The dominant interpretation ofMetaphysicsΘ.8 commits Aristotle to the claim that the heavenly bodies’ eternal movements are not the exercises of capacities. Against this, I argue that these movements are the result of necessarily exercised capacities. I clarify what it is for a heavenly body to possess a nature and argue that a body’s nature cannot be a final cause unless the natural body possesses capacities that are exercised for the sake of its naturequaform. This discussion yields a better understanding of (...) what capacities are, what explanatory work capacities do, and what it is to possess a nature. (shrink)