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.
If any one ask me WHAT this space I speak of IS, I will tell him when he tells me what his extension is.