This paper examines Aristotle’s analysis of unenacted capacities to show the role they play in his discovery of the concept of actuality. I first argue that Aristotle begins Metaphysics IX by focusing on active and passive capacities, after which I discuss Aristotle’s confrontation with the Megarians, the philosophers who maintain that a capacity is present only insofar as it is being enacted. Using Heidegger’s interpretation as a guide, I show that Aristotle’s rejection of the Megarian position leads him to propose (...) that presence cannot be confined to activity. I also argue that this provides the context for Aristotle to realize that the relation between capacity and activity can be generalized as the relation between two ways of being. (shrink)