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

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 believe.

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 poetry.

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 solution.

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 sequence.

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 arithmetic.

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 letters.

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 conceive.

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 intervene.

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 dreams.


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 vessel.

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 1 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 1 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 awaken.

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 truth.

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 preferments.


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