Book II - Chapter IV Idea of Solidity 1. We receive this idea from touch. There is no idea which we receive more constantly from sensation than solidity. That which thus hinders the approach of two bodies, when they are moved 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 mathematicians use it in.
Solidity fills space.
This is the idea which belongs to body, whereby we conceive it to fill space. This idea of it, the bodies which we ordinarily handle sufficiently furnish us with. Distinct from space. This resistance, whereby it keeps other bodies out of the space which it possesses, is so great, that no force, how great soever, can surmount it. I do not ask, whether bodies do so exist, that the motion of one body cannot really be without the motion of another.