My topic is an episode in what I take to have been the most interesting philosophical debate in the latter half of the seventeenth century. The debate was between the Cartesians and the Gassendists, and the episode concerns the divisibility of matter. The Gassendists plumped almost by definition for an ontology of atoms and the void, while the Cartesians of course were almost invariably plenum theorists who argued the infinite divisibility of matter. My thesis is that those who argued atomism in the period 1666–82 were moving away from atomism as a physical theory toward a metaphysical theory that found its most important expression in Locke. Arguing the case for Locke is far beyond my resources here; instead, I shall discuss the relatively minor figures who prepared the way for him.