According to John Locke, solidity is an idea that we receive by our touch. It is the most constant idea obtained from sensation. For instance, a moving or resting man always feels something under him that supports him. The floor resists to the entrance of man’s body into the place the floor possesses. When staying on a solid floor, a man is not sinking downwards. There is something that hinders the approach of a man and a floor, when they are moved one towards another. This something is called solidity. Literally, solidity is impenetrability, but it is more a consequence of solidity than solidity itself.

Imagine that a space is taken up by a solid substance. Filling space, a solid body keeps other bodies out of this space. This resistance, by which it excludes all other solid substances out of space, is so great that no force can surmount it. This is how idea of solidity is distinguished from pure space. The extension of body is also distinguished from the extension of space. When the body is extended, we can observe the cohesion or continuity of solid, separable, movable parts. Contrary to the extension of body, the extension of space is being nothing but the continuity of unsolid, inseparable, and immovable parts.      

Solidity is differenced from hardness, in that solidity consists in an utter exclusion of other bodies our of the space it possesses. Unlike solidity, hardness consists in a firm cohesion of the parts of matter. So, it is a whole that does not easily change its figure. We call things hard or soft in relation to the constitutions of our own bodies. For instance, if we press something hard violently, this body will put us to pain sooner than change figure by the pressure. A soft body, on the contrary, will change the situation of its parts upon an unpainful touch.

Bibliography:

  • Locke, John, Essay Concerning Human Understanding in Modern Philosophy, an anthology of primary sources, second edition, edited by Roger Ariew and Eric Watkins, Hackett Publishing Company, Inc. 2009