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.