Aristotle’s most fundamental distinction between changes and other activities is not that ofMetaphysicsΘ.6, between end-exclusive and end-inclusive activities, but one implicit inPhysics3.1’s definition of change, between the activity of something incomplete and the activity of something complete. Notably, only the latter distinction can account for Aristotle’s view, inPhysics3.3, that ‘agency’—effecting change in something, e.g. teaching—does not qualify strictly as a change. This distinction informsDe Anima2.5 and imparts unity to Aristotle’s extended treatment of change inPhysics3.1-3.