extension in it; the same reason will be as valid, I suppose, to prove that space is not body, because it includes not the idea of solidity in it; SPACE and SOLIDITY being as distinct ideas as THINKING and EXTENSION, and as wholly separable in the mind one from another. Body then and extension, it is evident, are two distinct ideas. For, 12. Extension not solidity. First, Extension includes no solidity, nor resistance to the motion of body, as body does. 13. The parts of space inseparable, both really and mentally. Secondly, The parts of pure space are inseparable one from the other; so that the continuity cannot be separated, both neither really nor mentally. For I demand of any one to remove any part of it from another, with which it is continued, even so much as in thought. To divide and separate actually is, as I think, by removing the parts one from another, to make two superficies, where before there was a continuity: and to divide mentally is, to make in the mind two superficies, where before there was a continuity, and consider them as removed one from the other; which can only be done in things considered by the mind as capable of being separated; and by separation, of acquiring new distinct superficies, which they then have not, but are capable of. But neither of these ways of separation, whether real or mental, is, as I think, compatible to pure space. It is true, a man may consider so much of such a space as is answerable or commensurate to a foot, without considering the rest, which is, indeed, a partial consideration, but not so much as mental separation or division; since a man can no more mentally divide, without considering two superficies separate one from the other, than he can actually divide, without making two superficies disjoined one from the other: but a partial consideration is not separating. A man may consider light in the sun without its heat, or mobility in body without its extension, without thinking of their separation. One is only a partial consideration, terminating in one alone; and the other is a consideration of both, as existing separately. 14. The parts of space immovable. Thirdly, The parts of pure space are immovable, which follows from their inseparability; motion being nothing but change of distance between any two things; but this cannot be between parts that are inseparable, which, therefore, must needs be at perpetual rest one amongst another. Thus the determined idea of simple space distinguishes it plainly and sufficiently from body; since its parts are inseparable, immovable, and without resistance to the motion of body. 15. The Definition of Extension explains it not.