BOOK THIRD.
EXTENSION AND SPACE.
[CHAPTER I.]
EXTENSION INSEPARABLE FROM THE IDEA OF BODY.
1. Having seen that among the objects of our sensations, extension alone has any external existence for us as any thing more than a principle of causality, let us now try to understand what extension is.
The idea of extension seems to be inseparable from that of body; at least, I am unable to conceive a body without extension. Take away extension, and the parts disappear, and with them all that has relation with our senses; there is no longer an object, or, if the object remains, it is something altogether different from what is contained in the idea of body. Imagine an apple, for instance, from which you suddenly take away extension. What will remain of it?
I am not now going to examine whether Descartes is right when he says, that the essence of body consists in extension; all that I here assert is that a body cannot be conceived without extension. I do not affirm the identity of two things, but only the inseparability of two ideas in our mind. It is not an opinion, but a fact asserted by consciousness, which is now under discussion.
Abstracting extension, I can conceive, it is true, a substance, or, to speak more generally, a being; but, then, there is no idea of body, unless we confound this idea with, that of substance or of being, in general.