Many ideas require others, as necessary to their existence or conception, which yet are very distinct ideas.

Motion can neither be, nor be conceived, without space; and yet motion is not space, nor space motion; space can exist without it, and they are very distinct ideas; and so, I think, are those of space and solidity.

Solidity is so inseparable an idea from body, that upon that depends its filling of space, its contact, impulse, and communication of motion upon impulse.

And if it be a reason to prove that spirit is different from body, because thinking includes not the idea of 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.