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 dividedinto six Parts: and, in the first, will be found variousconsiderations touching the Sciences; in the second, the principalrules 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 ofGod and of the Human Soul, which are the foundations of his Metaphysic;in the fifth, the order of the Physical questions which he hasinvestigated, and, in particular, the explication of the motion of theheart and of some other difficulties pertaining to Medicine, as alsothe difference between the soul of man and that of the brutes; and, inthe last, what the Author believes to be required in order to greateradvancement in the investigation of Nature than has yet been made, withthe reasons that have induced him to write. 

PART I

Good sense is, of all things among men, the most equally distributed;for every one thinks himself so abundantly provided with it, that thoseeven who are the most difficult to satisfy in everything else, do notusually desire a larger measure of this quality than they alreadypossess. And in this it is not likely that all are mistaken theconviction is rather to be held as testifying that the power of judgingaright and of distinguishing truth from error, which is properly whatis called good sense or reason, is by nature equal in all men; andthat the diversity of our opinions, consequently, does not arise fromsome being endowed with a larger share of reason than others, butsolely from this, that we conduct our thoughts along different ways, and do not fix our attention on the same objects. For to be possessedof a vigorous mind is not enough; the prime requisite is rightly toapply it. The greatest minds, as they are capable of the highestexcellences, are open likewise to the greatest aberrations; and thosewho travel very slowly may yet make far greater progress, provided theykeep 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 moreperfect than those of the generality; on the contrary, I have oftenwished that I were equal to some others in promptitude of thought, orin clearness and distinctness of imagination, or in fullness andreadiness of memory. And besides these, I know of no other qualitiesthat contribute to the perfection of the mind; for as to the reason orsense, inasmuch as it is that alone which constitutes us men, anddistinguishes us from the brutes, I am disposed to believe that it isto be found complete in each individual; and on this point to adopt thecommon opinion of philosophers, who say that the difference of greaterand less holds only among the accidents, and not among the forms ornatures of individuals of the same species. 

I will not hesitate, however, to avow my belief that it has been mysingular good fortune to have very early in life fallen in withcertain tracks which have conducted me to considerations and maxims, ofwhich I have formed a method that gives me the means, as I think, ofgradually augmenting my knowledge, and of raising it by little andlittle to the highest point which the mediocrity of my talents and thebrief duration of my life will permit me to reach. For I have alreadyreaped from it such fruits that, although I have been accustomed tothink lowly enough of myself, and although when I look with the eye ofa philosopher at the varied courses and pursuits of mankind at large, Ifind scarcely one which does not appear in vain and useless, Inevertheless derive the highest satisfaction from the progress Iconceive myself to have already made in the search after truth, andcannot help entertaining such expectations of the future as to believethat if, among the occupations of men as men, there is any one reallyexcellent and important, it is that which I have chosen. 

After all, it is possible I may be mistaken; and it is but a littlecopper and glass, perhaps, that I take for gold and diamonds. I knowhow very liable we are to delusion in what relates to ourselves, andalso how much the judgments of our friends are to be suspected whengiven in our favor. But I shall endeavor in this discourse to describethe paths I have followed, and to delineate my life as in a picture, inorder that each one may also be able to judge of them for himself, andthat in the general opinion entertained of them, as gathered fromcurrent report, I myself may have a new help towards instruction to beadded to those I have been in the habit of employing. 

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

From my childhood, I have been familiar with letters; and as I wasgiven to believe that by their help a clear and certain knowledge ofall that is useful in life might be acquired, I was ardently desirousof instruction. But as soon as I had finished the entire course ofstudy, at the close of which it is customary to be admitted into theorder of the learned, I completely changed my opinion. For I foundmyself involved in so many doubts and errors, that I was convinced Ihad advanced no farther in all my attempts at learning, than thediscovery at every turn of my own ignorance. And yet I was studying inone of the most celebrated schools in Europe, in which I thought theremust be learned men, if such were anywhere to be found. I had beentaught all that others learned there; and not contented with thesciences actually taught us, I had, in addition, read all the booksthat had fallen into my hands, treating of such branches as areesteemed the most curious and rare. I knew the judgment which othershad formed of me; and I did not find that I was considered inferior tomy fellows, although there were among them some who were already markedout to fill the places of our instructors. And, in fine, our ageappeared to me as flourishing, and as fertile in powerful minds as anypreceding one. I was thus led to take the liberty of judging of allother men by myself, and of concluding that there was no science inexistence that was of such a nature as I had previously been given tobelieve. 

I still continued, however, to hold in esteem the studies of theschools. I was aware that the languages taught in them are necessaryto the understanding of the writings of the ancients; that the grace offable stirs the mind; that the memorable deeds of history elevate it;and, if read with discretion, aid in forming the judgment; that theperusal of all excellent books is, as it were, to interview with thenoblest men of past ages, who have written them, and even a studiedinterview, in which are discovered to us only their choicest thoughts;that eloquence has incomparable force and beauty; that poesy has itsravishing graces and delights; that in the mathematics there are manyrefined discoveries eminently suited to gratify the inquisitive, aswell as further all the arts an lessen the labour of man; that numeroushighly useful precepts and exhortations to virtue are contained intreatises on morals; that theology points out the path to heaven; thatphilosophy affords the means of discoursing with an appearance of truthon all matters, and commands the admiration of the more simple; thatjurisprudence, medicine, and the other sciences, secure for theircultivators honors and riches; and, in fine, that it is useful tobestow some attention upon all, even upon those abounding the most insuperstition and error, that we may be in a position to determine theirreal 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 theirhistories and fables. For to hold converse with those of other agesand to travel, are almost the same thing. It is useful to knowsomething of the manners of different nations, that we may be enabledto form a more correct judgment regarding our own, and be preventedfrom thinking that everything contrary to our customs is ridiculous andirrational, a conclusion usually come to by those whose experience hasbeen limited to their own country. On the other hand, when too muchtime is occupied in traveling, we become strangers to our nativecountry; and the over curious in the customs of the past are generallyignorant of those of the present. Besides, fictitious narratives leadus to imagine the possibility of many events that are impossible; andeven the most faithful histories, if they do not wholly misrepresentmatters, or exaggerate their importance to render the account of themmore worthy of perusal, omit, at least, almost always the meanest andleast striking of the attendant circumstances; hence it happens thatthe remainder does not represent the truth, and that such as regulatetheir conduct by examples drawn from this source, are apt to fall intothe extravagances of the knight-errants of romance, and to entertainprojects that exceed their powers. 

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

I was especially delighted with the mathematics, on account of thecertitude and evidence of their reasonings; but I had not as yet aprecise knowledge of their true use; and thinking that they butcontributed to the advancement of the mechanical arts, I was astonishedthat foundations, so strong and solid, should have had no loftiersuperstructure reared on them. On the other hand, I compared thedisquisitions of the ancient moralists to very towering and magnificentpalaces with no better foundation than sand and mud: they laud thevirtues very highly, and exhibit them as estimable far above anythingon earth; but they give us no adequate criterion of virtue, andfrequently 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 opento the most ignorant than to the most learned, and that the revealedtruths which lead to heaven are above our comprehension, I did notpresume to subject them to the impotency of my reason; and I thoughtthat in order competently to undertake their examination, there wasneed 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 hadbeen cultivated for many ages by the most distinguished men, and thatyet there is not a single matter within its sphere which is not stillin dispute, and nothing, therefore, which is above doubt, I did notpresume to anticipate that my success would be greater in it than thatof others; and further, when I considered the number of conflictingopinions 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 thatwas only probable. 

As to the other sciences, inasmuch as these borrow their principlesfrom philosophy, I judged that no solid superstructures could be rearedon foundations so infirm; and neither the honor nor the gain held outby them was sufficient to determine me to their cultivation: for I wasnot, thank Heaven, in a condition which compelled me to makemerchandise of science for the bettering of my fortune; and though Imight not profess to scorn glory as a cynic, I yet made very slightaccount of that honor which I hoped to acquire only through fictitioustitles. And, in fine, of false sciences I thought I knew the worthsufficiently to escape being deceived by the professions of analchemist, the predictions of an astrologer, the impostures of amagician, or by the artifices and boasting of any of those who professto know things of which they are ignorant. 

For these reasons, as soon as my age permitted me to pass from underthe control of my instructors, I entirely abandoned the study ofletters, and resolved no longer to seek any other science than theknowledge of myself, or of the great book of the world. I spent theremainder of my youth in traveling, in visiting courts and armies, inholding intercourse with men of different dispositions and ranks, incollecting varied experience, in proving myself in the differentsituations into which fortune threw me, and, above all, in making suchreflection on the matter of my experience as to secure my improvement. For it occurred to me that I should find much more truth in thereasonings of each individual with reference to the affairs in which heis personally interested, and the issue of which must presently punishhim if he has judged amiss, than in those conducted by a man of lettersin his study, regarding speculative matters that are of no practicalmoment, and followed by no consequences to himself, farther, perhaps, than that they foster his vanity the better the more remote they arefrom common sense; requiring, as they must in this case, the exerciseof greater ingenuity and art to render them probable. In addition, Ihad always a most earnest desire to know how to distinguish the truefrom the false, in order that I might be able clearly to discriminatethe right path in life, and proceed in it with confidence. 

It is true that, while busied only in considering the manners of othermen, I found here, too, scarce any ground for settled conviction, andremarked hardly less contradiction among them than in the opinions ofthe philosophers. So that the greatest advantage I derived from thestudy consisted in this, that, observing many things which, howeverextravagant and ridiculous to our apprehension, are yet by commonconsent received and approved by other great nations, I learned toentertain too decided a belief in regard to nothing of the truth ofwhich I had been persuaded merely by example and custom; and thus Igradually extricated myself from many errors powerful enough to darkenour natural intelligence, and incapacitate us in great measure fromlistening to reason. But after I had been occupied several years inthus studying the book of the world, and in essaying to gather someexperience, I at length resolved to make myself an object of study, andto employ all the powers of my mind in choosing the paths I ought tofollow, an undertaking which was accompanied with greater success thanit 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 wasreturning to the army from the coronation of the emperor, the settingin of winter arrested me in a locality where, as I found no society tointerest me, and was besides fortunately undisturbed by any cares orpassions, I remained the whole day in seclusion, with full opportunityto occupy my attention with my own thoughts. Of these one of the veryfirst that occurred to me was, that there is seldom so much perfectionin works composed of many separate parts, upon which different handshad been employed, as in those completed by a single master. Thus itis observable that the buildings which a single architect has plannedand executed, are generally more elegant and commodious than thosewhich several have attempted to improve, by making old walls serve forpurposes for which they were not originally built. Thus also, thoseancient cities which, from being at first only villages, have become, in course of time, large towns, are usually but ill laid out comparedwith the regularity constructed towns which a professional architecthas freely planned on an open plain; so that although the severalbuildings of the former may often equal or surpass in beauty those ofthe latter, yet when one observes their indiscriminate juxtaposition, there a large one and here a small, and the consequent crookedness andirregularity of the streets, one is disposed to allege that chancerather than any human will guided by reason must have led to such anarrangement. And if we consider that nevertheless there have been atall times certain officers whose duty it was to see that privatebuildings contributed to public ornament, the difficulty of reachinghigh perfection with but the materials of others to operate on, will bereadily acknowledged. In the same way I fancied that those nationswhich, starting from a semi-barbarous state and advancing tocivilization by slow degrees, have had their laws successivelydetermined, and, as it were, forced upon them simply by experience ofthe hurtfulness of particular crimes and disputes, would by thisprocess come to be possessed of less perfect institutions than thosewhich, from the commencement of their association as communities, havefollowed the appointments of some wise legislator. It is thus quitecertain that the constitution of the true religion, the ordinances ofwhich are derived from God, must be incomparably superior to that ofevery other. And, to speak of human affairs, I believe that thepre-eminence of Sparta was due not to the goodness of each of its lawsin particular, for many of these were very strange, and even opposed togood morals, but to the circumstance that, originated by a singleindividual, they all tended to a single end. In the same way I thoughtthat the sciences contained in books (such of them at least as are madeup of probable reasonings, without demonstrations), composed as theyare of the opinions of many different individuals massed together, arefarther removed from truth than the simple inferences which a man ofgood sense using his natural and unprejudiced judgment draws respectingthe matters of his experience. And because we have all to pass througha state of infancy to manhood, and have been of necessity, for a lengthof time, governed by our desires and preceptors (whose dictates werefrequently conflicting, while neither perhaps always counseled us forthe best), I farther concluded that it is almost impossible that ourjudgments can be so correct or solid as they would have been, had ourreason been mature from the moment of our birth, and had we always beenguided by it alone. 

It is true, however, that it is not customary to pull down all thehouses of a town with the single design of rebuilding them differently, and thereby rendering the streets more handsome; but it often happensthat a private individual takes down his own with the view of erectingit anew, and that people are even sometimes constrained to this whentheir houses are in danger of falling from age, or when the foundationsare insecure. With this before me by way of example, I was persuadedthat it would indeed be preposterous for a private individual to thinkof reforming a state by fundamentally changing it throughout, andoverturning it in order to set it up amended; and the same I thoughtwas true of any similar project for reforming the body of the sciences, or the order of teaching them established in the schools: but as forthe opinions which up to that time I had embraced, I thought that Icould not do better than resolve at once to sweep them wholly away, that I might afterwards be in a position to admit either others morecorrect, or even perhaps the same when they had undergone the scrutinyof reason. I firmly believed that in this way I should much bettersucceed in the conduct of my life, than if I built only upon oldfoundations, and leaned upon principles which, in my youth, I had takenupon trust. For although I recognized various difficulties in thisundertaking, these were not, however, without remedy, nor once to becompared with such as attend the slightest reformation in publicaffairs. Large bodies, if once overthrown, are with great difficultyset up again, or even kept erect when once seriously shaken, and thefall of such is always disastrous. Then if there are any imperfectionsin the constitutions of states (and that many such exist the diversityof constitutions is alone sufficient to assure us), custom has withoutdoubt materially smoothed their inconveniences, and has even managed tosteer altogether clear of, or insensibly corrected a number whichsagacity could not have provided against with equal effect; and, infine, the defects are almost always more tolerable than the changenecessary for their removal; in the same manner that highways whichwind among mountains, by being much frequented, become gradually sosmooth and commodious, that it is much better to follow them than toseek a straighter path by climbing over the tops of rocks anddescending to the bottoms of precipices. 

Hence it is that I cannot in any degree approve of those restless andbusy meddlers who, called neither by birth nor fortune to take part inthe management of public affairs, are yet always projecting reforms;and if I thought that this tract contained aught which might justifythe suspicion that I was a victim of such folly, I would by no meanspermit its publication. I have never contemplated anything higher thanthe reformation of my own opinions, and basing them on a foundationwholly my own. And although my own satisfaction with my work has ledme to present here a draft of it, I do not by any means thereforerecommend to every one else to make a similar attempt. Those whom Godhas endowed with a larger measure of genius will entertain, perhaps, designs still more exalted; but for the many I am much afraid lest eventhe present undertaking be more than they can safely venture toimitate. The single design to strip one's self of all past beliefs isone that ought not to be taken by every one. The majority of men iscomposed of two classes, for neither of which would this be at all abefitting resolution: in the first place, of those who with more thana due confidence in their own powers, are precipitate in theirjudgments and want the patience requisite for orderly and circumspectthinking; whence it happens, that if men of this class once take theliberty to doubt of their accustomed opinions, and quit the beatenhighway, they will never be able to thread the byway that would leadthem by a shorter course, and will lose themselves and continue towander for life; in the second place, of those who, possessed ofsufficient sense or modesty to determine that there are others whoexcel them in the power of discriminating between truth and error, andby whom they may be instructed, ought rather to content themselves withthe 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 knownthe diversities of opinion that from time immemorial have prevailedamong men of the greatest learning. But I had become aware, even soearly as during my college life, that no opinion, however absurd andincredible, can be imagined, which has not been maintained by some onof the philosophers; and afterwards in the course of my travels Iremarked that all those whose opinions are decidedly repugnant to oursare not in that account barbarians and savages, but on the contrarythat many of these nations make an equally good, if not better, use oftheir reason than we do. I took into account also the very differentcharacter which a person brought up from infancy in France or Germanyexhibits, from that which, with the same mind originally, thisindividual would have possessed had he lived always among the Chineseor with savages, and the circumstance that in dress itself the fashionwhich pleased us ten years ago, and which may again, perhaps, bereceived into favor before ten years have gone, appears to us at thismoment extravagant and ridiculous. I was thus led to infer that theground of our opinions is far more custom and example than any certainknowledge. And, finally, although such be the ground of our opinions, I remarked that a plurality of suffrages is no guarantee of truth whereit is at all of difficult discovery, as in such cases it is much morelikely that it will be found by one than by many. I could, however, select from the crowd no one whose opinions seemed worthy ofpreference, and thus I found myself constrained, as it were, to use myown reason in the conduct of my life. 

But like one walking alone and in the dark, I resolved to proceed soslowly and with such circumspection, that if I did not advance far, Iwould at least guard against falling. I did not even choose to dismisssummarily any of the opinions that had crept into my belief withouthaving been introduced by reason, but first of all took sufficient timecarefully to satisfy myself of the general nature of the task I wassetting myself, and ascertain the true method by which to arrive at theknowledge of whatever lay within the compass of my powers. 

Among the branches of philosophy, I had, at an earlier period, givensome attention to logic, and among those of the mathematics togeometrical analysis and algebra, --three arts or sciences which ought, as I conceived, to contribute something to my design. But, onexamination, I found that, as for logic, its syllogisms and themajority of its other precepts are of avail--rather in thecommunication of what we already know, or even as the art of Lully, inspeaking without judgment of things of which we are ignorant, than inthe investigation of the unknown; and although this science containsindeed a number of correct and very excellent precepts, there are, nevertheless, so many others, and these either injurious orsuperfluous, mingled with the former, that it is almost quite asdifficult to effect a severance of the true from the false as it is toextract a Diana or a Minerva from a rough block of marble. Then as tothe analysis of the ancients and the algebra of the moderns, besidesthat they embrace only matters highly abstract, and, to appearance, ofno use, the former is so exclusively restricted to the consideration offigures, that it can exercise the understanding only on condition ofgreatly fatiguing the imagination; and, in the latter, there is socomplete a subjection to certain rules and formulas, that there resultsan art full of confusion and obscurity calculated to embarrass, insteadof a science fitted to cultivate the mind. By these considerations Iwas induced to seek some other method which would comprise theadvantages of the three and be exempt from their defects. And as amultitude of laws often only hampers justice, so that a state is bestgoverned when, with few laws, these are rigidly administered; in likemanner, instead of the great number of precepts of which logic iscomposed, I believed that the four following would prove perfectlysufficient for me, provided I took the firm and unwavering resolutionnever in a single instance to fail in observing them. 

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

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

The third, to conduct my thoughts in such order that, by commencingwith objects the simplest and easiest to know, I might ascend by littleand little, and, as it were, step by step, to the knowledge of the morecomplex; assigning in thought a certain order even to those objectswhich in their own nature do not stand in a relation of antecedence andsequence. 

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

The long chains of simple and easy reasonings by means of whichgeometers are accustomed to reach the conclusions of their mostdifficult demonstrations, had led me to imagine that all things, to theknowledge of which man is competent, are mutually connected in the sameway, and that there is nothing so far removed from us as to be beyondour reach, or so hidden that we cannot discover it, provided only weabstain from accepting the false for the true, and always preserve inour thoughts the order necessary for the deduction of one truth fromanother. And I had little difficulty in determining the objects withwhich it was necessary to commence, for I was already persuaded that itmust be with the simplest and easiest to know, and, considering that ofall those who have hitherto sought truth in the sciences, themathematicians alone have been able to find any demonstrations, thatis, any certain and evident reasons, I did not doubt but that such musthave been the rule of their investigations. I resolved to commence, therefore, with the examination of the simplest objects, notanticipating, however, from this any other advantage than that to befound in accustoming my mind to the love and nourishment of truth, andto a distaste for all such reasonings as were unsound. But I had nointention on that account of attempting to master all the particularsciences commonly denominated mathematics: but observing that, howeverdifferent their objects, they all agree in considering only the variousrelations or proportions subsisting among those objects, I thought itbest for my purpose to consider these proportions in the most generalform possible, without referring them to any objects in particular, except such as would most facilitate the knowledge of them, and withoutby any means restricting them to these, that afterwards I might thus bethe better able to apply them to every other class of objects to whichthey are legitimately applicable. Perceiving further, that in order tounderstand these relations I should sometimes have to consider them oneby one and sometimes only to bear them in mind, or embrace them in theaggregate, I thought that, in order the better to consider themindividually, I should view them as subsisting between straight lines, than which I could find no objects more simple, or capable of beingmore distinctly represented to my imagination and senses; and on theother hand, that in order to retain them in the memory or embrace anaggregate of many, I should express them by certain characters thebriefest possible. In this way I believed that I could borrow all thatwas best both in geometrical analysis and in algebra, and correct allthe defects of the one by help of the other. 

And, in point of fact, the accurate observance of these few preceptsgave me, I take the liberty of saying, such ease in unraveling all thequestions embraced in these two sciences, that in the two or threemonths I devoted to their examination, not only did I reach solutionsof questions I had formerly deemed exceedingly difficult but even asregards questions of the solution of which I continued ignorant, I wasenabled, as it appeared to me, to determine the means whereby, and theextent to which a solution was possible; results attributable to thecircumstance that I commenced with the simplest and most generaltruths, and that thus each truth discovered was a rule available in thediscovery of subsequent ones Nor in this perhaps shall I appear toovain, if it be considered that, as the truth on any particular point isone whoever apprehends the truth, knows all that on that point can beknown. The child, for example, who has been instructed in the elementsof arithmetic, and has made a particular addition, according to rule, may be assured that he has found, with respect to the sum of thenumbers before him, and that in this instance is within the reach ofhuman genius. Now, in conclusion, the method which teaches adherenceto the true order, and an exact enumeration of all the conditions ofthe thing sought includes all that gives certitude to the rules ofarithmetic. 

But the chief ground of my satisfaction with thus method, was theassurance I had of thereby exercising my reason in all matters, if notwith absolute perfection, at least with the greatest attainable by me:besides, I was conscious that by its use my mind was becoming graduallyhabituated to clearer and more distinct conceptions of its objects; andI hoped also, from not having restricted this method to any particularmatter, to apply it to the difficulties of the other sciences, with notless success than to those of algebra. I should not, however, on thisaccount have ventured at once on the examination of all thedifficulties of the sciences which presented themselves to me, for thiswould have been contrary to the order prescribed in the method, butobserving that the knowledge of such is dependent on principlesborrowed from philosophy, in which I found nothing certain, I thoughtit necessary first of all to endeavor to establish its principles. Andbecause I observed, besides, that an inquiry of this kind was of allothers of the greatest moment, and one in which precipitancy andanticipation in judgment were most to be dreaded, I thought that Iought not to approach it till I had reached a more mature age (being atthat time but twenty-three), and had first of all employed much of mytime in preparation for the work, as well by eradicating from my mindall the erroneous opinions I had up to that moment accepted, as byamassing variety of experience to afford materials for my reasonings, and by continually exercising myself in my chosen method with a view toincreased skill in its application. 

PART III

And finally, as it is not enough, before commencing to rebuild thehouse in which we live, that it be pulled down, and materials andbuilders provided, or that we engage in the work ourselves, accordingto a plan which we have beforehand carefully drawn out, but as it islikewise necessary that we be furnished with some other house in whichwe may live commodiously during the operations, so that I might notremain irresolute in my actions, while my reason compelled me tosuspend my judgement, and that I might not be prevented from livingthenceforward in the greatest possible felicity, I formed a provisorycode of morals, composed of three or four maxims, with which I amdesirous to make you acquainted. 

The first was to obey the laws and customs of my country, adheringfirmly to the faith in which, by the grace of God, I had been educatedfrom my childhood and regulating my conduct in every other matteraccording to the most moderate opinions, and the farthest removed fromextremes, which should happen to be adopted in practice with generalconsent 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 noughtbecause I wished to subject them all to examination, I was convincedthat I could not do better than follow in the meantime the opinions ofthe most judicious; and although there are some perhaps among thePersians and Chinese as judicious as among ourselves, expediency seemedto dictate that I should regulate my practice conformably to theopinions of those with whom I should have to live; and it appeared tome that, in order to ascertain the real opinions of such, I oughtrather to take cognizance of what they practised than of what theysaid, not only because, in the corruption of our manners, there are fewdisposed to speak exactly as they believe, but also because very manyare not aware of what it is that they really believe; for, as the actof mind by which a thing is believed is different from that by which weknow 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 mostmoderate, as much for the reason that these are always the mostconvenient for practice, and probably the best (for all excess isgenerally vicious), as that, in the event of my falling into error, Imight be at less distance from the truth than if, having chosen one ofthe extremes, it should turn out to be the other which I ought to haveadopted. And I placed in the class of extremes especially all promisesby which somewhat of our freedom is abridged; not that I disapproved ofthe laws which, to provide against the instability of men of feebleresolution, when what is sought to be accomplished is some good, permitengagements by vows and contracts binding the parties to persevere init, or even, for the security of commerce, sanction similar engagementswhere the purpose sought to be realized is indifferent: but because Idid not find anything on earth which was wholly superior to change, andbecause, for myself in particular, I hoped gradually to perfect myjudgments, and not to suffer them to deteriorate, I would have deemedit a grave sin against good sense, if, for the reason that I approvedof something at a particular time, I therefore bound myself to hold itfor good at a subsequent time, when perhaps it had ceased to be so, orI had ceased to esteem it such. 

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

My third maxim was to endeavor always to conquer myself rather thanfortune, and change my desires rather than the order of the world, andin general, accustom myself to the persuasion that, except our ownthoughts, there is nothing absolutely in our power; so that when wehave done our best in things external to us, all wherein we fail ofsuccess is to be held, as regards us, absolutely impossible: and thissingle principle seemed to me sufficient to prevent me from desiringfor the future anything which I could not obtain, and thus render mecontented; for since our will naturally seeks those objects alone whichthe understanding represents as in some way possible of attainment, itis plain, that if we consider all external goods as equally beyond ourpower, we shall no more regret the absence of such goods as seem due toour birth, when deprived of them without any fault of ours, than ournot possessing the kingdoms of China or Mexico, and thus making, so tospeak, a virtue of necessity, we shall no more desire health indisease, or freedom in imprisonment, than we now do bodiesincorruptible as diamonds, or the wings of birds to fly with. But Iconfess there is need of prolonged discipline and frequently repeatedmeditation to accustom the mind to view all objects in this light; andI believe that in this chiefly consisted the secret of the power ofsuch philosophers as in former times were enabled to rise superior tothe influence of fortune, and, amid suffering and poverty, enjoy ahappiness which their gods might have envied. For, occupiedincessantly with the consideration of the limits prescribed to theirpower by nature, they became so entirely convinced that nothing was attheir disposal except their own thoughts, that this conviction was ofitself sufficient to prevent their entertaining any desire of otherobjects; and over their thoughts they acquired a sway so absolute, thatthey had some ground on this account for esteeming themselves more richand more powerful, more free and more happy, than other men who, whatever be the favors heaped on them by nature and fortune, ifdestitute of this philosophy, can never command the realization of alltheir desires. 

In fine, to conclude this code of morals, I thought of reviewing thedifferent occupations of men in this life, with the view of makingchoice of the best. And, without wishing to offer any remarks on theemployments of others, I may state that it was my conviction that Icould 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 makingthe greatest progress I was able in the knowledge of truth, on theprinciples of the method which I had prescribed to myself. Thismethod, from the time I had begun to apply it, had been to me thesource of satisfaction so intense as to lead me to, believe that moreperfect or more innocent could not be enjoyed in this life; and as byits means I daily discovered truths that appeared to me of someimportance, and of which other men were generally ignorant, thegratification thence arising so occupied my mind that I was whollyindifferent to every other object. Besides, the three preceding maximswere founded singly on the design of continuing the work ofself-instruction. For since God has endowed each of us with some lightof reason by which to distinguish truth from error, I could not havebelieved that I ought for a single moment to rest satisfied with theopinions of another, unless I had resolved to exercise my own judgmentin examining these whenever I should be duly qualified for the task. Nor could I have proceeded on such opinions without scruple, had Isupposed that I should thereby forfeit any advantage for attainingstill more accurate, should such exist. And, in fine, I could not haverestrained my desires, nor remained satisfied had I not followed a pathin which I thought myself certain of attaining all the knowledge to theacquisition of which I was competent, as well as the largest amount ofwhat is truly good which I could ever hope to secure Inasmuch as weneither seek nor shun any object except in so far as our understandingrepresents it as good or bad, all that is necessary to right action isright judgment, and to the best action the most correct judgment, thatis, to the acquisition of all the virtues with all else that is trulyvaluable and within our reach; and the assurance of such an acquisitioncannot fail to render us contented. 

Having thus provided myself with these maxims, and having placed themin reserve along with the truths of faith, which have ever occupiedthe first place in my belief, I came to the conclusion that I mightwith freedom set about ridding myself of what remained of my opinions. And, inasmuch as I hoped to be better able successfully to accomplishthis work by holding intercourse with mankind, than by remaining longershut up in the retirement where these thoughts had occurred to me, Ibetook me again to traveling before the winter was well ended. And, during the nine subsequent years, I did nothing but roam from one placeto another, desirous of being a spectator rather than an actor in theplays exhibited on the theater of the world; and, as I made it mybusiness in each matter to reflect particularly upon what might fairlybe doubted and prove a source of error, I gradually rooted out from mymind all the errors which had hitherto crept into it. Not that in thisI imitated the sceptics who doubt only that they may doubt, and seeknothing beyond uncertainty itself; for, on the contrary, my design wassingly to find ground of assurance, and cast aside the loose earth andsand, that I might reach the rock or the clay. In this, as appears tome, I was successful enough; for, since I endeavored to discover thefalsehood or incertitude of the propositions I examined, not by feebleconjectures, but by clear and certain reasonings, I met with nothing sodoubtful as not to yield some conclusion of adequate certainty, although this were merely the inference, that the matter in questioncontained nothing certain. And, just as in pulling down an old house, we usually reserve the ruins to contribute towards the erection, so, indestroying such of my opinions as I judged to be Ill-founded, I made avariety of observations and acquired an amount of experience of which Iavailed myself in the establishment of more certain. And further, Icontinued to exercise myself in the method I had prescribed; for, besides taking care in general to conduct all my thoughts according toits rules, I reserved some hours from time to time which I expresslydevoted to the employment of the method in the solution of mathematicaldifficulties, or even in the solution likewise of some questionsbelonging to other sciences, but which, by my having detached them fromsuch principles of these sciences as were of inadequate certainty, wererendered almost mathematical: the truth of this will be manifest fromthe numerous examples contained in this volume. And thus, without inappearance living otherwise than those who, with no other occupationthan that of spending their lives agreeably and innocently, study tosever pleasure from vice, and who, that they may enjoy their leisurewithout ennui, have recourse to such pursuits as are honorable, I wasnevertheless prosecuting my design, and making greater progress in theknowledge of truth, than I might, perhaps, have made had I been engagedin the perusal of books merely, or in holding converse with men ofletters. 

These nine years passed away, however, before I had come to anydeterminate judgment respecting the difficulties which form matter ofdispute among the learned, or had commenced to seek the principles ofany philosophy more certain than the vulgar. And the examples of manymen of the highest genius, who had, in former times, engaged in thisinquiry, but, as appeared to me, without success, led me to imagine itto be a work of so much difficulty, that I would not perhaps haveventured on it so soon had I not heard it currently rumored that I hadalready completed the inquiry. I know not what were the grounds ofthis opinion; and, if my conversation contributed in any measure to itsrise, this must have happened rather from my having confessed myIgnorance with greater freedom than those are accustomed to do who havestudied a little, and expounded perhaps, the reasons that led me todoubt of many of those things that by others are esteemed certain, thanfrom my having boasted of any system of philosophy. But, as I am of adisposition that makes me unwilling to be esteemed different from whatI really am, I thought it necessary to endeavor by all means to rendermyself worthy of the reputation accorded to me; and it is now exactlyeight years since this desire constrained me to remove from all thoseplaces where interruption from any of my acquaintances was possible, and betake myself to this country, in which the long duration of thewar has led to the establishment of such discipline, that the armiesmaintained seem to be of use only in enabling the inhabitants to enjoymore securely the blessings of peace and where, in the midst of a greatcrowd actively engaged in business, and more careful of their ownaffairs than curious about those of others, I have been enabled to livewithout being deprived of any of the conveniences to be had in the mostpopulous cities, and yet as solitary and as retired as in the midst ofthe most remote deserts. 

PART IV

I am in doubt as to the propriety of making my first meditations in theplace above mentioned matter of discourse; for these are sometaphysical, and so uncommon, as not, perhaps, to be acceptable toevery one. And yet, that it may be determined whether the foundationsthat I have laid are sufficiently secure, I find myself in a measureconstrained to advert to them. I had long before remarked that, inrelation to practice, it is sometimes necessary to adopt, as if abovedoubt, opinions which we discern to be highly uncertain, as has beenalready said; but as I then desired to give my attention solely to thesearch after truth, I thought that a procedure exactly the opposite wascalled for, and that I ought to reject as absolutely false all opinionsin regard to which I could suppose the least ground for doubt, in orderto ascertain whether after that there remained aught in my belief thatwas wholly indubitable. Accordingly, seeing that our senses sometimesdeceive us, I was willing to suppose that there existed nothing reallysuch 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 falseall the reasonings I had hitherto taken for demonstrations; andfinally, when I considered that the very same thoughts (presentations)which we experience when awake may also be experienced when we areasleep, while there is at that time not one of them true, I supposedthat all the objects (presentations) that had ever entered into my mindwhen awake, had in them no more truth than the illusions of my dreams. But immediately upon this I observed that, whilst I thus wished tothink that all was false, it was absolutely necessary that I, who thusthought, should be somewhat; and as I observed that this truth, Ithink, therefore I am (COGITO ERGO SUM), was so certain and of suchevidence that no ground of doubt, however extravagant, could be allegedby the sceptics capable of shaking it, I concluded that I might, without scruple, accept it as the first principle of the philosophy ofwhich I was in search. 

In the next place, I attentively examined what I was and as I observedthat I could suppose that I had no body, and that there was no worldnor any place in which I might be; but that I could not thereforesuppose that I was not; and that, on the contrary, from the verycircumstance that I thought to doubt of the truth of other things, itmost clearly and certainly followed that I was; while, on the otherhand, if I had only ceased to think, although all the other objectswhich I had ever imagined had been in reality existent, I would havehad no reason to believe that I existed; I thence concluded that I wasa substance whose whole essence or nature consists only in thinking, and which, that it may exist, has need of no place, nor is dependent onany material thing; so that "I, " that is to say, the mind by which I amwhat I am, is wholly distinct from the body, and is even more easilyknown 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 truthand certainty of a proposition; for since I had discovered one which Iknew to be true, I thought that I must likewise be able to discover theground 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 oftheir truth beyond this, that I see very clearly that in order to thinkit is necessary to exist, I concluded that I might take, as a generalrule, the principle, that all the things which we very clearly anddistinctly conceive are true, only observing, however, that there issome difficulty in rightly determining the objects which we distinctlyconceive. 

In the next place, from reflecting on the circumstance that I doubted, and that consequently my being was not wholly perfect (for I clearlysaw that it was a greater perfection to know than to doubt), I was ledto inquire whence I had learned to think of something more perfect thanmyself; and I clearly recognized that I must hold this notion from somenature which in reality was more perfect. As for the thoughts of manyother 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 themsuperior to myself, I could believe that, if these were true, they weredependencies on my own nature, in so far as it possessed a certainperfection, and, if they were false, that I held them from nothing, that is to say, that they were in me because of a certain imperfectionof my nature. But this could not be the case with-the idea of a naturemore perfect than myself; for to receive it from nothing was a thingmanifestly impossible; and, because it is not less repugnant that themore perfect should be an effect of, and dependence on the lessperfect, than that something should proceed from nothing, it wasequally impossible that I could hold it from myself: accordingly, itbut remained that it had been placed in me by a nature which was inreality more perfect than mine, and which even possessed within itselfall the perfections of which I could form any idea; that is to say, ina single word, which was God. And to this I added that, since I knewsome perfections which I did not possess, I was not the only being inexistence (I will here, with your permission, freely use the terms ofthe schools); but, on the contrary, that there was of necessity someother more perfect Being upon whom I was dependent, and from whom I hadreceived all that I possessed; for if I had existed alone, andindependently of every other being, so as to have had from myself allthe perfection, however little, which I actually possessed, I shouldhave been able, for the same reason, to have had from myself the wholeremainder of perfection, of the want of which I was conscious, and thuscould of myself have become infinite, eternal, immutable, omniscient, all-powerful, and, in fine, have possessed all the perfections which Icould recognize in God. For in order to know the nature of God (whoseexistence has been established by the preceding reasonings), as far asmy own nature permitted, I had only to consider in reference to all theproperties of which I found in my mind some idea, whether theirpossession was a mark of perfection; and I was assured that no onewhich indicated any imperfection was in him, and that none of the restwas awanting. Thus I perceived that doubt, inconstancy, sadness, andsuch like, could not be found in God, since I myself would have beenhappy to be free from them. Besides, I had ideas of many sensible andcorporeal things; for although I might suppose that I was dreaming, andthat 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 hadalready very clearly recognized in myself that the intelligent natureis distinct from the corporeal, and as I observed that all compositionis an evidence of dependency, and that a state of dependency ismanifestly a state of imperfection, I therefore determined that itcould not be a perfection in God to be compounded of these two naturesand that consequently he was not so compounded; but that if there wereany bodies in the world, or even any intelligences, or other naturesthat were not wholly perfect, their existence depended on his power insuch 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 hadrepresented to myself the object of the geometers, which I conceived tobe a continuous body or a space indefinitely extended in length, breadth, and height or depth, divisible into divers parts which admitof different figures and sizes, and of being moved or transposed in allmanner of ways (for all this the geometers suppose to be in the objectthey contemplate), I went over some of their simplest demonstrations. And, in the first place, I observed, that the great certitude which bycommon consent is accorded to these demonstrations, is founded solelyupon this, that they are clearly conceived in accordance with the rulesI have already laid down In the next place, I perceived that there wasnothing at all in these demonstrations which could assure me of theexistence of their object: thus, for example, supposing a triangle tobe given, I distinctly perceived that its three angles were necessarilyequal to two right angles, but I did not on that account perceiveanything which could assure me that any triangle existed: while, onthe contrary, recurring to the examination of the idea of a PerfectBeing, I found that the existence of the Being was comprised in theidea in the same way that the equality of its three angles to two rightangles is comprised in the idea of a triangle, or as in the idea of asphere, the equidistance of all points on its surface from the center, or even still more clearly; and that consequently it is at least ascertain that God, who is this Perfect Being, is, or exists, as anydemonstration of geometry can be. 

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

Finally, if there be still persons who are not sufficiently persuadedof 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, ofthe truth of which they deem themselves perhaps more assured, as thatwe 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 thesethings, which is so strong that there is an appearance of extravagancein doubting of their existence, yet at the same time no one, unless hisintellect is impaired, can deny, when the question relates to ametaphysical certitude, that there is sufficient reason to excludeentire assurance, in the observation that when asleep we can in thesame way imagine ourselves possessed of another body and that we seeother stars and another earth, when there is nothing of the kind. Forhow do we know that the thoughts which occur in dreaming are falserather than those other which we experience when awake, since theformer are often not less vivid and distinct than the latter? Andthough men of the highest genius study this question as long as theyplease, I do not believe that they will be able to give any reasonwhich can be sufficient to remove this doubt, unless they presupposethe existence of God. For, in the first place even the principle whichI have already taken as a rule, viz. , that all the things which weclearly and distinctly conceive are true, is certain only because Godis or exists and because he is a Perfect Being, and because all that wepossess is derived from him: whence it follows that our ideas ornotions, which to the extent of their clearness and distinctness arereal, and proceed from God, must to that extent be true. Accordingly, whereas we not infrequently have ideas or notions in which some falsityis contained, this can only be the case with such as are to some extentconfused and obscure, and in this proceed from nothing (participate ofnegation), that is, exist in us thus confused because we are not whollyperfect. And it is evident that it is not less repugnant that falsityor imperfection, in so far as it is imperfection, should proceed fromGod, than that truth or perfection should proceed from nothing. But ifwe did not know that all which we possess of real and true proceedsfrom a Perfect and Infinite Being, however clear and distinct our ideasmight be, we should have no ground on that account for the assurancethat they possessed the perfection of being true. 

But after the knowledge of God and of the soul has rendered us certainof this rule, we can easily understand that the truth of the thoughtswe experience when awake, ought not in the slightest degree to becalled in question on account of the illusions of our dreams. For ifit happened that an individual, even when asleep, had some verydistinct idea, as, for example, if a geometer should discover some newdemonstration, the circumstance of his being asleep would not militateagainst its truth; and as for the most ordinary error of our dreams, which consists in their representing to us various objects in the sameway as our external senses, this is not prejudicial, since it leads usvery properly to suspect the truth of the ideas of sense; for we arenot infrequently deceived in the same manner when awake; as whenpersons in the jaundice see all objects yellow, or when the stars orbodies at a great distance appear to us much smaller than they are. For, in fine, whether awake or asleep, we ought never to allowourselves to be persuaded of the truth of anything unless on theevidence 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 todetermine that it is only of the size which our sense of sightpresents; and we may very distinctly imagine the head of a lion joinedto the body of a goat, without being therefore shut up to theconclusion that a chimaera exists; for it is not a dictate of reasonthat what we thus see or imagine is in reality existent; but it plainlytells us that all our ideas or notions contain in them some truth; forotherwise it could not be that God, who is wholly perfect andveracious, should have placed them in us. And because our reasoningsare never so clear or so complete during sleep as when we are awake, although sometimes the acts of our imagination are then as lively anddistinct, if not more so than in our waking moments, reason furtherdictates that, since all our thoughts cannot be true because of ourpartial imperfection, those possessing truth must infallibly be foundin the experience of our waking moments rather than in that of ourdreams. 

PART V

I would here willingly have proceeded to exhibit the whole chain oftruths which I deduced from these primary but as with a view to this itwould have been necessary now to treat of many questions in disputeamong the earned, with whom I do not wish to be embroiled, I believethat it will be better for me to refrain from this exposition, and onlymention in general what these truths are, that the more judicious maybe able to determine whether a more special account of them wouldconduce to the public advantage. I have ever remained firm in myoriginal resolution to suppose no other principle than that of which Ihave recently availed myself in demonstrating the existence of God andof the soul, and to accept as true nothing that did not appear to memore clear and certain than the demonstrations of the geometers hadformerly appeared; and yet I venture to state that not only have Ifound means to satisfy myself in a short time on all the principaldifficulties which are usually treated of in philosophy, but I havealso observed certain laws established in nature by God in such amanner, and of which he has impressed on our minds such notions, thatafter we have reflected sufficiently upon these, we cannot doubt thatthey are accurately observed in all that exists or takes place in theworld and farther, by considering the concatenation of these laws, itappears to me that I have discovered many truths more useful and moreimportant than all I had before learned, or even had expected to learn. 

But because I have essayed to expound the chief of these discoveries ina treatise which certain considerations prevent me from publishing, Icannot make the results known more conveniently than by here giving asummary of the contents of this treatise. It was my design to comprisein it all that, before I set myself to write it, I thought I knew ofthe nature of material objects. But like the painters who, findingthemselves unable to represent equally well on a plain surface all thedifferent faces of a solid body, select one of the chief, on whichalone 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 lookingat the principal one; so, fearing lest I should not be able to compensein my discourse all that was in my mind, I resolved to expound singly, though at considerable length, my opinions regarding light; then totake the opportunity of adding something on the sun and the fixedstars, since light almost wholly proceeds from them; on the heavenssince they transmit it; on the planets, comets, and earth, since theyreflect it; and particularly on all the bodies that are upon the earth, since they are either colored, or transparent, or luminous; and finallyon man, since he is the spectator of these objects. Further, to enableme to cast this variety of subjects somewhat into the shade, and toexpress my judgment regarding them with greater freedom, without beingnecessitated to adopt or refute the opinions of the learned, I resolvedto leave all the people here to their disputes, and to speak only ofwhat would happen in a new world, if God were now to create somewherein the imaginary spaces matter sufficient to compose one, and were toagitate variously and confusedly the different parts of this matter, sothat there resulted a chaos as disordered as the poets ever feigned, and after that did nothing more than lend his ordinary concurrence tonature, and allow her to act in accordance with the laws which he hadestablished. On this supposition, I, in the first place, describedthis matter, and essayed to represent it in such a manner that to mymind there can be nothing clearer and more intelligible, except whathas been recently said regarding God and the soul; for I even expresslysupposed that it possessed none of those forms or qualities which areso debated in the schools, nor in general anything the knowledge ofwhich is not so natural to our minds that no one can so much as imaginehimself ignorant of it. Besides, I have pointed out what are the lawsof nature; and, with no other principle upon which to found myreasonings except the infinite perfection of God, I endeavored todemonstrate all those about which there could be any room for doubt, and to prove that they are such, that even if God had created moreworlds, there could have been none in which these laws were notobserved. Thereafter, I showed how the greatest part of the matter ofthis chaos must, in accordance with these laws, dispose and arrangeitself in such a way as to present the appearance of heavens; how inthe meantime some of its parts must compose an earth and some planetsand comets, and others a sun and fixed stars. And, making a digressionat this stage on the subject of light, I expounded at considerablelength what the nature of that light must be which is found in the sunand the stars, and how thence in an instant of time it traverses theimmense spaces of the heavens, and how from the planets and comets itis reflected towards the earth. To this I likewise added muchrespecting the substance, the situation, the motions, and all thedifferent qualities of these heavens and stars; so that I thought I hadsaid enough respecting them to show that there is nothing observable inthe heavens or stars of our system that must not, or at least may notappear precisely alike in those of the system which I described. Icame next to speak of the earth in particular, and to show how, eventhough I had expressly supposed that God had given no weight to thematter of which it is composed, this should not prevent all its partsfrom tending exactly to its center; how with water and air on itssurface, the disposition of the heavens and heavenly bodies, moreespecially of the moon, must cause a flow and ebb, like in all itscircumstances to that observed in our seas, as also a certain currentboth of water and air from east to west, such as is likewise observedbetween the tropics; how the mountains, seas, fountains, and riversmight 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 bodieswhich are commonly denominated mixed or composite might be generatedand, among other things in the discoveries alluded to inasmuch asbesides the stars, I knew nothing except fire which produces light, Ispared no pains to set forth all that pertains to its nature, --themanner of its production and support, and to explain how heat issometimes found without light, and light without heat; to show how itcan induce various colors upon different bodies and other diversequalities; how it reduces some to a liquid state and hardens others;how it can consume almost all bodies, or convert them into ashes andsmoke; and finally, how from these ashes, by the mere intensity of itsaction, it forms glass: for as this transmutation of ashes into glassappeared to me as wonderful as any other in nature, I took a specialpleasure in describing it. I was not, however, disposed, from thesecircumstances, to conclude that this world had been created in themanner I described; for it is much more likely that God made it at thefirst such as it was to be. But this is certain, and an opinioncommonly received among theologians, that the action by which he nowsustains it is the same with that by which he originally created it; sothat even although he had from the beginning given it no other formthan that of chaos, provided only he had established certain laws ofnature, and had lent it his concurrence to enable it to act as it iswont to do, it may be believed, without discredit to the miracle ofcreation, that, in this way alone, things purely material might, incourse of time, have become such as we observe them at present; andtheir nature is much more easily conceived when they are beheld comingin this manner gradually into existence, than when they are onlyconsidered as produced at once in a finished and perfect state. 

From the description of inanimate bodies and plants, I passed toanimals, and particularly to man. But since I had not as yetsufficient knowledge to enable me to treat of these in the same manneras of the rest, that is to say, by deducing effects from their causes, and by showing from what elements and in what manner nature mustproduce them, I remained satisfied with the supposition that God formedthe body of man wholly like to one of ours, as well in the externalshape of the members as in the internal conformation of the organs, ofthe same matter with that I had described, and at first placed in it norational soul, nor any other principle, in room of the vegetative orsensitive soul, beyond kindling in the heart one of those fires withoutlight, such as I had already described, and which I thought was notdifferent from the heat in hay that has been heaped together before itis dry, or that which causes fermentation in new wines before they arerun clear of the fruit. For, when I examined the kind of functionswhich might, as consequences of this supposition, exist in this body, Ifound precisely all those which may exist in us independently of allpower of thinking, and consequently without being in any measure owingto the soul; in other words, to that part of us which is distinct fromthe body, and of which it has been said above that the naturedistinctively consists in thinking, functions in which the animals voidof reason may be said wholly to resemble us; but among which I couldnot discover any of those that, as dependent on thought alone, belongto us as men, while, on the other hand, I did afterwards discover theseas soon as I supposed God to have created a rational soul, and to haveannexed 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 togive the explication of the motion of the heart and arteries, which, asthe first and most general motion observed in animals, will afford themeans of readily determining what should be thought of all the rest. And that there may be less difficulty in understanding what I am aboutto say on this subject, I advise those who are not versed in anatomy, before they commence the perusal of these observations, to take thetrouble of getting dissected in their presence the heart of some largeanimal possessed of lungs (for this is throughout sufficiently like thehuman), and to have shown to them its two ventricles or cavities: inthe first place, that in the right side, with which correspond two veryample tubes, viz. , the hollow vein (vena cava), which is the principalreceptacle of the blood, and the trunk of the tree, as it were, ofwhich all the other veins in the body are branches; and the arterialvein (vena arteriosa), inappropriately so denominated, since it is intruth only an artery, which, taking its rise in the heart, is divided, after passing out from it, into many branches which presently dispersethemselves all over the lungs; in the second place, the cavity in theleft side, with which correspond in the same manner two canals in sizeequal to or larger than the preceding, viz. , the venous artery (arteriavenosa), likewise inappropriately thus designated, because it is simplya vein which comes from the lungs, where it is divided into manybranches, interlaced with those of the arterial vein, and those of thetube called the windpipe, through which the air we breathe enters; andthe great artery which, issuing from the heart, sends its branches allover the body. I should wish also that such persons were carefullyshown the eleven pellicles which, like so many small valves, open andshut the four orifices that are in these two cavities, viz. , three atthe entrance of the hollow veins where they are disposed in such amanner as by no means to prevent the blood which it contains fromflowing into the right ventricle of the heart, and yet exactly toprevent its flowing out; three at the entrance to the arterial vein, which, arranged in a manner exactly the opposite of the former, readilypermit the blood contained in this cavity to pass into the lungs, buthinder that contained in the lungs from returning to this cavity; and, in like manner, two others at the mouth of the venous artery, whichallow the blood from the lungs to flow into the left cavity of theheart, but preclude its return; and three at the mouth of the greatartery, which suffer the blood to flow from the heart, but prevent itsreflux. Nor do we need to seek any other reason for the number ofthese pellicles beyond this that the orifice of the venous artery beingof an oval shape from the nature of its situation, can be adequatelyclosed with two, whereas the others being round are more convenientlyclosed with three. Besides, I wish such persons to observe that thegrand artery and the arterial vein are of much harder and firmertexture than the venous artery and the hollow vein; and that the twolast expand before entering the heart, and there form, as it were, twopouches denominated the auricles of the heart, which are composed of asubstance similar to that of the heart itself; and that there is alwaysmore warmth in the heart than in any other part of the body--andfinally, that this heat is capable of causing any drop of blood thatpasses into the cavities rapidly to expand and dilate, just as allliquors do when allowed to fall drop by drop into a highly heatedvessel. 

For, after these things, it is not necessary for me to say anythingmore with a view to explain the motion of the heart, except that whenits cavities are not full of blood, into these the blood of necessityflows, --from the hollow vein into the right, and from the venous arteryinto the left; because these two vessels are always full of blood, andtheir orifices, which are turned towards the heart, cannot then beclosed. But as soon as two drops of blood have thus passed, one intoeach of the cavities, these drops which cannot but be very large, because the orifices through which they pass are wide, and the vesselsfrom which they come full of blood, are immediately rarefied, anddilated by the heat they meet with. In this way they cause the wholeheart to expand, and at the same time press home and shut the fivesmall valves that are at the entrances of the two vessels from whichthey flow, and thus prevent any more blood from coming down into theheart, and becoming more and more rarefied, they push open the sixsmall valves that are in the orifices of the other two vessels, throughwhich they pass out, causing in this way all the branches of thearterial vein and of the grand artery to expand almost simultaneouslywith the heart which immediately thereafter begins to contract, as doalso 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 ofthe venous artery open anew and allow a passage to other two drops ofblood, which cause the heart and the arteries again to expand asbefore. And, because the blood which thus enters into the heart passesthrough these two pouches called auricles, it thence happens that theirmotion is the contrary of that of the heart, and that when it expandsthey contract. But lest those who are ignorant of the force ofmathematical demonstrations and who are not accustomed to distinguishtrue reasons from mere verisimilitudes, should venture, withoutexamination, to deny what has been said, I wish it to be consideredthat the motion which I have now explained follows as necessarily fromthe very arrangement of the parts, which may be observed in the heartby 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 doesthe motion of a clock from the power, the situation, and shape of itscounterweights and wheels. 

But if it be asked how it happens that the blood in the veins, flowingin this way continually into the heart, is not exhausted, and why thearteries do not become too full, since all the blood which passesthrough the heart flows into them, I need only mention in reply whathas been written by a physician of England, who has the honor of havingbroken the ice on this subject, and of having been the first to teachthat there are many small passages at the extremities of the arteries, through which the blood received by them from the heart passes into thesmall branches of the veins, whence it again returns to the heart; sothat its course amounts precisely to a perpetual circulation. Of thiswe have abundant proof in the ordinary experience of surgeons, who, bybinding the arm with a tie of moderate straitness above the part wherethey open the vein, cause the blood to flow more copiously than itwould have done without any ligature; whereas quite the contrary wouldhappen were they to bind it below; that is, between the hand and theopening, or were to make the ligature above the opening very tight. For it is manifest that the tie, moderately straightened, whileadequate to hinder the blood already in the arm from returning towardsthe heart by the veins, cannot on that account prevent new blood fromcoming forward through the arteries, because these are situated belowthe veins, and their coverings, from their greater consistency, aremore difficult to compress; and also that the blood which comes fromthe heart tends to pass through them to the hand with greater forcethan 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 madein one of the veins, there must of necessity be certain passages belowthe ligature, that is, towards the extremities of the arm through whichit can come thither from the arteries. This physician likewiseabundantly establishes what he has advanced respecting the motion ofthe blood, from the existence of certain pellicles, so disposed invarious places along the course of the veins, in the manner of smallvalves, as not to permit the blood to pass from the middle of the bodytowards the extremities, but only to return from the extremities to theheart; and farther, from experience which shows that all the bloodwhich is in the body may flow out of it in a very short time through asingle artery that has been cut, even although this had been closelytied in the immediate neighborhood of the heart and cut between theheart and the ligature, so as to prevent the supposition that the bloodflowing out of it could come from any other quarter than the heart. 

But there are many other circumstances which evince that what I havealleged is the true cause of the motion of the blood: thus, in thefirst place, the difference that is observed between the blood whichflows from the veins, and that from the arteries, can only arise fromthis, that being rarefied, and, as it were, distilled by passingthrough the heart, it is thinner, and more vivid, and warmerimmediately after leaving the heart, in other words, when in thearteries, than it was a short time before passing into either, in otherwords, when it was in the veins; and if attention be given, it will befound that this difference is very marked only in the neighborhood ofthe heart; and is not so evident in parts more remote from it. In thenext place, the consistency of the coats of which the arterial vein andthe great artery are composed, sufficiently shows that the blood isimpelled against them with more force than against the veins. And whyshould the left cavity of the heart and the great artery be wider andlarger than the right cavity and the arterial vein, were it not thatthe blood of the venous artery, having only been in the lungs after ithas passed through the heart, is thinner, and rarefies more readily, and in a higher degree, than the blood which proceeds immediately fromthe hollow vein? And what can physicians conjecture from feeling thepulse unless they know that according as the blood changes its natureit can be rarefied by the warmth of the heart, in a higher or lowerdegree, and more or less quickly than before? And if it be inquiredhow this heat is communicated to the other members, must it not beadmitted that this is effected by means of the blood, which, passingthrough the heart, is there heated anew, and thence diffused over allthe body? Whence it happens, that if the blood be withdrawn from anypart, the heat is likewise withdrawn by the same means; and althoughthe heart were as-hot as glowing iron, it would not be capable ofwarming the feet and hands as at present, unless it continually sentthither new blood. We likewise perceive from this, that the true useof respiration is to bring sufficient fresh air into the lungs, tocause the blood which flows into them from the right ventricle of theheart, where it has been rarefied and, as it were, changed into vapors, to become thick, and to convert it anew into blood, before it flowsinto the left cavity, without which process it would be unfit for thenourishment of the fire that is there. This receives confirmation fromthe circumstance, that it is observed of animals destitute of lungsthat they have also but one cavity in the heart, and that in childrenwho cannot use them while in the womb, there is a hole through whichthe 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 thegrand artery without passing through the lung. In the next place, howcould digestion be carried on in the stomach unless the heartcommunicated heat to it through the arteries, and along with thiscertain of the more fluid parts of the blood, which assist in thedissolution of the food that has been taken in? Is not also theoperation which converts the juice of food into blood easilycomprehended, when it is considered that it is distilled by passing andrepassing through the heart perhaps more than one or two hundred timesin a day? And what more need be adduced to explain nutrition, and theproduction of the different humors of the body, beyond saying, that theforce with which the blood, in being rarefied, passes from the hearttowards the extremities of the arteries, causes certain of its parts toremain in the members at which they arrive, and there occupy the placeof some others expelled by them; and that according to the situation, shape, or smallness of the pores with which they meet, some ratherthan others flow into certain parts, in the same way that some sievesare observed to act, which, by being variously perforated, serve toseparate different species of grain? And, in the last place, whatabove all is here worthy of observation, is the generation of theanimal spirits, which are like a very subtle wind, or rather a verypure and vivid flame which, continually ascending in great abundancefrom the heart to the brain, thence penetrates through the nerves intothe muscles, and gives motion to all the members; so that to accountfor 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 thearteries which carry them thither proceed from the heart in the mostdirect lines, and that, according to the rules of mechanics which arethe same with those of nature, when many objects tend at once to thesame point where there is not sufficient room for all (as is the casewith the parts of the blood which flow forth from the left cavity ofthe heart and tend towards the brain), the weaker and less agitatedparts must necessarily be driven aside from that point by the strongerwhich alone in this way reach it I had expounded all these matters withsufficient minuteness in the treatise which I formerly thought ofpublishing. And after these, I had shown what must be the fabric ofthe nerves and muscles of the human body to give the animal spiritscontained in it the power to move the members, as when we see headsshortly after they have been struck off still move and bite the earth, although no longer animated; what changes must take place in the brainto produce waking, sleep, and dreams; how light, sounds, odors, tastes, heat, and all the other qualities of external objects impress it withdifferent ideas by means of the senses; how hunger, thirst, and theother internal affections can likewise impress upon it divers ideas;what must be understood by the common sense (sensus communis) in whichthese ideas are received, by the memory which retains them, by thefantasy which can change them in various ways, and out of them composenew ideas, and which, by the same means, distributing the animalspirits through the muscles, can cause the members of such a body tomove in as many different ways, and in a manner as suited, whether tothe objects that are presented to its senses or to its internalaffections, as can take place in our own case apart from the guidanceof the will. Nor will this appear at all strange to those who areacquainted with the variety of movements performed by the differentautomata, or moving machines fabricated by human industry, and thatwith help of but few pieces compared with the great multitude of bones, muscles, nerves, arteries, veins, and other parts that are found in thebody of each animal. Such persons will look upon this body as amachine made by the hands of God, which is incomparably betterarranged, and adequate to movements more admirable than is any machineof human invention. And here I specially stayed to show that, werethere such machines exactly resembling organs and outward form an apeor any other irrational animal, we could have no means of knowing thatthey were in any respect of a different nature from these animals; butif there were machines bearing the image of our bodies, and capable ofimitating our actions as far as it is morally possible, there wouldstill remain two most certain tests whereby to know that they were nottherefore really men. Of these the first is that they could never usewords or other signs arranged in such a manner as is competent to us inorder to declare our thoughts to others: for we may easily conceive amachine to be so constructed that it emits vocables, and even that itemits some correspondent to the action upon it of external objectswhich cause a change in its organs; for example, if touched in aparticular place it may demand what we wish to say to it; if in anotherit may cry out that it is hurt, and such like; but not that it shouldarrange them variously so as appositely to reply to what is said in itspresence, as men of the lowest grade of intellect can do. The secondtest is, that although such machines might execute many things withequal or perhaps greater perfection than any of us, they would, withoutdoubt, fail in certain others from which it could be discovered thatthey did not act from knowledge, but solely from the disposition oftheir organs: for while reason is an universal instrument that isalike available on every occasion, these organs, on the contrary, needa particular arrangement for each particular action; whence it must bemorally impossible that there should exist in any machine a diversityof organs sufficient to enable it to act in all the occurrences oflife, in the way in which our reason enables us to act. Again, bymeans of these two tests we may likewise know the difference betweenmen and brutes. For it is highly deserving of remark, that there areno men so dull and stupid, not even idiots, as to be incapable ofjoining together different words, and thereby constructing adeclaration by which to make their thoughts understood; and that on theother hand, there is no other animal, however perfect or happilycircumstanced, which can do the like. Nor does this inability arisefrom want of organs: for we observe that magpies and parrots can utterwords like ourselves, and are yet unable to speak as we do, that is, soas to show that they understand what they say; in place of which menborn 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 habitof spontaneously inventing certain signs by which they discover theirthoughts to those who, being usually in their company, have leisure tolearn their language. And this proves not only that the brutes haveless reason than man, but that they have none at all: for we see thatvery little is required to enable a person to speak; and since acertain inequality of capacity is observable among animals of the samespecies, as well as among men, and since some are more capable of beinginstructed than others, it is incredible that the most perfect ape orparrot of its species, should not in this be equal to the most stupidinfant of its kind or at least to one that was crack-brained, unlessthe soul of brutes were of a nature wholly different from ours. And weought not to confound speech with the natural movements which indicatethe passions, and can be imitated by machines as well as manifested byanimals; nor must it be thought with certain of the ancients, that thebrutes speak, although we do not understand their language. For ifsuch were the case, since they are endowed with many organs analogousto ours, they could as easily communicate their thoughts to us as totheir fellows. It is also very worthy of remark, that, though thereare many animals which manifest more industry than we in certain oftheir actions, the same animals are yet observed to show none at all inmany others: so that the circumstance that they do better than we doesnot prove that they are endowed with mind, for it would thence followthat they possessed greater reason than any of us, and could surpass usin all things; on the contrary, it rather proves that they aredestitute of reason, and that it is nature which acts in them accordingto the disposition of their organs: thus it is seen, that a clockcomposed only of wheels and weights can number the hours and measuretime more exactly than we with all our skin. 

I had after this described the reasonable soul, and shown that it couldby no means be educed from the power of matter, as the other things ofwhich I had spoken, but that it must be expressly created; and that itis not sufficient that it be lodged in the human body exactly like apilot in a ship, unless perhaps to move its members, but that it isnecessary for it to be joined and united more closely to the body, inorder to have sensations and appetites similar to ours, and thusconstitute a real man. I here entered, in conclusion, upon the subjectof the soul at considerable length, because it is of the greatestmoment: for after the error of those who deny the existence of God, anerror which I think I have already sufficiently refuted, there is nonethat is more powerful in leading feeble minds astray from the straightpath of virtue than the supposition that the soul of the brutes is ofthe same nature with our own; and consequently that after this life wehave nothing to hope for or fear, more than flies and ants; in place ofwhich, when we know how far they differ we much better comprehend thereasons which establish that the soul is of a nature wholly independentof the body, and that consequently it is not liable to die with thelatter and, finally, because no other causes are observed capable ofdestroying it, we are naturally led thence to judge that it is immortal. 

PART VI

Three years have now elapsed since I finished the treatise containingall these matters; and I was beginning to revise it, with the view toput it into the hands of a printer, when I learned that persons to whomI greatly defer, and whose authority over my actions is hardly lessinfluential than is my own reason over my thoughts, had condemned acertain doctrine in physics, published a short time previously byanother individual to which I will not say that I adhered, but onlythat, previously to their censure I had observed in it nothing which Icould imagine to be prejudicial either to religion or to the state, andnothing therefore which would have prevented me from giving expressionto it in writing, if reason had persuaded me of its truth; and this ledme to fear lest among my own doctrines likewise some one might be foundin which I had departed from the truth, notwithstanding the great careI have always taken not to accord belief to new opinions of which I hadnot the most certain demonstrations, and not to give expression toaught that might tend to the hurt of any one. This has been sufficientto make me alter my purpose of publishing them; for although thereasons by which I had been induced to take this resolution were verystrong, yet my inclination, which has always been hostile to writingbooks, enabled me immediately to discover other considerationssufficient to excuse me for not undertaking the task. And thesereasons, on one side and the other, are such, that not only is it insome 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 employbeyond satisfying myself on some difficulties belonging to thespeculative sciences, or endeavoring to regulate my actions accordingto the principles it taught me, I never thought myself bound to publishanything respecting it. For in what regards manners, every one is sofull of his own wisdom, that there might be found as many reformers asheads, if any were allowed to take upon themselves the task of mendingthem, except those whom God has constituted the supreme rulers of hispeople or to whom he has given sufficient grace and zeal to beprophets; and although my speculations greatly pleased myself, Ibelieved 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 fromthe principles that have been employed up to the present time, Ibelieved that I could not keep them concealed without sinninggrievously against the law by which we are bound to promote, as far asin us lies, the general good of mankind. For by them I perceived it tobe possible to arrive at knowledge highly useful in life; and in roomof the speculative philosophy usually taught in the schools, todiscover a practical, by means of which, knowing the force and actionof fire, water, air the stars, the heavens, and all the other bodiesthat surround us, as distinctly as we know the various crafts of ourartisans, we might also apply them in the same way to all the uses towhich they are adapted, and thus render ourselves the lords andpossessors of nature. And this is a result to be desired, not only inorder to the invention of an infinity of arts, by which we might beenabled to enjoy without any trouble the fruits of the earth, and allits comforts, but also and especially for the preservation of health, which is without doubt, of all the blessings of this life, the firstand fundamental one; for the mind is so intimately dependent upon thecondition and relation of the organs of the body, that if any means canever be found to render men wiser and more ingenious than hitherto, Ibelieve that it is in medicine they must be sought for. It is truethat the science of medicine, as it now exists, contains few thingswhose utility is very remarkable: but without any wish to depreciateit, I am confident that there is no one, even among those whoseprofession it is, who does not admit that all at present known in it isalmost nothing in comparison of what remains to be discovered; and thatwe could free ourselves from an infinity of maladies of body as well asof mind, and perhaps also even from the debility of age, if we hadsufficiently ample knowledge of their causes, and of all the remediesprovided for us by nature. But since I designed to employ my wholelife in the search after so necessary a science, and since I had fallenin with a path which seems to me such, that if any one follow it hemust inevitably reach the end desired, unless he be hindered either bythe shortness of life or the want of experiments, I judged that therecould be no more effectual provision against these two impediments thanif I were faithfully to communicate to the public all the little Imight myself have found, and incite men of superior genius to strive toproceed farther, by contributing, each according to his inclination andability, to the experiments which it would be necessary to make, andalso by informing the public of all they might discover, so that, bythe last beginning where those before them had left off, and thusconnecting the lives and labours of many, we might collectively proceedmuch farther than each by himself could do. 

I remarked, moreover, with respect to experiments, that they becomealways more necessary the more one is advanced in knowledge; for, atthe commencement, it is better to make use only of what isspontaneously presented to our senses, and of which we cannot remainignorant, provided we bestow on it any reflection, however slight, thanto concern ourselves about more uncommon and recondite phenomena: thereason of which is, that the more uncommon often only mislead us solong as the causes of the more ordinary are still unknown; and thecircumstances upon which they depend are almost always so special andminute as to be highly difficult to detect. But in this I have adoptedthe following order: first, I have essayed to find in general theprinciples, or first causes of all that is or can be in the world, without taking into consideration for this end anything but God himselfwho has created it, and without educing them from any other source thanfrom certain germs of truths naturally existing in our minds In thesecond place, I examined what were the first and most ordinary effectsthat could be deduced from these causes; and it appears to me that, inthis way, I have found heavens, stars, an earth, and even on the earthwater, air, fire, minerals, and some other things of this kind, whichof all others are the most common and simple, and hence the easiest toknow. Afterwards when I wished to descend to the more particular, somany diverse objects presented themselves to me, that I believed it tobe impossible for the human mind to distinguish the forms or species ofbodies that are upon the earth, from an infinity of others which mighthave been, if it had pleased God to place them there, or consequentlyto apply them to our use, unless we rise to causes through theireffects, and avail ourselves of many particular experiments. Thereupon, turning over in my mind I the objects that had ever beenpresented to my senses I freely venture to state that I have neverobserved any which I could not satisfactorily explain by the principleshad discovered. But it is necessary also to confess that the power ofnature is so ample and vast, and these principles so simple andgeneral, that I have hardly observed a single particular effect which Icannot at once recognize as capable of being deduced in man differentmodes from the principles, and that my greatest difficulty usually isto discover in which of these modes the effect is dependent upon them;for out of this difficulty cannot otherwise extricate myself than byagain seeking certain experiments, which may be such that their resultis not the same, if it is in the one of these modes at we must explainit, as it would be if it were to be explained in the other. As to whatremains, I am now in a position to discern, as I think, with sufficientclearness what course must be taken to make the majority thoseexperiments which may conduce to this end: but I perceive likewisethat they are such and so numerous, that neither my hands nor myincome, though it were a thousand times larger than it is, would besufficient for them all; so that according as henceforward I shall havethe means of making more or fewer experiments, I shall in the sameproportion 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 thepublic, as to induce all who have the common good of man at heart, thatis, all who are virtuous in truth, and not merely in appearance, oraccording to opinion, as well to communicate to me the experiments theyhad 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 havebeen led to change my opinion, and to think that I ought indeed to goon 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 samecare upon them as I would have done had it been my design to publishthem. This course commended itself to me, as well because I thusafforded myself more ample inducement to examine them thoroughly, fordoubtless that is always more narrowly scrutinized which we believewill be read by many, than that which is written merely for our privateuse (and frequently what has seemed to me true when I first conceivedit, has appeared false when I have set about committing it to writing), as because I thus lost no opportunity of advancing the interests of thepublic, as far as in me lay, and since thus likewise, if my writingspossess any value, those into whose hands they may fall after my deathmay be able to put them to what use they deem proper. But I resolvedby no means to consent to their publication during my lifetime, lesteither the oppositions or the controversies to which they might giverise, or even the reputation, such as it might be, which they wouldacquire for me, should be any occasion of my losing the time that I hadset apart for my own improvement. For though it be true that every oneis 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 islikewise true that our cares ought to extend beyond the present, and itis good to omit doing what might perhaps bring some profit to theliving, when we have in view the accomplishment of other ends that willbe of much greater advantage to posterity. And in truth, I am quitewilling it should be known that the little I have hitherto learned isalmost nothing in comparison with that of which I am ignorant, and tothe knowledge of which I do not despair of being able to attain; for itis much the same with those who gradually discover truth in thesciences, as with those who when growing rich find less difficulty inmaking great acquisitions, than they formerly experienced when poor inmaking acquisitions of much smaller amount. Or they may be compared tothe commanders of armies, whose forces usually increase in proportionto their victories, and who need greater prudence to keep together theresidue of their troops after a defeat than after a victory to taketowns and provinces. For he truly engages in battle who endeavors tosurmount all the difficulties and errors which prevent him fromreaching the knowledge of truth, and he is overcome in fight who admitsa false opinion touching a matter of any generality and importance, andhe requires thereafter much more skill to recover his former positionthan to make great advances when once in possession of thoroughlyascertained principles. As for myself, if I have succeeded indiscovering any truths in the sciences (and I trust that what iscontained in this volume I will show that I have found some), I candeclare that they are but the consequences and results of five or sixprincipal difficulties which I have surmounted, and my encounters withwhich I reckoned as battles in which victory declared for me. I willnot hesitate even to avow my belief that nothing further is wanting toenable me fully to realize my designs than to gain two or three similarvictories; and that I am not so far advanced in years but that, according to the ordinary course of nature, I may still have sufficientleisure for this end. But I conceive myself the more bound to husbandthe time that remains the greater my expectation of being able toemploy 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 arealmost all so evident that to assent to them no more is needed thansimply to understand them, and although there is not one of them ofwhich I do not expect to be able to give demonstration, yet, as it isimpossible that they can be in accordance with all the diverse opinionsof others, I foresee that I should frequently be turned aside from mygrand design, on occasion of the opposition which they would be sure toawaken. 

It may be said, that these oppositions would be useful both in makingme aware of my errors, and, if my speculations contain anything ofvalue, in bringing others to a fuller understanding of it; and stillfarther, as many can see better than one, in leading others who are nowbeginning to avail themselves of my principles, to assist me in turnwith their discoveries. But though I recognize my extreme liability toerror, and scarce ever trust to the first thoughts which occur to me, yet-the experience I have had of possible objections to my viewsprevents me from anticipating any profit from them. For I have alreadyhad frequent proof of the judgments, as well of those I esteemedfriends, as of some others to whom I thought I was an object ofindifference, and even of some whose malignancy and envy would, I knew, determine them to endeavor to discover what partiality concealed fromthe eyes of my friends. But it has rarely happened that anything hasbeen objected to me which I had myself altogether overlooked, unless itwere something far removed from the subject: so that I have never metwith a single critic of my opinions who did not appear to me eitherless rigorous or less equitable than myself. And further, I have neverobserved that any truth before unknown has been brought to light by thedisputations that are practised in the schools; for while each strivesfor the victory, each is much more occupied in making the best of mereverisimilitude, than in weighing the reasons on both sides of thequestion; and those who have been long good advocates are notafterwards on that account the better judges. 

As for the advantage that others would derive from the communication ofmy thoughts, it could not be very great; because I have not yet so farprosecuted them as that much does not remain to be added before theycan be applied to practice. And I think I may say without vanity, thatif there is any one who can carry them out that length, it must bemyself rather than another: not that there may not be in the worldmany minds incomparably superior to mine, but because one cannot sowell seize a thing and make it one's own, when it has been learned fromanother, as when one has himself discovered it. And so true is this ofthe present subject that, though I have often explained some of myopinions to persons of much acuteness, who, whilst I was speaking, appeared to understand them very distinctly, yet, when they repeatedthem, I have observed that they almost always changed them to such anextent that I could no longer acknowledge them as mine. I am glad, bythe way, to take this opportunity of requesting posterity never tobelieve on hearsay that anything has proceeded from me which has notbeen published by myself; and I am not at all astonished at theextravagances attributed to those ancient philosophers whose ownwritings we do not possess; whose thoughts, however, I do not on thataccount suppose to have been really absurd, seeing they were among theablest men of their times, but only that these have been falselyrepresented to us. It is observable, accordingly, that scarcely in asingle instance has any one of their disciples surpassed them; and I amquite sure that the most devoted of the present followers of Aristotlewould think themselves happy if they had as much knowledge of nature ashe possessed, were it even under the condition that they should neverafterwards attain to higher. In this respect they are like the ivywhich never strives to rise above the tree that sustains it, and whichfrequently even returns downwards when it has reached the top; for itseems to me that they also sink, in other words, render themselves lesswise than they would be if they gave up study, who, not contented withknowing all that is intelligibly explained in their author, desire inaddition to find in him the solution of many difficulties of which hesays not a word, and never perhaps so much as thought. Their fashionof philosophizing, however, is well suited to persons whose abilitiesfall below mediocrity; for the obscurity of the distinctions andprinciples of which they make use enables them to speak of all thingswith as much confidence as if they really knew them, and to defend allthat they say on any subject against the most subtle and skillful, without its being possible for any one to convict them of error. Inthis they seem to me to be like a blind man, who, in order to fight onequal terms with a person that sees, should have made him descend tothe bottom of an intensely dark cave: and I may say that such personshave an interest in my refraining from publishing the principles of thephilosophy of which I make use; for, since these are of a kind thesimplest and most evident, I should, by publishing them, do much thesame as if I were to throw open the windows, and allow the light of dayto enter the cave into which the combatants had descended. But evensuperior men have no reason for any great anxiety to know theseprinciples, for if what they desire is to be able to speak of allthings, and to acquire a reputation for learning, they will gain theirend 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 andthat only in some departments, while it obliges us, when we have tospeak of others, freely to confess our ignorance. If, however, theyprefer the knowledge of some few truths to the vanity of appearingignorant of none, as such knowledge is undoubtedly much to bepreferred, and, if they choose to follow a course similar to mine, theydo not require for this that I should say anything more than I havealready said in this discourse. For if they are capable of makinggreater advancement than I have made, they will much more be able ofthemselves to discover all that I believe myself to have found; sinceas I have never examined aught except in order, it is certain that whatyet remains to be discovered is in itself more difficult and recondite, than that which I have already been enabled to find, and thegratification would be much less in learning it from me than indiscovering it for themselves. Besides this, the habit which they willacquire, by seeking first what is easy, and then passing onward slowlyand step by step to the more difficult, will benefit them more than allmy instructions. Thus, in my own case, I am persuaded that if I hadbeen taught from my youth all the truths of which I have since soughtout demonstrations, and had thus learned them without labour, I shouldnever, perhaps, have known any beyond these; at least, I should neverhave acquired the habit and the facility which I think I possess inalways discovering new truths in proportion as I give myself to thesearch. And, in a single word, if there is any work in the world whichcannot 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 tothis end, that one man is not equal to the task of making them all; butyet he can advantageously avail himself, in this work, of no handsbesides 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 greatefficacy) might stimulate to accuracy in the performance of what wasprescribed to them. For as to those who, through curiosity or a desireof learning, of their own accord, perhaps, offer him their services, besides that in general their promises exceed their performance, andthat they sketch out fine designs of which not one is ever realized, they will, without doubt, expect to be compensated for their trouble bythe explication of some difficulties, or, at least, by compliments anduseless speeches, in which he cannot spend any portion of his timewithout loss to himself. And as for the experiments that others havealready made, even although these parties should be willing ofthemselves to communicate them to him (which is what those who esteemthem secrets will never do), the experiments are, for the most part, accompanied with so many circumstances and superfluous elements, as tomake it exceedingly difficult to disentangle the truth from itsadjuncts--besides, he will find almost all of them so ill described, oreven so false (because those who made them have wished to see in themonly such facts as they deemed conformable to their principles), that, if in the entire number there should be some of a nature suited to hispurpose, still their value could not compensate for the time what wouldbe necessary to make the selection. So that if there existed any onewhom we assuredly knew to be capable of making discoveries of thehighest kind, and of the greatest possible utility to the public; andif all other men were therefore eager by all means to assist him insuccessfully prosecuting his designs, I do not see that they could doaught else for him beyond contributing to defray the expenses of theexperiments that might be necessary; and for the rest, prevent hisbeing deprived of his leisure by the unseasonable interruptions of anyone. But besides that I neither have so high an opinion of myself asto be willing to make promise of anything extraordinary, nor feed onimaginations so vain as to fancy that the public must be muchinterested in my designs; I do not, on the other hand, own a soul somean as to be capable of accepting from any one a favor of which itcould be supposed that I was unworthy. 

These considerations taken together were the reason why, for the lastthree years, I have been unwilling to publish the treatise I had onhand, and why I even resolved to give publicity during my life to noother that was so general, or by which the principles of my physicsmight be understood. But since then, two other reasons have come intooperation that have determined me here to subjoin some particularspecimens, and give the public some account of my doings and designs. Of these considerations, the first is, that if I failed to do so, manywho were cognizant of my previous intention to publish some writings, might have imagined that the reasons which induced me to refrain fromso doing, were less to my credit than they really are; for although Iam not immoderately desirous of glory, or even, if I may venture so tosay, although I am averse from it in so far as I deem it hostile torepose which I hold in greater account than aught else, yet, at thesame time, I have never sought to conceal my actions as if they werecrimes, nor made use of many precautions that I might remain unknown;and this partly because I should have thought such a course of conducta wrong against myself, and partly because it would have occasioned mesome sort of uneasiness which would again have been contrary to theperfect mental tranquillity which I court. And forasmuch as, whilethus indifferent to the thought alike of fame or of forgetfulness, Ihave yet been unable to prevent myself from acquiring some sort ofreputation, I have thought it incumbent on me to do my best to savemyself at least from being ill-spoken of. The other reason that hasdetermined me to commit to writing these specimens of philosophy is, that I am becoming daily more and more alive to the delay which mydesign of self-instruction suffers, for want of the infinity ofexperiments I require, and which it is impossible for me to makewithout the assistance of others: and, without flattering myself somuch as to expect the public to take a large share in my interests, Iam yet unwilling to be found so far wanting in the duty I owe tomyself, as to give occasion to those who shall survive me to make itmatter of reproach against me some day, that I might have left themmany things in a much more perfect state than I have done, had I nottoo much neglected to make them aware of the ways in which they couldhave promoted the accomplishment of my designs. 

And I thought that it was easy for me to select some matters whichshould neither be obnoxious to much controversy, nor should compel meto expound more of my principles than I desired, and which should yetbe sufficient clearly to exhibit what I can or cannot accomplish in thesciences. Whether or not I have succeeded in this it is not for me tosay; and I do not wish to forestall the judgments of others by speakingmyself 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 anyobjections to make to them, to take the trouble of forwarding these tomy publisher, who will give me notice of them, that I may endeavor tosubjoin at the same time my reply; and in this way readers seeing bothat once will more easily determine where the truth lies; for I do notengage in any case to make prolix replies, but only with perfectfrankness to avow my errors if I am convinced of them, or if I cannotperceive them, simply to state what I think is required for defense ofthe matters I have written, adding thereto no explication of any newmatte that it may not be necessary to pass without end from one thingto 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 Icall them hypotheses and seem indifferent about giving proof of them, Irequest a patient and attentive reading of the whole, from which I hopethose hesitating will derive satisfaction; for it appears to me thatthe reasonings are so mutually connected in these treatises, that, asthe last are demonstrated by the first which are their causes, thefirst are in their turn demonstrated by the last which are theireffects. Nor must it be imagined that I here commit the fallacy whichthe logicians call a circle; for since experience renders the majorityof these effects most certain, the causes from which I deduce them donot serve so much to establish their reality as to explain theirexistence; but on the contrary, the reality of the causes isestablished by the reality of the effects. Nor have I called themhypotheses with any other end in view except that it may be known thatI think I am able to deduce them from those first truths which I havealready expounded; and yet that I have expressly determined not to doso, to prevent a certain class of minds from thence taking occasion tobuild some extravagant philosophy upon what they may take to be myprinciples, and my being blamed for it. I refer to those who imaginethat they can master in a day all that another has taken twenty yearsto think out, as soon as he has spoken two or three words to them onthe subject; or who are the more liable to error and the less capableof perceiving truth in very proportion as they are more subtle andlively. As to the opinions which are truly and wholly mine, I offer noapology for them as new, --persuaded as I am that if their reasons bewell considered they will be found to be so simple and so conformed, tocommon sense as to appear less extraordinary and less paradoxical thanany others which can be held on the same subjects; nor do I even boastof being the earliest discoverer of any of them, but only of havingadopted them, neither because they had nor because they had not beenheld by others, but solely because reason has convinced me of theirtruth. 

Though artisans may not be able at once to execute the invention whichis explained in the "Dioptrics, " I do not think that any one on thataccount is entitled to condemn it; for since address and practice arerequired in order so to make and adjust the machines described by me asnot to overlook the smallest particular, I should not be lessastonished if they succeeded on the first attempt than if a person werein one day to become an accomplished performer on the guitar, by merelyhaving excellent sheets of music set up before him. And if I write inFrench, which is the language of my country, in preference to Latin, which is that of my preceptors, it is because I expect that those whomake use of their unprejudiced natural reason will be better judges ofmy opinions than those who give heed to the writings of the ancientsonly; and as for those who unite good sense with habits of study, whomalone I desire for judges, they will not, I feel assured, be so partialto Latin as to refuse to listen to my reasonings merely because Iexpound them in the vulgar tongue. 

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