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. |