Superphysics Superphysics
Section 1b

The Truth About Matter

by Descartes Icon
6 minutes  • 1225 words
Table of contents

4 The nature of body consists not in weight hardness, colour and the like, but in extension alone. *

*Superphysics Note: Descartes reiterates that the nature of matter is it occupying space

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.


5 This truth regarding the nature of body, being extension, is obscured by the opinions on rarefaction and vacuum.

Many people think that

The first is the prevalent opinion, that

When rarefied, they have greater extension than when condensed. Some even have subtilized to the point that they 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, width, and depth, we are not in the habit of saying that body is there,

People think that void space is merely a negation of space.

6 How does rarefaction take place?

If we watch our own thoughts, we will discover that the rarefaction and condensation of a body is merely a change of shape in the rarefied or condensed body.

In other words, rare bodies have more numerous distances between their parts filled with other bodies.

Dense bodies, on the other hand, are those whose parts approach each other, either diminish these distances or removing them.

The body, however, does not have less extension when condensed than when the parts embrace more space, owing to their removal from each other, and their dispersion into branches.

We should 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.

A sponge full of water only has wider pores.

  • This makes its body more diffused over a larger space.
  • We do not suppose that this makes each part of the sponge have greater extension than when compressed and dry

7 Rarefaction should only be thought in that way.

Some say that rarefaction is the result of the augmentation of the quantity of body.

  • I explain that this augmentation is an example of the sponge.

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.

But we still suppose something that is unintelligible so that we can explain the rarefaction of bodies.

  • This is better than inventing the concept of a new body that fills the pores or distances between the parts which are increased in size.

Nor should we 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.

Any other explanation will create a contradiction.

  • It will suppose that any body was increased by a quantity or extension which it did not have 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.

Numbers are Imaginary

8 Quantity and number differ only in thought (RATIONE) from that which has quantity and is numbered.

Quantity differs from extended substance, and number from what is numbered, not in reality but merely in our thought.

For example, we may consider the whole nature of a corporeal substance which occupies a space of 10 feet, even if we do not measure the 10 feet.

This is because the thing conceived is of the same nature in any part of that space as in the whole.

On the other hand, we can conceive the number 10, as also a continuous quantity of 10 feet, without thinking of this determinate substance. This is because the concept of the number 10 is manifestly the same whether we consider a number of 10 feet or 10 of anything else.

We can conceive a continuous quantity of 10 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.

9 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 people distinguish (corporeal) substance from extension or quantity, they either:

  • mean nothing by the word (corporeal) substance, or
  • 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
    • This 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.

10 What is space or internal place?

Space or internal place, and the corporeal substance which is comprised in it, are not different in reality.

These are 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.

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 a generic unity to extension.

  • 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.