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Extension and Body not the same.       §11. There are some that would persuade us, that Body and
Extension are the same thing; who either change the Signification of
Words, which I would not suspect them of, they having so severely
condemned the Philosophy of others, because it hath been too much
placed in the uncertain meaning, or deceitful obscurity of doubtful
or insignificant Terms. If therefore they mean by Body and Extension
the same, that other People do, viz. by Body something that is solid,
and extended, whose parts are separable and movable different
ways; and by Extension, only the Space that lies between the
Extremities of those solid coherent Parts, and which is possessed by
them, they confound very different Ideas one with another. For I
appeal to every Man’s own Thoughts, whether the Idea of Space be
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not as distinct from that of Solidity, as it is from the Idea of Scarlet-
Colour? ’Tis true, Solidity cannot exist without Extension, neither
can Scarlet-Colour exist without Extension; but this hinders not,
but that they are distinct Ideas. 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, ’tis evident,
are two distinct Ideas. For,
Locke Hum II, 13, §11, pp. 171-172