The prominent place of corpuscularian mechanism in Locke's Essay is nowadays universally acknowledged. Certainly, Locke's discussions of the primary/secondary quality distinction and of real essences cannot be understood without reference to the corpuscularian science of his day, which held that all macroscopic bodily phenomena should be explained in terms of the motions and impacts of submicroscopic particles, or corpuscles, each of which can be fully characterized in terms of a strictly limited range of properties: size, shape, motion, and, perhaps, solidity (...) or impenetrability. Indeed, Locke's lists of primary qualities are quite consistent with those found in the work of his friend Robert Boyle, a prominent defender of the corpuscularian program; his real essences of substances appear to be corpuscular constitutions, arrangements of particles. (shrink)