 Aristotle distinguishes between two different senses of the term dunamis. In the strictest sense, a dunamis is the power that a thing has to produce a change. A thing has a dunamis in this sense when it has within it “a starting-point of change in another thing or in itself insofar as it is other” (Θ.1, 1046a12; cf. Δ.12). The exercise of such a power is a kinêsis—a movement or process. So, for example, the housebuilder’s craft is a power whose exercise is the process of housebuilding. But there is a second sense of dunamis—and it is the one in which Aristotle is mainly interested—that might be better translated as ‘potentiality’. For, as Aristotle tells us, in this sense dunamis is related not to movement (kinêsis) but to activity (energeia)(Θ.6, 1048a25). A dunamis in this sense is not a thing’s power to produce a change but rather its capacity to be in a different and more completed state. Aristotle thinks that potentiality so understood is indefinable (1048a37), claiming that the general idea can be grasped from a consideration of cases. Activity is to potentiality, Aristotle tells us, as “what is awake is in relation to what is asleep, and what is seeing is in relation to what has its eyes closed but has sight, and what has been shaped out of the matter is in relation to the matter” (1048b1–3).