Change, motion, and explanation › Why motion is an incomplete actuality

In III.1, Aristotle defines motion through the actuality of what is potential, precisely insofar as it is potential. The final qualification prevents the definition from collapsing the process into its completed result. What is buildable is actualized as buildable while it is being built. When the house is finished, the same building process is over (Physics III.1–2).

Consider water being heated. Before heating, it may be capable of becoming warmer without undergoing that change. While heating, it is actually undergoing a process toward a warmer condition. When the target condition has been reached and heating ceases, that particular warming process has ended. This illustration separates the capacity, its ongoing realization, and the stipulated completion without claiming that water has one natural target temperature.

Aristotle also argues that the mover's action and the moved thing's undergoing can be one process described differently. Teaching and learning illustrate how an activity can be attributed to an agent and to the recipient without becoming two disconnected changes (Physics III.3). That analysis raises questions about how to locate a process; it does not make teacher and learner the same person.