  Whatever his ultimate view of the corpuscular hypothesis, Locke inevitably faces the atomist’s problem about cohesion, accepting as he does void space (see II.xiii.11, 12–14, 21–23), and holding that our ideas of body depend fundamentally upon cohesion. One of the ideas “proper and peculiar” to body, he writes, is “the cohesion of solid, and consequently separable parts” (E II.xxiii.17, p. 306), and the extension of body, as opposed to the extension of space, is “nothing, but the cohesion or continuity of solid, separable, moveable Parts”(E II.iv.5, p. 126). Yet we have no understanding of cohesion, and so our idea of body does not rest on any genuine understanding of it. In trying to understand how bodies are extended, we are as much in the dark as when we try to understand how the soul thinks.