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Chapter IV

Of Solidity.
We receive this Idea from touch.       §1. The Idea of Solidity we receive by our Touch; and it arises from
the resistance which we find in Body, to the entrance of any other
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Body into the Place it possesses, till it has left it. There is no Idea,
which we receive more constantly from Sensation, than Solidity.
Whether we move, or rest, in what Posture soever we are, we always
feel something under us, that supports us, and hinders our farther
sinking downwards; and the Bodies which we daily handle, make us
perceive, that whilst they remain between them, they do by an
insurmountable Force, hinder the approach of the parts of our
Hands that press them. That which thus hinders the approach of
two Bodies, when they are moving one towards another, I call
Solidity. I will not dispute, whether this acceptation of the Word
solid be nearer to its Original Signification, than that which Mathe-
maticians use it in: It suffices, that I think, the common Notion of
Solidity will allow, if not justifie, this use of it; but if any one think
it better to call it Impenetrability, he has my Consent. Only I have
thought the Term Solidity, the more proper to express this Idea, not
only because of its vulgar use in that Sense; but also, because it
carries something more of positive in it, than Impenetrability, which
is negative, and is, perhaps, more a consequence of Solidity, than
Solidity it self. This of all other, seems the Idea most intimately
connected with, and essential to Body, so as no where else to be
found or imagin’d, but only in matter: and though our Senses take
no notice of it, but in masses of matter, of a bulk sufficient to cause
a Sensation in us; Yet the Mind, having once got this Idea from such
grosser sensible Bodies, traces it farther; and considers it, as well as
Figure, in the minutest Particle of Matter, that can exist; and finds
it inseparably inherent in Body, where-ever, or however modified.
Locke Hum II, 4, §1, pp. 122-123