The notion of a capacity (dunamis) in the sense of a power to bring about or undergo change plays a key role in Aristotle’s theories about the natural world. However, in Metaphysics Θ Aristotle also extends ‘capacity’, and the corresponding concept of ‘activity’ (energeia), to cases where we want to say that something is in capacity, or in activity, such and such but not, or not directly, in virtue of being capable of initiating or undergoing change. This paper seeks to clarify and confirm a certain view of how Aristotle wishes us to see the relationship between the two uses of ‘capacity’ and ‘activity’. To that end, I consider also Aristotle’s employment of the terms in the De Anima, which sheds light on the key examples which direct the discussion in Metaph. Θ.