to a
metaphysical certitude, that there is sufficient reason to exclude
entire assurance, in the observation that when asleep we can in the
same way imagine ourselves possessed of another body and that we see
other stars and another earth, when there is nothing of the kind.  For
how do we know that the thoughts which occur in dreaming are false
rather than those other which we experience when awake, since the
former are often not less vivid and distinct than the latter?  And
though men of the highest genius study this question as long as they
please, I do not believe that they will be able to give any reason
which can be sufficient to remove this doubt, unless they presuppose
the existence of God.  For, in the first place even the principle which
I have already taken as a rule, viz., that all the things which we
clearly and distinctly conceive are true, is certain only because God
is or exists and because he is a Perfect Being, and because all that we
possess is derived from him:  whence it follows that our ideas or
notions, which to the extent of their clearness and distinctness are
real, and proceed from God, must to that extent be true.  Accordingly,
whereas we not infrequently have ideas or notions in which some falsity
is contained, this can only be the case with such as are to some extent
confused and obscure, and in this proceed from nothing (participate of
negation), that is, exist in us thus confused because we are not wholly
perfect.  And it is evident that it is not less repugnant that falsity
or imperfection, in so far as it is imperfection, should proceed from
God, than that truth or perfection should proceed from nothing.  But if
we did not know that all which we possess of real and true proceeds
from a Perfect and Infinite Being, however clear and distinct our ideas
might be, we should have no ground on that account for the assurance
that they possessed the perfection of being true.

But after the knowledge of God and of the soul has rendered us certain
of this rule, we can easily understand that the truth of the thoughts
we experience when awake, ought not in the slightest degree to be
called in question on account of the illusions of our dreams.  For if
it happened that an individual, even when asleep, had some very
distinct idea, as, for example, if a geometer should discover some new
demonstration, the circumstance of his being asleep would not militate
against its truth; and as for the most ordinary error of our dreams,
which consists in their representing to us various objects in the same
way as our external senses, this is not prejudicial, since it leads us
very properly to suspect the truth of the ideas of sense; for we are
not infrequently deceived in the same manner when awake; as when
persons in the jaundice see all objects yellow, or when the stars or
bodies at a great distance appear to us much smaller than they are.
For, in fine, whether awake or asleep, we ought never to allow
ourselves to be persuaded of the truth of anything unless on the
evidence of our reason.  And it must be noted that I say of our reason,
and not of our imagination or of our senses:  thus, for example,
although we very clearly see the sun, we ought not therefore to
determine that it is only of the size which our sense of sight
presents; and we may very distinctly imagine the head of a lion joined
to the body of a goat, without being therefore shut up to the
conclusion that a chimaera exists; for it is not a dictate of reason
that what we thus see or imagine is in reality existent; but it plainly
tells us that all our ideas or notions contain in them some truth; for
otherwise it could not be that God, who is wholly perfect and
veracious, should have placed them in us.  And because our reasonings
are never so clear or so complete during sleep as when we are awake,
although sometimes the acts of our imagination are then as lively and
distinct, if not more so than in our waking moments, reason further
dictates that, since all our thoughts cannot be true because of our
partial imperfection, those possessing truth must infallibly be found
in the experience of our waking moments rather than in that of our


I would here willingly have proceeded to exhibit the whole chain of
truths which I deduced from these primary but as with a view to this it
would have been necessary now to treat of many questions in dispute
among the earned, with whom I do not wish to be embroiled, I believe
that it will be better for me to refrain from this exposition, and only
mention in general what these truths are, that the more judicious may
be able to determine whether a more special account of them would
conduce to the public advantage.  I have ever remained firm in my
original resolution to suppose no other principle than that of which I
have recently availed myself in demonstrating the existence of God and
of the soul, and to accept as true nothing that did not appear to me
more clear and certain than the demonstrations of the geometers had
formerly appeared; and yet I venture to state that not only have I
found means to satisfy myself in a short time on all the principal
difficulties which are usually treated of in philosophy, but I have
also observed certain laws established in nature by God in such a
manner, and of which he has impressed on our minds such notions, that
after we have reflected sufficiently upon these, we cannot doubt that
they are accurately observed in all that exists or takes place in the
world and farther, by considering the concatenation of these laws, it
appears to me that I have discovered many truths more useful and more
important than all I had before learned, or even had expected to learn.

But because I have essayed to expound the chief of these discoveries in
a treatise which certain considerations prevent me from publishing, I
cannot make the results known more conveniently than by here giving a
summary of the contents of this treatise.  It was my design to comprise
in it all that, before I set myself to write it, I thought I knew of
the nature of material objects.  But like the painters who, finding
themselves unable to represent equally well on a plain surface all the
different faces of a solid body, select one of the chief, on which
alone they make the light fall, and throwing the rest into the shade,
allow them to appear only in so far as they can be seen while looking
at the principal one; so, fearing lest I should not be able to compense
in my discourse all that was in my mind, I resolved to expound singly,
though at considerable length, my opinions regarding light; then to
take the opportunity of adding something on the sun and the fixed
stars, since light almost wholly proceeds from them; on the heavens
since they transmit it; on the planets, comets, and earth, since they
reflect it; and particularly on all the bodies that are upon the earth,
since they are either colored, or transparent, or luminous; and finally
on man, since he is the spectator of these objects.  Further, to enable
me to cast this variety of subjects somewhat into the shade, and to
express my judgment regarding them with greater freedom, without being
necessitated to adopt or refute the opinions of the learned, I resolved
to leave all the people here to their disputes, and to speak only of
what would happen in a new world, if God were now to create somewhere
in the imaginary spaces matter sufficient to compose one, and were to
agitate variously and confusedly the different parts of this matter, so
that there resulted a chaos as disordered as the poets ever feigned,
and after that did nothing more than lend his ordinary concurrence to
nature, and allow her to act in accordance with the laws which he had
established.  On this supposition, I, in the first place, described
this matter, and essayed to represent it in such a manner that to my
mind there can be nothing clearer and more intelligible, except what
has been recently said regarding God and the soul; for I even expressly
supposed that it possessed none of those forms or qualities which are
so debated in the schools, nor in general anything the knowledge of
which is not so natural to our minds that no one can so much as imagine
himself ignorant of it.  Besides, I have pointed out what are the laws
of nature; and, with no other principle upon which to found my
reasonings except the infinite perfection of God, I endeavored to
demonstrate all those about which there could be any room for doubt,
and to prove that they are such, that even if God had created more
worlds, there could have been none in which these laws were not
observed.  Thereafter, I showed how the greatest part of the matter of
this chaos must, in accordance with these laws, dispose and arrange
itself in such a way as to present the appearance of heavens; how in
the meantime some of its parts must compose an earth and some planets
and comets, and others a sun and fixed stars.  And, making a digression
at this stage on the subject of light, I expounded at considerable
length what the nature of that light must be which is found in the sun
and the stars, and how thence in an instant of time it traverses the
immense spaces of the heavens, and how from the planets and comets it
is reflected towards the earth.  To this I likewise added much
respecting the substance, the situation, the motions, and all the
different qualities of these heavens and stars; so that I thought I had
said enough respecting them to show that there is nothing observable in
the heavens or stars of our system that must not, or at least may not
appear precisely alike in those of the system which I described.  I
came next to speak of the earth in particular, and to show how, even
though I had expressly supposed that God had given no weight to the
matter of which it is composed, this should not prevent all its parts
from tending exactly to its center; how with water and air on its
surface, the disposition of the heavens and heavenly bodies, more
especially of the moon, must cause a flow and ebb, like in all its
circumstances to that observed in our seas, as also a certain current
both of water and air from east to west, such as is likewise observed
between the tropics; how the mountains, seas, fountains, and rivers
might naturally be formed in it, and the metals produced in the mines,
and the plants grow in the fields and in general, how all the bodies
which are commonly denominated mixed or composite might be generated
and, among other things in the discoveries alluded to inasmuch as
besides the stars, I knew nothing except fire which produces light, I
spared no pains to set forth all that pertains to its nature,--the
manner of its production and support, and to explain how heat is
sometimes found without light, and light without heat; to show how it
can induce various colors upon different bodies and other diverse
qualities; how it reduces some to a liquid state and hardens others;
how it can consume almost all bodies, or convert them into ashes and
smoke; and finally, how from these ashes, by the mere intensity of its
action, it forms glass:  for as this transmutation of ashes into glass
appeared to me as wonderful as any other in nature, I took a special
pleasure in describing it.  I was not, however, disposed, from these
circumstances, to conclude that this world had been created in the
manner I described; for it is much more likely that God made it at the
first such as it was to be.  But this is certain, and an opinion
commonly received among theologians, that the action by which he now
sustains it is the same with that by which he originally created it; so
that even although he had from the beginning given it no other form
than that of chaos, provided only he had established certain laws of
nature, and had lent it his concurrence to enable it to act as it is
wont to do, it may be believed, without discredit to the miracle of
creation, that, in this way alone, things purely material might, in
course of time, have become such as we observe them at present; and
their nature is much more easily conceived when they are beheld coming
in this manner gradually into existence, than when they are only
considered as produced at once in a finished and perfect state.

From the description of inanimate bodies and plants, I passed to
animals, and particularly to man.  But since I had not as yet
sufficient knowledge to enable me to treat of these in the same manner
as of the rest, that is to say, by deducing effects from their causes,
and by showing from what elements and in what manner nature must
produce them, I remained satisfied with the supposition that God formed
the body of man wholly like to one of ours, as well in the external
shape of the members as in the internal conformation of the organs, of
the same matter with that I had described, and at first placed in it no
rational soul, nor any other principle, in room of the vegetative or
sensitive soul, beyond kindling in the heart one of those fires without
light, such as I had already described, and which I thought was not
different from the heat in hay that has been heaped together before it
is dry, or that which causes fermentation in new wines before they are
run clear of the fruit.  For, when I examined the kind of functions
which might, as consequences of this supposition, exist in this body, I
found precisely all those which may exist in us independently of all
power of thinking, and consequently without being in any measure owing
to the soul; in other words, to that part of us which is distinct from
the body, and of which it has been said above that the nature
distinctively consists in thinking, functions in which the animals void
of reason may be said wholly to resemble us; but among which I could
not discover any of those that, as dependent on thought alone, belong
to us as men, while, on the other hand, I did afterwards discover these
as soon as I supposed God to have created a rational soul, and to have
annexed it to this body in a particular manner which I described.

But, in order to show how I there handled this matter, I mean here to
give the explication of the motion of the heart and arteries, which, as
the first and most general motion observed in animals, will afford the
means of readily determining what should be thought of all the rest.
And that there may be less difficulty in understanding what I am about
to say on this subject, I advise those who are not versed in anatomy,
before they commence the perusal of these observations, to take the
trouble of getting dissected in their presence the heart of some large
animal possessed of lungs (for this is throughout sufficiently like the
human), and to have shown to them its two ventricles or cavities:  in
the first place, that in the right side, with which correspond two very
ample tubes, viz., the hollow vein (vena cava), which is the principal
receptacle of the blood, and the trunk of the tree, as it were, of
which all the other veins in the body are branches; and the arterial
vein (vena arteriosa), inappropriately so denominated, since it is in
truth only an artery, which, taking its rise in the heart, is divided,
after passing out from it, into many branches which presently disperse
themselves all over the lungs; in the second place, the cavity in the
left side, with which correspond in the same manner two canals in size
equal to or larger than the preceding, viz., the venous artery (arteria
venosa), likewise inappropriately thus designated, because it is simply
a vein which comes from the lungs, where it is divided into many
branches, interlaced with those of the arterial vein, and those of the
tube called the windpipe, through which the air we breathe enters; and
the great artery which, issuing from the heart, sends its branches all
over the body.  I should wish also that such persons were carefully
shown the eleven pellicles which, like so many small valves, open and
shut the four orifices that are in these two cavities, viz., three at
the entrance of the hollow veins where they are disposed in such a
manner as by no means to prevent the blood which it contains from
flowing into the right ventricle of the heart, and yet exactly to
prevent its flowing out; three at the entrance to the arterial vein,
which, arranged in a manner exactly the opposite of the former, readily
permit the blood contained in this cavity to pass into the lungs, but
hinder that contained in the lungs from returning to this cavity; and,
in like manner, two others at the mouth of the venous artery, which
allow the blood from the lungs to flow into the left cavity of the
heart, but preclude its return; and three at the mouth of the great
artery, which suffer the blood to flow from the heart, but prevent its
reflux.  Nor do we need to seek any other reason for the number of
these pellicles beyond this that the orifice of the venous artery being
of an oval shape from the nature of its situation, can be adequately
closed with two, whereas the others being round are more conveniently
closed with three.  Besides, I wish such persons to observe that the
grand artery and the arterial vein are of much harder and firmer
texture than the venous artery and the hollow vein; and that the two
last expand before entering the heart, and there form, as it were, two
pouches denominated the auricles of the heart, which are composed of a
substance similar to that of the heart itself; and that there is always
more warmth in the heart than in any other part of the body--and
finally, that this heat is capable of causing any drop of blood that
passes into the cavities rapidly to expand and dilate, just as all
liquors do when allowed to fall drop by drop into a highly heated

For, after these things, it is not necessary for me to say anything
more with a view to explain the motion of the heart, except that when
its cavities are not full of blood, into these the blood of necessity
flows,--from the hollow vein into the right, and from the venous artery
into the left; because these two vessels are always full of blood, and
their orifices, which are turned towards the heart, cannot then be
closed.  But as soon as two drops of blood have thus passed, one into
each of the cavities, these drops which cannot but be very large,
because the orifices through which they pass are wide, and the vessels
from which they come full of blood, are immediately rarefied, and
dilated by the heat they meet with.  In this way they cause the whole
heart to expand, and at the same time press home and shut the five
small valves that are at the entrances of the two vessels from which
they flow, and thus prevent any more blood from coming down into the
heart, and becoming more and more rarefied, they push open the six
small valves that are in the orifices of the other two vessels, through
which they pass out, causing in this way all the branches of the
arterial vein and of the grand artery to expand almost simultaneously
with the heart which immediately thereafter begins to contract, as do
also the arteries, because the blood that has entered them has cooled,
and the six small valves close, and the five of the hollow vein and of
the venous artery open anew and allow a passage to other two drops of
blood, which cause the heart and the arteries again to expand as
before.  And, because the blood which thus enters into the heart passes
through these two pouches called auricles, it thence happens that their
motion is the contrary of that of the heart, and that when it expands
they contract.  But lest those who are ignorant of the force of
mathematical demonstrations and who are not accustomed to distinguish
true reasons from mere verisimilitudes, should venture, without
examination, to deny what has been said, I wish it to be considered
that the motion which I have now explained follows as necessarily from
the very arrangement of the parts, which may be observed in the heart
by the eye alone, and from the heat which may be felt with the fingers,
and from the nature of the blood as learned from experience, as does
the motion of a clock from the power, the situation, and shape of its
counterweights and wheels.

But if it be asked how it happens that the blood in the veins, flowing
in this way continually into the heart, is not exhausted, and why the
arteries do not become too full, since all the blood which passes
through the heart flows into them, I need only mention in reply what
has been written by a physician of England, who has the honor of having
broken the ice on this subject, and of having been the first to teach
that there are many small passages at the extremities of the arteries,
through which the blood received by them from the heart passes into the
small branches of the veins, whence it again returns to the heart; so
that its course amounts precisely to a perpetual circulation.  Of this
we have abundant proof in the ordinary experience of surgeons, who, by
binding the arm with a tie of moderate straitness above the part where
they open the vein, cause the blood to flow more copiously than it
would have done without any ligature; whereas quite the contrary would
happen were they to bind it below; that is, between the hand and the
opening, or were to make the ligature above the opening very tight.
For it is manifest that the tie, moderately straightened, while
adequate to hinder the blood already in the arm from returning towards
the heart by the veins, cannot on that account prevent new blood from
coming forward through the arteries, because these are situated below
the veins, and their coverings, from their greater consistency, are
more difficult to compress; and also that the blood which comes from
the heart tends to pass through them to the hand with greater force
than it does to return from the hand to the heart through the veins.
And since the latter current escapes from the arm by the opening made
in one of the veins, there must of necessity be certain passages below
the ligature, that is, towards the extremities of the arm through which
it can come thither from the arteries.  This physician likewise
abundantly establishes what he has advanced respecting the motion of
the blood, from the existence of certain pellicles, so disposed in
various places along the course of the veins, in the manner of small
valves, as not to permit the blood to pass from the middle of the body
towards the extremities, but only to return from the extremities to the
heart; and farther, from experience which shows that all the blood
which is in the body may flow out of it in a very short time through a
single artery that has been cut, even although this had been closely
tied in the immediate neighborhood of the heart and cut between the
heart and the ligature, so as to prevent the supposition that the blood
flowing out of it could come from any other quarter than the heart.

But there are many other circumstances which evince that what I have
alleged is the true cause of the motion of the blood:  thus, in the
first place, the difference that  is observed between the blood which
flows from the veins, and that from the arteries, can only arise from
this, that being rarefied, and, as it were, distilled by passing
through the heart, it is thinner, and more vivid, and warmer
immediately after leaving the heart, in other words, when in the
arteries, than it was a short time before passing into either, in other
words, when it was in the veins; and if attention be given, it will be
found that this difference is very marked only in the neighborhood of
the heart; and is not so evident in parts more remote from it.  In the
next place, the consistency of the coats of which the arterial vein and
the great artery are  composed, sufficiently shows that the blood is
impelled  against them with more force than against the veins.  And why
should the left cavity of the heart and the  great artery be wider and
larger than the right cavity and the arterial vein, were it not that
the blood of the  venous artery, having only been in the lungs after it
has passed through the heart, is thinner, and rarefies more readily,
and in a higher degree, than the blood which proceeds immediately from
the hollow vein?  And what can physicians conjecture from feeling the
pulse unless they know that according as the blood changes its nature
it can be rarefied by the warmth of the heart, in a higher or lower
degree, and more or less quickly than before?  And if it be inquired
how this heat is communicated to the other members, must it not be
admitted that this is effected by means of the blood, which, passing
through the heart, is there heated anew, and thence diffused over all
the body?  Whence it happens, that if the blood be withdrawn from any
part, the heat is likewise withdrawn by the same means; and although
the heart were as-hot as glowing iron, it would not be capable of
warming the feet and hands as at present, unless it continually sent
thither new blood.  We likewise perceive from this, that the true use
of respiration is to bring sufficient fresh air into the lungs, to
cause the blood which flows into them from the right ventricle of the
heart, where it has been rarefied and, as it were, changed into vapors,
to become thick, and to convert it anew into blood, before it flows
into the left cavity, without which process it would be unfit for the
nourishment of the fire that is there.  This receives confirmation from
the circumstance, that it is observed of animals destitute of lungs
that they have also but one cavity in the heart, and that in children
who cannot use them while in the womb, there is a hole through which
the blood flows from the hollow vein into the left cavity of the heart,
and a tube through which it passes from the arterial vein into the
grand artery without passing through the lung.  In the next place, how
could digestion be carried on in the stomach unless the heart
communicated heat to it through the arteries, and along with this
certain of the more fluid parts of the blood, which assist in the
dissolution of the food that has been taken in?  Is not also the
operation which converts the juice of food into blood easily
comprehended, when it is considered that it is distilled by passing and
repassing through the heart perhaps more than one or two hundred times
in a day?  And what more need be adduced to explain nutrition, and the
production of the different humors of the body, beyond saying, that the
force with which the blood, in being rarefied, passes from the heart
towards the extremities of the arteries, causes certain of its parts to
remain in the members at which they arrive, and there occupy the place
of some others expelled by them; and that according to the situation,
shape, or smallness of the pores with which they meet, some rather
than others flow into certain parts, in the same way that some sieves
are observed to act, which, by being variously perforated, serve to
separate different species of grain?  And, in the last place, what
above all is here worthy of observation, is the generation of the
animal spirits, which are like a very subtle wind, or rather a very
pure and vivid flame which, continually ascending in great abundance
from the heart to the brain, thence penetrates through the nerves into
the muscles, and gives motion to all the members; so that to account
for other parts of the blood which, as most agitated and penetrating,
are the fittest to compose these spirits, proceeding towards the brain,
it is not necessary to suppose any other cause, than simply, that the
arteries which carry them thither proceed from the heart in the most
direct lines, and that, according to the rules of mechanics which are
the same with those of nature, when many objects tend at once to the
same point where there is not sufficient room for all (as is the case
with the parts of the blood which flow forth from the left cavity of
the heart and tend towards the brain), the weaker and less agitated
parts must necessarily be driven aside from that point by the stronger
which alone in this way reach it I had expounded all these matters with
sufficient minuteness in the treatise which I formerly thought of
publishing.  And after these, I had shown what must be the fabric of
the nerves and muscles of the human body to give the animal spirits
contained in it the power to move the members, as when we see heads
shortly after they have been struck off still move and bite the earth,
although no longer animated; what changes must take place in the brain
to produce waking, sleep, and dreams; how light, sounds, odors, tastes,
heat, and all the other qualities of external objects impress it with
different ideas by means of the senses; how hunger, thirst, and the
other internal affections can likewise impress upon it divers ideas;
what must be understood by the common sense (sensus communis) in which
these ideas are received, by the memory which retains them, by the
fantasy which can change them in various ways, and out of them compose
new ideas, and which, by the same means, distributing the animal
spirits through the muscles, can cause the members of such a body to
move in as many different ways, and in a manner as suited, whether to
the objects that are presented to its senses or to its internal
affections, as can take place in our own case apart from the guidance
of the will.  Nor will this appear at all strange to those who are
acquainted with the variety of movements performed by the different
automata, or moving machines fabricated by human industry, and that
with help of but few pieces compared with the great multitude of bones,
muscles, nerves, arteries, veins, and other parts that are found in the
body of each animal.  Such persons will look upon this body as a
machine made by the hands of God, which is incomparably better
arranged, and adequate to movements more admirable than is any machine
of human invention.  And here I specially stayed to show that, were
there such machines exactly resembling organs and outward form an ape
or any other irrational animal, we could have no means of knowing that
they were in any respect of a different nature from these animals; but
if there were machines bearing the image of our bodies, and capable of
imitating our actions as far as it is morally possible, there would
still remain two most certain tests whereby to know that they were not
therefore really men.  Of these the first is that they could never use
words or other signs arranged in such a manner as is competent to us in
order to declare our thoughts to others:  for we may easily conceive a
machine to be so constructed that it emits vocables, and even that it
emits some correspondent to the action upon it of external objects
which cause a change in its organs; for example, if touched in a
particular place it may demand what we wish to say to it; if in another
it may cry out that it is hurt, and such like; but not that it should
arrange them variously so as appositely to reply to what is said in its
presence, as men of the lowest grade of intellect can do.  The second
test is, that although such machines might execute many things with
equal or perhaps greater perfection than any of us, they would, without
doubt, fail in certain others from which it could be discovered that
they did not act from knowledge, but solely from the disposition of
their organs:  for while reason is an universal instrument that is
alike available on every occasion, these organs, on the contrary, need
a particular arrangement for each particular action; whence it must be
morally impossible that there should exist in any machine a diversity
of organs sufficient to enable it to act in all the occurrences of
life, in the way in which our reason enables us to act.  Again, by
means of these two tests we may likewise know the difference between
men and brutes.  For it is highly deserving of remark, that there are
no men so dull and stupid, not even idiots, as to be incapable of
joining together different words, and thereby constructing a
declaration by which to make their thoughts understood; and that on the
other hand, there is no other animal, however perfect or happily
circumstanced, which can do the like.  Nor does this inability arise
from want of organs:  for we observe that magpies and parrots can utter
words like ourselves, and are yet unable to speak as we do, that is, so
as to show that they understand what they say; in place of which men
born deaf and dumb, and thus not less, but rather more than the brutes,
destitute of the organs which others use in speaking, are in the habit
of spontaneously inventing certain signs by which they discover their
thoughts to those who, being usually in their company, have leisure to
learn their language.  And this proves not only that the brutes have
less reason than man, but that they have none at all:  for we see that
very little is required to enable a person to speak; and since a
certain inequality of capacity is observable among animals of the same
species, as well as among men, and since some are more capable of being
instructed than others, it is incredible that the most perfect ape or
parrot of its species, should not in this be equal to the most stupid
infant of its kind or at least to one that was crack-brained, unless
the soul of brutes were of a nature wholly different from ours.  And we
ought not to confound speech with the natural movements which indicate
the passions, and can be imitated by machines as well as manifested by
animals; nor must it be thought with certain of the ancients, that the
brutes speak, although we do not understand their language.  For if
such were the case, since they are endowed with many organs analogous
to ours, they could as easily communicate their thoughts to us as to
their fellows.  It is also very worthy of remark, that, though there
are many animals which manifest more industry than we in certain of
their actions, the same animals are yet observed to show none at all in
many others:  so that the circumstance that they do better than we does
not prove that they are endowed with mind, for it would thence follow
that they possessed greater reason than any of us, and could surpass us
in all things; on the contrary, it rather proves that they are
destitute of reason, and that it is nature which acts in them according
to the disposition of their organs:  thus it is seen, that a clock
composed only of wheels and weights can number the hours and measure
time more exactly than we with all our skin.

I had after this described the reasonable soul, and shown that it could
by no means be educed from the power of matter, as the other things of
which I had spoken, but that it must be expressly created; and that it
is not sufficient that it be lodged in the human body exactly like a
pilot in a ship, unless perhaps to move its members, but that it is
necessary for it to be joined and united more closely to the body, in
order to have sensations and appetites similar to ours, and thus
constitute a real man.  I here entered, in conclusion, upon the subject
of the soul at considerable length, because it is of the greatest
moment:  for after the error of those who deny the existence of God, an
error which I think I have already sufficiently refuted, there is none
that is more powerful in leading feeble minds astray from the straight
path of virtue than the supposition that the soul of the brutes is of
the same nature with our own; and consequently that after this life we
have nothing to hope for or fear, more than flies and ants; in place of
which, when we know how far they differ we much better comprehend the
reasons which establish that the soul is of a nature wholly independent
of the body, and that consequently it is not liable to die with the
latter and, finally, because no other causes are observed capable of
destroying it, we are naturally led thence to judge that it is immortal.


Three years have now elapsed since I finished the treatise containing
all these matters; and I was beginning to revise it, with the view to
put it into the hands of a printer, when I learned that persons to whom
I greatly defer, and whose authority over my actions is hardly less
influential than is my own reason over my thoughts, had condemned a
certain doctrine in physics, published a short time previously by
another individual to which I will not say that I adhered, but only
that, previously to their censure I had observed in it nothing which I
could imagine to be prejudicial either to religion or to the state, and
nothing therefore which would have prevented me from giving expression
to it in writing, if reason had persuaded me of its truth; and this led
me to fear lest among my own doctrines likewise some one might be found
in which I had departed from the truth, notwithstanding the great care
I have always taken not to accord belief to new opinions of which I had
not the most certain demonstrations, and not to give expression to
aught that might tend to the hurt of any one.  This has been sufficient
to make me alter my purpose of publishing them; for although the
reasons by which I had been induced to take this resolution were very
strong, yet my inclination, which has always been hostile to writing
books, enabled me immediately to discover other considerations
sufficient to excuse me for not undertaking the task.  And these
reasons, on one side and the other, are such, that not only is it in
some measure my interest here to state them, but that of the public,
perhaps, to know them.

I have never made much account of what has proceeded from my own mind;
and so long as I gathered no other advantage from the method I employ
beyond satisfying myself on some difficulties belonging to the
speculative sciences, or endeavoring to regulate my actions according
to the principles it taught me, I never thought myself bound to publish
anything respecting it.  For in what regards manners, every one is so
full of his own wisdom, that there might be found as many reformers as
heads, if any were allowed to take upon themselves the task of mending
them, except those whom God has constituted the supreme rulers of his
people or to whom he has given sufficient grace and zeal to be
prophets; and although my speculations greatly pleased myself, I
believed that others had theirs, which perhaps pleased them still more.
But as soon as I had acquired some general notions respecting physics,
and beginning to make trial of them in various particular difficulties,
had observed how far they can carry us, and how much they differ from
the principles that have been employed up to the present time, I
believed that I could not keep them concealed without sinning
grievously against the law by which we are bound to promote, as far as
in us lies, the general good of mankind.  For by them I perceived it to
be possible to arrive at knowledge highly useful in life; and in room
of the speculative philosophy usually taught in the schools, to
discover a practical, by means of which, knowing the force and action
of fire, water, air the stars, the heavens, and all the other bodies
that surround us, as distinctly as we know the various crafts of our
artisans, we might also apply them in the same way to all the uses to
which they are adapted, and thus render ourselves the lords and
possessors of nature.  And this is a result to be desired, not only in
order to the invention of an infinity of arts, by which we might be
enabled to enjoy without any trouble the fruits of the earth, and all
its comforts, but also and especially for the preservation of health,
which is without doubt, of all the blessings of this life, the first
and fundamental one; for the mind is so intimately dependent upon the
condition and relation of the organs of the body, that if any means can
ever be found to render men wiser and more ingenious than hitherto, I
believe that it is in medicine they must be sought for.  It is true
that the science of medicine, as it now exists, contains few things
whose utility is very remarkable:  but without any wish to depreciate
it, I am confident that there is no one, even among those whose
profession it is, who does not admit that all at present known in it is
almost nothing in comparison of what remains to be discovered; and that
we could free ourselves from an infinity of maladies of body as well as
of mind, and perhaps also even from the debility of age, if we had
sufficiently ample knowledge of their causes, and of all the remedies
provided for us by nature.  But since I designed to employ my whole
life in the search after so necessary a science, and since I had fallen
in with a path which seems to me such, that if any one follow it he
must inevitably reach the end desired, unless he be hindered either by
the shortness of life or the want of experiments, I judged that there
could be no more effectual provision against these two impediments than
if I were faithfully to communicate to the public all the little I
might myself have found, and incite men of superior genius to strive to
proceed farther, by contributing, each according to his inclination and
ability, to the experiments which it would be necessary to make, and
also by informing the public of all they might discover, so that, by
the last beginning where those before them had left off, and thus
connecting the lives and labours of many, we might collectively proceed
much farther than each by himself could do.

I remarked, moreover, with respect to experiments, that they become
always more necessary the more one is advanced in knowledge; for, at
the commencement, it is better to make use only of what is
spontaneously presented to our senses, and of which we cannot remain
ignorant, provided we bestow on it any reflection, however slight, than
to concern ourselves about more uncommon and recondite phenomena:  the
reason of which is, that the more uncommon often only mislead us so
long as the causes of the more ordinary are still unknown; and the
circumstances upon which they depend are almost always so special and
minute as to be highly difficult to detect.  But in this I have adopted
the following order:  first, I have essayed to find in general the
principles, or first causes of all that is or can be in the world,
without taking into consideration for this end anything but God himself
who has created it, and without educing them from any other source than
from certain germs of truths naturally existing in our minds In the
second place, I examined what were the first and most ordinary effects
that could be deduced from these causes; and it appears to me that, in
this way, I have found heavens, stars, an earth, and even on the earth
water, air, fire, minerals, and some other things of this kind, which
of all others are the most common and simple, and hence the easiest to
know.  Afterwards when I wished to descend to the more particular, so
many diverse objects presented themselves to me, that I believed it to
be impossible for the human mind to distinguish the forms or species of
bodies that are upon the earth, from an infinity of others which might
have been, if it had pleased God to place them there, or consequently
to apply them to our use, unless we rise to causes through their
effects, and avail ourselves of many particular experiments.
Thereupon, turning over in my mind I the objects that had ever been
presented to my senses I freely venture to state that I have never
observed any which I could not satisfactorily explain by the principles
had discovered.  But it is necessary also to confess that the power of
nature is so ample and vast, and these principles so simple and
general, that I have hardly observed a single particular effect which I
cannot at once recognize as capable of being deduced in man different
modes from the principles, and that my greatest difficulty usually is
to discover in which of these modes the effect is dependent upon them;
for out of this difficulty cannot otherwise extricate myself than by
again seeking certain experiments, which may be such that their result
is not the same, if it is in the one of these modes at we must explain
it, as it would be if it were to be explained in the other.  As to what
remains, I am now in a position to discern, as I think, with sufficient
clearness what course must be taken to make the majority those
experiments which may conduce to this end:  but I perceive likewise
that they are such and so numerous, that neither my hands nor my
income, though it were a thousand times larger than it is, would be
sufficient for them all; so that according as henceforward I shall have
the means of making more or fewer experiments, I shall in the same
proportion make greater or less progress in the knowledge of nature.
This was what I had hoped to make known by the treatise I had written,
and so clearly to exhibit the advantage that would thence accrue to the
public, as to induce all who have the common good of man at heart, that
is, all who are virtuous in truth, and not merely in appearance, or
according to opinion, as well to communicate to me the experiments they
had already made, as to assist me in those that remain to be made.

But since that time other reasons have occurred to me, by which I have
been led to change my opinion, and to think that I ought indeed to go
on committing to writing all the results which I deemed of any moment,
as soon as I should have tested their truth, and to bestow the same
care upon them as I would have done had it been my design to publish
them.  This course commended itself to me, as well because I thus
afforded myself more ample inducement to examine them thoroughly, for
doubtless that is always more narrowly scrutinized which we believe
will be read by many, than that which is written merely for our private
use (and frequently what has seemed to me true when I first conceived
it, has appeared false when I have set about committing it to writing),
as because I thus lost no opportunity of advancing the interests of the
public, as far as in me lay, and since thus likewise, if my writings
possess any value, those into whose hands they may fall after my death
may be able to put them to what use they deem proper.  But I resolved
by no means to consent to their publication during my lifetime, lest
either the oppositions or the controversies to which they might give
rise, or even the reputation, such as it might be, which they would
acquire for me, should be any occasion of my losing the time that I had
set apart for my own improvement.  For though it be true that every one
is bound to promote to the extent of his ability the good of others,
and that to be useful to no one is really to be worthless, yet it is
likewise true that our cares ought to extend beyond the present, and it
is good to omit doing what might perhaps bring some profit to the
living, when we have in view the accomplishment of other ends that will
be of much greater advantage to posterity.  And in truth, I am quite
willing it should be known that the little I have hitherto learned is
almost nothing in comparison with that of which I am ignorant, and to
the knowledge of which I do not despair of being able to attain; for it
is much the same with those who gradually discover truth in the
sciences, as with those who when growing rich find less difficulty in
making great acquisitions, than they formerly experienced when poor in
making acquisitions of much smaller amount.  Or they may be compared to
the commanders of armies, whose forces usually increase in proportion
to their victories, and who need greater prudence to keep together the
residue of their troops after a defeat than after a victory to take
towns and provinces.  For he truly engages in battle who endeavors to
surmount all the difficulties and errors which prevent him from
reaching the knowledge of truth, and he is overcome in fight who admits
a false opinion touching a matter of any generality and importance, and
he requires thereafter much more skill to recover his former position
than to make great advances when once in possession of thoroughly
ascertained principles.  As for myself, if I have succeeded in
discovering any truths in the sciences (and I trust that what is
contained in this volume I will show that I have found some), I can
declare that they are but the consequences and results of five or six
principal difficulties which I have surmounted, and my encounters with
which I reckoned as battles in which victory declared for me.  I will
not hesitate even to avow my belief that nothing further is wanting to
enable me fully to realize my designs than to gain two or three similar
victories; and that I am not so far advanced in years but that,
according to the ordinary course of nature, I may still have sufficient
leisure for this end.  But I conceive myself the more bound to husband
the time that remains the greater my expectation of being able to
employ it aright, and I should doubtless have much to rob me of it,
were I to publish the principles of my physics:  for although they are
almost all so evident that to assent to them no more is needed than
simply to understand them, and although there is not one of them of
which I do not expect to be able to give demonstration, yet, as it is
impossible that they can be in accordance with all the diverse opinions
of others, I foresee that I should frequently be turned aside from my
grand design, on occasion of the opposition which they would be sure to

It may be said, that these oppositions would be useful both in making
me aware of my errors, and, if my speculations contain anything of
value, in bringing others to a fuller understanding of it; and still
farther, as many can see better than one, in leading others who are now
beginning to avail themselves of my principles, to assist me in turn
with their discoveries.  But though I recognize my extreme liability to
error, and scarce ever trust to the first thoughts which occur to me,
yet-the experience I have had of possible objections to my views
prevents me from anticipating any profit from them.  For I have already
had frequent proof of the judgments, as well of those I esteemed
friends, as of some others to whom I thought I was an object of
indifference, and even of some whose malignancy and envy would, I knew,
determine them to endeavor to discover what partiality concealed from
the eyes of my friends.  But it has rarely happened that anything has
been objected to me which I had myself altogether overlooked, unless it
were something far removed from the subject:  so that I have never met
with a single critic of my opinions who did not appear to me either
less rigorous or less equitable than myself.  And further, I have never
observed that any truth before unknown has been brought to light by the
disputations that are practised in the schools; for while each strives
for the victory, each is much more occupied in making the best of mere
verisimilitude, than in weighing the reasons on both sides of the
question; and those who have been long good advocates are not
afterwards on that account the better judges.

As for the advantage that others would derive from the communication of
my thoughts, it could not be very great; because I have not yet so far
prosecuted them as that much does not remain to be added before they
can be applied to practice.  And I think I may say without vanity, that
if there is any one who can carry them out that length, it must be
myself rather than another:  not that there may not be in the world
many minds incomparably superior to mine, but because one cannot so
well seize a thing and make it one's own, when it has been learned from
another, as when one has himself discovered it.  And so true is this of
the present subject that, though I have often explained some of my
opinions to persons of much acuteness, who, whilst I was speaking,
appeared to understand them very distinctly, yet, when they repeated
them, I have observed that they almost always changed them to such an
extent that I could no longer acknowledge them as mine.  I am glad, by
the way, to take this opportunity of requesting posterity never to
believe on hearsay that anything has proceeded from me which has not
been published by myself; and I am not at all astonished at the
extravagances attributed to those ancient philosophers whose own
writings we do not possess; whose thoughts, however, I do not on that
account suppose to have been really absurd, seeing they were among the
ablest men of their times, but only that these have been falsely
represented to us.  It is observable, accordingly, that scarcely in a
single instance has any one of their disciples surpassed them; and I am
quite sure that the most devoted of the present followers of Aristotle
would think themselves happy if they had as much knowledge of nature as
he possessed, were it even under the condition that they should never
afterwards attain to higher.  In this respect they are like the ivy
which never strives to rise above the tree that sustains it, and which
frequently even returns downwards when it has reached the top; for it
seems to me that they also sink, in other words, render themselves less
wise than they would be if they gave up study, who, not contented with
knowing all that is intelligibly explained in their author, desire in
addition to find in him the solution of many difficulties of which he
says not a word, and never perhaps so much as thought.  Their fashion
of philosophizing, however, is well suited to persons whose abilities
fall below mediocrity; for the obscurity of the distinctions and
principles of which they make use enables them to speak of all things
with as much confidence as if they really knew them, and to defend all
that they say on any subject against the most subtle and skillful,
without its being possible for any one to convict them of error.  In
this they seem to me to be like a blind man, who, in order to fight on
equal terms with a person that sees, should have made him descend to
the bottom of an intensely dark cave:  and I may say that such persons
have an interest in my refraining from publishing the principles of the
philosophy of which I make use; for, since these are of a kind the
simplest and most evident, I should, by publishing them, do much the
same as if I were to throw open the windows, and allow the light of day
to enter the cave into which the combatants had descended.  But even
superior men have no reason for any great anxiety to know these
principles, for if what they desire is to be able to speak of all
things, and to acquire a reputation for learning, they will gain their
end more easily by remaining satisfied with the appearance of truth,
which can be found without much difficulty in all sorts of matters,
than by seeking the truth itself which unfolds itself but slowly and
that only in some departments, while it obliges us, when we have to
speak of others, freely to confess our ignorance.  If, however, they
prefer the knowledge of some few truths to the vanity of appearing
ignorant of none, as such knowledge is undoubtedly much to be
preferred, and, if they choose to follow a course similar to mine, they
do not require for this that I should say anything more than I have
already said in this discourse.  For if they are capable of making
greater advancement than I have made, they will much more be able of
themselves to discover all that I believe myself to have found; since
as I have never examined aught except in order, it is certain that what
yet remains to be discovered is in itself more difficult and recondite,
than that which I have already been enabled to find, and the
gratification would be much less in learning it from me than in
discovering it for themselves.  Besides this, the habit which they will
acquire, by seeking first what is easy, and then passing onward slowly
and step by step to the more difficult, will benefit them more than all
my instructions.  Thus, in my own case, I am persuaded that if I had
been taught from my youth all the truths of which I have since sought
out demonstrations, and had thus learned them without labour, I should
never, perhaps, have known any beyond these; at least, I should never
have acquired the habit and the facility which I think I possess in
always discovering new truths in proportion as I give myself to the
search.  And, in a single word, if there is any work in the world which
cannot be so well finished by another as by him who has commenced it,
it is that at which I labour.

It is true, indeed, as regards the experiments which may conduce to
this end, that one man is not equal to the task of making them all; but
yet he can advantageously avail himself, in this work, of no hands
besides his own, unless those of artisans, or parties of the same kind,
whom he could pay, and whom the hope of gain (a means of great
efficacy) might stimulate to accuracy in the performance of what was
prescribed to them.  For as to those who, through curiosity or a desire
of learning, of their own accord, perhaps, offer him their services,
besides that in general their promises exceed their performance, and
that they sketch out fine designs of which not one is ever realized,
they will, without doubt, expect to be compensated for their trouble by
the explication of some difficulties, or, at least, by compliments and
useless speeches, in which he cannot spend any portion of his time
without loss to himself.  And as for the experiments that others have
already made, even although these parties should be willing of
themselves to communicate them to him (which is what those who esteem
them secrets will never do), the experiments are, for the most part,
accompanied with so many circumstances and superfluous elements, as to
make it exceedingly difficult to disentangle the truth from its
adjuncts--besides, he will find almost all of them so ill described, or
even so false (because those who made them have wished to see in them
only such facts as they deemed conformable to their principles), that,
if in the entire number there should be some of a nature suited to his
purpose, still their value could not compensate for the time what would
be necessary to make the selection.  So that if there existed any one
whom we assuredly knew to be capable of making discoveries of the
highest kind, and of the greatest possible utility to the public; and
if all other men were therefore eager by all means to assist him in
successfully prosecuting his designs, I do not see that they could do
aught else for him beyond contributing to defray the expenses of the
experiments that might be necessary; and for the rest, prevent his
being deprived of his leisure by the unseasonable interruptions of any
one.  But besides that I neither have so high an opinion of myself as
to be willing to make promise of anything extraordinary, nor feed on
imaginations so vain as to fancy that the public must be much
interested in my designs; I do not, on the other hand, own a soul so
mean as to be capable of accepting from any one a favor of which it
could be supposed that I was unworthy.

These considerations taken together were the reason why, for the last
three years, I have been unwilling to publish the treatise I had on
hand, and why I even resolved to give publicity during my life to no
other that was so general, or by which the principles of my physics
might be understood.  But since then, two other reasons have come into
operation that have determined me here to subjoin some particular
specimens, and give the public some account of my doings and designs.
Of these considerations, the first is, that if I failed to do so, many
who were cognizant of my previous intention to publish some writings,
might have imagined that the reasons which induced me to refrain from
so doing, were less to my credit than they really are; for although I
am not immoderately desirous of glory, or even, if I may venture so to
say, although I am averse from it in so far as I deem it hostile to
repose which I hold in greater account than aught else, yet, at the
same time, I have never sought to conceal my actions as if they were
crimes, nor made use of many precautions that I might remain unknown;
and this partly because I should have thought such a course of conduct
a wrong against myself, and partly because it would have occasioned me
some sort of uneasiness which would again have been contrary to the
perfect mental tranquillity which I court.  And forasmuch as, while
thus indifferent to the thought alike of fame or of forgetfulness, I
have yet been unable to prevent myself from acquiring some sort of
reputation, I have thought it incumbent on me to do my best to save
myself at least from being ill-spoken of.  The other reason that has
determined me to commit to writing these specimens of philosophy is,
that I am becoming daily more and more alive to the delay which my
design of self-instruction suffers, for want of the infinity of
experiments I require, and which it is impossible for me to make
without the assistance of others:  and, without flattering myself so
much as to expect the public to take a large share in my interests, I
am yet unwilling to be found so far wanting in the duty I owe to
myself, as to give occasion to those who shall survive me to make it
matter of reproach against me some day, that I might have left them
many things in a much more perfect state than I have done, had I not
too much neglected to make them aware of the ways in which they could
have promoted the accomplishment of my designs.

And I thought that it was easy for me to select some matters which
should neither be obnoxious to much controversy, nor should compel me
to expound more of my principles than I desired, and which should yet
be sufficient clearly to exhibit what I can or cannot accomplish in the
sciences.  Whether or not I have succeeded in this it is not for me to
say; and I do not wish to forestall the judgments of others by speaking
myself of my writings; but it will gratify me if they be examined, and,
to afford the greater inducement to this I request all who may have any
objections to make to them, to take the trouble of forwarding these to
my publisher, who will give me notice of them, that I may endeavor to
subjoin at the same time my reply; and in this way readers seeing both
at once will more easily determine where the truth lies; for I do not
engage in any case to make prolix replies, but only with perfect
frankness to avow my errors if I am convinced of them, or if I cannot
perceive them, simply to state what I think is required for defense of
the matters I have written, adding thereto no explication of any new
matte that it may not be necessary to pass without end from one thing
to another.

If some of the matters of which I have spoken in the beginning of the
"Dioptrics" and "Meteorics" should offend at first sight, because I
call them hypotheses and seem indifferent about giving proof of them, I
request a patient and attentive reading of the whole, from which I hope
those hesitating will derive satisfaction; for it appears to me that
the reasonings are so mutually connected in these treatises, that, as
the last are demonstrated by the first which are their causes, the
first are in their turn demonstrated by the last which are their
effects.  Nor must it be imagined that I here commit the fallacy which
the logicians call a circle; for since experience renders the majority
of these effects most certain, the causes from which I deduce them do
not serve so much to establish their reality as to explain their
existence; but on the contrary, the reality of the causes is
established by the reality of the effects.  Nor have I called them
hypotheses with any other end in view except that it may be known that
I think I am able to deduce them from those first truths which I have
already expounded; and yet that I have expressly determined not to do
so, to prevent a certain class of minds from thence taking occasion to
build some extravagant philosophy upon what they may take to be my
principles, and my being blamed for it.  I refer to those who imagine
that they can master in a day all that another has taken twenty years
to think out, as soon as he has spoken two or three words to them on
the subject; or who are the more liable to error and the less capable
of perceiving truth in very proportion as they are more subtle and
lively.  As to the opinions which are truly and wholly mine, I offer no
apology for them as new,--persuaded as I am that if their reasons be
well considered they will be found to be so simple and so conformed, to
common sense as to appear less extraordinary and less paradoxical than
any others which can be held on the same subjects; nor do I even boast
of being the earliest discoverer of any of them, but only of having
adopted them, neither because they had nor because they had not been
held by others, but solely because reason has convinced me of their

Though artisans may not be able at once to execute the invention which
is explained in the "Dioptrics," I do not think that any one on that
account is entitled to condemn it; for since address and practice are
required in order so to make and adjust the machines described by me as
not to overlook the smallest particular, I should not be less
astonished if they succeeded on the first attempt than if a person were
in one day to become an accomplished performer on the guitar, by merely
having excellent sheets of music set up before him.  And if I write in
French, which is the language of my country, in preference to Latin,
which is that of my preceptors, it is because I expect that those who
make use of their unprejudiced natural reason will be better judges of
my opinions than those who give heed to the writings of the ancients
only; and as for those who unite good sense with habits of study, whom
alone I desire for judges, they will not, I feel assured, be so partial
to Latin as to refuse to listen to my reasonings merely because I
expound them in the vulgar tongue.

In conclusion, I am unwilling here to say anything very specific of the
progress which I expect to make for the future in the sciences, or to
bind myself to the public by any promise which I am not certain of
being able to fulfill; but this only will I say, that I have resolved
to devote what time I may still have to live to no other occupation
than that of endeavoring to acquire some knowledge of Nature, which
shall be of such a kind as to enable us therefrom to deduce rules in
medicine of greater certainty than those at present in use; and that my
inclination is so much opposed to all other pursuits, especially to
such as cannot be useful to some without being hurtful to others, that
if, by any circumstances, I had been constrained to engage in such, I
do not believe that I should have been able to succeed.  Of this I here
make a public declaration, though well aware that it cannot serve to
procure for me any consideration in the world, which, however, I do not
in the least affect; and I shall always hold myself more obliged to
those through whose favor I am permitted to enjoy my retirement without
interruption than to any who might offer me the highest earthly

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