These chapters of Aristotle's treatise are about physical interactions. In his innovative commentary, Philoponus discusses Aristotle's idea that certain qualities of the elements are basic. In what way are they basic? he asks. To what extent can the other qualities be reduced to the basic ones? And if the other qualities depend on the basic ones, how is it that they can vary independently of each other when the basic qualities change? Philoponus develops the idea that the other qualities merely supervene on the basic ones, rather than resulting from them. Moreover, physical qualities admit of...