Historians of fourteenth-century science have long recognized the extraordinary work at both Oxford and Paris in which natural philosophy was becoming highly mathematical. The movement to subject natural philosophy to a mathematical analysis and to quantify such qualities as heat, color, and of course speed surely stands as one of the most significant aspects of late medieval science. Yet as Edith Sylla has observed, because qualities and quantities pertain to different categories in Aristotelian theory, one might expect Aristotelian theorists to (...) avoid quantifying qualities. Even more serious still, the very task of quantifying physical qualities exposes a tension in the nature of science that was discussed first by Aristotle in his Posterior Analytics. (shrink)