 Questions about abilities have figured most prominently in debates over compatibilism. ‘Compatibilism’ is used in many ways, but let us understand it here as the thesis that the ability to perform actions one does not perform is compossible with the truth of determinism, which we may take to be the view that the facts about the past and the laws jointly determine the facts about the present and all future moments. (We should sharply distinguish this view, which we might call classical compatibilism, from more recent views such as the ‘semi-compatibilism’ of Fischer and Ravizza 1998). Insofar as compatibilism, so understood, has been explicitly defended, these defenses have made appeal to theories of ability, notably the conditional analysis and its variants, as well as the dispositionalist analysis favored by the new dispositionalists.