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PART II. OF THE PRINCIPLES OF MATERIAL THINGS
I. The grounds on which the existence of material things may be
known with certainty.
Although we are all sufficiently persuaded of the existence of
material things, yet, since this was before called in question by
us, and since we reckoned the persuasion of their existence as among
the prejudices of our childhood, it is now necessary for us to
investigate the grounds on which this truth may be known with
certainty. In the first place, then, it cannot be doubted that every
perception we have comes to us from some object different from our
mind; for it is not in our power to cause ourselves to experience
one perception rather than another, the perception being entirely
dependent on the object which affects our senses. It may, indeed, be
matter of inquiry whether that object be God, or something different
from God; but because we perceive, or rather, stimulated by sense,
clearly and distinctly apprehend, certain matter extended in length,
breadth, and thickness, the various parts of which have different
figures and motions, and give rise to the sensation we have of
colours, smells, pain, etc., God would, without question, deserve to
be regarded as a deceiver, if he directly and of himself presented
to our mind the idea of this extended matter, or merely caused it to
be presented to us by some object which possessed neither extension,
figure, nor motion. For we clearly conceive this matter as entirely
distinct from God, and from ourselves, or our mind; and appear even
clearly to discern that the idea of it is formed in us on occasion
of objects existing out of our minds, to which it is in every
respect similar. But since God cannot deceive us, for this is
repugnant to his nature, as has been already remarked, we must
unhesitatingly conclude that there exists a certain object extended
in length, breadth, and thickness, and possessing all those
properties which we clearly apprehend to belong to what is extended.
And this extended substance is what we call body or matter.
II. How we likewise know that the human body is closely connected
with the mind.
We ought also to conclude that a certain body is more closely united
to our mind than any other, because we clearly observe that pain and
other sensations affect us without our foreseeing them; and these,
the mind is conscious, do not arise from itself alone, nor pertain
to it, in so far as it is a thing which thinks, but only in so far
as it is united to another thing extended and movable, which is
called the human body. But this is not the place to treat in detail
of this matter.
III. That the perceptions of the senses do not teach us what is in
reality in things, but what is beneficial of hurtful to the
composite whole of mind and body.
It will be sufficient to remark that the perceptions of the senses
are merely to be referred to this intimate union of the human body
and mind, and that they usually make us aware of what, in external
objects, may be useful or adverse to this union, but do not present
to us these objects as they are in themselves, unless occasionally
and by accident. For, after this observation, we will without
difficulty lay aside the prejudices of the senses, and will have
recourse to our understanding alone on this question by reflecting
carefully on the ideas implanted in it by nature.
IV. That the nature of body consists not in weight hardness, colour
and the like, but in extension alone.
In this way we will discern that the nature of matter or body,
considered in general, does not consist in its being hard, or
ponderous, or coloured, or that which affects our senses in any
other way, but simply in its being a substance extended in length,
breadth, and depth. For with respect to hardness, we know nothing of
it by sense farther than that the parts of hard bodies resist the
motion of our hands on coming into contact with them; but if every
time our hands moved towards any part, all the bodies in that place
receded as quickly as our hands approached, we should never feel
hardness; and yet we have no reason to believe that bodies which
might thus recede would on this account lose that which makes them
bodies. The nature of body does not, therefore, consist in hardness.
In the same way, it may be shown that weight, colour, and all the
other qualities of this sort, which are perceived in corporeal
matter, may be taken from it, itself meanwhile remaining entire: it
thus follows that the nature of body depends on none of these.
V. That the truth regarding the nature of body is obscured by the
opinions respecting rarefaction and a vacuum with which we are pre-
occupied.
There still remain two causes to prevent its being fully admitted
that the true nature of body consists in extension alone. The first
is the prevalent opinion, that most bodies admit of being so
rarefied and condensed that, when rarefied, they have greater
extension than when condensed; and some even have subtilized to such
a degree as to make a distinction between the substance of body and
its quantity, and between quantity itself and extension. The second
cause is this, that where we conceive only extension in length,
breadth, and depth, we are not in the habit of saying that body is
there, but only space and further void space, which the generality
believe to be a mere negation.
VI. In what way rarefaction takes place.
But with regard to rarefaction and condensation, whoever gives his
attention to his own thoughts, and admits nothing of which he is not
clearly conscious, will not suppose that there is anything in those
processes further than a change of figure in the body rarefied or
condensed: so that, in other words, rare bodies are those between
the parts of which there are numerous distances filled with other
bodies; and dense bodies, on the other hand, those whose parts
approaching each other, either diminish these distances or take them
wholly away, in the latter of which cases the body is rendered
absolutely dense. The body, however, when condensed, has not,
therefore, less extension than when the parts embrace a greater
space, owing to their removal from each other, and their dispersion
into branches. For we ought not to attribute to it the extension of
the pores or distances which its parts do not occupy when it is
rarefied, but to the other bodies that fill these interstices; just
as when we see a sponge full of water or any other liquid, we do not
suppose that each part of the sponge has on this account greater
extension than when compressed and dry, but only that its pores are
wider, and therefore that the body is diffused over a larger space.
VII. That rarefaction cannot be intelligibly explained unless in
the way here proposed.
And indeed I am unable to discover the force of the reasons which
have induced some to say that rarefaction is the result of the
augmentation of the quantity of body, rather than to explain it on
the principle exemplified in the case of a sponge. For although when
air or water is rarefied we do not see any of the pores that are
rendered large, or the new body that is added to occupy them, it is
yet less agreeable to reason to suppose something that is
unintelligible for the purpose of giving a verbal and merely
apparent explanation of the rarefaction of bodies, than to conclude,
because of their rarefaction, that there are pores or distances
between the parts which are increased in size, and filled with some
new body. Nor ought we to refrain from assenting to this
explanation, because we perceive this new body by none of our
senses, for there is no reason which obliges us to believe that we
should perceive by our senses all the bodies in existence. And we
see that it is very easy to explain rarefaction in this manner, but
impossible in any other; for, in fine, there would be, as appears to
me, a manifest contradiction in supposing that any body was
increased by a quantity or extension which it had not before,
without the addition to it of a new extended substance, in other
words, of another body, because it is impossible to conceive any
addition of extension or quantity to a thing without supposing the
addition of a substance having quantity or extension, as will more
clearly appear from what follows.
VIII. That quantity and number differ only in thought (RATIONE)
from that which has quantity and is numbered.
For quantity differs from extended substance, and number from what
is numbered, not in reality but merely in our thought; so that, for
example, we may consider the whole nature of a corporeal substance
which is comprised in a space of ten feet, although we do not attend
to this measure of ten feet, for the obvious reason that the thing
conceived is of the same nature in any part of that space as in the
whole; and, on the other hand, we can conceive the number ten, as
also a continuous quantity of ten feet, without thinking of this
determinate substance, because the concept of the number ten is
manifestly the same whether we consider a number of ten feet or ten
of anything else; and we can conceive a continuous quantity of ten
feet without thinking of this or that determinate substance,
although we cannot conceive it without some extended substance of
which it is the quantity. It is in reality, however, impossible that
any, even the least part, of such quantity or extension, can be
taken away, without the retrenchment at the same time of as much of
the substance, nor, on the other hand, can we lessen the substance,
without at the same time taking as much from the quantity or
extension.
IX. That corporeal substance, when distinguished from its quantity,
is confusedly conceived as something incorporeal.
Although perhaps some express themselves otherwise on this matter, I
am nevertheless convinced that they do not think differently from
what I have now said: for when they distinguish (corporeal)
substance from extension or quantity, they either mean nothing by
the word (corporeal) substance, or they form in their minds merely a
confused idea of incorporeal substance, which they falsely attribute
to corporeal, and leave to extension the true idea of this corporeal
substance; which extension they call an accident, but with such
impropriety as to make it easy to discover that their words are not
in harmony with their thoughts.
X. What space or internal place is.
Space or internal place, and the corporeal substance which is
comprised in it, are not different in reality, but merely in the
mode in which they are wont to be conceived by us. For, in truth,
the same extension in length, breadth, and depth, which constitutes
space, constitutes body; and the difference between them lies only
in this, that in body we consider extension as particular, and
conceive it to change with the body; whereas in space we attribute
to extension a generic unity, so that after taking from a certain
space the body which occupied it, we do not suppose that we have at
the same time removed the extension of the space, because it appears
to us that the same extension remains there so long as it is of the
same magnitude and figure, and preserves the same situation in
respect to certain bodies around it, by means of which we determine
this space.
XI. How space is not in reality different from corporeal substance.
And indeed it will be easy to discern that it is the same extension
which constitutes the nature of body as of space, and that these two
things are mutually diverse only as the nature of the genus and
species differs from that of the individual, provided we reflect on
the idea we have of any body, taking a stone for example, and reject
all that is not essential to the nature of body. In the first place,
then, hardness may be rejected, because if the stone were liquefied
or reduced to powder, it would no longer possess hardness, and yet
would not cease to be a body; colour also may be thrown out of
account, because we have frequently seen stones so transparent as to
have no colour; again, we may reject weight, because we have the
case of fire, which, though very light, is still a body; and,
finally, we may reject cold, heat, and all the other qualities of
this sort, either because they are not considered as in the stone,
or because, with the change of these qualities, the stone is not
supposed to have lost the nature of body. After this examination we
will find that nothing remains in the idea of body, except that it
is something extended in length, breadth, and depth; and this
something is comprised in our idea of space, not only of that which
is full of body, but even of what is called void space.
XII. How space differs from body in our mode of conceiving it.
There is, however, some difference between them in the mode of
conception; for if we remove a stone from the space or place in
which it was, we conceive that its extension also is taken away,
because we regard this as particular, and inseparable from the stone
itself: but meanwhile we suppose that the same extension of place in
which this stone was remains, although the place of the stone be
occupied by wood, water, air, or by any other body, or be even
supposed vacant, because we now consider extension in general, and
think that the same is common to stones, wood, water, air, and other
bodies, and even to a vacuum itself, if there is any such thing,
provided it be of the same magnitude and figure as before, and
preserve the same situation among the external bodies which
determine this space.
XIII. What external place is.
The reason of which is, that the words place and space signify
nothing really different from body which is said to be in place, but
merely designate its magnitude, figure, and situation among other
bodies. For it is necessary, in order to determine this situation,
to regard certain other bodies which we consider as immovable; and,
according as we look to different bodies, we may see that the same
thing at the same time does and does not change place. For example,
when a vessel is being carried out to sea, a person sitting at the
stern may be said to remain always in one place, if we look to the
parts of the vessel, since with respect to these he preserves the
same situation; and on the other hand, if regard be had to the
neighbouring shores, the same person will seem to be perpetually
changing place, seeing he is constantly receding from one shore and
approaching another. And besides, if we suppose that the earth
moves, and that it makes precisely as much way from west to east as
the vessel from east to west, we will again say that the person at
the stern does not change his place, because this place will be
determined by certain immovable points which we imagine to be in the
heavens. But if at length we are persuaded that there are no points
really immovable in the universe, as will hereafter be shown to be
probable, we will thence conclude that nothing has a permanent place
unless in so far as it is fixed by our thought.
XIV. Wherein place and space differ.
The terms place and space, however, differ in signification, because
place more expressly designates situation than magnitude or figure,
while, on the other hand, we think of the latter when we speak of
space. For we frequently say that a thing succeeds to the place of
another, although it be not exactly of the same magnitude or figure;
but we do not therefore admit that it occupies the same space as the
other; and when the situation is changed we say that the place also
is changed, although there are the same magnitude and figure as
before: so that when we say that a thing is in a particular place,
we mean merely that it is situated in a determinate way in respect
of certain other objects; and when we add that it occupies such a
space or place, we understand besides that it is of such determinate
magnitude and figure as exactly to fill this space.
XV. How external place is rightly taken for the superficies of the
surrounding body.
And thus we never indeed distinguish space from extension in length,
breadth, and depth; we sometimes, however, consider place as in the
thing placed, and at other times as out of it. Internal place indeed
differs in no way from space; but external place may be taken for
the superficies that immediately surrounds the thing placed. It
ought to be remarked that by superficies we do not here understand
any part of the surrounding body, but only the boundary between the
surrounding and surrounded bodies, which is nothing more than a
mode; or at least that we speak of superficies in general which is
no part of one body rather than another, but is always considered
the same, provided it retain the same magnitude and figure. For
although the whole surrounding body with its superficies were
changed, it would not be supposed that the body which was surrounded
by it had therefore changed its place, if it meanwhile preserved the
same situation with respect to the other bodies that are regarded as
immovable. Thus, if we suppose that a boat is carried in one
direction by the current of a stream, and impelled by the wind in
the opposite with an equal force, so that its situation with respect
to the banks is not changed, we will readily admit that it remains
in the same place, although the whole superficies which surrounds it
is incessantly changing.
XVI. That a vacuum or space in which there is absolutely no body is
repugnant to reason.
With regard to a vacuum, in the philosophical sense of the term,
that is, a space in which there is no substance, it is evident that
such does not exist, seeing the extension of space or internal place
is not different from that of body. For since from this alone, that
a body has extension in length, breadth, and depth, we have reason
to conclude that it is a substance, it being absolutely
contradictory that nothing should possess extension, we ought to
form a similar inference regarding the space which is supposed void,
viz., that since there is extension in it there is necessarily also
substance.
XVII. That a vacuum in the ordinary use of the term does not
exclude all body.
And, in truth, by the term vacuum in its common use, we do not mean
a place or space in which there is absolutely nothing, but only a
place in which there is none of those things we presume ought to be
there. Thus, because a pitcher is made to hold water, it is said to
be empty when it is merely filled with air; or if there are no fish
in a fish-pond, we say there is nothing in it, although it be full
of water; thus a vessel is said to be empty, when, in place of the
merchandise which it was designed to carry, it is loaded with sand
only, to enable it to resist the violence of the wind; and, finally,
it is in the same sense that we say space is void when it contains
nothing sensible, although it contain created and self-subsisting
matter; for we are not in the habit of considering the bodies near
us, unless in so far as they cause in our organs of sense,
impressions strong enough to enable us to perceive them. And if, in
place of keeping in mind what ought to be understood by these terms
a vacuum and nothing, we afterwards suppose that in the space we
called a vacuum, there is not only no sensible object, but no object
at all, we will fall into the same error as if, because a pitcher in
which there is nothing but air, is, in common speech, said to be
empty, we were therefore to judge that the air contained in it is
not a substance (RES SUBSISTENS).
XVIII. How the prejudice of an absolute vacuum is to be corrected.
We have almost all fallen into this error from the earliest age,
for, observing that there is no necessary connection between a
vessel and the body it contains, we thought that God at least could
take from a vessel the body which occupied it, without it being
necessary that any other should be put in the place of the one
removed. But that we may be able now to correct this false opinion,
it is necessary to remark that there is in truth no connection
between the vessel and the particular body which it contains, but
that there is an absolutely necessary connection between the concave
figure of the vessel and the extension considered generally which
must be comprised in this cavity; so that it is not more
contradictory to conceive a mountain without a valley than such a
cavity without the extension it contains, or this extension apart
from an extended substance, for, as we have often said, of nothing
there can be no extension. And accordingly, if it be asked what
would happen were God to remove from a vessel all the body contained
in it, without permitting another body to occupy its place, the
answer must be that the sides of the vessel would thus come into
proximity with each other. For two bodies must touch each other when
there is nothing between them, and it is manifestly contradictory
for two bodies to be apart, in other words, that there should be a
distance between them, and this distance yet be nothing; for all
distance is a mode of extension, and cannot therefore exist without
an extended substance.
XIX. That this confirms what was said of rarefaction.
After we have thus remarked that the nature of corporeal substance
consists only in its being an extended thing, and that its extension
is not different from that which we attribute to space, however
empty, it is easy to discover the impossibility of any one of its
parts in any way whatsoever occupying more space at one time than at
another, and thus of being otherwise rarefied than in the way
explained above; and it is easy to perceive also that there cannot
be more matter or body in a vessel when it is filled with lead or
gold, or any other body however heavy and hard, than when it but
contains air and is supposed to be empty: for the quantity of the
parts of which a body is composed does not depend on their weight or
hardness, but only on the extension, which is always equal in the
same vase.
XX. That from this the non-existence of atoms may likewise be
demonstrated.
We likewise discover that there cannot exist any atoms or parts of
matter that are of their own nature indivisible. For however small
we suppose these parts to be, yet because they are necessarily
extended, we are always able in thought to divide any one of them
into two or more smaller parts, and may accordingly admit their
divisibility. For there is nothing we can divide in thought which we
do not thereby recognize to be divisible; and, therefore, were we to
judge it indivisible our judgment would not be in harmony with the
knowledge we have of the thing; and although we should even suppose
that God had reduced any particle of matter to a smallness so
extreme that it did not admit of being further divided, it would
nevertheless be improperly styled indivisible, for though God had
rendered the particle so small that it was not in the power of any
creature to divide it, he could not however deprive himself of the
ability to do so, since it is absolutely impossible for him to
lessen his own omnipotence, as was before observed. Wherefore,
absolutely speaking, the smallest extended particle is always
divisible, since it is such of its very nature.
XXI. It is thus also demonstrated that the extension of the world
is indefinite.
We further discover that this world or the whole (universitas) of
corporeal substance, is extended without limit, for wherever we fix
a limit, we still not only imagine beyond it spaces indefinitely
extended, but perceive these to be truly imaginable, in other words,
to be in reality such as we imagine them; so that they contain in
them corporeal substance indefinitely extended, for, as has been
already shown at length, the idea of extension which we conceive in
any space whatever is plainly identical with the idea of corporeal
substance.
XXII. It also follows that the matter of the heavens and earth is
the same, and that there cannot be a plurality of worlds.
And it may also be easily inferred from all this that the earth and
heavens are made of the same matter; and that even although there
were an infinity of worlds, they would all be composed of this
matter; from which it follows that a plurality of worlds is
impossible, because we clearly conceive that the matter whose nature
consists only in its being an extended substance, already wholly
occupies all the imaginable spaces where these other worlds could
alone be, and we cannot find in ourselves the idea of any other
matter.
XXIII. That all the variety of matter, or the diversity of its
forms, depends on motion.
There is therefore but one kind of matter in the whole universe, and
this we know only by its being extended. All the properties we
distinctly perceive to belong to it are reducible to its capacity of
being divided and moved according to its parts; and accordingly it
is capable of all those affections which we perceive can arise from
the motion of its parts. For the partition of matter in thought
makes no change in it; but all variation of it, or diversity of
form, depends on motion. The philosophers even seem universally to
have observed this, for they said that nature was the principle of
motion and rest, and by nature they understood that by which all
corporeal things become such as they are found in experience.
XXIV. What motion is, taking the term in its common use.
But motion (viz., local, for I can conceive no other kind of motion,
and therefore I do not think we ought to suppose there is any other
in nature), in the ordinary sense of the term, is nothing more than
the action by which a body passes from one place to another. And
just as we have remarked above that the same thing may be said to
change and not to change place at the same time, so also we may say
that the same thing is at the same time moved and not moved. Thus,
for example, a person seated in a vessel which is setting sail,
thinks he is in motion if he look to the shore that he has left, and
consider it as fixed; but not if he regard the ship itself, among
the parts of which he preserves always the same situation. Moreover,
because we are accustomed to suppose that there is no motion without
action, and that in rest there is the cessation of action, the
person thus seated is more properly said to be at rest than in
motion, seeing he is not conscious of being in action.
XXV. What motion is properly so called.
But if, instead of occupying ourselves with that which has no
foundation, unless in ordinary usage, we desire to know what ought
to be understood by motion according to the truth of the thing, we
may say, in order to give it a determinate nature, that it is THE
TRANSPORTING OF ONE PART OF MATTER OR OF ONE BODY FROM THE VICINITY
OF THOSE BODIES THAT ARE IN IMMEDIATE CONTACT WITH IT, OR WHICH WE
REGARD AS AT REST, to the vicinity of other bodies. By a body as a
part of matter, I understand all that which is transferred together,
although it be perhaps composed of several parts, which in
themselves have other motions; and I say that it is the transporting
and not the force or action which transports, with the view of
showing that motion is always in the movable thing, not in that
which moves; for it seems to me that we are not accustomed to
distinguish these two things with sufficient accuracy. Farther, I
understand that it is a mode of the movable thing, and not a
substance, just as figure is a property of the thing figured, and
repose of that which is at rest. _
Read next: PART III. OF THE VISIBLE WORLD
Read previous: PART I. OF THE PRINCIPLES OF HUMAN KNOWLEDGE
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