Discourse on the Method of Rightly Conducting the
Reason,
and Seeking Truth in the Sciences (Continued...)
PART V.
I would here willingly have proceeded to exhibit the whole chain of truths which I
deduced from these primary but as with a view to this it would have been necessary now to
treat of many questions in dispute among the earned, with whom I do not wish to be
embroiled, I believe that it will be better for me to refrain from this exposition, and
only mention in general what these truths are, that the more judicious may be able to
determine whether a more special account of them would conduce to the public advantage. I
have ever remained firm in my original resolution to suppose no other principle than that
of which I have recently availed myself in demonstrating the existence of God and of the
soul, and to accept as true nothing that did not appear to me more clear and certain than
the demonstrations of the geometers had formerly appeared; and yet I venture to state that
not only have I found means to satisfy myself in a short time on all the principal
difficulties which are usually treated of in philosophy, but I have also observed certain
laws established in nature by God in such a manner, and of which he has impressed on our
minds such notions, that after we have reflected sufficiently upon these, we cannot doubt
that they are accurately observed in all that exists or takes place in the world and
farther, by considering the concatenation of these laws, it appears to me that I have
discovered many truths more useful and more important than all I had before learned, or
even had expected to learn.
But because I have essayed to expound the chief of these discoveries in a treatise
which certain considerations prevent me from publishing, I cannot make the results known
more conveniently than by here giving a summary of the contents of this treatise. It was
my design to comprise in it all that, before I set myself to write it, I thought I knew of
the nature of material objects. But like the painters who, finding themselves unable to
represent equally well on a plain surface all the different faces of a solid body, select
one of the chief, on which alone they make the light fall, and throwing the rest into the
shade, allow them to appear only in so far as they can be seen while looking at the
principal one; so, fearing lest I should not be able to compense in my discourse all that
was in my mind, I resolved to expound singly, though at considerable length, my opinions
regarding light; then to take the opportunity of adding something on the sun and the fixed
stars, since light almost wholly proceeds from them; on the heavens since they transmit
it; on the planets, comets, and earth, since they reflect it; and particularly on all the
bodies that are upon the earth, since they are either colored, or transparent, or
luminous; and finally on man, since he is the spectator of these objects. Further, to
enable me to cast this variety of subjects somewhat into the shade, and to express my
judgment regarding them with greater freedom, without being necessitated to adopt or
refute the opinions of the learned, I resolved to leave all the people here to their
disputes, and to speak only of what would happen in a new world, if God were now to create
somewhere in the imaginary spaces matter sufficient to compose one, and were to agitate
variously and confusedly the different parts of this matter, so that there resulted a
chaos as disordered as the poets ever feigned, and after that did nothing more than lend
his ordinary concurrence to nature, and allow her to act in accordance with the laws which
he had established. On this supposition, I, in the first place, described this matter, and
essayed to represent it in such a manner that to my mind there can be nothing clearer and
more intelligible, except what has been recently said regarding God and the soul; for I
even expressly supposed that it possessed none of those forms or qualities which are so
debated in the schools, nor in general anything the knowledge of which is not so natural
to our minds that no one can so much as imagine himself ignorant of it. Besides, I have
pointed out what are the laws of nature; and, with no other principle upon which to found
my reasonings except the infinite perfection of God, I endeavored to demonstrate all those
about which there could be any room for doubt, and to prove that they are such, that even
if God had created more worlds, there could have been none in which these laws were not
observed. Thereafter, I showed how the greatest part of the matter of this chaos must, in
accordance with these laws, dispose and arrange itself in such a way as to present the
appearance of heavens; how in the meantime some of its parts must compose an earth and
some planets and comets, and others a sun and fixed stars. And, making a digression at
this stage on the subject of light, I expounded at considerable length what the nature of
that light must be which is found in the sun and the stars, and how thence in an instant
of time it traverses the immense spaces of the heavens, and how from the planets and
comets it is reflected towards the earth. To this I likewise added much respecting the
substance, the situation, the motions, and all the different qualities of these heavens
and stars; so that I thought I had said enough respecting them to show that there is
nothing observable in the heavens or stars of our system that must not, or at least may
not appear precisely alike in those of the system which I described. I came next to speak
of the earth in particular, and to show how, even though I had expressly supposed that God
had given no weight to the matter of which it is composed, this should not prevent all its
parts from tending exactly to its center; how with water and air on its surface, the
disposition of the heavens and heavenly bodies, more especially of the moon, must cause a
flow and ebb, like in all its circumstances to that observed in our seas, as also a
certain current both of water and air from east to west, such as is likewise observed
between the tropics; how the mountains, seas, fountains, and rivers might naturally be
formed in it, and the metals produced in the mines, and the plants grow in the fields and
in general, how all the bodies which are commonly denominated mixed or composite might be
generated and, among other things in the discoveries alluded to inasmuch as besides the
stars, I knew nothing except fire which produces light, I spared no pains to set forth all
that pertains to its nature, -- the manner of its production and support, and to explain
how heat is sometimes found without light, and light without heat; to show how it can
induce various colors upon different bodies and other diverse qualities; how it reduces
some to a liquid state and hardens others; how it can consume almost all bodies, or
convert them into ashes and smoke; and finally, how from these ashes, by the mere
intensity of its action, it forms glass: for as this transmutation of ashes into glass
appeared to me as wonderful as any other in nature, I took a special pleasure in
describing it. I was not, however, disposed, from these circumstances, to conclude that
this world had been created in the manner I described; for it is much more likely that God
made it at the first such as it was to be. But this is certain, and an opinion commonly
received among theologians, that the action by which he now sustains it is the same with
that by which he originally created it; so that even although he had from the beginning
given it no other form than that of chaos, provided only he had established certain laws
of nature, and had lent it his concurrence to enable it to act as it is wont to do, it may
be believed, without discredit to the miracle of creation, that, in this way alone, things
purely material might, in course of time, have become such as we observe them at present;
and their nature is much more easily conceived when they are beheld coming in this manner
gradually into existence, than when they are only considered as produced at once in a
finished and perfect state.
From the description of inanimate bodies and plants, I passed to animals, and
particularly to man. But since I had not as yet sufficient knowledge to enable me to treat
of these in the same manner as of the rest, that is to say, by deducing effects from their
causes, and by showing from what elements and in what manner nature must produce them, I
remained satisfied with the supposition that God formed the body of man wholly like to one
of ours, as well in the external shape of the members as in the internal conformation of
the organs, of the same matter with that I had described, and at first placed in it no
rational soul, nor any other principle, in room of the vegetative or sensitive soul,
beyond kindling in the heart one of those fires without light, such as I had already
described, and which I thought was not different from the heat in hay that has been heaped
together before it is dry, or that which causes fermentation in new wines before they are
run clear of the fruit. For, when I examined the kind of functions which might, as
consequences of this supposition, exist in this body, I found precisely all those which
may exist in us independently of all power of thinking, and consequently without being in
any measure owing to the soul; in other words, to that part of us which is distinct from
the body, and of which it has been said above that the nature distinctively consists in
thinking, functions in which the animals void of reason may be said wholly to resemble us;
but among which I could not discover any of those that, as dependent on thought alone,
belong to us as men, while, on the other hand, I did afterwards discover these as soon as
I supposed God to have created a rational soul, and to have annexed it to this body in a
particular manner which I described.
But, in order to show how I there handled this matter, I mean here to give the
explication of the motion of the heart and arteries, which, as the first and most general
motion observed in animals, will afford the means of readily determining what should be
thought of all the rest. And that there may be less difficulty in understanding what I am
about to say on this subject, I advise those who are not versed in anatomy, before they
commence the perusal of these observations, to take the trouble of getting dissected in
their presence the heart of some large animal possessed of lungs (for this is throughout
sufficiently like the human), and to have shown to them its two ventricles or cavities: in
the first place, that in the right side, with which correspond two very ample tubes, viz.,
the hollow vein (vena cava), which is the principal receptacle of the blood, and the trunk
of the tree, as it were, of which all the other veins in the body are branches; and the
arterial vein (vena arteriosa), inappropriately so denominated, since it is in truth only
an artery, which, taking its rise in the heart, is divided, after passing out from it,
into many branches which presently disperse themselves all over the lungs; in the second
place, the cavity in the left side, with which correspond in the same manner two canals in
size equal to or larger than the preceding, viz., the venous artery (arteria venosa),
likewise inappropriately thus designated, because it is simply a vein which comes from the
lungs, where it is divided into many branches, interlaced with those of the arterial vein,
and those of the tube called the windpipe, through which the air we breathe enters; and
the great artery which, issuing from the heart, sends its branches all over the body. I
should wish also that such persons were carefully shown the eleven pellicles which, like
so many small valves, open and shut the four orifices that are in these two cavities,
viz., three at the entrance of the hollow veins where they are disposed in such a manner
as by no means to prevent the blood which it contains from flowing into the right
ventricle of the heart, and yet exactly to prevent its flowing out; three at the entrance
to the arterial vein, which, arranged in a manner exactly the opposite of the former,
readily permit the blood contained in this cavity to pass into the lungs, but hinder that
contained in the lungs from returning to this cavity; and, in like manner, two others at
the mouth of the venous artery, which allow the blood from the lungs to flow into the left
cavity of the heart, but preclude its return; and three at the mouth of the great artery,
which suffer the blood to flow from the heart, but prevent its reflux. Nor do we need to
seek any other reason for the number of these pellicles beyond this that the orifice of
the venous artery being of an oval shape from the nature of its situation, can be
adequately closed with two, whereas the others being round are more conveniently closed
with three. Besides, I wish such persons to observe that the grand artery and the arterial
vein are of much harder and firmer texture than the venous artery and the hollow vein; and
that the two last expand before entering the heart, and there form, as it were, two
pouches denominated the auricles of the heart, which are composed of a substance similar
to that of the heart itself; and that there is always more warmth in the heart than in any
other part of the body- and finally, that this heat is capable of causing any drop of
blood that passes into the cavities rapidly to expand and dilate, just as all liquors do
when allowed to fall drop by drop into a highly heated vessel.
For, after these things, it is not necessary for me to say anything more with a view to
explain the motion of the heart, except that when its cavities are not full of blood, into
these the blood of necessity flows, - - from the hollow vein into the right, and from the
venous artery into the left; because these two vessels are always full of blood, and their
orifices, which are turned towards the heart, cannot then be closed. But as soon as two
drops of blood have thus passed, one into each of the cavities, these drops which cannot
but be very large, because the orifices through which they pass are wide, and the vessels
from which they come full of blood, are immediately rarefied, and dilated by the heat they
meet with. In this way they cause the whole heart to expand, and at the same time press
home and shut the five small valves that are at the entrances of the two vessels from
which they flow, and thus prevent any more blood from coming down into the heart, and
becoming more and more rarefied, they push open the six small valves that are in the
orifices of the other two vessels, through which they pass out, causing in this way all
the branches of the arterial vein and of the grand artery to expand almost simultaneously
with the heart which immediately thereafter begins to contract, as do also the arteries,
because the blood that has entered them has cooled, and the six small valves close, and
the five of the hollow vein and of the venous artery open anew and allow a passage to
other two drops of blood, which cause the heart and the arteries again to expand as
before. And, because the blood which thus enters into the heart passes through these two
pouches called auricles, it thence happens that their motion is the contrary of that of
the heart, and that when it expands they contract. But lest those who are ignorant of the
force of mathematical demonstrations and who are not accustomed to distinguish true
reasons from mere verisimilitudes, should venture. without examination, to deny what has
been said, I wish it to be considered that the motion which I have now explained follows
as necessarily from the very arrangement of the parts, which may be observed in the heart
by the eye alone, and from the heat which may be felt with the fingers, and from the
nature of the blood as learned from experience, as does the motion of a clock from the
power, the situation, and shape of its counterweights and wheels.
But if it be asked how it happens that the blood in the veins, flowing in this way
continually into the heart, is not exhausted, and why the arteries do not become too full,
since all the blood which passes through the heart flows into them, I need only mention in
reply what has been written by a physician 1 of England, who has the honor of having
broken the ice on this subject, and of having been the first to teach that there are many
small passages at the extremities of the arteries, through which the blood received by
them from the heart passes into the small branches of the veins, whence it again returns
to the heart; so that its course amounts precisely to a perpetual circulation. Of this we
have abundant proof in the ordinary experience of surgeons, who, by binding the arm with a
tie of moderate straitness above the part where they open the vein, cause the blood to
flow more copiously than it would have done without any ligature; whereas quite the
contrary would happen were they to bind it below; that is, between the hand and the
opening, or were to make the ligature above the opening very tight. For it is manifest
that the tie, moderately straightened, while adequate to hinder the blood already in the
arm from returning towards the heart by the veins, cannot on that account prevent new
blood from coming forward through the arteries, because these are situated below the
veins, and their coverings, from their greater consistency, are more difficult to
compress; and also that the blood which comes from the heart tends to pass through them to
the hand with greater force than it does to return from the hand to the heart through the
veins. And since the latter current escapes from the arm by the opening made in one of the
veins, there must of necessity be certain passages below the ligature, that is, towards
the extremities of the arm through which it can come thither from the arteries. This
physician likewise abundantly establishes what he has advanced respecting the motion of
the blood, from the existence of certain pellicles, so disposed in various places along
the course of the veins, in the manner of small valves, as not to permit the blood to pass
from the middle of the body towards the extremities, but only to return from the
extremities to the heart; and farther, from experience which shows that all the blood
which is in the body may flow out of it in a very short time through a single artery that
has been cut, even although this had been closely tied in the immediate neighborhood of
the heart and cut between the heart and the ligature, so as to prevent the supposition
that the blood flowing out of it could come from any other quarter than the heart.
But there are many other circumstances which evince that what I have alleged is the
true cause of the motion of the blood: thus, in the first place, the difference that is
observed between the blood which flows from the veins, and that from the arteries, can
only arise from this, that being rarefied, and, as it were, distilled by passing through
the heart, it is thinner, and more vivid, and warmer immediately after leaving the heart,
in other words, when in the arteries, than it was a short time before passing into either,
in other words, when it was in the veins; and if attention be given, it will be found that
this difference is very marked only in the neighborhood of the heart; and is not so
evident in parts more remote from it. In the next place, the consistency of the coats of
which the arterial vein and the great artery are composed, sufficiently shows that the
blood is impelled against them with more force than against the veins. And why should the
left cavity of the heart and the great artery be wider and larger than the right cavity
and the arterial vein, were it not that the blood of the venous artery, having only been
in the lungs after it has passed through the heart, is thinner, and rarefies more readily,
and in a higher degree, than the blood which proceeds immediately from the hollow vein?
And what can physicians conjecture from feeling the pulse unless they know that according
as the blood changes its nature it can be rarefied by the warmth of the heart, in a higher
or lower degree, and more or less quickly than before? And if it be inquired how this heat
is communicated to the other members, must it not be admitted that this is effected by
means of the blood, which, passing through the heart, is there heated anew, and thence
diffused over all the body? Whence it happens, that if the blood be withdrawn from any
part, the heat is likewise withdrawn by the same means; and although the heart were as-hot
as glowing iron, it would not be capable of warming the feet and hands as at present,
unless it continually sent thither new blood. We likewise perceive from this, that the
true use of respiration is to bring sufficient fresh air into the lungs, to cause the
blood which flows into them from the right ventricle of the heart, where it has been
rarefied and, as it were, changed into vapors, to become thick, and to convert it anew
into blood, before it flows into the left cavity, without which process it would be unfit
for the nourishment of the fire that is there. This receives confirmation from the
circumstance, that it is observed of animals destitute of lungs that they have also but
one cavity in the heart, and that in children who cannot use them while in the womb, there
is a hole through which the blood flows from the hollow vein into the left cavity of the
heart, and a tube through which it passes from the arterial vein into the grand artery
without passing through the lung. In the next place, how could digestion be carried on in
the stomach unless the heart communicated heat to it through the arteries, and along with
this certain of the more fluid parts of the blood, which assist in the dissolution of the
food that has been taken in? Is not also the operation which converts the juice of food
into blood easily comprehended, when it is considered that it is distilled by passing and
repassing through the heart perhaps more than one or two hundred times in a day? And what
more need be adduced to explain nutrition, and the production of the different humors of
the body, beyond saying, that the force with which the blood, in being rarefied, passes
from the heart towards the extremities of the arteries, causes certain of its parts to
remain in the members at which they arrive, and there occupy the place of some others
expelled by them; and that according to the situation, shape, or smallness of the pores
with which they meet, some rather than others flow into certain parts, in the same way
that some sieves are observed to act, which, by being variously perforated, serve to
separate different species of grain? And, in the last place, what above all is here worthy
of observation, is the generation of the animal spirits, which are like a very subtle
wind, or rather a very pure and vivid flame which, continually ascending in great
abundance from the heart to the brain, thence penetrates through the nerves into the
muscles, and gives motion to all the members; so that to account for other parts of the
blood which, as most agitated and penetrating, are the fittest to compose these spirits,
proceeding towards the brain, it is not necessary to suppose any other cause, than simply,
that the arteries which carry them thither proceed from the heart in the most direct
lines, and that, according to the rules of mechanics which are the same with those of
nature, when many objects tend at once to the same point where there is not sufficient
room for all (as is the case with the parts of the blood which flow forth from the left
cavity of the heart and tend towards the brain), the weaker and less agitated parts must
necessarily be driven aside from that point by the stronger which alone in this way reach
it I had expounded all these matters with sufficient minuteness in the treatise which I
formerly thought of publishing. And after these, I had shown what must be the fabric of
the nerves and muscles of the human body to give the animal spirits contained in it the
power to move the members, as when we see heads shortly after they have been struck off
still move and bite the earth, although no longer animated; what changes must take place
in the brain to produce waking, sleep, and dreams; how light, sounds, odors, tastes, heat,
and all the other qualities of external objects impress it with different ideas by means
of the senses; how hunger, thirst, and the other internal affections can likewise impress
upon it divers ideas; what must be understood by the common sense (sensus communis) in
which these ideas are received, by the memory which retains them, by the fantasy which can
change them in various ways, and out of them compose new ideas, and which, by the same
means, distributing the animal spirits through the muscles, can cause the members of such
a body to move in as many different ways, and in a manner as suited, whether to the
objects that are presented to its senses or to its internal affections, as can take place
in our own case apart from the guidance of the will. Nor will this appear at all strange
to those who are acquainted with the variety of movements performed by the different
automata, or moving machines fabricated by human industry, and that with help of but few
pieces compared with the great multitude of bones, muscles, nerves, arteries, veins, and
other parts that are found in the body of each animal. Such persons will look upon this
body as a machine made by the hands of God, which is incomparably better arranged, and
adequate to movements more admirable than is any machine of human invention. And here I
specially stayed to show that, were there such machines exactly resembling organs and
outward form an ape or any other irrational animal, we could have no means of knowing that
they were in any respect of a different nature from these animals; but if there were
machines bearing the image of our bodies, and capable of imitating our actions as far as
it is morally possible, there would still remain two most certain tests whereby to know
that they were not therefore really men. Of these the first is that they could never use
words or other signs arranged in such a manner as is competent to us in order to declare
our thoughts to others: for we may easily conceive a machine to be so constructed that it
emits vocables, and even that it emits some correspondent to the action upon it of
external objects which cause a change in its organs; for example, if touched in a
particular place it may demand what we wish to say to it; if in another it may cry out
that it is hurt, and such like; but not that it should arrange them variously so as
appositely to reply to what is said in its presence, as men of the lowest grade of
intellect can do. The second test is, that although such machines might execute many
things with equal or perhaps greater perfection than any of us, they would, without doubt,
fail in certain others from which it could be discovered that they did not act from
knowledge, but solely from the disposition of their organs: for while reason is an
universal instrument that is alike available on every occasion, these organs, on the
contrary, need a particular arrangement for each particular action; whence it must be
morally impossible that there should exist in any machine a diversity of organs sufficient
to enable it to act in all the occurrences of life, in the way in which our reason enables
us to act. Again, by means of these two tests we may likewise know the difference between
men and brutes. For it is highly deserving of remark, that there are no men so dull and
stupid, not even idiots, as to be incapable of joining together different words, and
thereby constructing a declaration by which to make their thoughts understood; and that on
the other hand, there is no other animal, however perfect or happily circumstanced, which
can do the like. Nor does this inability arise from want of organs: for we observe that
magpies and parrots can utter words like ourselves, and are yet unable to speak as we do,
that is, so as to show that they understand what they say; in place of which men born deaf
and dumb, and thus not less, but rather more than the brutes, destitute of the organs
which others use in speaking, are in the habit of spontaneously inventing certain signs by
which they discover their thoughts to those who, being usually in their company, have
leisure to learn their language. And this proves not only that the brutes have less reason
than man, but that they have none at all: for we see that very little is required to
enable a person to speak; and since a certain inequality of capacity is observable among
animals of the same species, as well as among men, and since some are more capable of
being instructed than others, it is incredible that the most perfect ape or parrot of its
species, should not in this be equal to the most stupid infant of its kind or at least to
one that was crack-brained, unless the soul of brutes were of a nature wholly different
from ours. And we ought not to confound speech with the natural movements which indicate
the passions, and can be imitated by machines as well as manifested by animals; nor must
it be thought with certain of the ancients, that the brutes speak, although we do not
understand their language. For if such were the case, since they are endowed with many
organs analogous to ours, they could as easily communicate their thoughts to us as to
their fellows. It is also very worthy of remark, that, though there are many animals which
manifest more industry than we in certain of their actions, the same animals are yet
observed to show none at all in many others: so that the circumstance that they do better
than we does not prove that they are endowed with mind, for it would thence follow that
they possessed greater reason than any of us, and could surpass us in all things; on the
contrary, it rather proves that they are destitute of reason, and that it is nature which
acts in them according to the disposition of their organs: thus it is seen, that a clock
composed only of wheels and weights can number the hours and measure time more exactly
than we with all our skin.
I had after this described the reasonable soul, and shown that it could by no means be
educed from the power of matter, as the other things of which I had spoken, but that it
must be expressly created; and that it is not sufficient that it be lodged in the human
body exactly like a pilot in a ship, unless perhaps to move its members, but that it is
necessary for it to be joined and united more closely to the body, in order to have
sensations and appetites similar to ours, and thus constitute a real man. I here entered,
in conclusion, upon the subject of the soul at considerable length, because it is of the
greatest moment: for after the error of those who deny the existence of God, an error
which I think I have already sufficiently refuted, there is none that is more powerful in
leading feeble minds astray from the straight path of virtue than the supposition that the
soul of the brutes is of the same nature with our own; and consequently that after this
life we have nothing to hope for or fear, more than flies and ants; in place of which,
when we know how far they differ we much better comprehend the reasons which establish
that the soul is of a nature wholly independent of the body, and that consequently it is
not liable to die with the latter and, finally, because no other causes are observed
capable of destroying it, we are naturally led thence to judge that it is immortal.
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