  The four problematic phenomena winnow away the components of the corpuscular hypothesis, as defined at the outset of this article.  The problem about sensation threatens the corpuscular hypothesis’ promise of reducing secondary, tertiary, and macrolevel primary qualities to microlevel primary qualities. Newton’s results about gravitational phenomena cast grave doubts upon the contact action proviso, and according to some commentators, those results lead Locke to abandon the belief that impulse is the only means of causal interaction. A corpuscular theorist might hope to preserve some part of the theory by insisting that impulse is still the means by which most other causal interactions are effected; but this runs up against the problem about impulse, in that the process by which motion is communicated seems utterly obscure. Finally, even the core claim that observable bodies are composed of tiny corpuscles is threatened by the problem of cohesion. This last problem threatens to be the most serious of four phenomena, for as James Hill has pointed out (2004, p. 628), the problems about gravity, sensation, and motion arise subsequent to our having conceived of body, whereas the problem about cohesion may thwart our very ability to conceive clearly of body.