Discourse on the Method E-book

                                      1637
                            DISCOURSE ON THE METHOD
      OF RIGHTLY CONDUCTING THE REASON, AND SEEKING TRUTH IN THE SCIENCES

                               by Rene Descartes

                        translated by John Veitch, LL.D.






Electronically Enhanced Text (c) Copyright 1996, World Library(R)



                     PREFATORY NOTE BY THE AUTHOR
-
  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.


                                PART I
-
  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 fulness and
readiness of memory. And besides these, I know of no other qualities
that contribute to the perfection of the mind; for as to the reason or
sense, inasmuch as it is that alone which constitutes us men, and
distinguishes us from the brutes, I am disposed to believe that it
is to be found complete in each individual; and on this point to adopt
the common opinion of philosophers, who say that the difference of
greater and less holds only among the accidents, and not among the
forms or natures of individuals of the same species.
                                                       
  I will not hesitate, however, to avow my belief that it has been
my singular good fortune to have very early in life fallen in with
certain tracks which have conducted me to considerations and maxims,
of which I have formed a method that gives me the means, as I think,
of gradually augmenting my knowledge, and of raising it by little
and little to the highest point which the mediocrity of my talents and
the brief duration of my life will permit me to reach. For I have
already reaped from it such fruits that, although I have been
accustomed to think lowly enough of myself, and although when I look
with the eye of a philosopher at the varied courses and pursuits of
mankind at large, I find scarcely one which does not appear 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 favour. But I shall endeavour 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 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 endeavoured 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 favour 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 and 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 honours 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 travelling, 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
skilfully 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 honour 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 honour 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 travelling, 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.


                               PART II
-
  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 regularly 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 civilisation 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 past 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 counselled
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.
-
  * Literally, in a room heated by means of a stove.- Tr.
-
  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 leant upon principles which, in my youth, I had taken
upon trust. For although I recognised 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 one 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 on that account barbarians and
savages, but on the contrary that many of these nations make an
equally good, if not a 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 favour
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
judgment 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 unravelling 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, all
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 this 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 endeavour 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.


                               PART III
-
  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 judgment, 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 race 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 cognisance 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 realised 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 travellers 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 endeavour 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 respect of 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 favours heaped on them by nature and fortune,
if destitute of this philosophy, can never command the realisation
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 travelling 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 theatre 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 endeavoured 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 honourable, 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.
-
  * The "Discourse on Method" was originally published along with
the "Dioptrics," the "Meteorics," and the "Geometry."- Tr.
-
  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 rumoured 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 endeavour 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.
                                                    
-
  * Holland; to which country he withdrew in 1629.- Tr.


                               PART IV
-
  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 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 (cogito ergo sum), 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 recognised 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 recognise 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 recognised 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 centre, 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 themselves 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 odours, 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 unfrequently 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 unfrequently 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.


                                PART V
-
  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 learned, 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
comprise 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 coloured, 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 endeavoured 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 centre; 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 colours 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 vein, 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 * of England, who has the
honour 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 straitened, 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 neighbourhood 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.
-
  * Harvey- Lat. Tr.
-
                                                      
  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
neighbourhood 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 vapours, 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 humours 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, odours, 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 in 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 skill.
  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.


                               PART VI
-
  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.
-
  * Galileo.- Tr.
-
  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 endeavouring 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, and, 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 all 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 I 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
recognise as capable of being deduced in many 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 I 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 that 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 of
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 scrutinised 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 endeavours 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 * 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 realise 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.
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  * See Part III.
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  It may be said, that these oppositions would be useful both in
making me aware of my er