In John Locke's terminology, a body's exclusion of another body from the space it occupies. This is not the material-science notion of hardness: John Locke treats water as solid in this sense while distinguishing its yielding response from a diamond's resistance.[ref]
An Essay Concerning Human Understanding by John Locke. Book II, chapter IV, especially section 4: barryfvaughan.org/text/philtext/locke/bk2/4.html
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