Stephen Puryear

I argue that Leibniz's rejection of the hypothesis of thinking matter on grounds of unintelligibility conflicts with his position on sensible qualities such as color. In the former case, he argues that thought must be a modification of something immaterial because we cannot explain thought in mechanical terms. In the latter case, however, he (rightly) grants that we cannot explain sensible qualities in mechanical terms, that is, cannot explain why a certain complex mechanical quality gives rise to the appearance of a certain sensible quality, even while insisting that sensible qualities are modifications of bodies. I argue that the two cases are analogous in the relevant respects, and that Leibniz's (plausible) position on sensible qualities should have thrown his Principle of Intelligibility into doubt.

In the texts of the middle years (roughly, the 1680s and 90s), Leibniz appears to endorse two incompatible approaches to motion, one a realist approach, the other a phenomenalist approach. I argue that once we attend to certain nuances in his account we can see that in fact he has only one, coherent approach to motion during this period. I conclude by considering whether the view of motion I want to impute to Leibniz during his middle years ranks as a kind of realism or rather as some kind of phenomenalism or idealism.