— 126 —
On Solidity depends Impulse, Resistance, and Protrusion.       §5. By this Idea of Solidity, is the Extension of Body distinguished
from the Extension of Space. The Extension of Body being nothing,
but the cohesion or continuity of solid, separable, moveable Parts;
and the Extension of Space, the continuity of unsolid, inseparable,
and immoveable Parts. Upon the Solidity of Bodies also depends their
mutual Impulse, Resistance, and Protrusion. Of pure Space then, and
Solidity, there are several (amongst which, I confess my self one)
who persuade themselves, they have clear and distinct Ideas ; and
that they can think on Space, without any thing in it, that resists,
or is protruded by Body. This is the Idea of pure Space, which they
think they have as clear, as any Idea they can have of the Extension
of Body: the Idea of the distance, between the opposite Parts of a
concave Superficies, being equally as clear, without, as with the Idea
of any solid Parts between: and on the other side, they persuade
themselves, That they have, distinct from that of pure Space, the
Idea of something that fills Space, that can be protruded by the
impulse of other Bodies, or resist their Motion. If there be others,
that have not these two Ideas distinct but confound them, and make
but one of them, I know not, how Men, who have the same Idea,
under different Names, or different Ideas, under the same Name,
can, in that case, talk with one another, any more than a Man, who
not being blind, or deaf, has distinct Ideas of the Colour of Scarlet,
and the sound of a Trumpet, could discourse concerning Scarlet-
Colour with the blind Man, I mention in another Place, who
fancied, that the Idea of Scarlet was like the sound of a Trumpet.
Locke Hum II, 4, §5, p. 126