_
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. _