Literature Essay

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we have a moral assurance of these things, which is so strong that there is an appearance of

extravagance in doubting of their existence, yet at the same time no one, unless his intellect is

impaired, can deny, when the question relates to a metaphysical certitude, that there is sufficient

reason to exclude entire assurance, in the observation that when asleep we can in the same way

imagine ourselves possessed of another body and that we see other stars and another earth, when

there is nothing of the kind. For how do we know that the thoughts which occur in dreaming are

false rather than those other which we experience when awake, since the former are often not less

vivid and distinct than the latter? And though men of the highest genius study this question as

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

sufficient to remove this doubt, unless they presuppose the existence of God. For, in the first

place even the principle which I have already taken as a rule, viz., that all the things which we

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

a Perfect Being, and because all that we possess is derived from him: whence it follows that our

ideas or notions, which to the extent of their clearness and distinctness are real, and proceed from

God, must to that extent be true. Accordingly, whereas we not infrequently have ideas or notions

in which some falsity is contained, this can only be the case with such as are to some extent

confused and obscure, and in this proceed from nothing (participate of negation), that is, exist in

us thus confused because we are not wholly perfect. And it is evident that it is not less repugnant

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

truth or perfection should proceed from nothing. But if we did not know that all which we possess

of real and true proceeds from a Perfect and Infinite Being, however clear and distinct our ideas

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

perfection of being true.

But after the knowledge of God and of the soul has rendered us certain of this rule, we can

easily understand that the truth of the thoughts we experience when awake, ought not in the

slightest degree to be called in question on account of the illusions of our dreams. For if it

happened that an individual, even when asleep, had some very distinct idea, as, for example, if a

geometer should discover some new demonstration, the circumstance of his being asleep would

not militate against its truth; and as for the most ordinary error of our dreams, which consists in

their representing to us various objects in the same way as our external senses, this is not

prejudicial, since it leads us very properly to suspect the truth of the ideas of sense; for we are not

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

objects yellow, or when the stars or bodies at a great distance appear to us much smaller than they

are. For, in fine, whether awake or asleep, we ought never to allow ourselves to be persuaded of

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

reason, and not of our imagination or of our senses: thus, for example, although we very clearly

see the sun, we ought not therefore to determine that it is only of the size which our sense of sight

presents; and we may very distinctly imagine the head of a lion joined to the body of a goat,

without being therefore shut up to the conclusion that a chimaera exists; for it is not a dictate of

reason that what we thus see or imagine is in reality existent; but it plainly tells us that all our

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

perfect and veracious, should have placed them in us. And because our reasonings are never so

clear or so complete during sleep as when we are awake, although sometimes the acts of our

imagination are then as lively and distinct, if not more so than in our waking moments, reason

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

those possessing truth must infallibly be found in the experience of our waking moments rather

than in that of our dreams.

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Chapter 5

I would here willingly have proceeded to exhibit the whole chain of truths which I deduced

from these primary but as with a view to this it would have been necessary now to treat of many

questions in dispute among the earned, with whom I do not wish to be embroiled, I believe that it

will be better for me to refrain from this exposition, and only mention in general what these truths

are, that the more judicious may be able to determine whether a more special account of them

would conduce to the public advantage. I have ever remained firm in my original resolution to

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

existence of God and of the soul, and to accept as true nothing that did not appear to me more

clear and certain than the demonstrations of the geometers had formerly appeared; and yet I

venture to state that not only have I found means to satisfy myself in a short time on all the

principal difficulties which are usually treated of in philosophy, but I have also observed certain

laws established in nature by God in such a manner, and of which he has impressed on our minds

such notions, that after we have reflected sufficiently upon these, we cannot doubt that they are

accurately observed in all that exists or takes place in the world and farther, by considering the

concatenation of these laws, it appears to me that I have discovered many truths more useful and

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

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

certain considerations prevent me from publishing, I cannot make the results known more

conveniently than by here giving a summary of the contents of this treatise. It was my design to

comprise in it all that, before I set myself to write it, I thought I knew of the nature of material

objects. But like the painters who, finding themselves unable to represent equally well on a plain

surface all the different faces of a solid body, select one of the chief, on which alone they make

the light fall, and throwing the rest into the shade, allow them to appear only in so far as they can

be seen while looking at the principal one; so, fearing lest I should not be able to compense in my

discourse all that was in my mind, I resolved to expound singly, though at considerable length,

my opinions regarding light; then to take the opportunity of adding something on the sun and the

fixed stars, since light almost wholly proceeds from them; on the heavens since they transmit it;

on the planets, comets, and earth, since they reflect it; and particularly on all the bodies that are

upon the earth, since they are either colored, or transparent, or luminous; and finally on man,

since he is the spectator of these objects. Further, to enable me to cast this variety of subjects

somewhat into the shade, and to express my judgment regarding them with greater freedom,

without being necessitated to adopt or refute the opinions of the learned, I resolved to leave all

the people here to their disputes, and to speak only of what would happen in a new world, if God

were now to create somewhere in the imaginary spaces matter sufficient to compose one, and

were to agitate variously and confusedly the different parts of this matter, so that there resulted a

chaos as disordered as the poets ever feigned, and after that did nothing more than lend his

ordinary concurrence to nature, and allow her to act in accordance with the laws which he had

established. On this supposition, I, in the first place, described this matter, and essayed to

represent it in such a manner that to my mind there can be nothing clearer and more intelligible,

except what has been recently said regarding God and the soul; for I even expressly supposed that

it possessed none of those forms or qualities which are so debated in the schools, nor in general

anything the knowledge of which is not so natural to our minds that no one can so much as

imagine himself ignorant of it. Besides, I have pointed out what are the laws of nature; and, with

no other principle upon which to found my reasonings except the infinite perfection of God, I

endeavored to demonstrate all those about which there could be any room for doubt, and to prove

that they are such, that even if God had created more worlds, there could have been none in

which these laws were not observed. Thereafter, I showed how the greatest part of the matter of

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this chaos must, in accordance with these laws, dispose and arrange itself in such a way as to

present the appearance of heavens; how in the meantime some of its parts must compose an earth

and some planets and comets, and others a sun and fixed stars. And, making a digression at this

stage on the subject of light, I expounded at considerable length what the nature of that light must

be which is found in the sun and the stars, and how thence in an instant of time it traverses the

immense spaces of the heavens, and how from the planets and comets it is reflected towards the

earth. To this I likewise added much respecting the substance, the situation, the motions, and all

the different qualities of these heavens and stars; so that I thought I had said enough respecting

them to show that there is nothing observable in the heavens or stars of our system that must not,

or at least may not appear precisely alike in those of the system which I described. I came next to

speak of the earth in particular, and to show how, even though I had expressly supposed that God

had given no weight to the matter of which it is composed, this should not prevent all its parts

from tending exactly to its center; how with water and air on its surface, the disposition of the

heavens and heavenly bodies, more especially of the moon, must cause a flow and ebb, like in all

its circumstances to that observed in our seas, as also a certain current both of water and air from

east to west, such as is likewise observed between the tropics; how the mountains, seas, fountains,

and rivers might naturally be formed in it, and the metals produced in the mines, and the plants

grow in the fields and in general, how all the bodies which are commonly denominated mixed or

composite might be generated and, among other things in the discoveries alluded to inasmuch as

besides the stars, I knew nothing except fire which produces light, I spared no pains to set forth

all that pertains to its nature, -- the manner of its production and support, and to explain how heat

is sometimes found without light, and light without heat; to show how it can induce various

colors upon different bodies and other diverse qualities; how it reduces some to a liquid state and

hardens others; how it can consume almost all bodies, or convert them into ashes and smoke; and

finally, how from these ashes, by the mere intensity of its action, it forms glass: for as this

transmutation of ashes into glass appeared to me as wonderful as any other in nature, I took a

special pleasure in describing it. I was not, however, disposed, from these circumstances, to

conclude that this world had been created in the manner I described; for it is much more likely

that God made it at the first such as it was to be. But this is certain, and an opinion commonly

received among theologians, that the action by which he now sustains it is the same with that by

which he originally created it; so that even although he had from the beginning given it no other

form than that of chaos, provided only he had established certain laws of nature, and had lent it

his concurrence to enable it to act as it is wont to do, it may be believed, without discredit to the

miracle of creation, that, in this way alone, things purely material might, in course of time, have

become such as we observe them at present; and their nature is much more easily conceived when

they are beheld coming in this manner gradually into existence, than when they are only

considered as produced at once in a finished and perfect state.

From the description of inanimate bodies and plants, I passed to animals, and particularly to

man. But since I had not as yet sufficient knowledge to enable me to treat of these in the same

manner as of the rest, that is to say, by deducing effects from their causes, and by showing from

what elements and in what manner nature must produce them, I remained satisfied with the

supposition that God formed the body of man wholly like to one of ours, as well in the external

shape of the members as in the internal conformation of the organs, of the same matter with that I

had described, and at first placed in it no rational soul, nor any other principle, in room of the

vegetative or sensitive soul, beyond kindling in the heart one of those fires without light, such as I

had already described, and which I thought was not different from the heat in hay that has been

heaped together before it is dry, or that which causes fermentation in new wines before they are

run clear of the fruit. For, when I examined the kind of functions which might, as consequences

of this supposition, exist in this body, I found precisely all those which may exist in us

independently of all power of thinking, and consequently without being in any measure owing to

the soul; in other words, to that part of us which is distinct from the body, and of which it has

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been said above that the nature distinctively consists in thinking, functions in which the animals

void of reason may be said wholly to resemble us; but among which I could not discover any of

those that, as dependent on thought alone, belong to us as men, while, on the other hand, I did

afterwards discover these as soon as I supposed God to have created a rational soul, and to have

annexed it to this body in a particular manner which I described.

But, in order to show how I there handled this matter, I mean here to give the explication of

the motion of the heart and arteries, which, as the first and most general motion observed in

animals, will afford the means of readily determining what should be thought of all the rest. And

that there may be less difficulty in understanding what I am about to say on this subject, I advise

those who are not versed in anatomy, before they commence the perusal of these observations, to

take the trouble of getting dissected in their presence the heart of some large animal possessed of

lungs (for this is throughout sufficiently like the human), and to have shown to them its two

ventricles or cavities: in the first place, that in the right side, with which correspond two very

ample tubes, viz., the hollow vein (vena cava), which is the principal receptacle of the blood, and

the trunk of the tree, as it were, of which all the other veins in the body are branches; and the

arterial vein (vena arteriosa), inappropriately so denominated, since it is in truth only an artery,

which, taking its rise in the heart, is divided, after passing out from it, into many branches which

presently disperse themselves all over the lungs; in the second place, the cavity in the left side,

with which correspond in the same manner two canals in size equal to or larger than the

preceding, viz., the venous artery (arteria venosa), likewise inappropriately thus designated,

because it is simply a vein which comes from the lungs, where it is divided into many branches,

interlaced with those of the arterial vein, and those of the tube called the windpipe, through which

the air we breathe enters; and the great artery which, issuing from the heart, sends its branches all

over the body. I should wish also that such persons were carefully shown the eleven pellicles

which, like so many small valves, open and shut the four orifices that are in these two cavities,

viz., three at the entrance of the hollow veins where they are disposed in such a manner as by no

means to prevent the blood which it contains from flowing into the right ventricle of the heart,

and yet exactly to prevent its flowing out; three at the entrance to the arterial vein, which,

arranged in a manner exactly the opposite of the former, readily permit the blood contained in this

cavity to pass into the lungs, but hinder that contained in the lungs from returning to this cavity;

and, in like manner, two others at the mouth of the venous artery, which allow the blood from the

lungs to flow into the left cavity of the heart, but preclude its return; and three at the mouth of the

great artery, which suffer the blood to flow from the heart, but prevent its reflux. Nor do we need

to seek any other reason for the number of these pellicles beyond this that the orifice of the

venous artery being of an oval shape from the nature of its situation, can be adequately closed

with two, whereas the others being round are more conveniently closed with three. Besides, I

wish such persons to observe that the grand artery and the arterial vein are of much harder and

firmer texture than the venous artery and the hollow vein; and that the two last expand before

entering the heart, and there form, as it were, two pouches denominated the auricles of the heart,

which are composed of a substance similar to that of the heart itself; and that there is always more

warmth in the heart than in any other part of the body- and finally, that this heat is capable of

causing any drop of blood that passes into the cavities rapidly to expand and dilate, just as all

liquors do when allowed to fall drop by drop into a highly heated vessel.

For, after these things, it is not necessary for me to say anything more with a view to

explain the motion of the heart, except that when its cavities are not full of blood, into these the

blood of necessity flows, - - from the hollow vein into the right, and from the venous artery into

the left; because these two vessels are always full of blood, and their orifices, which are turned

towards the heart, cannot then be closed. But as soon as two drops of blood have thus passed, one

into each of the cavities, these drops which cannot but be very large, because the orifices through

which they pass are wide, and the vessels from which they come full of blood, are immediately

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rarefied, and dilated by the heat they meet with. In this way they cause the whole heart to expand,

and at the same time press home and shut the five small valves that are at the entrances of the two

vessels from which they flow, and thus prevent any more blood from coming down into the heart,

and becoming more and more rarefied, they push open the six small valves that are in the orifices

of the other two vessels, through which they pass out, causing in this way all the branches of the

arterial vein and of the grand artery to expand almost simultaneously with the heart which

immediately thereafter begins to contract, as do also the arteries, because the blood that has

entered them has cooled, and the six small valves close, and the five of the hollow vein and of the

venous artery open anew and allow a passage to other two drops of blood, which cause the heart

and the arteries again to expand as before. And, because the blood which thus enters into the heart

passes through these two pouches called auricles, it thence happens that their motion is the

contrary of that of the heart, and that when it expands they contract. But lest those who are

ignorant of the force of mathematical demonstrations and who are not accustomed to distinguish

true reasons from mere verisimilitudes, should venture. without examination, to deny what has

been said, I wish it to be considered that the motion which I have now explained follows as

necessarily from the very arrangement of the parts, which may be observed in the heart by the eye

alone, and from the heat which may be felt with the fingers, and from the nature of the blood as

learned from experience, as does the motion of a clock from the power, the situation, and shape

of its counterweights and wheels.

But if it be asked how it happens that the blood in the veins, flowing in this way continually

into the heart, is not exhausted, and why the arteries do not become too full, since all the blood

which passes through the heart flows into them, I need only mention in reply what has been

written by a physician 1 of England, who has the honor of having broken the ice on this subject,

and of having been the first to teach that there are many small passages at the extremities of the

arteries, through which the blood received by them from the heart passes into the small branches

of the veins, whence it again returns to the heart; so that its course amounts precisely to a

perpetual circulation. Of this we have abundant proof in the ordinary experience of surgeons,

who, by binding the arm with a tie of moderate straitness above the part where they open the

vein, cause the blood to flow more copiously than it would have done without any ligature;

whereas quite the contrary would happen were they to bind it below; that is, between the hand

and the opening, or were to make the ligature above the opening very tight. For it is manifest that

the tie, moderately straightened, while adequate to hinder the blood already in the arm from

returning towards the heart by the veins, cannot on that account prevent new blood from coming

forward through the arteries, because these are situated below the veins, and their coverings, from

their greater consistency, are more difficult to compress; and also that the blood which comes

from the heart tends to pass through them to the hand with greater force than it does to return

from the hand to the heart through the veins. And since the latter current escapes from the arm by

the opening made in one of the veins, there must of necessity be certain passages below the

ligature, that is, towards the extremities of the arm through which it can come thither from the

arteries. This physician likewise abundantly establishes what he has advanced respecting the

motion of the blood, from the existence of certain pellicles, so disposed in various places along

the course of the veins, in the manner of small valves, as not to permit the blood to pass from the

middle of the body towards the extremities, but only to return from the extremities to the heart;

and farther, from experience which shows that all the blood which is in the body may flow out of

it in a very short time through a single artery that has been cut, even although this had been

closely tied in the immediate neighborhood of the heart and cut between the heart and the

ligature, so as to prevent the supposition that the blood flowing out of it could come from any

other quarter than the heart.

But there are many other circumstances which evince that what I have alleged is the true

cause of the motion of the blood: thus, in the first place, the difference that is observed between

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the blood which flows from the veins, and that from the arteries, can only arise from this, that

being rarefied, and, as it were, distilled by passing through the heart, it is thinner, and more vivid,

and warmer immediately after leaving the heart, in other words, when in the arteries, than it was a

short time before passing into either, in other words, when it was in the veins; and if attention be

given, it will be found that this difference is very marked only in the neighborhood of the heart;

and is not so evident in parts more remote from it. In the next place, the consistency of the coats

of which the arterial vein and the great artery are composed, sufficiently shows that the blood is

impelled against them with more force than against the veins. And why should the left cavity of

the heart and the great artery be wider and larger than the right cavity and the arterial vein, were it

not that the blood of the venous artery, having only been in the lungs after it has passed through

the heart, is thinner, and rarefies more readily, and in a higher degree, than the blood which

proceeds immediately from the hollow vein? And what can physicians conjecture from feeling

the pulse unless they know that according as the blood changes its nature it can be rarefied by the

warmth of the heart, in a higher or lower degree, and more or less quickly than before? And if it

be inquired how this heat is communicated to the other members, must it not be admitted that this

is effected by means of the blood, which, passing through the heart, is there heated anew, and

thence diffused over all the body? Whence it happens, that if the blood be withdrawn from any

part, the heat is likewise withdrawn by the same means; and although the heart were as-hot as

glowing iron, it would not be capable of warming the feet and hands as at present, unless it

continually sent thither new blood. We likewise perceive from this, that the true use of respiration

is to bring sufficient fresh air into the lungs, to cause the blood which flows into them from the

right ventricle of the heart, where it has been rarefied and, as it were, changed into vapors, to

become thick, and to convert it anew into blood, before it flows into the left cavity, without which

process it would be unfit for the nourishment of the fire that is there. This receives confirmation

from the circumstance, that it is observed of animals destitute of lungs that they have also but one

cavity in the heart, and that in children who cannot use them while in the womb, there is a hole

through which the blood flows from the hollow vein into the left cavity of the heart, and a tube

through which it passes from the arterial vein into the grand artery without passing through the

lung. In the next place, how could digestion be carried on in the stomach unless the heart

communicated heat to it through the arteries, and along with this certain of the more fluid parts of

the blood, which assist in the dissolution of the food that has been taken in? Is not also the

operation which converts the juice of food into blood easily comprehended, when it is considered

that it is distilled by passing and repassing through the heart perhaps more than one or two

hundred times in a day? And what more need be adduced to explain nutrition, and the production

of the different humors of the body, beyond saying, that the force with which the blood, in being

rarefied, passes from the heart towards the extremities of the arteries, causes certain of its parts to

remain in the members at which they arrive, and there occupy the place of some others expelled

by them; and that according to the situation, shape, or smallness of the pores with which they

meet, some rather than others flow into certain parts, in the same way that some sieves are

observed to act, which, by being variously perforated, serve to separate different species of grain?

And, in the last place, what above all is here worthy of observation, is the generation of the

animal spirits, which are like a very subtle wind, or rather a very pure and vivid flame which,

continually ascending in great abundance from the heart to the brain, thence penetrates through

the nerves into the muscles, and gives motion to all the members; so that to account for other

parts of the blood which, as most agitated and penetrating, are the fittest to compose these spirits,

proceeding towards the brain, it is not necessary to suppose any other cause, than simply, that the

arteries which carry them thither proceed from the heart in the most direct lines, and that,

according to the rules of mechanics which are the same with those of nature, when many objects

tend at once to the same point where there is not sufficient room for all (as is the case with the

parts of the blood which flow forth from the left cavity of the heart and tend towards the brain),

the weaker and less agitated parts must necessarily be driven aside from that point by the stronger

which alone in this way reach it I had expounded all these matters with sufficient minuteness in

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the treatise which I formerly thought of publishing. And after these, I had shown what must be

the fabric of the nerves and muscles of the human body to give the animal spirits contained in it

the power to move the members, as when we see heads shortly after they have been struck off

still move and bite the earth, although no longer animated; what changes must take place in the

brain to produce waking, sleep, and dreams; how light, sounds, odors, tastes, heat, and all the

other qualities of external objects impress it with different ideas by means of the senses; how

hunger, thirst, and the other internal affections can likewise impress upon it divers ideas; what

must be understood by the common sense (sensus communis) in which these ideas are received,

by the memory which retains them, by the fantasy which can change them in various ways, and

out of them compose new ideas, and which, by the same means, distributing the animal spirits

through the muscles, can cause the members of such a body to move in as many different ways,

and in a manner as suited, whether to the objects that are presented to its senses or to its internal

affections, as can take place in our own case apart from the guidance of the will. Nor will this

appear at all strange to those who are acquainted with the variety of movements performed by the

different automata, or moving machines fabricated by human industry, and that with help of but

few pieces compared with the great multitude of bones, muscles, nerves, arteries, veins, and other

parts that are found in the body of each animal. Such persons will look upon this body as a

machine made by the hands of God, which is incomparably better arranged, and adequate to

movements more admirable than is any machine of human invention. And here I specially stayed

to show that, were there such machines exactly resembling organs and outward form an ape or

any other irrational animal, we could have no means of knowing that they were in any respect of

a different nature from these animals; but if there were machines bearing the image of our bodies,

and capable of imitating our actions as far as it is morally possible, there would still remain two

most certain tests whereby to know that they were not therefore really men. Of these the first is

that they could never use words or other signs arranged in such a manner as is competent to us in

order to declare our thoughts to others: for we may easily conceive a machine to be so

constructed that it emits vocables, and even that it emits some correspondent to the action upon it

of external objects which cause a change in its organs; for example, if touched in a particular

place it may demand what we wish to say to it; if in another it may cry out that it is hurt, and such

like; but not that it should arrange them variously so as appositely to reply to what is said in its

presence, as men of the lowest grade of intellect can do. The second test is, that although such

machines might execute many things with equal or perhaps greater perfection than any of us, they

would, without doubt, fail in certain others from which it could be discovered that they did not act

from knowledge, but solely from the disposition of their organs: for while reason is an universal

instrument that is alike available on every occasion, these organs, on the contrary, need a

particular arrangement for each particular action; whence it must be morally impossible that there

should exist in any machine a diversity of organs sufficient to enable it to act in all the

occurrences of life, in the way in which our reason enables us to act. Again, by means of these

two tests we may likewise know the difference between men and brutes. For it is highly deserving

of remark, that there are no men so dull and stupid, not even idiots, as to be incapable of joining

together different words, and thereby constructing a declaration by which to make their thoughts

understood; and that on the other hand, there is no other animal, however perfect or happily

circumstanced, which can do the like. Nor does this inability arise from want of organs: for we

observe that magpies and parrots can utter words like ourselves, and are yet unable to speak as we

do, that is, so as to show that they understand what they say; in place of which men born deaf and

dumb, and thus not less, but rather more than the brutes, destitute of the organs which others use

in speaking, are in the habit of spontaneously inventing certain signs by which they discover their

thoughts to those who, being usually in their company, have leisure to learn their language. And

this proves not only that the brutes have less reason than man, but that they have none at all: for

we see that very little is required to enable a person to speak; and since a certain inequality of

capacity is observable among animals of the same species, as well as among men, and since some

are more capable of being instructed than others, it is incredible that the most perfect ape or

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parrot of its species, should not in this be equal to the most stupid infant of its kind or at least to

one that was crack-brained, unless the soul of brutes were of a nature wholly different from ours.

And we ought not to confound speech with the natural movements which indicate the passions,

and can be imitated by machines as well as manifested by animals; nor must it be thought with

certain of the ancients, that the brutes speak, although we do not understand their language. For if

such were the case, since they are endowed with many organs analogous to ours, they could as

easily communicate their thoughts to us as to their fellows. It is also very worthy of remark, that,

though there are many animals which manifest more industry than we in certain of their actions,

the same animals are yet observed to show none at all in many others: so that the circumstance

that they do better than we does not prove that they are endowed with mind, for it would thence

follow that they possessed greater reason than any of us, and could surpass us in all things; on the

contrary, it rather proves that they are destitute of reason, and that it is nature which acts in them

according to the disposition of their organs: thus it is seen, that a clock composed only of wheels

and weights can number the hours and measure time more exactly than we with all our skin.

I had after this described the reasonable soul, and shown that it could by no means be

educed from the power of matter, as the other things of which I had spoken, but that it must be

expressly created; and that it is not sufficient that it be lodged in the human body exactly like a

pilot in a ship, unless perhaps to move its members, but that it is necessary for it to be joined and

united more closely to the body, in order to have sensations and appetites similar to ours, and thus

constitute a real man. I here entered, in conclusion, upon the subject of the soul at considerable

length, because it is of the greatest moment: for after the error of those who deny the existence of

God, an error which I think I have already sufficiently refuted, there is none that is more powerful

in leading feeble minds astray from the straight path of virtue than the supposition that the soul of

the brutes is of the same nature with our own; and consequently that after this life we have

nothing to hope for or fear, more than flies and ants; in place of which, when we know how far

they differ we much better comprehend the reasons which establish that the soul is of a nature

wholly independent of the body, and that consequently it is not liable to die with the latter and,

finally, because no other causes are observed capable of destroying it, we are naturally led thence

to judge that it is immortal.

Chapter 6

Three years have now elapsed since I finished the treatise containing all these matters; and I

was beginning to revise it, with the view to put it into the hands of a printer, when I learned that

persons to whom I greatly defer, and whose authority over my actions is hardly less influential

than is my own reason over my thoughts, had condemned a certain doctrine in physics, published

a short time previously by another individual to which I will not say that I adhered, but only that,

previously to their censure I had observed in it nothing which I could imagine to be prejudicial

either to religion or to the state, and nothing therefore which would have prevented me from

giving expression to it in writing, if reason had persuaded me of its truth; and this led me to fear

lest among my own doctrines likewise some one might be found in which I had departed from the

truth, notwithstanding the great care I have always taken not to accord belief to new opinions of

which I had not the most certain demonstrations, and not to give expression to aught that might

tend to the hurt of any one. This has been sufficient to make me alter my purpose of publishing

them; for although the reasons by which I had been induced to take this resolution were very

strong, yet my inclination, which has always been hostile to writing books, enabled me

immediately to discover other considerations sufficient to excuse me for not undertaking the task.

And these reasons, on one side and the other, are such, that not only is it in some measure my

interest here to state them, but that of the public, perhaps, to know them.

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I have never made much account of what has proceeded from my own mind; and so long as

I gathered no other advantage from the method I employ beyond satisfying myself on some

difficulties belonging to the speculative sciences, or endeavoring to regulate my actions according

to the principles it taught me, I never thought myself bound to publish anything respecting it. For

in what regards manners, every one is so full of his own wisdom, that there might be found as

many reformers as heads, if any were allowed to take upon themselves the task of mending them,

except those whom God has constituted the supreme rulers of his people or to whom he has given

sufficient grace and zeal to be prophets; and although my speculations greatly pleased myself, I

believed that others had theirs, which perhaps pleased them still more. But as soon as I had

acquired some general notions respecting physics, and beginning to make trial of them in various

particular difficulties, had observed how far they can carry us, and how much they differ from the

principles that have been employed up to the present time, I believed that I could not keep them

concealed without sinning grievously against the law by which we are bound to promote, as far as

in us lies, the general good of mankind. For by them I perceived it to be possible to arrive at

knowledge highly useful in life; and in room of the speculative philosophy usually taught in the

schools, to discover a practical, by means of which, knowing the force and action of fire, water,

air the stars, the heavens, and all the other bodies that surround us, as distinctly as we know the

various crafts of our artisans, we might also apply them in the same way to all the uses to which

they are adapted, and thus render ourselves the lords and possessors of nature. And this is a result

to be desired, not only in order to the invention of an infinity of arts, by which we might be

enabled to enjoy without any trouble the fruits of the earth, and all its comforts, but also and

especially for the preservation of health, which is without doubt, of all the blessings of this life,

the first and fundamental one; for the mind is so intimately dependent upon the condition and

relation of the organs of the body, that if any means can ever be found to render men wiser and

more ingenious than hitherto, I believe that it is in medicine they must be sought for. It is true that

the science of medicine, as it now exists, contains few things whose utility is very remarkable:

but without any wish to depreciate it, I am confident that there is no one, even among those

whose profession it is, who does not admit that all at present known in it is almost nothing in

comparison of what remains to be discovered; and that we could free ourselves from an infinity

of maladies of body as well as of mind, and perhaps also even from the debility of age, if we had

sufficiently ample knowledge of their causes, and of all the remedies provided for us by nature.

But since I designed to employ my whole life in the search after so necessary a science, and since

I had fallen in with a path which seems to me such, that if any one follow it he must inevitably

reach the end desired, unless he be hindered either by the shortness of life or the want of

experiments, I judged that there could be no more effectual provision against these two

impediments than if I were faithfully to communicate to the public all the little I might myself

have found, and incite men of superior genius to strive to proceed farther, by contributing, each

according to his inclination and ability, to the experiments which it would be necessary to make,

and also by informing the public of all they might discover, so that, by the last beginning where

those before them had left off, and thus connecting the lives and labours of many, we might

collectively proceed much farther than each by himself could do.

I remarked, moreover, with respect to experiments, that they become always more

necessary the more one is advanced in knowledge; for, at the commencement, it is better to make

use only of what is spontaneously presented to our senses, and of which we cannot remain

ignorant, provided we bestow on it any reflection, however slight, than to concern ourselves

about more uncommon and recondite phenomena: the reason of which is, that the more

uncommon often only mislead us so long as the causes of the more ordinary are still unknown;

and the circumstances upon which they depend are almost always so special and minute as to be

highly difficult to detect. But in this I have adopted the following order: first, I have essayed to

find in general the principles, or first causes of all that is or can be in the world, without taking

into consideration for this end anything but God himself who has created it, and without educing

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them from any other source than from certain germs of truths naturally existing in our minds In

the second place, I examined what were the first and most ordinary effects that could be deduced

from these causes; and it appears to me that, in this way, I have found heavens, stars, an earth,

and even on the earth water, air, fire, minerals, and some other things of this kind, which of all

others are the most common and simple, and hence the easiest to know. Afterwards when I

wished to descend to the more particular, so many diverse objects presented themselves to me,

that I believed it to be impossible for the human mind to distinguish the forms or species of

bodies that are upon the earth, from an infinity of others which might have been, if it had pleased

God to place them there, or consequently to apply them to our use, unless we rise to causes

through their effects, and avail ourselves of many particular experiments. Thereupon, turning

over in my mind I the objects that had ever been presented to my senses I freely venture to state

that I have never observed any which I could not satisfactorily explain by the principles had

discovered. But it is necessary also to confess that the power of nature is so ample and vast, and

these principles so simple and general, that I have hardly observed a single particular effect which

I cannot at once recognize as capable of being deduced in man different modes from the

principles, and that my greatest difficulty usually is to discover in which of these modes the effect

is dependent upon them; for out of this difficulty cannot otherwise extricate myself than by again

seeking certain experiments, which may be such that their result is not the same, if it is in the one

of these modes at we must explain it, as it would be if it were to be explained in the other. As to

what remains, I am now in a position to discern, as I think, with sufficient clearness what course

must be taken to make the majority those experiments which may conduce to this end: but I

perceive likewise that they are such and so numerous, that neither my hands nor my income,

though it were a thousand times larger than it is, would be sufficient for them all; so that

according as henceforward I shall have the means of making more or fewer experiments, I shall

in the same proportion make greater or less progress in the knowledge of nature. This was what I

had hoped to make known by the treatise I had written, and so clearly to exhibit the advantage

that would thence accrue to the public, as to induce all who have the common good of man at

heart, that is, all who are virtuous in truth, and not merely in appearance, or according to opinion,

as well to communicate to me the experiments they had already made, as to assist me in those that

remain to be made.

But since that time other reasons have occurred to me, by which I have been led to change

my opinion, and to think that I ought indeed to go on committing to writing all the results which I

deemed of any moment, as soon as I should have tested their truth, and to bestow the same care

upon them as I would have done had it been my design to publish them. This course commended

itself to me, as well because I thus afforded myself more ample inducement to examine them

thoroughly, for doubtless that is always more narrowly scrutinized which we believe will be read

by many, than that which is written merely for our private use (and frequently what has seemed to

me true when I first conceived it, has appeared false when I have set about committing it to

writing), as because I thus lost no opportunity of advancing the interests of the public, as far as in

me lay, and since thus likewise, if my writings possess any value, those into whose hands they

may fall after my death may be able to put them to what use they deem proper. But I resolved by

no means to consent to their publication during my lifetime, lest either the oppositions or the

controversies to which they might give rise, or even the reputation, such as it might be, which

they would acquire for me, should be any occasion of my losing the time that I had set apart for

my own improvement. For though it be true that every one is bound to promote to the extent of

his ability the good of others, and that to be useful to no one is really to be worthless, yet it is

likewise true that our cares ought to extend beyond the present, and it is good to omit doing what

might perhaps bring some profit to the living, when we have in view the accomplishment of other

ends that will be of much greater advantage to posterity. And in truth, I am quite willing it should

be known that the little I have hitherto learned is almost nothing in comparison with that of which

I am ignorant, and to the knowledge of which I do not despair of being able to attain; for it is

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much the same with those who gradually discover truth in the sciences, as with those who when

growing rich find less difficulty in making great acquisitions, than they formerly experienced

when poor in making acquisitions of much smaller amount. Or they may be compared to the

commanders of armies, whose forces usually increase in proportion to their victories, and who

need greater prudence to keep together the residue of their troops after a defeat than after a

victory to take towns and provinces. For he truly engages in battle who endeavors to surmount all

the difficulties and errors which prevent him from reaching the knowledge of truth, and he is

overcome in fight who admits a false opinion touching a matter of any generality and importance,

and he requires thereafter much more skill to recover his former position than to make great

advances when once in possession of thoroughly ascertained principles. As for myself, if I have

succeeded in discovering any truths in the sciences (and I trust that what is contained in this

volume 1 will show that I have found some), I can declare that they are but the consequences and

results of five or six principal difficulties which I have surmounted, and my encounters with

which I reckoned as battles in which victory declared for me. I will not hesitate even to avow my

belief that nothing further is wanting to enable me fully to realize my designs than to gain two or

three similar victories; and that I am not so far advanced in years but that, according to the

ordinary course of nature, I may still have sufficient leisure for this end. But I conceive myself

the more bound to husband the time that remains the greater my expectation of being able to

employ it aright, and I should doubtless have much to rob me of it, were I to publish the

principles of my physics: for although they are almost all so evident that to assent to them no

more is needed than simply to understand them, and although there is not one of them of which I

do not expect to be able to give demonstration, yet, as it is impossible that they can be in

accordance with all the diverse opinions of others, I foresee that I should frequently be turned

aside from my grand design, on occasion of the opposition which they would be sure to awaken.

It may be said, that these oppositions would be useful both in making me aware of my

errors, and, if my speculations contain anything of value, in bringing others to a fuller

understanding of it; and still farther, as many can see better than one, in leading others who are

now beginning to avail themselves of my principles, to assist me in turn with their discoveries.

But though I recognize my extreme liability to error, and scarce ever trust to the first thoughts

which occur to me, yet-the experience I have had of possible objections to my views prevents me

from anticipating any profit from them. For I have already had frequent proof of the judgments,

as well of those I esteemed friends, as of some others to whom I thought I was an object of

indifference, and even of some whose malignancy and envy would, I knew, determine them to

endeavor to discover what partiality concealed from the eyes of my friends. But it has rarely

happened that anything has been objected to me which I had myself altogether overlooked, unless

it were something far removed from the subject: so that I have never met with a single critic of

my opinions who did not appear to me either less rigorous or less equitable than myself. And

further, I have never observed that any truth before unknown has been brought to light by the

disputations that are practised in the schools; for while each strives for the victory, each is much

more occupied in making the best of mere verisimilitude, than in weighing the reasons on both

sides of the question; and those who have been long good advocates are not afterwards on that

account the better judges.

As for the advantage that others would derive from the communication of my thoughts, it

could not be very great; because I have not yet so far prosecuted them as that much does not

remain to be added before they can be applied to practice. And I think I may say without vanity,

that if there is any one who can carry them out that length, it must be myself rather than another:

not that there may not be in the world many minds incomparably superior to mine, but because

one cannot so well seize a thing and make it one's own, when it has been learned from another, as

when one has himself discovered it. And so true is this of the present subject that, though I have

often explained some of my opinions to persons of much acuteness, who, whilst I was speaking,

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appeared to understand them very distinctly, yet, when they repeated them, I have observed that

they almost always changed them to such an extent that I could no longer acknowledge them as

mine. I am glad, by the way, to take this opportunity of requesting posterity never to believe on

hearsay that anything has proceeded from me which has not been published by myself; and I am

not at all astonished at the extravagances attributed to those ancient philosophers whose own

writings we do not possess; whose thoughts, however, I do not on that account suppose to have

been really absurd, seeing they were among the ablest men of their times, but only that these have

been falsely represented to us. It is observable, accordingly, that scarcely in a single instance has

any one of their disciples surpassed them; and I am quite sure that the most devoted of the present

followers of Aristotle would think themselves happy if they had as much knowledge of nature as

he possessed, were it even under the condition that they should never afterwards attain to higher.

In this respect they are like the ivy which never strives to rise above the tree that sustains it, and

which frequently even returns downwards when it has reached the top; for it seems to me that

they also sink, in other words, render themselves less wise than they would be if they gave up

study, who, not contented with knowing all that is intelligibly explained in their author, desire in

addition to find in him the solution of many difficulties of which he says not a word, and never

perhaps so much as thought. Their fashion of philosophizing, however, is well suited to persons

whose abilities fall below mediocrity; for the obscurity of the distinctions and principles of which

they make use enables them to speak of all things with as much confidence as if they really knew

them, and to defend all that they say on any subject against the most subtle and skillful, without

its being possible for any one to convict them of error. In this they seem to me to be like a blind

man, who, in order to fight on equal terms with a person that sees, should have made him descend

to the bottom of an intensely dark cave: and I may say that such persons have an interest in my

refraining from publishing the principles of the philosophy of which I make use; for, since these

are of a kind the simplest and most evident, I should, by publishing them, do much the same as if

I were to throw open the windows, and allow the light of day to enter the cave into which the

combatants had descended. But even superior men have no reason for any great anxiety to know

these principles, for if what they desire is to be able to speak of all things, and to acquire a

reputation for learning, they will gain their end more easily by remaining satisfied with the

appearance of truth, which can be found without much difficulty in all sorts of matters, than by

seeking the truth itself which unfolds itself but slowly and that only in some departments, while it

obliges us, when we have to speak of others, freely to confess our ignorance. If, however, they

prefer the knowledge of some few truths to the vanity of appearing ignorant of none, as such

knowledge is undoubtedly much to be preferred, and, if they choose to follow a course similar to

mine, they do not require for this that I should say anything more than I have already said in this

discourse. For if they are capable of making greater advancement than I have made, they will

much more be able of themselves to discover all that I believe myself to have found; since as I

have never examined aught except in order, it is certain that what yet remains to be discovered is

in itself more difficult and recondite, than that which I have already been enabled to find, and the

gratification would be much less in learning it from me than in discovering it for themselves.

Besides this, the habit which they will acquire, by seeking first what is easy, and then passing

onward slowly and step by step to the more difficult, will benefit them more than all my

instructions. Thus, in my own case, I am persuaded that if I had been taught from my youth all

the truths of which I have since sought out demonstrations, and had thus learned them without

labour, I should never, perhaps, have known any beyond these; at least, I should never have

acquired the habit and the facility which I think I possess in always discovering new truths in

proportion as I give myself to the search. And, in a single word, if there is any work in the world

which cannot be so well finished by another as by him who has commenced it, it is that at which I

labour.

It is true, indeed, as regards the experiments which may conduce to this end, that one man

is not equal to the task of making them all; but yet he can advantageously avail himself, in this

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work, of no hands besides his own, unless those of artisans, or parties of the same kind, whom he

could pay, and whom the hope of gain (a means of great efficacy) might stimulate to accuracy in

the performance of what was prescribed to them. For as to those who, through curiosity or a

desire of learning, of their own accord, perhaps, offer him their services, besides that in general

their promises exceed their performance, and that they sketch out fine designs of which not one is

ever realized, they will, without doubt, expect to be compensated for their trouble by the

explication of some difficulties, or, at least, by compliments and useless speeches, in which he

cannot spend any portion of his time without loss to himself. And as for the experiments that

others have already made, even although these parties should be willing of themselves to

communicate them to him (which is what those who esteem them secrets will never do), the

experiments are, for the most part, accompanied with so many circumstances and superfluous

elements, as to make it exceedingly difficult to disentangle the truth from its adjuncts- besides, he

will find almost all of them so ill described, or even so false (because those who made them have

wished to see in them only such facts as they deemed conformable to their principles), that, if in

the entire number there should be some of a nature suited to his purpose, still their value could

not compensate for the time what would be necessary to make the selection. So that if there

existed any one whom we assuredly knew to be capable of making discoveries of the highest

kind, and of the greatest possible utility to the public; and if all other men were therefore eager by

all means to assist him in successfully prosecuting his designs, I do not see that they could do

aught else for him beyond contributing to defray the expenses of the experiments that might be

necessary; and for the rest, prevent his being deprived of his leisure by the unseasonable

interruptions of any one. But besides that I neither have so high an opinion of myself as to be

willing to make promise of anything extraordinary, nor feed on imaginations so vain as to fancy

that the public must be much interested in my designs; I do not, on the other hand, own a soul so

mean as to be capable of accepting from any one a favor of which it could be supposed that I was

unworthy.

These considerations taken together were the reason why, for the last three years, I have

been unwilling to publish the treatise I had on hand, and why I even resolved to give publicity

during my life to no other that was so general, or by which the principles of my physics might be

understood. But since then, two other reasons have come into operation that have determined me

here to subjoin some particular specimens, and give the public some account of my doings and

designs. Of these considerations, the first is, that if I failed to do so, many who were cognizant of

my previous intention to publish some writings, might have imagined that the reasons which

induced me to refrain from so doing, were less to my credit than they really are; for although I am

not immoderately desirous of glory, or even, if I may venture so to say, although I am averse

from it in so far as I deem it hostile to repose which I hold in greater account than aught else, yet,

at the same time, I have never sought to conceal my actions as if they were crimes, nor made use

of many precautions that I might remain unknown; and this partly because I should have thought

such a course of conduct a wrong against myself, and partly because it would have occasioned me

some sort of uneasiness which would again have been contrary to the perfect mental tranquillity

which I court. And forasmuch as, while thus indifferent to the thought alike of fame or of

forgetfulness, I have yet been unable to prevent myself from acquiring some sort of reputation, I

have thought it incumbent on me to do my best to save myself at least from being ill-spoken of.

The other reason that has determined me to commit to writing these specimens of philosophy is,

that I am becoming daily more and more alive to the delay which my design of self-instruction

suffers, for want of the infinity of experiments I require, and which it is impossible for me to

make without the assistance of others: and, without flattering myself so much as to expect the

public to take a large share in my interests, I am yet unwilling to be found so far wanting in the

duty I owe to myself, as to give occasion to those who shall survive me to make it matter of

reproach against me some day, that I might have left them many things in a much more perfect

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state than I have done, had I not too much neglected to make them aware of the ways in which

they could have promoted the accomplishment of my designs.

And I thought that it was easy for me to select some matters which should neither be

obnoxious to much controversy, nor should compel me to expound more of my principles than I

desired, and which should yet be sufficient clearly to exhibit what I can or cannot accomplish in

the sciences. Whether or not I have succeeded in this it is not for me to say; and I do not wish to

forestall the judgments of others by speaking myself of my writings; but it will gratify me if they

be examined, and, to afford the greater inducement to this I request all who may have any

objections to make to them, to take the trouble of forwarding these to my publisher, who will give

me notice of them, that I may endeavor to subjoin at the same time my reply; and in this way

readers seeing both at once will more easily determine where the truth lies; for I do not engage in

any case to make prolix replies, but only with perfect frankness to avow my errors if I am

convinced of them, or if I cannot perceive them, simply to state what I think is required for

defense of the matters I have written, adding thereto no explication of any new matte that it may

not be necessary to pass without end from one thing to another.

If some of the matters of which I have spoken in the beginning of the "Dioptrics" and

"Meteorics" should offend at first sight, because I call them hypotheses and seem indifferent

about giving proof of them, I request a patient and attentive reading of the whole, from which I

hope those hesitating will derive satisfaction; for it appears to me that the reasonings are so

mutually connected in these treatises, that, as the last are demonstrated by the first which are their

causes, the first are in their turn demonstrated by the last which are their effects. Nor must it be

imagined that I here commit the fallacy which the logicians call a circle; for since experience

renders the majority of these effects most certain, the causes from which I deduce them do not

serve so much to establish their reality as to explain their existence; but on the contrary, the

reality of the causes is established by the reality of the effects. Nor have I called them hypotheses

with any other end in view except that it may be known that I think I am able to deduce them

from those first truths which I have already expounded; and yet that I have expressly determined

not to do so, to prevent a certain class of minds from thence taking occasion to build some

extravagant philosophy upon what they may take to be my principles, and my being blamed for it.

I refer to those who imagine that they can master in a day all that another has taken twenty years

to think out, as soon as he has spoken two or three words to them on the subject; or who are the

more liable to error and the less capable of perceiving truth in very proportion as they are more

subtle and lively. As to the opinions which are truly and wholly mine, I offer no apology for them

as new, -- persuaded as I am that if their reasons be well considered they will be found to be so

simple and so conformed, to common sense as to appear less extraordinary and less paradoxical

than any others which can be held on the same subjects; nor do I even boast of being the earliest

discoverer of any of them, but only of having adopted them, neither because they had nor because

they had not been held by others, but solely because reason has convinced me of their truth.

Though artisans may not be able at once to execute the invention which is explained in the

"Dioptrics," I do not think that any one on that account is entitled to condemn it; for since address

and practice are required in order so to make and adjust the machines described by me as not to

overlook the smallest particular, I should not be less astonished if they succeeded on the first

attempt than if a person were in one day to become an accomplished performer on the guitar, by

merely having excellent sheets of music set up before him. And if I write in French, which is the

language of my country, in preference to Latin, which is that of my preceptors, it is because I

expect that those who make use of their unprejudiced natural reason will be better judges of my

opinions than those who give heed to the writings of the ancients only; and as for those who unite

good sense with habits of study, whom alone I desire for judges, they will not, I feel assured, be

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so partial to Latin as to refuse to listen to my reasonings merely because I expound them in the

vulgar tongue.

In conclusion, I am unwilling here to say anything very specific of the progress which I

expect to make for the future in the sciences, or to bind myself to the public by any promise

which I am not certain of being able to fulfill; but this only will I say, that I have resolved to

devote what time I may still have to live to no other occupation than that of endeavoring to

acquire some knowledge of Nature, which shall be of such a kind as to enable us therefrom to

deduce rules in medicine of greater certainty than those at present in use; and that my inclination

is so much opposed to all other pursuits, especially to such as cannot be useful to some without

being hurtful to others, that if, by any circumstances, I had been constrained to engage in such, I

do not believe that I should have been able to succeed. Of this I here make a public declaration,

though well aware that it cannot serve to procure for me any consideration in the world, which,

however, I do not in the least affect; and I shall always hold myself more obliged to those through

whose favor I am permitted to enjoy my retirement without interruption than to any who might

offer me the highest earthly preferments.