Abstract
In the context of Aristotle's metaphysics and natural philosophy, 'prime matter' refers to that material cause which is both the proximate material cause of the four sublunary elements and the ultimate material cause of all perishable substances. On the traditional view, prime matter is pure potentiality, without any determinate nature of its own. Against this view, I argue that prime matter must be physical, extended, and movable matter if it is to fulfil its role as the substratum persisting through the generation and corruption of these elements and the individuating subject in which their defining properties are found.