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

by Rene Descartes

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 1

Good sense is, of all things among men, the most equally distributed; for

every one thinks himself so abundantly provided with it, that those even

who are the most difficult to satisfy in everything else, do not usually

desire a larger measure of this quality than they already possess. And in

this it is not likely that all are mistaken the conviction is rather to be

held as testifying that the power of judging aright and of distinguishing

truth from error, which is properly what is called good sense or reason,

is by nature equal in all men; and that the diversity of our opinions,

consequently, does not arise from some being endowed with a larger share

of reason than others, but solely from this, that we conduct our thoughts

along different ways, and do not fix our attention on the same objects.

For to be possessed of a vigorous mind is not enough; the prime requisite

is rightly to apply it. The greatest minds, as they are capable of the

highest excellences, are open likewise to the greatest aberrations; and

those who travel very slowly may yet make far greater progress, provided

they keep always to the straight road, than those who, while they run,

forsake it.

For myself, I have never fancied my mind to be in any respect more perfect

than those of the generality; on the contrary, I have often wished that I

were equal to some others in promptitude of thought, or in clearness and

distinctness of imagination, or in fullness and readiness of memory. And

besides these, I know of no other qualities that contribute to the

perfection of the mind; for as to the reason or sense, inasmuch as it is

that alone which constitutes us men, and distinguishes us from the brutes,

I am disposed to believe that it is to be found complete in each

individual; and on this point to adopt the common opinion of philosophers,

who say that the difference of greater and less holds only among the

accidents, and not among the forms or natures of individuals of the same

species.

I will not hesitate, however, to avow my belief that it has been my

singular good fortune to have very early in life fallen in with certain

tracks which have conducted me to considerations and maxims, of which I

have formed a method that gives me the means, as I think, of gradually

augmenting my knowledge, and of raising it by little and little to the

highest point which the mediocrity of my talents and the brief duration of

my life will permit me to reach. For I have already reaped from it such

fruits that, although I have been accustomed to think lowly enough of

myself, and although when I look with the eye of a philosopher at the

varied courses and pursuits of mankind at large, I find scarcely one which

does not appear in vain and useless, I nevertheless derive the highest

satisfaction from the progress I conceive myself to have already made in

the search after truth, and cannot help entertaining such expectations of

the future as to believe that if, among the occupations of men as men, there

is any one really excellent and important, it is that which I have chosen.

After all, it is possible I may be mistaken; and it is but a little

copper and glass, perhaps, that I take for gold and diamonds. I know how

very liable we are to delusion in what relates to ourselves, and also how

much the judgments of our friends are to be suspected when given in our

favor. But I shall endeavor in this discourse to describe the paths I

have followed, and to delineate my life as in a picture, in order that

each one may also be able to judge of them for himself, and that in the

general opinion entertained of them, as gathered from current report, I

myself may have a new help towards instruction to be added to those I have

been in the habit of employing.

My present design, then, is not to teach the method which each ought to

follow for the right conduct of his reason, but solely to describe the way

in which I have endeavored to conduct my own. They who set themselves to

give precepts must of course regard themselves as possessed of greater skill

than those to whom they prescribe; and if they err in the slightest particular,

they subject themselves to censure. But as this tract is put forth merely

as a history, or, if you will, as a tale, in which, amid some examples worthy

of imitation, there will be found, perhaps, as many more which it were

advisable not to follow, I hope it will prove useful to some without being

hurtful to any, and that my openness will find some favor with all.

From my childhood, I have been familiar with letters; and as I was given

to believe that by their help a clear and certain knowledge of all that is

useful in life might be acquired, I was ardently desirous of instruction.

But as soon as I had finished the entire course of study, at the close of

which it is customary to be admitted into the order of the learned, I

completely changed my opinion. For I found myself involved in so many

doubts and errors, that I was convinced I had advanced no farther in all

my attempts at learning, than the discovery at every turn of my own

ignorance. And yet I was studying in one of the most celebrated schools in

Europe, in which I thought there must be learned men, if such were

anywhere to be found. I had been taught all that others learned there;

and not contented with the sciences actually taught us, I had, in

addition, read all the books that had fallen into my hands, treating of

such branches as are esteemed the most curious and rare. I knew the

judgment which others had formed of me; and I did not find that I was

considered inferior to my fellows, although there were among them some who

were already marked out to fill the places of our instructors. And, in

fine, our age appeared to me as flourishing, and as fertile in powerful

minds as any preceding one. I was thus led to take the liberty of judging

of all other men by myself, and of concluding that there was no science in

existence that was of such a nature as I had previously been given to believe.

I still continued, however, to hold in esteem the studies of the schools.

I was aware that the languages taught in them are necessary to the

understanding of the writings of the ancients; that the grace of fable

stirs the mind; that the memorable deeds of history elevate it; and, if

read with discretion, aid in forming the judgment; that the perusal of all

excellent books is, as it were, to interview with the noblest men of past

ages, who have written them, and even a studied interview, in which are

discovered to us only their choicest thoughts; that eloquence has

incomparable force and beauty; that poesy has its ravishing graces and

delights; that in the mathematics there are many refined discoveries

eminently suited to gratify the inquisitive, as well as further all the

arts an lessen the labour of man; that numerous highly useful precepts and

exhortations to virtue are contained in treatises on morals; that theology

points out the path to heaven; that philosophy affords the means of

discoursing with an appearance of truth on all matters, and commands the

admiration of the more simple; that jurisprudence, medicine, and the other

sciences, secure for their cultivators honors and riches; and, in fine,

that it is useful to bestow some attention upon all, even upon those

abounding the most in superstition and error, that we may be in a position

to determine their real value, and guard against being deceived.

But I believed that I had already given sufficient time to languages, and

likewise to the reading of the writings of the ancients, to their

histories and fables. For to hold converse with those of other ages and

to travel, are almost the same thing. It is useful to know something of

the manners of different nations, that we may be enabled to form a more

correct judgment regarding our own, and be prevented from thinking that

everything contrary to our customs is ridiculous and irrational, a

conclusion usually come to by those whose experience has been limited to

their own country. On the other hand, when too much time is occupied in

traveling, we become strangers to our native country; and the over

curious in the customs of the past are generally ignorant of those of the

present. Besides, fictitious narratives lead us to imagine the possibility

of many events that are impossible; and even the most faithful histories,

if they do not wholly misrepresent matters, or exaggerate their importance

to render the account of them more worthy of perusal, omit, at least, almost

always the meanest and least striking of the attendant circumstances; hence

it happens that the remainder does not represent the truth, and that such as

regulate their conduct by examples drawn from this source, are apt to fall

into the extravagances of the knight-errants of romance, and to entertain

projects that exceed their powers.

I esteemed eloquence highly, and was in raptures with poesy; but I thought

that both were gifts of nature rather than fruits of study. Those in whom

the faculty of reason is predominant, and who most skillfully dispose their

thoughts with a view to render them clear and intelligible, are always the

best able to persuade others of the truth of what they lay down, though

they should speak only in the language of Lower Brittany, and be wholly

ignorant of the rules of rhetoric; and those whose minds are stored with

the most agreeable fancies, and who can give expression to them with the

greatest embellishment and harmony, are still the best poets, though

unacquainted with the art of poetry.

I was especially delighted with the mathematics, on account of the

certitude and evidence of their reasonings; but I had not as yet a

precise knowledge of their true use; and thinking that they but

contributed to the advancement of the mechanical arts, I was astonished

that foundations, so strong and solid, should have had no loftier

superstructure reared on them. On the other hand, I compared the

disquisitions of the ancient moralists to very towering and magnificent

palaces with no better foundation than sand and mud: they laud the virtues

very highly, and exhibit them as estimable far above anything on earth;

but they give us no adequate criterion of virtue, and frequently that

which they designate with so fine a name is but apathy, or pride,

or despair, or parricide.

I revered our theology, and aspired as much as any one to reach heaven:

but being given assuredly to understand that the way is not less open to

the most ignorant than to the most learned, and that the revealed truths

which lead to heaven are above our comprehension, I did not presume to

subject them to the impotency of my reason; and I thought that in order

competently to undertake their examination, there was need of some special

help from heaven, and of being more than man.

Of philosophy I will say nothing, except that when I saw that it had been

cultivated for many ages by the most distinguished men, and that yet there

is not a single matter within its sphere which is not still in dispute,

and nothing, therefore, which is above doubt, I did not presume to

anticipate that my success would be greater in it than that of others; and

further, when I considered the number of conflicting opinions touching a

single matter that may be upheld by learned men, while there can be but

one true, I reckoned as well-nigh false all that was only probable.

As to the other sciences, inasmuch as these borrow their principles from

philosophy, I judged that no solid superstructures could be reared on

foundations so infirm; and neither the honor nor the gain held out by them

was sufficient to determine me to their cultivation: for I was not, thank

Heaven, in a condition which compelled me to make merchandise of science

for the bettering of my fortune; and though I might not profess to scorn

glory as a cynic, I yet made very slight account of that honor which I

hoped to acquire only through fictitious titles. And, in fine, of false

sciences I thought I knew the worth sufficiently to escape being deceived

by the professions of an alchemist, the predictions of an astrologer, the

impostures of a magician, or by the artifices and boasting of any of those

who profess to know things of which they are ignorant.

For these reasons, as soon as my age permitted me to pass from under the

control of my instructors, I entire y abandoned the study of letters, and

resolved no longer to seek any other science than the knowledge of myself,

or of the great book of the world. I spent the remainder of my youth in

traveling, in visiting courts and armies, in holding intercourse with men

of different dispositions and ranks, in collecting varied experience, in

proving myself in the different situations into which fortune threw me,

and, above all, in making such reflection on the matter of my experience

as to secure my improvement. For it occurred to me that I should find

much more truth in the reasonings of each individual with reference to the

affairs in which he is personally interested, and the issue of which must

presently punish him if he has judged amiss, than in those conducted by a

man of letters in his study, regarding speculative matters that are of no

practical moment, and followed by no consequences to himself, farther,

perhaps, than that they foster his vanity the better the more remote they

are from common sense; requiring, as they must in this case, the exercise

of greater ingenuity and art to render them probable. In addition, I had

always a most earnest desire to know how to distinguish the true from the

false, in order that I might be able clearly to discriminate the right

path in life, and proceed in it with confidence.

It is true that, while busied only in considering the manners of other

men, I found here, too, scarce any ground for settled conviction, and

remarked hardly less contradiction among them than in the opinions of the

philosophers. So that the greatest advantage I derived from the study

consisted in this, that, observing many things which, however extravagant

and ridiculous to our apprehension, are yet by common consent received and

approved by other great nations, I learned to entertain too decided a

belief in regard to nothing of the truth of which I had been persuaded

merely by example and custom; and thus I gradually extricated myself from

many errors powerful enough to darken our natural intelligence, and

incapacitate us in great measure from listening to reason. But after I had

been occupied several years in thus studying the book of the world, and in

essaying to gather some experience, I at length resolved to make myself an

object of study, and to employ all the powers of my mind in choosing the

paths I ought to follow, an undertaking which was accompanied with greater

success than it would have been had I never quitted my country or my books.

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 regularity constructed towns which a

professional architect has freely planned on an open plain; so that

although the several buildings of the former may often equal or surpass in

beauty those of the latter, yet when one observes their indiscriminate

juxtaposition, there a large one and here a small, and the consequent

crookedness and irregularity of the streets, one is disposed to allege

that chance rather than any human will guided by reason must have led to

such an arrangement. And if we consider that nevertheless there have been

at all times certain officers whose duty it was to see that private

buildings contributed to public ornament, the difficulty of reaching high

perfection with but the materials of others to operate on, will be readily

acknowledged. In the same way I fancied that those nations which, starting

from a semi-barbarous state and advancing to civilization by slow degrees,

have had their laws successively determined, and, as it were, forced upon

them simply by experience of the hurtfulness of particular crimes and

disputes, would by this process come to be possessed of less perfect

institutions than those which, from the commencement of their association

as communities, have followed the appointments of some wise legislator. It

is thus quite certain that the constitution of the true religion, the

ordinances of which are derived from God, must be incomparably superior to

that of every other. And, to speak of human affairs, I believe that the

pre-eminence of Sparta was due not to the goodness of each of its laws in

particular, for many of these were very strange, and even opposed to good

morals, but to the circumstance that, originated by a single individual,

they all tended to a single end. In the same way I thought that the

sciences contained in books (such of them at least as are made up of

probable reasonings, without demonstrations), composed as they are of the

opinions of many different individuals massed together, are farther

removed from truth than the simple inferences which a man of good sense

using his natural and unprejudiced judgment draws respecting the matters

of his experience. And because we have all to pass through a state of

infancy to manhood, and have been of necessity, for a length of time,

governed by our desires and preceptors (whose dictates were frequently

conflicting, while neither perhaps always counseled us for the best), I

farther concluded that it is almost impossible that our judgments can be

so correct or solid as they would have been, had our reason been mature

from the moment of our birth, and had we always been guided by it alone.

It is true, however, that it is not customary to pull down all the houses

of a town with the single design of rebuilding them differently, and

thereby rendering the streets more handsome; but it often happens that a

private individual takes down his own with the view of erecting it anew,

and that people are even sometimes constrained to this when their houses

are in danger of falling from age, or when the foundations are insecure.

With this before me by way of example, I was persuaded that it would

indeed be preposterous for a private individual to think of reforming a

state by fundamentally changing it throughout, and overturning it in order

to set it up amended; and the same I thought was true of any similar

project for reforming the body of the sciences, or the order of teaching

them established in the schools: but as for the opinions which up to that

time I had embraced, I thought that I could not do better than resolve at

once to sweep them wholly away, that I might afterwards be in a position

to admit either others more correct, or even perhaps the same when they

had undergone the scrutiny of reason. I firmly believed that in this way I

should much better succeed in the conduct of my life, than if I built only

upon old foundations, and leaned upon principles which, in my youth, I had

taken upon trust. For although I recognized various difficulties in this

undertaking, these were not, however, without remedy, nor once to be

compared with such as attend the slightest reformation in public affairs.

Large bodies, if once overthrown, are with great difficulty set up again,

or even kept erect when once seriously shaken, and the fall of such is

always disastrous. Then if there are any imperfections in the

constitutions of states (and that many such exist the diversity of

constitutions is alone sufficient to assure us), custom has without doubt

materially smoothed their inconveniences, and has even managed to steer

altogether clear of, or insensibly corrected a number which sagacity could

not have provided against with equal effect; and, in fine, the defects are

almost always more tolerable than the change necessary for their removal;

in the same manner that highways which wind among mountains, by being much

frequented, become gradually so smooth and commodious, that it is much

better to follow them than to seek a straighter path by climbing over the

tops of rocks and descending to the bottoms of precipices.

Hence it is that I cannot in any degree approve of those restless and busy

meddlers who, called neither by birth nor fortune to take part in the

management of public affairs, are yet always projecting reforms; and if I

thought that this tract contained aught which might justify the suspicion

that I was a victim of such folly, I would by no means permit its

publication. I have never contemplated anything higher than the

reformation of my own opinions, and basing them on a foundation wholly my

own. And although my own satisfaction with my work has led me to present

here a draft of it, I do not by any means therefore recommend to every one

else to make a similar attempt. Those whom God has endowed with a larger

measure of genius will entertain, perhaps, designs still more exalted; but

for the many I am much afraid lest even the present undertaking be more

than they can safely venture to imitate. The single design to strip one's

self of all past beliefs is one that ought not to be taken by every one.

The majority of men is composed of two classes, for neither of which would

this be at all a befitting resolution: in the first place, of those who

with more than a due confidence in their own powers, are precipitate in

their judgments and want the patience requisite for orderly and

circumspect thinking; whence it happens, that if men of this class once

take the liberty to doubt of their accustomed opinions, and quit the

beaten highway, they will never be able to thread the byway that would

lead them by a shorter course, and will lose themselves and continue to

wander for life; in the second place, of those who, possessed of

sufficient sense or modesty to determine that there are others who excel

them in the power of discriminating between truth and error, and by whom

they may be instructed, ought rather to content themselves with the

opinions of such than trust for more correct to their own reason.

For my own part, I should doubtless have belonged to the latter class, had

I received instruction from but one master, or had I never known the

diversities of opinion that from time immemorial have prevailed among men

of the greatest learning. But I had become aware, even so early as during

my college life, that no opinion, however absurd and incredible, can be

imagined, which has not been maintained by some on of the philosophers;

and afterwards in the course of my travels I remarked that all those whose

opinions are decidedly repugnant to ours are not in that account

barbarians and savages, but on the contrary that many of these nations

make an equally good, if not better, use of their reason than we do. I

took into account also the very different character which a person brought

up from infancy in France or Germany exhibits, from that which, with the

same mind originally, this individual would have possessed had he lived

always among the Chinese or with savages, and the circumstance that in

dress itself the fashion which pleased us ten years ago, and which may

again, perhaps, be received into favor before ten years have gone,

appears to us at this moment extravagant and ridiculous. I was thus led

to infer that the ground of our opinions is far more custom and example

than any certain knowledge. And, finally, although such be the ground of

our opinions, I remarked that a plurality of suffrages is no guarantee of

truth where it is at all of difficult discovery, as in such cases it is

much more likely that it will be found by one than by many. I could,

however, select from the crowd no one whose opinions seemed worthy of

preference, and thus I found myself constrained, as it were, to use my own

reason in the conduct of my life.

But like one walking alone and in the dark, I resolved to proceed so

slowly and with such circumspection, that if I did not advance far, I

would at least guard against falling. I did not even choose to dismiss

summarily any of the opinions that had crept into my belief without having

been introduced by reason, but first of all took sufficient time carefully

to satisfy myself of the general nature of the task I was setting myself,

and ascertain the true method by which to arrive at the knowledge of

whatever lay within the compass of my powers.

Among the branches of philosophy, I had, at an earlier period, given some

attention to logic, and among those of the mathematics to geometrical

analysis and algebra, -- three arts or sciences which ought, as I

conceived, to contribute something to my design. But, on examination, I

found that, as for logic, its syllogisms and the majority of its other

precepts are of avail- rather in the communication of what we already

know, or even as the art of Lully, in speaking without judgment of things

of which we are ignorant, than in the investigation of the unknown; and

although this science contains indeed a number of correct and very

excellent precepts, there are, nevertheless, so many others, and these

either injurious or superfluous, mingled with the former, that it is

almost quite as difficult to effect a severance of the true from the false

as it is to extract a Diana or a Minerva from a rough block of marble.

Then as to the analysis of the ancients and the algebra of the moderns,

besides that they embrace only matters highly abstract, and, to

appearance, of no use, the former is so exclusively restricted to the

consideration of figures, that it can exercise the understanding only on

condition of greatly fatiguing the imagination; and, in the latter, there

is so complete a subjection to certain rules and formulas, that there

results an art full of confusion and obscurity calculated to embarrass,

instead of a science fitted to cultivate the mind. By these considerations

I was induced to seek some other method which would comprise the

advantages of the three and be exempt from their defects. And as a

multitude of laws often only hampers justice, so that a state is best

governed when, with few laws, these are rigidly administered; in like

manner, instead of the great number of precepts of which logic is

composed, I believed that the four following would prove perfectly

sufficient for me, provided I took the firm and unwavering resolution

never in a single instance to fail in observing them.

The first was never to accept anything for true which I did not clearly know

to be such; that is to say, carefully to avoid precipitancy and prejudice,

and to comprise nothing more in my judgement than what was presented to

my mind so clearly and distinctly as to exclude all ground of doubt.

The second, to divide each of the difficulties under examination into as many

parts as possible, and as might be necessary for its adequate solution.

The third, to conduct my thoughts in such order that, by commencing with

objects the simplest and easiest to know, I might ascend by little and

little, and, as it were, step by step, to the knowledge of the more complex;

assigning in thought a certain order even to those objects which in their

own nature do not stand in a relation of antecedence and sequence.

And the last, in every case to make enumerations so complete, and reviews

so general, that I might be assured that nothing was omitted.

The long chains of simple and easy reasonings by means of which

geometers are accustomed to reach the conclusions of their most

difficult demonstrations, had led me to imagine that all things,

to the knowledge of which man is competent, are mutually connected

in the same way, and that there is nothing so far removed from us

as to be beyond our reach, or so hidden that we cannot discover it,

provided only we abstain from accepting the false for the true, and

always preserve in our thoughts the order necessary for the deduction

of one truth from another. And I had little difficulty in determining

the objects with which it was necessary to commence, for I was already

persuaded that it must be with the simplest and easiest to know, and,

considering that of all those who have hitherto sought truth in the sciences,

the mathematicians alone have been able to find any demonstrations, that is,

any certain and evident reasons, I did not doubt but that such must have been

the rule of their investigations. I resolved to commence, therefore, with the

examination of the simplest objects, not anticipating, however, from this any

other advantage than that to be found in accustoming my mind to the love and

nourishment of truth, and to a distaste for all such reasonings as were

unsound. But I had no intention on that account of attempting to master all

the particular sciences commonly denominated mathematics: but observing that,

however different their objects, they all agree in considering only the

various relations or proportions subsisting among those objects, I thought

it best for my purpose to consider these proportions in the most general

form possible, without referring them to any objects in particular, except

such as would most facilitate the knowledge of them, and without by any

means restricting them to these, that afterwards I might thus be the

better able to apply them to every other class of objects to which they

are legitimately applicable. Perceiving further, that in order to

understand these relations I should sometimes have to consider them one by

one and sometimes only to bear them in mind, or embrace them in the

aggregate, I thought that, in order the better to consider them

individually, I should view them as subsisting between straight lines,

than which I could find no objects more simple, or capable of being more

distinctly represented to my imagination and senses; and on the other

hand, that in order to retain them in the memory or embrace an aggregate

of many, I should express them by certain characters the briefest

possible. In this way I believed that I could borrow all that was best

both in geometrical analysis and in algebra, and correct all the defects

of the one by help of the other.

And, in point of fact, the accurate observance of these few precepts gave me,

I take the liberty of saying, such ease in unraveling all the questions

embraced in these two sciences, that in the two or three months

I devoted to their examination, not only did I reach solutions of

questions I had formerly deemed exceedingly difficult but even as regards

questions of the solution of which I continued ignorant, I was enabled, as

it appeared to me, to determine the means whereby, and the extent to which

a solution was possible; results attributable to the circumstance that I

commenced with the simplest and most general truths, and that thus each

truth discovered was a rule available in the discovery of subsequent ones

Nor in this perhaps shall I appear too vain, if it be considered that, as

the truth on any particular point is one whoever apprehends the truth,

knows all that on that point can be known. The child, for example, who

has been instructed in the elements of arithmetic, and has made a

particular addition, according to rule, may be assured that he has found,

with respect to the sum of the numbers before him, and that in this

instance is within the reach of human genius. Now, in conclusion, the

method which teaches adherence to the true order, and an exact enumeration

of all the conditions of the thing .sought includes all that gives

certitude to the rules of arithmetic.

But the chief ground of my satisfaction with thus method, was the

assurance I had of thereby exercising my reason in all matters, if not

with absolute perfection, at least with the greatest attainable by me:

besides, I was conscious that by its use my mind was becoming gradually

habituated to clearer and more distinct conceptions of its objects; and I

hoped also, from not having restricted this method to any particular

matter, to apply it to the difficulties of the other sciences, with not

less success than to those of algebra. I should not, however, on this

account have ventured at once on the examination of all the difficulties

of the sciences which presented themselves to me, for this would have been

contrary to the order prescribed in the method, but observing that the

knowledge of such is dependent on principles borrowed from philosophy, in

which I found nothing certain, I thought it necessary first of all to

endeavor to establish its principles. .And because I observed, besides,

that an inquiry of this kind was of all others of the greatest moment, and

one in which precipitancy and anticipation in judgment were most to be

dreaded, I thought that I ought not to approach it till I had reached a

more mature age (being at that time but twenty-three), and had first of

all employed much of my time in preparation for the work, as well by

eradicating from my mind all the erroneous opinions I had up to that

moment accepted, as by amassing variety of experience to afford materials

for my reasonings, and by continually exercising myself in my chosen

method with a view to increased skill in its application.

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 judgement, and

that I might not be prevented from living thenceforward in the greatest

possible felicity, I formed a provisory code of morals, composed of three

or four maxims, with which I am desirous to make you acquainted.

The first was to obey the laws and customs of my country, adhering firmly

to the faith in which, by the grace of God, I had been educated from my

childhood and regulating my conduct in every other matter according to the

most moderate opinions, and the farthest removed from extremes, which

should happen to be adopted in practice with general consent of the most

judicious of those among whom I might be living. For as I had from that

time begun to hold my own opinions for nought because I wished to subject

them all to examination, I was convinced that I could not do better than

follow in the meantime the opinions of the most judicious; and although

there are some perhaps among the Persians and Chinese as judicious as

among ourselves, expediency seemed to dictate that I should regulate my

practice conformably to the opinions of those with whom I should have to

live; and it appeared to me that, in order to ascertain the real opinions

of such, I ought rather to take cognizance of what they practised than of

what they said, not only because, in the corruption of our manners, there

are few disposed to speak exactly as they believe, but also because very

many are not aware of what it is that they really believe; for, as the act

of mind by which a thing is believed is different from that by which we

know that we believe it, the one act is often found without the other.

Also, amid many opinions held in equal repute, I chose always the most

moderate, as much for the reason that these are always the most convenient

for practice, and probably the best (for all excess is generally vicious),

as that, in the event of my falling into error, I might be at less

distance from the truth than if, having chosen one of the extremes, it

should turn out to be the other which I ought to have adopted. And I

placed in the class of extremes especially all promises by which somewhat

of our freedom is abridged; not that I disapproved of the laws which, to

provide against the instability of men of feeble resolution, when what is

sought to be accomplished is some good, permit engagements by vows and

contracts binding the parties to persevere in it, or even, for the

security of commerce, sanction similar engagements where the purpose

sought to be realized is indifferent: but because I did not find anything

on earth which was wholly superior to change, and because, for myself in

particular, I hoped gradually to perfect my judgments, and not to suffer

them to deteriorate, I would have deemed it a grave sin against good

sense, if, for the reason that I approved of something at a particular

time, I therefore bound myself to hold it for good at a subsequent time,

when perhaps it had ceased to be so, or I had ceased to esteem it such.

My second maxim was to be as firm and resolute in my actions as I was

able, and not to adhere less steadfastly to the most doubtful opinions,

when once adopted, than if they had been highly certain; imitating in this

the example of travelers who, when they have lost their way in a forest,

ought not to wander from side to side, far less remain in one place, but

proceed constantly towards the same side in as straight a line as

possible, without changing their direction for slight reasons, although

perhaps it might be chance alone which at first determined the selection;

for in this way, if they do not exactly reach the point they desire, they

will come at least in the end to some place that will probably be

preferable to the middle of a forest. In the same way, since in action it

frequently happens that no delay is permissible, it is very certain that,

when it is not in our power to determine what is true, we ought to act

according to what is most probable; and even although we should not remark

a greater probability in one opinion than in another, we ought

notwithstanding to choose one or the other, and afterwards consider it, in

so far as it relates to practice, as no longer dubious, but manifestly

true and certain, since the reason by which our choice has been

determined is itself possessed of these qualities. This principle was

sufficient thenceforward to rid me of all those repentings and pangs of

remorse that usually disturb the consciences of such feeble and uncertain

minds as, destitute of any clear and determinate principle of choice,

allow themselves one day to adopt a course of action as the best, which

they abandon the next, as the opposite.

My third maxim was to endeavor always to conquer myself rather than

fortune, and change my desires rather than the order of the world, and in

general, accustom myself to the persuasion that, except our own thoughts,

there is nothing absolutely in our power; so that when we have done our

best in things external to us, all wherein we fail of success is to be

held, as regards us, absolutely impossible: and this single principle

seemed to me sufficient to prevent me from desiring for the future

anything which I could not obtain, and thus render me contented; for since

our will naturally seeks those objects alone which the understanding

represents as in some way possible of attainment, it is plain, that if we

consider all external goods as equally beyond our power, we shall no more

regret the absence of such goods as seem due to our birth, when deprived

of them without any fault of ours, than our not possessing the kingdoms

of China or Mexico, and thus making, so to speak, a virtue of necessity,

we shall no more desire health in disease, or freedom in imprisonment,

than we now do bodies incorruptible as diamonds, or the wings of birds to

fly with. But I confess there is need of prolonged discipline and

frequently repeated meditation to accustom the mind to view all objects in

this light; and I believe that in this chiefly consisted the secret of the

power of such philosophers as in former times were enabled to rise

superior to the influence of fortune, and, amid suffering and poverty,

enjoy a happiness which their gods might have envied. For, occupied

incessantly with the consideration of the limits prescribed to their power

by nature, they became so entirely convinced that nothing was at their

disposal except their own thoughts, that this conviction was of itself

sufficient to prevent their entertaining any desire of other objects; and

over their thoughts they acquired a sway so absolute, that they had some

ground on this account for esteeming themselves more rich and more

powerful, more free and more happy, than other men who, whatever be the

favors heaped on them by nature and fortune, if destitute of this

philosophy, can never command the realization of all their desires.

In fine, to conclude this code of morals, I thought of reviewing the

different occupations of men in this life, with the view of making choice

of the best. And, without wishing to offer any remarks on the employments

of others, I may state that it was my conviction that I could not do

better than continue in that in which I was engaged, viz., in devoting my

whole life to the culture of my reason, and in making the greatest

progress I was able in the knowledge of truth, on the principles of the

method which I had prescribed to myself. This method, from the time I had

begun to apply it, had been to me the source of satisfaction so intense as

to lead me to, believe that more perfect or more innocent could not be

enjoyed in this life; and as by its means I daily discovered truths that

appeared to me of some importance, and of which other men were generally

ignorant, the gratification thence arising so occupied my mind that I was

wholly indifferent to every other object. Besides, the three preceding

maxims were founded singly on the design of continuing the work of self-

instruction. For since God has endowed each of us with some light of

reason by which to distinguish truth from error, I could not have believed

that I ought for a single moment to rest satisfied with the opinions of

another, unless I had resolved to exercise my own judgment in examining

these whenever I should be duly qualified for the task. Nor could I have

proceeded on such opinions without scruple, had I supposed that I should

thereby forfeit any advantage for attaining still more accurate, should

such exist. And, in fine, I could not have restrained my desires, nor

remained satisfied had I not followed a path in which I thought myself

certain of attaining all the knowledge to the acquisition of which I was

competent, as well as the largest amount of what is truly good which I

could ever hope to secure Inasmuch as we neither seek nor shun any object

except in so far as our understanding represents it as good or bad, all

that is necessary to right action is right judgment, and to the best

action the most correct judgment, that is, to the acquisition of all the

virtues with all else that is truly valuable and within our reach; and the

assurance of such an acquisition cannot fail to render us contented.

Having thus provided myself with these maxims, and having placed them in

reserve along with the truths of faith, which have ever occupied the

first place in my belief, I came to the conclusion that I might with

freedom set about ridding myself of what remained of my opinions. And,

inasmuch as I hoped to be better able successfully to accomplish this work

by holding intercourse with mankind, than by remaining longer shut up in

the retirement where these thoughts had occurred to me, I betook me again

to traveling before the winter was well ended. And, during the nine

subsequent years, I did nothing but roam from one place to another,

desirous of being a spectator rather than an actor in the plays exhibited

on the theater of the world; and, as I made it my business in each matter

to reflect particularly upon what might fairly be doubted and prove a

source of error, I gradually rooted out from my mind all the errors which

had hitherto crept into it. Not that in this I imitated the sceptics who

doubt only that they may doubt, and seek nothing beyond uncertainty

itself; for, on the contrary, my design was singly to find ground of

assurance, and cast aside the loose earth and sand, that I might reach

the rock or the clay. In this, as appears to me, I was successful enough;

for, since I endeavored to discover the falsehood or incertitude of the

propositions I examined, not by feeble conjectures, but by clear and

certain reasonings, I met with nothing so doubtful as not to yield some

conclusion of adequate certainty, although this were merely the inference,

that the matter in question contained nothing certain. And, just as in

pulling down an old house, we usually reserve the ruins to contribute

towards the erection, so, in destroying such of my opinions as I judged to

be Ill-founded, I made a variety of observations and acquired an amount of

experience of which I availed myself in the establishment of more certain.

And further, I continued to exercise myself in the method I had

prescribed; for, besides taking care in general to conduct all my thoughts

according to its rules, I reserved some hours from time to time which I

expressly devoted to the employment of the method in the solution of

mathematical difficulties, or even in the solution likewise of some

questions belonging to other sciences, but which, by my having detached

them from such principles of these sciences as were of inadequate

certainty, were rendered almost mathematical: the truth of this will be

manifest from the numerous examples contained in this volume. And thus,

without in appearance living otherwise than those who, with no other

occupation than that of spending their lives agreeably and innocently,

study to sever pleasure from vice, and who, that they may enjoy their

leisure without ennui, have recourse to such pursuits as are honorable, I

was nevertheless prosecuting my design, and making greater progress in the

knowledge of truth, than I might, perhaps, have made had I been engaged in

the perusal of books merely, or in holding converse with men of letters.

These nine years passed away, however, before I had come to any

determinate judgment respecting the difficulties which form matter of

dispute among the learned, or had commenced to seek the principles of any

philosophy more certain than the vulgar. And the examples of many men of

the highest genius, who had, in former times, engaged in this inquiry,

but, as appeared to me, without success, led me to imagine it to be a work

of so much difficulty, that I would not perhaps have ventured on it so

soon had I not heard it currently rumored that I had already completed

the inquiry. I know not what were the grounds of this opinion; and, if my

conversation contributed in any measure to its rise, this must have

happened rather from my having confessed my Ignorance with greater freedom

than those are accustomed to do who have studied a little, and expounded

perhaps, the reasons that led me to doubt of many of those things that by

others are esteemed certain, than from my having boasted of any system of

philosophy. But, as I am of a disposition that makes me unwilling to be

esteemed different from what I really am, I thought it necessary to

endeavor by all means to render myself worthy of the reputation accorded

to me; and it is now exactly eight years since this desire constrained me

to remove from all those places where interruption from any of my

acquaintances was possible, and betake myself to this country, in which

the long duration of the war has led to the establishment of such

discipline, that the armies maintained seem to be of use only in enabling

the inhabitants to enjoy more securely the blessings of peace and where,

in the midst of a great crowd actively engaged in business, and more

careful of their own affairs than curious about those of others, I have

been enabled to live without being deprived of any of the conveniences to

be had in the most populous cities, and yet as solitary and as retired as

in the midst of the most remote deserts.

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 I to the truth and

certainty of a proposition; for since I had discovered one which I knew to

be true, I thought that I must likewise be able to discover the ground of

this certitude. And as I observed that in the words I think, therefore I

am, there is nothing at all which gives me assurance of their truth beyond

this, that I see very clearly that in order to think it is necessary to

exist, I concluded that I might take, as a general rule, the principle,

that all the things which we very clearly and distinctly conceive are

true, only observing, however, that there is some difficulty in rightly

determining the objects which we distinctly conceive.

In the next place, from reflecting on the circumstance that I doubted, and

that consequently my being was not wholly perfect (for I clearly saw that

it was a greater perfection to know than to doubt), I was led to inquire

whence I had learned to think of something more perfect than myself; and I

clearly recognized that I must hold this notion from some nature which in

reality was more perfect. As for the thoughts of many other objects

external to me, as of the sky, the earth, light, heat, and a thousand

more, I was less at a loss to know whence these came; for since I remarked

in them nothing which seemed to render them superior to myself, I could

believe that, if these were true, they were dependencies on my own nature,

in so far as it possessed a certain perfection, and, if they were false,

that I held them from nothing, that is to say, that they were in me

because of a certain imperfection of my nature. But this could not be the

case with-the idea of a nature more perfect than myself; for to receive it

from nothing was a thing manifestly impossible; and, because it is not

less repugnant that the more perfect should be an effect of, and

dependence on the less perfect, than that something should proceed from

nothing, it was equally impossible that I could hold it from myself:

accordingly, it but remained that it had been placed in me by a nature

which was in reality more perfect than mine, and which even possessed

within itself all the perfections of which I could form any idea; that is

to say, in a single word, which was God. And to this I added that, since I

knew some perfections which I did not possess, I was not the only being in

existence (I will here, with your permission, freely use the terms of the

schools); but, on the contrary, that there was of necessity some other

more perfect Being upon whom I was dependent, and from whom I had received

all that I possessed; for if I had existed alone, and independently of

every other being, so as to have had from myself all the perfection,

however little, which I actually possessed, I should have been able, for

the same reason, to have had from myself the whole remainder of

perfection, of the want of which I was conscious, and thus could of myself

have become infinite, eternal, immutable, omniscient, all-powerful, and,

in fine, have possessed all the perfections which I could recognize in

God. For in order to know the nature of God (whose existence has been

established by the preceding reasonings), as far as my own nature

permitted, I had only to consider in reference to all the properties of

which I found in my mind some idea, whether their possession was a mark

of perfection; and I was assured that no one which indicated any

imperfection was in him, and that none of the rest was awanting. Thus I

perceived that doubt, inconstancy, sadness, and such like, could not be

found in God, since I myself would have been happy to be free from them.

Besides, I had ideas of many sensible and corporeal things; for although I

might suppose that I was dreaming, and that all which I saw or imagined

was false, I could not, nevertheless, deny that the ideas were in reality

in my thoughts. But, because I had already very clearly recognized in

myself that the intelligent nature is distinct from the corporeal, and as

I observed that all composition is an evidence of dependency, and that a

state of dependency is manifestly a state of imperfection, I therefore

determined that it could not be a perfection in God to be compounded of

these two natures and that consequently he was not so compounded; but that

if there were any bodies in the world, or even any intelligences, or other

natures that were not wholly perfect, their existence depended on his power

in such a way that they could not subsist without him for a single moment.

I was disposed straightway to search for other truths and when I had

represented to myself the object of the geometers, which I conceived to be

a continuous body or a space indefinitely extended in length, breadth, and

height or depth, divisible into divers parts which admit of different

figures and sizes, and of being moved or transposed in all manner of ways

(for all this the geometers suppose to be in the object they contemplate),

I went over some of their simplest demonstrations. And, in the first

place, I observed, that the great certitude which by common consent is

accorded to these demonstrations, is founded solely upon this, that they

are clearly conceived in accordance with the rules I have already laid

down In the next place, I perceived that there was nothing at all in these

demonstrations which could assure me of the existence of their object:

thus, for example, supposing a triangle to be given, I distinctly

perceived that its three angles were necessarily equal to two right

angles, but I did not on that account perceive anything which could assure

me that any triangle existed: while, on the contrary, recurring to the

examination of the idea of a Perfect Being, I found that the existence of

the Being was comprised in the idea in the same way that the equality of

its three angles to two right angles is comprised in the idea of a

triangle, or as in the idea of a sphere, the equidistance of all points on

its surface from the center, or even still more clearly; and that

consequently it is at least as certain that God, who is this Perfect

Being, is, or exists, as any demonstration of geometry can be.

But the reason which leads many to persuade them selves that there is a

difficulty in knowing this truth, and even also in knowing what their mind

really is, is that they never raise their thoughts above sensible objects,

and are so accustomed to consider nothing except by way of imagination,

which is a mode of thinking limited to material objects, that all that is

not imaginable seems to them not intelligible. The truth of this is

sufficiently manifest from the single circumstance, that the philosophers

of the schools accept as a maxim that there is nothing in the

understanding which was not previously in the senses, in which however it

is certain that the ideas of God and of the soul have never been; and it

appears to me that they who make use of their imagination to comprehend

these ideas do exactly the some thing as if, in order to hear sounds or

smell odors, they strove to avail themselves of their eyes; unless indeed

that there is this difference, that the sense of sight does not afford us

an inferior assurance to those of smell or hearing; in place of which,

neither our imagination nor our senses can give us assurance of anything

unless our understanding intervene.

Finally, if there be still persons who are not sufficiently persuaded of

the existence of God and of the soul, by the reasons I have adduced, I am

desirous that they should know that all the other propositions, of the

truth of which they deem themselves perhaps more assured, as that we have

a body, and that there exist stars and an earth, and such like, are less

certain; for, although we have a moral assurance of these things, which is

so strong that there is an appearance of extravagance in doubting of their

existence, yet at the same time no one, unless his intellect is impaired,

can deny, when the question relates to a metaphysical certitude, that

there is sufficient reason to exclude entire assurance, in the observation

that when asleep we can in the same way imagine ourselves possessed of

another body and that we see other stars and another earth, when there is

nothing of the kind. For how do we know that the thoughts which occur in

dreaming are false rather than those other which we experience when awake,

since the former are often not less vivid and distinct than the latter?

And though men of the highest genius study this question as long as they

please, I do not believe that they will be able to give any reason which

can be sufficient to remove this doubt, unless they presuppose the

existence of God. For, in the first place even the principle which I have

already taken as a rule, viz., that all the things which we clearly and

distinctly conceive are true, is certain only because God is or exists and

because he is a Perfect Being, and because all that we possess is derived

from him: whence it follows that our ideas or notions, which to the extent

of their clearness and distinctness are real, and proceed from God, must

to that extent be true. Accordingly, whereas we not infrequently have ideas

or notions in which some falsity is contained, this can only be the case with

such as are to some extent confused and obscure, and in this proceed from

nothing (participate of negation), that is, exist in us thus confused because

we are not wholly perfect. And it is evident that it is not less repugnant

that falsity or imperfection, in so far as it is imperfection, should proceed

from God, than that truth or perfection should proceed from nothing. But if

we did not know that all which we possess of real and true proceeds from a

Perfect and Infinite Being, however clear and distinct our ideas might be,

we should have no ground on that account for the assurance that they possessed

the perfection of being true.

But after the knowledge of God and of the soul has rendered us certain of

this rule, we can easily understand that the truth of the thoughts we

experience when awake, ought not in the slightest degree to be called in

question on account of the illusions of our dreams. For if it happened

that an individual, even when asleep, had some very distinct idea, as, for

example, if a geometer should discover some new demonstration, the

circumstance of his being asleep would not militate against its truth; and

as for the most ordinary error of our dreams, which consists in their

representing to us various objects in the same way as our external senses,

this is not prejudicial, since it leads us very properly to suspect the

truth of the ideas of sense; for we are not infrequently deceived in the

same manner when awake; as when persons in the jaundice see all objects

yellow, or when the stars or bodies at a great distance appear to us much

smaller than they are. For, in fine, whether awake or asleep, we ought

never to allow ourselves to be persuaded of the truth of anything unless

on the evidence of our reason. And it must be noted that I say of our

reason, and not of our imagination or of our senses: thus, for example,

although we very clearly see the sun, we ought not therefore to determine

that it is only of the size which our sense of sight presents; and we may

very distinctly imagine the head of a lion joined to the body of a goat,

without being therefore shut up to the conclusion that a chimaera exists;

for it is not a dictate of reason that what we thus see or imagine is in

reality existent; but it plainly tells us that all our ideas or notions

contain in them some truth; for otherwise it could not be that God, who is

wholly perfect and veracious, should have placed them in us. And because

our reasonings are never so clear or so complete during sleep as when we

are awake, although sometimes the acts of our imagination are then as

lively and distinct, if not more so than in our waking moments, reason

further dictates that, since all our thoughts cannot be true because of

our partial imperfection, those possessing truth must infallibly be found

in the experience of our waking moments rather than in that of our dreams.

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

earned, with whom I do not wish to be embroiled, I believe that it will be

better for me to refrain from this exposition, and only mention in general

what these truths are, that the more judicious may be able to determine

whether a more special account of them would conduce to the public

advantage. I have ever remained firm in my original resolution to suppose

no other principle than that of which I have recently availed myself in

demonstrating the existence of God and of the soul, and to accept as true

nothing that did not appear to me more clear and certain than the

demonstrations of the geometers had formerly appeared; and yet I venture

to state that not only have I found means to satisfy myself in a short

time on all the principal difficulties which are usually treated of in

philosophy, but I have also observed certain laws established in nature by

God in such a manner, and of which he has impressed on our minds such

notions, that after we have reflected sufficiently upon these, we cannot

doubt that they are accurately observed in all that exists or takes place

in the world and farther, by considering the concatenation of these laws,

it appears to me that I have discovered many truths more useful and more

important than all I had before learned, or even had expected to learn.

But because I have essayed to expound the chief of these discoveries in a

treatise which certain considerations prevent me from publishing, I cannot

make the results known more conveniently than by here giving a summary of

the contents of this treatise. It was my design to comprise in it all

that, before I set myself to write it, I thought I knew of the nature of

material objects. But like the painters who, finding themselves unable to

represent equally well on a plain surface all the different faces of a

solid body, select one of the chief, on which alone they make the light

fall, and throwing the rest into the shade, allow them to appear only in

so far as they can be seen while looking at the principal one; so, fearing

lest I should not be able to compense in my discourse all that was in my

mind, I resolved to expound singly, though at considerable length, my

opinions regarding light; then to take the opportunity of adding something

on the sun and the fixed stars, since light almost wholly proceeds from

them; on the heavens since they transmit it; on the planets, comets, and

earth, since they reflect it; and particularly on all the bodies that are

upon the earth, since they are either colored, or transparent, or

luminous; and finally on man, since he is the spectator of these objects.

Further, to enable me to cast this variety of subjects somewhat into the

shade, and to express my judgment regarding them with greater freedom,

without being necessitated to adopt or refute the opinions of the learned,

I resolved to leave all the people here to their disputes, and to speak

only of what would happen in a new world, if God were now to create

somewhere in the imaginary spaces matter sufficient to compose one, and

were to agitate variously and confusedly the different parts of this

matter, so that there resulted a chaos as disordered as the poets ever

feigned, and after that did nothing more than lend his ordinary

concurrence to nature, and allow her to act in accordance with the laws

which he had established. On this supposition, I, in the first place,

described this matter, and essayed to represent it in such a manner that

to my mind there can be nothing clearer and more intelligible, except what

has been recently said regarding God and the soul; for I even expressly

supposed that it possessed none of those forms or qualities which are so

debated in the schools, nor in general anything the knowledge of which is

not so natural to our minds that no one can so much as imagine himself

ignorant of it. Besides, I have pointed out what are the laws of nature;

and, with no other principle upon which to found my reasonings except the

infinite perfection of God, I endeavored to demonstrate all those about

which there could be any room for doubt, and to prove that they are such,

that even if God had created more worlds, there could have been none in

which these laws were not observed. Thereafter, I showed how the greatest

part of the matter of this chaos must, in accordance with these laws,

dispose and arrange itself in such a way as to present the appearance of

heavens; how in the meantime some of its parts must compose an earth and

some planets and comets, and others a sun and fixed stars. And, making a

digression at this stage on the subject of light, I expounded at

considerable length what the nature of that light must be which is found

in the sun and the stars, and how thence in an instant of time it

traverses the immense spaces of the heavens, and how from the planets and

comets it is reflected towards the earth. To this I likewise added much

respecting the substance, the situation, the motions, and all the

different qualities of these heavens and stars; so that I thought I had

said enough respecting them to show that there is nothing observable in

the heavens or stars of our system that must not, or at least may not

appear precisely alike in those of the system which I described. I came

next to speak of the earth in particular, and to show how, even though I

had expressly supposed that God had given no weight to the matter of which

it is composed, this should not prevent all its parts from tending exactly

to its center; how with water and air on its surface, the disposition of

the heavens and heavenly bodies, more especially of the moon, must cause a

flow and ebb, like in all its circumstances to that observed in our seas,

as also a certain current both of water and air from east to west, such as

is likewise observed between the tropics; how the mountains, seas,

fountains, and rivers might naturally be formed in it, and the metals

produced in the mines, and the plants grow in the fields and in general,

how all the bodies which are commonly denominated mixed or composite might

be generated and, among other things in the discoveries alluded to

inasmuch as besides the stars, I knew nothing except fire which produces

light, I spared no pains to set forth all that pertains to its nature, --

the manner of its production and support, and to explain how heat is

sometimes found without light, and light without heat; to show how it can

induce various colors upon different bodies and other diverse qualities;

how it reduces some to a liquid state and hardens others; how it can

consume almost all bodies, or convert them into ashes and smoke; and

finally, how from these ashes, by the mere intensity of its action, it

forms glass: for as this transmutation of ashes into glass appeared to me

as wonderful as any other in nature, I took a special pleasure in

describing it. I was not, however, disposed, from these circumstances, to

conclude that this world had been created in the manner I described; for

it is much more likely that God made it at the first such as it was to be.

But this is certain, and an opinion commonly received among theologians,

that the action by which he now sustains it is the same with that by which

he originally created it; so that even although he had from the beginning

given it no other form than that of chaos, provided only he had

established certain laws of nature, and had lent it his concurrence to

enable it to act as it is wont to do, it may be believed, without

discredit to the miracle of creation, that, in this way alone, things

purely material might, in course of time, have become such as we observe

them at present; and their nature is much more easily conceived when they

are beheld coming in this manner gradually into existence, than when they

are only considered as produced at once in a finished and perfect state.

From the description of inanimate bodies and plants, I passed to animals,

and particularly to man. But since I had not as yet sufficient knowledge

to enable me to treat of these in the same manner as of the rest, that is

to say, by deducing effects from their causes, and by showing from what

elements and in what manner nature must produce them, I remained satisfied

with the supposition that God formed the body of man wholly like to one of

ours, as well in the external shape of the members as in the internal

conformation of the organs, of the same matter with that I had described,

and at first placed in it no rational soul, nor any other principle, in

room of the vegetative or sensitive soul, beyond kindling in the heart one

of those fires without light, such as I had already described, and which I

thought was not different from the heat in hay that has been heaped

together before it is dry, or that which causes fermentation in new wines

before they are run clear of the fruit. For, when I examined the kind of

functions which might, as consequences of this supposition, exist in this

body, I found precisely all those which may exist in us independently of

all power of thinking, and consequently without being in any measure owing

to the soul; in other words, to that part of us which is distinct from the

body, and of which it has been said above that the nature distinctively

consists in thinking, functions in which the animals void of reason may be

said wholly to resemble us; but among which I could not discover any of

those that, as dependent on thought alone, belong to us as men, while, on

the other hand, I did afterwards discover these as soon as I supposed God

to have created a rational soul, and to have annexed it to this body in a

particular manner which I described.

But, in order to show how I there handled this matter, I mean here to give

the explication of the motion of the heart and arteries, which, as the

first and most general motion observed in animals, will afford the means

of readily determining what should be thought of all the rest. And that

there may be less difficulty in understanding what I am about to say on

this subject, I advise those who are not versed in anatomy, before they

commence the perusal of these observations, to take the trouble of getting

dissected in their presence the heart of some large animal possessed of

lungs (for this is throughout sufficiently like the human), and to have

shown to them its two ventricles or cavities: in the first place, that in

the right side, with which correspond two very ample tubes, viz., the

hollow vein (vena cava), which is the principal receptacle of the blood,

and the trunk of the tree, as it were, of which all the other veins in the

body are branches; and the arterial vein (vena arteriosa), inappropriately

so denominated, since it is in truth only an artery, which, taking its

rise in the heart, is divided, after passing out from it, into many

branches which presently disperse themselves all over the lungs; in the

second place, the cavity in the left side, with which correspond in the

same manner two canals in size equal to or larger than the preceding,

viz., the venous artery (arteria venosa), likewise inappropriately thus

designated, because it is simply a vein which comes from the lungs, where

it is divided into many branches, interlaced with those of the arterial

vein, and those of the tube called the windpipe, through which the air we

breathe enters; and the great artery which, issuing from the heart, sends

its branches all over the body. I should wish also that such persons were

carefully shown the eleven pellicles which, like so many small valves,

open and shut the four orifices that are in these two cavities, viz.,

three at the entrance of the hollow veins where they are disposed in such

a manner as by no means to prevent the blood which it contains from

flowing into the right ventricle of the heart, and yet exactly to prevent

its flowing out; three at the entrance to the arterial vein, which,

arranged in a manner exactly the opposite of the former, readily permit

the blood contained in this cavity to pass into the lungs, but hinder that

contained in the lungs from returning to this cavity; and, in like manner,

two others at the mouth of the venous artery, which allow the blood from

the lungs to flow into the left cavity of the heart, but preclude its

return; and three at the mouth of the great artery, which suffer the blood

to flow from the heart, but prevent its reflux. Nor do we need to seek any

other reason for the number of these pellicles beyond this that the

orifice of the venous artery being of an oval shape from the nature of its

situation, can be adequately closed with two, whereas the others being

round are more conveniently closed with three. Besides, I wish such

persons to observe that the grand artery and the arterial vein are of much

harder and firmer texture than the venous artery and the hollow vein; and

that the two last expand before entering the heart, and there form, as it

were, two pouches denominated the auricles of the heart, which are

composed of a substance similar to that of the heart itself; and that

there is always more warmth in the heart than in any other part of the

body- and finally, that this heat is capable of causing any drop of blood

that passes into the cavities rapidly to expand and dilate, just as all

liquors do when allowed to fall drop by drop into a highly heated vessel.

For, after these things, it is not necessary for me to say anything more

with a view to explain the motion of the heart, except that when its

cavities are not full of blood, into these the blood of necessity flows, -

- from the hollow vein into the right, and from the venous artery into the

left; because these two vessels are always full of blood, and their

orifices, which are turned towards the heart, cannot then be closed. But

as soon as two drops of blood have thus passed, one into each of the

cavities, these drops which cannot but be very large, because the orifices

through which they pass are wide, and the vessels from which they come

full of blood, are immediately rarefied, and dilated by the heat they meet

with. In this way they cause the whole heart to expand, and at the same

time press home and shut the five small valves that are at the entrances

of the two vessels from which they flow, and thus prevent any more blood

from coming down into the heart, and becoming more and more rarefied, they

push open the six small valves that are in the orifices of the other two

vessels, through which they pass out, causing in this way all the branches

of the arterial vein and of the grand artery to expand almost

simultaneously with the heart which immediately thereafter begins to

contract, as do also the arteries, because the blood that has entered them

has cooled, and the six small valves close, and the five of the hollow

vein and of the venous artery open anew and allow a passage to other two

drops of blood, which cause the heart and the arteries again to expand as

before. And, because the blood which thus enters into the heart passes

through these two pouches called auricles, it thence happens that their

motion is the contrary of that of the heart, and that when it expands they

contract. But lest those who are ignorant of the force of mathematical

demonstrations and who are not accustomed to distinguish true reasons from

mere verisimilitudes, should venture. without examination, to deny what

has been said, I wish it to be considered that the motion which I have now

explained follows as necessarily from the very arrangement of the parts,

which may be observed in the heart by the eye alone, and from the heat

which may be felt with the fingers, and from the nature of the blood as

learned from experience, as does the motion of a clock from the power, the

situation, and shape of its counterweights and wheels.

But if it be asked how it happens that the blood in the veins, flowing in

this way continually into the heart, is not exhausted, and why the

arteries do not become too full, since all the blood which passes through

the heart flows into them, I need only mention in reply what has been

written by a physician 1 of England, who has the honor of having broken

the ice on this subject, and of having been the first to teach that there

are many small passages at the extremities of the arteries, through which

the blood received by them from the heart passes into the small branches

of the veins, whence it again returns to the heart; so that its course

amounts precisely to a perpetual circulation. Of this we have abundant

proof in the ordinary experience of surgeons, who, by binding the arm with

a tie of moderate straitness above the part where they open the vein,

cause the blood to flow more copiously than it would have done without any

ligature; whereas quite the contrary would happen were they to bind it

below; that is, between the hand and the opening, or were to make the

ligature above the opening very tight. For it is manifest that the tie,

moderately straightened, while adequate to hinder the blood already in the

arm from returning towards the heart by the veins, cannot on that account

prevent new blood from coming forward through the arteries, because these

are situated below the veins, and their coverings, from their greater

consistency, are more difficult to compress; and also that the blood which

comes from the heart tends to pass through them to the hand with greater

force than it does to return from the hand to the heart through the veins.

And since the latter current escapes from the arm by the opening made in

one of the veins, there must of necessity be certain passages below the

ligature, that is, towards the extremities of the arm through which it can

come thither from the arteries. This physician likewise abundantly

establishes what he has advanced respecting the motion of the blood, from

the existence of certain pellicles, so disposed in various places along

the course of the veins, in the manner of small valves, as not to permit

the blood to pass from the middle of the body towards the extremities, but

only to return from the extremities to the heart; and farther, from

experience which shows that all the blood which is in the body may flow

out of it in a very short time through a single artery that has been cut,

even although this had been closely tied in the immediate neighborhood of

the heart and cut between the heart and the ligature, so as to prevent the

supposition that the blood flowing out of it could come from any other

quarter than the heart.

But there are many other circumstances which evince that what I have

alleged is the true cause of the motion of the blood: thus, in the first

place, the difference that is observed between the blood which flows from

the veins, and that from the arteries, can only arise from this, that

being rarefied, and, as it were, distilled by passing through the heart,

it is thinner, and more vivid, and warmer immediately after leaving the

heart, in other words, when in the arteries, than it was a short time

before passing into either, in other words, when it was in the veins; and

if attention be given, it will be found that this difference is very

marked only in the neighborhood of the heart; and is not so evident in

parts more remote from it. In the next place, the consistency of the coats

of which the arterial vein and the great artery are composed,

sufficiently shows that the blood is impelled against them with more

force than against the veins. And why should the left cavity of the heart

and the great artery be wider and larger than the right cavity and the

arterial vein, were it not that the blood of the venous artery, having

only been in the lungs after it has passed through the heart, is thinner,

and rarefies more readily, and in a higher degree, than the blood which

proceeds immediately from the hollow vein? And what can physicians

conjecture from feeling the pulse unless they know that according as the

blood changes its nature it can be rarefied by the warmth of the heart, in

a higher or lower degree, and more or less quickly than before? And if it

be inquired how this heat is communicated to the other members, must it

not be admitted that this is effected by means of the blood, which,

passing through the heart, is there heated anew, and thence diffused over

all the body? Whence it happens, that if the blood be withdrawn from any

part, the heat is likewise withdrawn by the same means; and although the

heart were as-hot as glowing iron, it would not be capable of warming the

feet and hands as at present, unless it continually sent thither new

blood. We likewise perceive from this, that the true use of respiration is

to bring sufficient fresh air into the lungs, to cause the blood which

flows into them from the right ventricle of the heart, where it has been

rarefied and, as it were, changed into vapors, to become thick, and to

convert it anew into blood, before it flows into the left cavity, without

which process it would be unfit for the nourishment of the fire that is

there. This receives confirmation from the circumstance, that it is

observed of animals destitute of lungs that they have also but one cavity

in the heart, and that in children who cannot use them while in the womb,

there is a hole through which the blood flows from the hollow vein into

the left cavity of the heart, and a tube through which it passes from the

arterial vein into the grand artery without passing through the lung. In

the next place, how could digestion be carried on in the stomach unless

the heart communicated heat to it through the arteries, and along with

this certain of the more fluid parts of the blood, which assist in the

dissolution of the food that has been taken in? Is not also the operation

which converts the juice of food into blood easily comprehended, when it

is considered that it is distilled by passing and repassing through the

heart perhaps more than one or two hundred times in a day? And what more

need be adduced to explain nutrition, and the production of the different

humors of the body, beyond saying, that the force with which the blood, in

being rarefied, passes from the heart towards the extremities of the

arteries, causes certain of its parts to remain in the members at which

they arrive, and there occupy the place of some others expelled by them;

and that according to the situation, shape, or smallness of the pores with

which they meet, some rather than others flow into certain parts, in the

same way that some sieves are observed to act, which, by being variously

perforated, serve to separate different species of grain? And, in the last

place, what above all is here worthy of observation, is the generation of

the animal spirits, which are like a very subtle wind, or rather a very

pure and vivid flame which, continually ascending in great abundance from

the heart to the brain, thence penetrates through the nerves into the

muscles, and gives motion to all the members; so that to account for other

parts of the blood which, as most agitated and penetrating, are the

fittest to compose these spirits, proceeding towards the brain, it is not

necessary to suppose any other cause, than simply, that the arteries which

carry them thither proceed from the heart in the most direct lines, and

that, according to the rules of mechanics which are the same with those of

nature, when many objects tend at once to the same point where there is

not sufficient room for all (as is the case with the parts of the blood

which flow forth from the left cavity of the heart and tend towards the

brain), the weaker and less agitated parts must necessarily be driven

aside from that point by the stronger which alone in this way reach it I

had expounded all these matters with sufficient minuteness in the treatise

which I formerly thought of publishing. And after these, I had shown what

must be the fabric of the nerves and muscles of the human body to give the

animal spirits contained in it the power to move the members, as when we

see heads shortly after they have been struck off still move and bite the

earth, although no longer animated; what changes must take place in the

brain to produce waking, sleep, and dreams; how light, sounds, odors,

tastes, heat, and all the other qualities of external objects impress it

with different ideas by means of the senses; how hunger, thirst, and the

other internal affections can likewise impress upon it divers ideas; what

must be understood by the common sense (sensus communis) in which these

ideas are received, by the memory which retains them, by the fantasy which

can change them in various ways, and out of them compose new ideas, and

which, by the same means, distributing the animal spirits through the

muscles, can cause the members of such a body to move in as many different

ways, and in a manner as suited, whether to the objects that are presented

to its senses or to its internal affections, as can take place in our own

case apart from the guidance of the will. Nor will this appear at all

strange to those who are acquainted with the variety of movements

performed by the different automata, or moving machines fabricated by

human industry, and that with help of but few pieces compared with the

great multitude of bones, muscles, nerves, arteries, veins, and other

parts that are found in the body of each animal. Such persons will look

upon this body as a machine made by the hands of God, which is

incomparably better arranged, and adequate to movements more admirable

than is any machine of human invention. And here I specially stayed to

show that, were there such machines exactly resembling organs and outward

form an ape or any other irrational animal, we could have no means of

knowing that they were in any respect of a different nature from these

animals; but if there were machines bearing the image of our bodies, and

capable of imitating our actions as far as it is morally possible, there

would still remain two most certain tests whereby to know that they were

not therefore really men. Of these the first is that they could never use

words or other signs arranged in such a manner as is competent to us in

order to declare our thoughts to others: for we may easily conceive a

machine to be so constructed that it emits vocables, and even that it

emits some correspondent to the action upon it of external objects which

cause a change in its organs; for example, if touched in a particular

place it may demand what we wish to say to it; if in another it may cry

out that it is hurt, and such like; but not that it should arrange them

variously so as appositely to reply to what is said in its presence, as

men of the lowest grade of intellect can do. The second test is, that

although such machines might execute many things with equal or perhaps

greater perfection than any of us, they would, without doubt, fail in

certain others from which it could be discovered that they did not act

from knowledge, but solely from the disposition of their organs: for while

reason is an universal instrument that is alike available on every

occasion, these organs, on the contrary, need a particular arrangement for

each particular action; whence it must be morally impossible that there

should exist in any machine a diversity of organs sufficient to enable it

to act in all the occurrences of life, in the way in which our reason

enables us to act. Again, by means of these two tests we may likewise know

the difference between men and brutes. For it is highly deserving of

remark, that there are no men so dull and stupid, not even idiots, as to

be incapable of joining together different words, and thereby constructing

a declaration by which to make their thoughts understood; and that on the

other hand, there is no other animal, however perfect or happily

circumstanced, which can do the like. Nor does this inability arise from

want of organs: for we observe that magpies and parrots can utter words

like ourselves, and are yet unable to speak as we do, that is, so as to

show that they understand what they say; in place of which men born deaf

and dumb, and thus not less, but rather more than the brutes, destitute of

the organs which others use in speaking, are in the habit of spontaneously

inventing certain signs by which they discover their thoughts to those

who, being usually in their company, have leisure to learn their language.

And this proves not only that the brutes have less reason than man, but

that they have none at all: for we see that very little is required to

enable a person to speak; and since a certain inequality of capacity is

observable among animals of the same species, as well as among men, and

since some are more capable of being instructed than others, it is

incredible that the most perfect ape or parrot of its species, should not

in this be equal to the most stupid infant of its kind or at least to one

that was crack-brained, unless the soul of brutes were of a nature wholly

different from ours. And we ought not to confound speech with the natural

movements which indicate the passions, and can be imitated by machines as

well as manifested by animals; nor must it be thought with certain of the

ancients, that the brutes speak, although we do not understand their

language. For if such were the case, since they are endowed with many

organs analogous to ours, they could as easily communicate their thoughts

to us as to their fellows. It is also very worthy of remark, that, though

there are many animals which manifest more industry than we in certain of

their actions, the same animals are yet observed to show none at all in

many others: so that the circumstance that they do better than we does not

prove that they are endowed with mind, for it would thence follow that

they possessed greater reason than any of us, and could surpass us in all

things; on the contrary, it rather proves that they are destitute of

reason, and that it is nature which acts in them according to the

disposition of their organs: thus it is seen, that a clock composed only

of wheels and weights can number the hours and measure time more exactly

than we with all our skin.

I had after this described the reasonable soul, and shown that it could by

no means be educed from the power of matter, as the other things of which

I had spoken, but that it must be expressly created; and that it is not

sufficient that it be lodged in the human body exactly like a pilot in a

ship, unless perhaps to move its members, but that it is necessary for it

to be joined and united more closely to the body, in order to have

sensations and appetites similar to ours, and thus constitute a real man.

I here entered, in conclusion, upon the subject of the soul at

considerable length, because it is of the greatest moment: for after the

error of those who deny the existence of God, an error which I think I

have already sufficiently refuted, there is none that is more powerful in

leading feeble minds astray from the straight path of virtue than the

supposition that the soul of the brutes is of the same nature with our

own; and consequently that after this life we have nothing to hope for or

fear, more than flies and ants; in place of which, when we know how far

they differ we much better comprehend the reasons which establish that the

soul is of a nature wholly independent of the body, and that consequently

it is not liable to die with the latter and, finally, because no other

causes are observed capable of destroying it, we are naturally led thence

to judge that it is immortal.

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.

I have never made much account of what has proceeded from my own mind; and

so long as I gathered no other advantage from the method I employ beyond

satisfying myself on some difficulties belonging to the speculative

sciences, or endeavoring to regulate my actions according to the

principles it taught me, I never thought myself bound to publish anything

respecting it. For in what regards manners, every one is so full of his

own wisdom, that there might be found as many reformers as heads, if any

were allowed to take upon themselves the task of mending them, except

those whom God has constituted the supreme rulers of his people or to whom

he has given sufficient grace and zeal to be prophets; and although my

speculations greatly pleased myself, I believed that others had theirs,

which perhaps pleased them still more. But as soon as I had acquired some

general notions respecting physics, and beginning to make trial of them in

various particular difficulties, had observed how far they can carry us,

and how much they differ from the principles that have been employed up to

the present time, I believed that I could not keep them concealed without

sinning grievously against the law by which we are bound to promote, as

far as in us lies, the general good of mankind. For by them I perceived it

to be possible to arrive at knowledge highly useful in life; and in room

of the speculative philosophy usually taught in the schools, to discover a

practical, by means of which, knowing the force and action of fire, water,

air the stars, the heavens, and all the other bodies that surround us, as

distinctly as we know the various crafts of our artisans, we might also

apply them in the same way to all the uses to which they are adapted, and

thus render ourselves the lords and possessors of nature. And this is a

result to be desired, not only in order to the invention of an infinity of

arts, by which we might be enabled to enjoy without any trouble the fruits

of the earth, and all its comforts, but also and especially for the

preservation of health, which is without doubt, of all the blessings of

this life, the first and fundamental one; for the mind is so intimately

dependent upon the condition and relation of the organs of the body, that

if any means can ever be found to render men wiser and more ingenious than

hitherto, I believe that it is in medicine they must be sought for. It is

true that the science of medicine, as it now exists, contains few things

whose utility is very remarkable: but without any wish to depreciate it, I

am confident that there is no one, even among those whose profession it

is, who does not admit that all at present known in it is almost nothing

in comparison of what remains to be discovered; and that we could free

ourselves from an infinity of maladies of body as well as of mind, and

perhaps also even from the debility of age, if we had sufficiently ample

knowledge of their causes, and of all the remedies provided for us by

nature. But since I designed to employ my whole life in the search after

so necessary a science, and since I had fallen in with a path which seems

to me such, that if any one follow it he must inevitably reach the end

desired, unless he be hindered either by the shortness of life or the want

of experiments, I judged that there could be no more effectual provision

against these two impediments than if I were faithfully to communicate to

the public all the little I might myself have found, and incite men of

superior genius to strive to proceed farther, by contributing, each

according to his inclination and ability, to the experiments which it

would be necessary to make, and also by informing the public of all they

might discover, so that, by the last beginning where those before them had

left off, and thus connecting the lives and labours of many, we might

collectively proceed much farther than each by himself could do.

I remarked, moreover, with respect to experiments, that they become always

more necessary the more one is advanced in knowledge; for, at the

commencement, it is better to make use only of what is spontaneously

presented to our senses, and of which we cannot remain ignorant, provided

we bestow on it any reflection, however slight, than to concern ourselves

about more uncommon and recondite phenomena: the reason of which is, that

the more uncommon often only mislead us so long as the causes of the more

ordinary are still unknown; and the circumstances upon which they depend

are almost always so special and minute as to be highly difficult to

detect. But in this I have adopted the following order: first, I have

essayed to find in general the principles, or first causes of all that is

or can be in the world, without taking into consideration for this end

anything but God himself who has created it, and without educing them from

any other source than from certain germs of truths naturally existing in

our minds In the second place, I examined what were the first and most

ordinary effects that could be deduced from these causes; and it appears

to me that, in this way, I have found heavens, stars, an earth, and even

on the earth water, air, fire, minerals, and some other things of this

kind, which of all others are the most common and simple, and hence the

easiest to know. Afterwards when I wished to descend to the more

particular, so many diverse objects presented themselves to me, that I

believed it to be impossible for the human mind to distinguish the forms

or species of bodies that are upon the earth, from an infinity of others

which might have been, if it had pleased God to place them there, or

consequently to apply them to our use, unless we rise to causes through

their effects, and avail ourselves of many particular experiments.

Thereupon, turning over in my mind I the objects that had ever been

presented to my senses I freely venture to state that I have never

observed any which I could not satisfactorily explain by the principles

had discovered. But it is necessary also to confess that the power of

nature is so ample and vast, and these principles so simple and general,

that I have hardly observed a single particular effect which I cannot at

once recognize as capable of being deduced in man different modes from the

principles, and that my greatest difficulty usually is to discover in

which of these modes the effect is dependent upon them; for out of this

difficulty cannot otherwise extricate myself than by again seeking certain

experiments, which may be such that their result is not the same, if it is

in the one of these modes at we must explain it, as it would be if it were

to be explained in the other. As to what remains, I am now in a position

to discern, as I think, with sufficient clearness what course must be taken

to make the majority those experiments which may conduce to this end: but

I perceive likewise that they are such and so numerous, that neither my

hands nor my income, though it were a thousand times larger than it is,

would be sufficient for them all; so that according as henceforward I

shall have the means of making more or fewer experiments, I shall in the

same proportion make greater or less progress in the knowledge of nature.

This was what I had hoped to make known by the treatise I had written, and

so clearly to exhibit the advantage that would thence accrue to the public,

as to induce all who have the common good of man at heart, that is, all who

are virtuous in truth, and not merely in appearance, or according to opinion,

as well to communicate to me the experiments they had already made, as to

assist me in those that remain to be made.

But since that time other reasons have occurred to me, by which I have

been led to change my opinion, and to think that I ought indeed to go on

committing to writing all the results which I deemed of any moment, as

soon as I should have tested their truth, and to bestow the same care upon

them as I would have done had it been my design to publish them. This

course commended itself to me, as well because I thus afforded myself more

ample inducement to examine them thoroughly, for doubtless that is always

more narrowly scrutinized which we believe will be read by many, than that

which is written merely for our private use (and frequently what has

seemed to me true when I first conceived it, has appeared false when I

have set about committing it to writing), as because I thus lost no

opportunity of advancing the interests of the public, as far as in me lay,

and since thus likewise, if my writings possess any value, those into

whose hands they may fall after my death may be able to put them to what

use they deem proper. But I resolved by no means to consent to their

publication during my lifetime, lest either the oppositions or the

controversies to which they might give rise, or even the reputation, such

as it might be, which they would acquire for me, should be any occasion of

my losing the time that I had set apart for my own improvement. For though

it be true that every one is bound to promote to the extent of his ability

the good of others, and that to be useful to no one is really to be

worthless, yet it is likewise true that our cares ought to extend beyond

the present, and it is good to omit doing what might perhaps bring some

profit to the living, when we have in view the accomplishment of other

ends that will be of much greater advantage to posterity. And in truth, I

am quite willing it should be known that the little I have hitherto

learned is almost nothing in comparison with that of which I am ignorant,

and to the knowledge of which I do not despair of being able to attain;

for it is much the same with those who gradually discover truth in the

sciences, as with those who when growing rich find less difficulty in

making great acquisitions, than they formerly experienced when poor in

making acquisitions of much smaller amount. Or they may be compared to the

commanders of armies, whose forces usually increase in proportion to their

victories, and who need greater prudence to keep together the residue of

their troops after a defeat than after a victory to take towns and

provinces. For he truly engages in battle who endeavors to surmount all

the difficulties and errors which prevent him from reaching the knowledge

of truth, and he is overcome in fight who admits a false opinion touching

a matter of any generality and importance, and he requires thereafter much

more skill to recover his former position than to make great advances when

once in possession of thoroughly ascertained principles. As for myself, if

I have succeeded in discovering any truths in the sciences (and I trust

that what is contained in this volume 1 will show that I have found some),

I can declare that they are but the consequences and results of five or

six principal difficulties which I have surmounted, and my encounters with

which I reckoned as battles in which victory declared for me. I will not

hesitate even to avow my belief that nothing further is wanting to enable

me fully to realize my designs than to gain two or three similar

victories; and that I am not so far advanced in years but that, according

to the ordinary course of nature, I may still have sufficient leisure for

this end. But I conceive myself the more bound to husband the time that

remains the greater my expectation of being able to employ it aright, and

I should doubtless have much to rob me of it, were I to publish the

principles of my physics: for although they are almost all so evident that

to assent to them no more is needed than simply to understand them, and

although there is not one of them of which I do not expect to be able to

give demonstration, yet, as it is impossible that they can be in

accordance with all the diverse opinions of others, I foresee that I

should frequently be turned aside from my grand design, on occasion of the

opposition which they would be sure to awaken.

It may be said, that these oppositions would be useful both in making me

aware of my errors, and, if my speculations contain anything of value, in

bringing others to a fuller understanding of it; and still farther, as

many can see better than one, in leading others who are now beginning to

avail themselves of my principles, to assist me in turn with their

discoveries. But though I recognize my extreme liability to error, and

scarce ever trust to the first thoughts which occur to me, yet-the

experience I have had of possible objections to my views prevents me from

anticipating any profit from them. For I have already had frequent proof

of the judgments, as well of those I esteemed friends, as of some others

to whom I thought I was an object of indifference, and even of some whose

malignancy and envy would, I knew, determine them to endeavor to discover

what partiality concealed from the eyes of my friends. But it has rarely

happened that anything has been objected to me which I had myself

altogether overlooked, unless it were something far removed from the

subject: so that I have never met with a single critic of my opinions who

did not appear to me either less rigorous or less equitable than myself.

And further, I have never observed that any truth before unknown has been

brought to light by the disputations that are practised in the schools;

for while each strives for the victory, each is much more occupied in

making the best of mere verisimilitude, than in weighing the reasons on

both sides of the question; and those who have been long good advocates

are not afterwards on that account the better judges.

As for the advantage that others would derive from the communication of my

thoughts, it could not be very great; because I have not yet so far

prosecuted them as that much does not remain to be added before they can

be applied to practice. And I think I may say without vanity, that if

there is any one who can carry them out that length, it must be myself

rather than another: not that there may not be in the world many minds

incomparably superior to mine, but because one cannot so well seize a

thing and make it one's own, when it has been learned from another, as

when one has himself discovered it. And so true is this of the present

subject that, though I have often explained some of my opinions to persons

of much acuteness, who, whilst I was speaking, appeared to understand them

very distinctly, yet, when they repeated them, I have observed that they

almost always changed them to such an extent that I could no longer

acknowledge them as mine. I am glad, by the way, to take this opportunity

of requesting posterity never to believe on hearsay that anything has

proceeded from me which has not been published by myself; and I am not at

all astonished at the extravagances attributed to those ancient

philosophers whose own writings we do not possess; whose thoughts,

however, I do not on that account suppose to have been really absurd,

seeing they were among the ablest men of their times, but only that these

have been falsely represented to us. It is observable, accordingly, that

scarcely in a single instance has any one of their disciples surpassed

them; and I am quite sure that the most devoted of the present followers

of Aristotle would think themselves happy if they had as much knowledge of

nature as he possessed, were it even under the condition that they should

never afterwards attain to higher. In this respect they are like the ivy

which never strives to rise above the tree that sustains it, and which

frequently even returns downwards when it has reached the top; for it

seems to me that they also sink, in other words, render themselves less

wise than they would be if they gave up study, who, not contented with

knowing all that is intelligibly explained in their author, desire in

addition to find in him the solution of many difficulties of which he says

not a word, and never perhaps so much as thought. Their fashion of

philosophizing, however, is well suited to persons whose abilities fall

below mediocrity; for the obscurity of the distinctions and principles of

which they make use enables them to speak of all things with as much

confidence as if they really knew them, and to defend all that they say on

any subject against the most subtle and skillful, without its being

possible for any one to convict them of error. In this they seem to me to

be like a blind man, who, in order to fight on equal terms with a person

that sees, should have made him descend to the bottom of an intensely dark

cave: and I may say that such persons have an interest in my refraining

from publishing the principles of the philosophy of which I make use; for,

since these are of a kind the simplest and most evident, I should, by

publishing them, do much the same as if I were to throw open the windows,

and allow the light of day to enter the cave into which the combatants had

descended. But even superior men have no reason for any great anxiety to

know these principles, for if what they desire is to be able to speak of

all things, and to acquire a reputation for learning, they will gain their

end more easily by remaining satisfied with the appearance of truth, which

can be found without much difficulty in all sorts of matters, than by

seeking the truth itself which unfolds itself but slowly and that only in

some departments, while it obliges us, when we have to speak of others,

freely to confess our ignorance. If, however, they prefer the knowledge of

some few truths to the vanity of appearing ignorant of none, as such

knowledge is undoubtedly much to be preferred, and, if they choose to

follow a course similar to mine, they do not require for this that I

should say anything more than I have already said in this discourse. For

if they are capable of making greater advancement than I have made, they

will much more be able of themselves to discover all that I believe myself

to have found; since as I have never examined aught except in order, it is

certain that what yet remains to be discovered is in itself more difficult

and recondite, than that which I have already been enabled to find, and

the gratification would be much less in learning it from me than in

discovering it for themselves. Besides this, the habit which they will

acquire, by seeking first what is easy, and then passing onward slowly and

step by step to the more difficult, will benefit them more than all my

instructions. Thus, in my own case, I am persuaded that if I had been

taught from my youth all the truths of which I have since sought out

demonstrations, and had thus learned them without labour, I should never,

perhaps, have known any beyond these; at least, I should never have

acquired the habit and the facility which I think I possess in always

discovering new truths in proportion as I give myself to the search.

And, in a single word, if there is any work in the world which cannot

be so well finished by another as by him who has commenced it, it is

that at which I labour.

It is true, indeed, as regards the experiments which may conduce to this

end, that one man is not equal to the task of making them all; but yet he

can advantageously avail himself, in this work, of no hands besides his

own, unless those of artisans, or parties of the same kind, whom he could

pay, and whom the hope of gain (a means of great efficacy) might stimulate

to accuracy in the performance of what was prescribed to them. For as to

those who, through curiosity or a desire of learning, of their own accord,

perhaps, offer him their services, besides that in general their promises

exceed their performance, and that they sketch out fine designs of which

not one is ever realized, they will, without doubt, expect to be

compensated for their trouble by the explication of some difficulties, or,

at least, by compliments and useless speeches, in which he cannot spend

any portion of his time without loss to himself. And as for the

experiments that others have already made, even although these parties

should be willing of themselves to communicate them to him (which is what

those who esteem them secrets will never do), the experiments are, for the

most part, accompanied with so many circumstances and superfluous

elements, as to make it exceedingly difficult to disentangle the truth

from its adjuncts- besides, he will find almost all of them so ill

described, or even so false (because those who made them have wished to

see in them only such facts as they deemed conformable to their

principles), that, if in the entire number there should be some of a

nature suited to his purpose, still their value could not compensate for

the time what would be necessary to make the selection. So that if there

existed any one whom we assuredly knew to be capable of making discoveries

of the highest kind, and of the greatest possible utility to the public;

and if all other men were therefore eager by all means to assist him in

successfully prosecuting his designs, I do not see that they could do

aught else for him beyond contributing to defray the expenses of the

experiments that might be necessary; and for the rest, prevent his being

deprived of his leisure by the unseasonable interruptions of any one. But

besides that I neither have so high an opinion of myself as to be willing

to make promise of anything extraordinary, nor feed on imaginations so

vain as to fancy that the public must be much interested in my designs;

I do not, on the other hand, own a soul so mean as to be capable of

accepting from any one a favor of which it could be supposed that

I was unworthy.

These considerations taken together were the reason why, for the last

three years, I have been unwilling to publish the treatise I had on hand,

and why I even resolved to give publicity during my life to no other that

was so general, or by which the principles of my physics might be

understood. But since then, two other reasons have come into operation

that have determined me here to subjoin some particular specimens, and

give the public some account of my doings and designs. Of these

considerations, the first is, that if I failed to do so, many who were

cognizant of my previous intention to publish some writings, might have

imagined that the reasons which induced me to refrain from so doing, were

less to my credit than they really are; for although I am not immoderately

desirous of glory, or even, if I may venture so to say, although I am

averse from it in so far as I deem it hostile to repose which I hold in

greater account than aught else, yet, at the same time, I have never

sought to conceal my actions as if they were crimes, nor made use of many

precautions that I might remain unknown; and this partly because I should

have thought such a course of conduct a wrong against myself, and partly

because it would have occasioned me some sort of uneasiness which would

again have been contrary to the perfect mental tranquillity which I court.

And forasmuch as, while thus indifferent to the thought alike of fame or

of forgetfulness, I have yet been unable to prevent myself from acquiring

some sort of reputation, I have thought it incumbent on me to do my best

to save myself at least from being ill-spoken of. The other reason that

has determined me to commit to writing these specimens of philosophy is,

that I am becoming daily more and more alive to the delay which my design

of self-instruction suffers, for want of the infinity of experiments I

require, and which it is impossible for me to make without the assistance

of others: and, without flattering myself so much as to expect the public

to take a large share in my interests, I am yet unwilling to be found so

far wanting in the duty I owe to myself, as to give occasion to those who

shall survive me to make it matter of reproach against me some day, that I

might have left them many things in a much more perfect state than I have

done, had I not too much neglected to make them aware of the ways in which

they could have promoted the accomplishment of my designs.

And I thought that it was easy for me to select some matters which should

neither be obnoxious to much controversy, nor should compel me to expound

more of my principles than I desired, and which should yet be sufficient

clearly to exhibit what I can or cannot accomplish in the sciences.

Whether or not I have succeeded in this it is not for me to say; and I do

not wish to forestall the judgments of others by speaking myself of my

writings; but it will gratify me if they be examined, and, to afford the

greater inducement to this I request all who may have any objections to

make to them, to take the trouble of forwarding these to my publisher, who

will give me notice of them, that I may endeavor to subjoin at the same

time my reply; and in this way readers seeing both at once will more easily

determine where the truth lies; for I do not engage in any case to make

prolix replies, but only with perfect frankness to avow my errors if I am

convinced of them, or if I cannot perceive them, simply to state what I

think is required for defense of the matters I have written, adding

thereto no explication of any new matte that it may not be necessary to

pass without end from one thing to another.

If some of the matters of which I have spoken in the beginning of the

"Dioptrics" and "Meteorics" should offend at first sight, because I call

them hypotheses and seem indifferent about giving proof of them, I request

a patient and attentive reading of the whole, from which I hope those

hesitating will derive satisfaction; for it appears to me that the

reasonings are so mutually connected in these treatises, that, as the last

are demonstrated by the first which are their causes, the first are in

their turn demonstrated by the last which are their effects. Nor must it

be imagined that I here commit the fallacy which the logicians call a

circle; for since experience renders the majority of these effects most

certain, the causes from which I deduce them do not serve so much to

establish their reality as to explain their existence; but on the

contrary, the reality of the causes is established by the reality of the

effects. Nor have I called them hypotheses with any other end in view

except that it may be known that I think I am able to deduce them from

those first truths which I have already expounded; and yet that I have

expressly determined not to do so, to prevent a certain class of minds

from thence taking occasion to build some extravagant philosophy upon what

they may take to be my principles, and my being blamed for it. I refer to

those who imagine that they can master in a day all that another has taken

twenty years to think out, as soon as he has spoken two or three words to

them on the subject; or who are the more liable to error and the less

capable of perceiving truth in very proportion as they are more subtle and

lively. As to the opinions which are truly and wholly mine, I offer no

apology for them as new, -- persuaded as I am that if their reasons be

well considered they will be found to be so simple and so conformed, to

common sense as to appear less extraordinary and less paradoxical than any

others which can be held on the same subjects; nor do I even boast of being

the earliest discoverer of any of them, but only of having adopted them,

neither because they had nor because they had not been held by others,

but solely because reason has convinced me of their truth.

Though artisans may not be able at once to execute the invention which is

explained in the "Dioptrics," I do not think that any one on that account

is entitled to condemn it; for since address and practice are required in

order so to make and adjust the machines described by me as not to

overlook the smallest particular, I should not be less astonished if they

succeeded on the first attempt than if a person were in one day to become

an accomplished performer on the guitar, by merely having excellent sheets

of music set up before him. And if I write in French, which is the

language of my country, in preference to Latin, which is that of my

preceptors, it is because I expect that those who make use of their

unprejudiced natural reason will be better judges of my opinions than

those who give heed to the writings of the ancients only; and as for those

who unite good sense with habits of study, whom alone I desire for judges,

they will not, I feel assured, be so partial to Latin as to refuse to

listen to my reasonings merely because I expound them in the vulgar tongue.

In conclusion, I am unwilling here to say anything very specific of the

progress which I expect to make for the future in the sciences, or to bind

myself to the public by any promise which I am not certain of being able

to fulfill; but this only will I say, that I have resolved to devote what

time I may still have to live to no other occupation than that of

endeavoring to acquire some knowledge of Nature, which shall be of such a

kind as to enable us therefrom to deduce rules in medicine of greater

certainty than those at present in use; and that my inclination is so much

opposed to all other pursuits, especially to such as cannot be useful to

some without being hurtful to others, that if, by any circumstances, I had

been constrained to engage in such, I do not believe that I should have

been able to succeed. Of this I here make a public declaration, though well

aware that it cannot serve to procure for me any consideration in the

world, which, however, I do not in the least affect; and I shall always

hold myself more obliged to those through whose favor I am permitted to

enjoy my retirement without interruption than to any who might offer me

the highest earthly preferments.

End of The Project Gutenberg Etext of Descartes' A Discourse on Method

Rene Descartes

I. The Method of Natural Philosophy

I. RULES OF REASONING IN PHILOSOPHY

We are to admit no more causes of natural Things than such as are both

true and sufficient to explain their appearances.

To this purpose the philosophers say that Nature does nothing in vain,

and more is in vain when less will serve; for Nature is pleased with

simplicity and affects not the pomp of superfluous causes.

RULE II

Therefore to the same natural effects we must, as tar as possible,

assign the same causes.

As to respiration in a man and in a beast, the descent of stones

in Europe and in America, the light of our culinary fire and of the

sun, the reflection of light in the earth and in the planets.

RULE III

The qualities of Bodies, which admit neither intensification nor

remission of degrees, and which are found to belong to all bodies

within the reach of our experiments, are to be esteemed the universal

qualities of all bodies whatsoever.

For since the qualities of bodies are only known to us by experim

ents, we are to hold for universal all such as universally agree wi

th experiments, and such as are not liable to diminution can never be

quite taken away. We are certainly not to relinquish the evidence of

experiments for the sake of dreams and vain fictions of our own

devising; nor are we to recede from the analogy of Nature, which is

wont to be simple and always consonant to itself. We in no other way

know the extension of bodies than by our senses, nor do these reach it

in all bodies; but because we perceive extension in all that are

sensible, therefore we ascribe it universally to allow others also.

That abundance of bodies are hard we learn by experience; and because

the hardness of the whole arises from the hardness of the parts, we

therefore justly infer the hardness of the undivided particles, not

only of the bodies we feel, but of all others. That all bodies are

impenetrable, we gather not from reason, but from sensation. The

bodies which we handle we find impenetrable, and (i thence conclude

impenetrability to be a universal property of all bodies whatsoever.

That all bodies are movable and endowed with certain powers (which we

call the inertia) of persevering in their motion, or in their rest, we

only infer from the like properties observed in the bodies which we

have seen. The extension, hardness, impenetrability, mobility, and

inertia of the whole result from the extension, hardness,

impenetrability, mobility, and inertia of the parts; and hence we

conclude the least particles of all bodies to be also all extended,

and hard and impenetrable, and movable, and endowed with their proper

inertia. And this is the foundation of all philosophy. Moreover, that

the divided but contiguous particles of bodies may be separated from

one another is a matter of observation; and, in the particles that

remain undivided, our minds are able to distinguish yet lesser parts,

as is mathematically demonstrated. But whether the parts so

distinguished and not yet divided may, by the powers of Nature, be

actually divided and separated from one another we cannot certainly

determine. Yet had we the proof of but one experiment that any

undivided particle, in breaking a hard and solid body, suffered a

division, we might by virtue of this rule conclude that the undivided

as well as the divided particles may be divided and actually separated

to infinity. Lastly, if it universally appears, by experiments and

astronomical observations, that all bodies about the earth gravitate

toward the earth, and that in proportion to the quantity of matter

which they severally contain; that the moon likewise, according to the

quantity of its matter, gravitates toward the earth; that, on the

other hand, our sea gravitates toward the moon; and all the planets

one toward another; and the comets in like manner toward the sun: we

must, in consequence of this rule, universally allow that all bodies

whatsoever are endowed with a principle of mutual gravitation. For the

argument from the appearances concludes with more force for the

universal gravitation of all bodies than for their impenetrability, of

which, among those in the celestial regions, we have no experiments

nor any manner of observation. Not that I affirm gravity to be

essential to bodies; by their vis insita I mean nothing but their

inertia. This is immutable. Their gravity is diminished as they recede

from the earth.

RULE IV

In experimental philosophy we are to look upon propositions inferred

by general induction from phenomena as accurately or very nearly true,

notwithstanding any contrary hypotheses that may be imagined, till

such time as other phenomena occur by which they may either be made

more accurate or liable to exceptions.

This rule we must follow, that the argument of induction may not be

evaded by hypotheses.

2. ON HYPOTHESES

From a Letter to Oldenburg

... For the best and safest method of philosophizing seems to

be, first, to inquire diligently into the properties of things and to

establish those properties by experiments, and to proceed later to

hypotheses for the explanation of things themselves. For hypotheses

ought to be applied only in the explanation of the properties of

things, and not made use of in determining them; except in so far as

they may furnish experiments. And if anyone offers conjectures about

the truth of things from the mere possibility of hypotheses, I do not

see by what stipulation anything certain can be determined in any

science; since one or another set of hypotheses may always be devised

which will appear to supply new difficulties. Hence I judged that one

should abstain from contemplating hypotheses, as from improper

argumentation....

From Letters to Cotes

I had yours of Feb. 18th, and the difficulty you mention which

lies in these words, "since every attraction is mutual," is removed by

considering that, as in geometry, the word 'hypothesis' is not taken

in so large a sense as to include the axioms and postulates; so, in

experimental philosophy, it is not to be taken in so large a sense as

to include the first principles or axioms, which I call the laws of

motion. I these principles are deduced from phenomena and made general

by induction, which is the highest evidence that a proposition can

have in this philosophy. And the word 'hypothesis' is here used by me

to signify only such a proposition as is not a phenomenon nor deduced

from any phenomena, but assumed or supposedÑwithout any experimental

proof. Now the mutual and mutually equal attraction of bodies is a

branch of the third law of motion, and how this branch is deduced from

phenomena you may see at the end of the corollaries of the laws of

motion.... If a body attracts another contiguous to it and is not

mutually attracted by the other, the attracted body will drive the

other before it, and both will go away together with an accelerated

motion in infinitum , as it were, by a self-moving principle contrary

to the first law of motion, whereas there is no such phenomenon in all

nature... . And for preventing exceptions against the use of the

word 'hypothesis,' I desire you to conclude the next paragraph in this

manner: "For anything which is not deduced from phenomena ought to be

called a hypothesis, and hypotheses of this kind, whether metaphysical

or physical, whether of occult qualities or mechanical, have no place

in experimental philosophy. In this philosophy, propositions are

deduced from phenomena, and afterward made general by induction."...

On Saturday last I wrote to you, representing that experimental

philosophy proceeds only upon phenomena and deduces general

propositions from them only by induction. And such is the proof of

mutual attraction. And the arguments for the impenetrability,

mobility, and force of all bodies and for the law- of motion are no

better. And he that in experimental philosophy would except against

any of these must draw his objection from some experiment or

phenomenon and not from a mere hypothesis, if the induction be of any

force....~

3. THE EXPERIMENTAL METHOD

From a letter to Oldenburg '

... I cannot think it effectual for determining truth to examine

the several ways by which phenomena may be explained, unless where

there can be a perfect enumeration of all those ways. You know, the

proper method for inquiring after the properties of things is to

deduce them from experiments. And I told you that the theory which I

propounded was evinced to me, not by inferring "is thus because not

otherwise, that is, not by deducing it only from a confutation of

contrary suppositions, but by deriving it from experiment concluding

positively and directly. The way therefore to examine it is by

considering whether the experiments which I propound do prove those

parts of the theory to which they are applied, or by prosecuting other

experiments which the theory may suggest for its examination. To

determine by these and such like queries seems the most proper and

direct way to a conclusion. And therefore I could wish all objections

were suspended from hypotheses or any other heads than these two: of

showing the insufficiency of experiments to determine these queries,

or prove any other parts of my theory, by assigning the flaws and

defects in my conclusions drawn from them; or of producing other

experiments which directly contradict me, if any such may seem to

occur. For if the experiments which I urge be defective, it cannot be

difficult to show the defects; hut if valid, then by proving the

theory, they must render all objections invalid.

II. Fundamental Principles of Natural Philosophy

I. NEWTON'S PREFACE TO THE FIRST EDITION OF THE PRINCIPIA

Since the ancients (as we are told by Pappus) esteemed the

science of mechanics of greatest importance in the investigation of

natural things, and the moderns, rejecting substantial forms and

occult qualities, have endeavored to subject the phenomena of nature

to the laws of mathematics, I have in this treatise cultivated

mathematics as far as it relates to philosophy. The ancients

considered mechanics in a twofold respect: as rational, which proceeds

accurately by demonstration, and practical!. To practical mechanics

all the manual arts belong, from which mechanics took its name. But as

artificers do not work with perfect accuracy, it comes to pass that

mechanics is so distinguished from geometry that what is perfectly

accurate is called geometrical; what is less so is called mechanical.

However, the errors are not in the art, but in the artificers. He that

works with less accuracy is an imperfect mechanic; and if any could

work with perfect accuracy, he would be the most perfect mechanic of

all; for the description of right lines and circles, upon which

geometry is founded, belongs to mechanics. Geometry does not teach us

to draw these lines, but requires them to be drawn; for it requires

that the learner should first be taught to describe these accurately

before he enters upon geometry, then it shows how by these operations

problems may be solved. To describe right lines and circles are

problems, but not geometrical problems. The solution of these problems

is required from mechanics, and by geometry the use of them, when so

solved, is shown; and it is the glory of geometry that from those few

principles, brought From without, it is able to produce so many

things. Therefore geometry is founded in mechanical practice and is

nothing but that part of universal mechanics which accurately proposes

and demonstrates the art of measuring. But since the manual arts are

chiefly employed in the moving of bodies, it happens that geometry is

commonly referred to their magnitude, and mechanics to their motion.

In this sense rational mechanics will be the science of motions

resulting from any forces whatsoever and of the forces required to

produce any motions, accurately proposed and demonstrated. This part

of mechanics, as far as it extended to the five powers which relate to

manual arts, was cultivated by the ancients, who considered gravity

(it not being a manual power) not otherwise than in moving weights by

those powers. But I consider philosophy rather than arts, and write

not concerning manual but natural powers, and consider chiefly those

things which relate to gravity, levity, elastic force, the resistance

of fluids, and the like forces, whether attractive or impulsive; and

therefore I offer this work as the mathematical principles of

philosophy, for the whole burden of philosophy seems to consist in

this: from the phenomena of motions to investigate the forces of

nature, and then from these forces to demonstrate the other phenomena;

and to this end the general propositions in the First and Second Books

are directed. In the Third Book I give an example of this in the

explication of the System of the World; for by the propositions

mathematically demonstrated in the former books, in the third I derive

from the celestial phenomena the forces of gravity with which bodies

tend to the sun and the several planets. Then from these forces, by

other propositions which are also mathematical, I deduce the motions

of the planets, the comets, the moon, and the sea. I wish we could

derive the rest of the phenomena of Nature by the same kind of

reasoning from mechanical principles, for I am induced by many reasons

to suspect that they may all depend upon certain forces by which the

particles of bodies, by some causes hitherto unknown, are either

mutually impelled toward one another and cohere in regular figures, or

are repelled and recede from one 1, another. These forces being

unknown, philosophers have hitherto attempted the search of Nature in

vain; but I hope the principles here laid down will afford some light

either to this or some truer method of philosophy. In the publication

of this work the most acute and universally learned Mr. Edmund Halley

not only assisted me in correcting the errors of the press and

preparing the geometrical figures, but it was through his

solicitations that it came to be published; for when he had obtained

of me my demonstrations of the figure of the celestial orbits, he

continually pressed me to communicate the same to the Royal Society,

who afterward, by their kind encouragement and entreaties, engaged me

to think of publishing them. But after I had begun to consider the

inequalities of the lunar motions, and had entered upon some other

things relating to the laws and measures of gravity and other forces;

and the figures that would be described by bodies attracted according

to given laws; and the motion of several bodies moving among

themselves; the motion of bodies in resisting mediums; the forces,

densities, and motions of mediums; the orbits of the comets, and

suchlike, I deferred that publication till I had made a search into

those matters and could put forth the whole together. What relates to

the lunar motions (being imperfect), I have put all together in the

corollaries of Proposition LXVI, to avoid being obliged to propose and

distinctly demonstrate the several things there contained in a method

more prolix than the subject deserved and interrupt the series of the

other propositions. Some things, found out after the rest, I chose to

insert in places less suitable, rather than change the number of the

propositions and the citations. I heartily beg that what I have here

done may be read with forbearance and that my labors in a subject so

difficult may be examined, not so much with the view to censure, as to

remedy their defects...