Ioannis Papachristou is writing a dissertation on Philoponus’ Commentary on Aristotle’s Physics IV (on place, time, and void) with a special emphasis on the Corollaria de loco et inani (Excursus on Place / Space and Void). His aim is to explain why Philoponus maintains, against Aristotle, the existence of a vacuum. In the context of this dispute with Aristotle, Philoponus introduced the concept of impetus, which constituted a radical innovation in the science of motion.