This paper offers an interpretation of Aristotle’s concepts of dynamis and energeia (commonly translated as potentiality and actuality), and of the thematic progression of Metaphysics IX. I first raise the question of where motion fits in Aristotle’s categories and argue that the locus of motion in the system of categories are the categories of doing and suffering, in which case dynamis and energeia in respect of motion can also be understood as the dynamis and energeia of doing and suffering. Next, (...) I argue that the analogy that Aristotle draws in IX.6 is an analogy between the dynamis and energeia of doing and suffering and the dynamis and energeia of substance. Finally, I try to show that it is this analogy between the kinetic and non-kinetic variants of dynamis and energeia—and not the distinction between end-inclusive and end-exclusive activities—that provides the key to understanding the structure of Metaphysics IX. (shrink)