 In the accounts we give of one another, claims about our abilities appear to be indispensable. Some abilities are so widespread that many who have them take them for granted, such as the ability to walk, or to write one’s name, or to tell a hawk from a handsaw. Others are comparatively rare and notable, such as the ability to hit a Major League fastball, or to compose a symphony, or to tell an elm from a beech. In either case, however, when we ascribe such abilities to one another we have the impression that we are making claims that, whether they are worth saying or not, are at least sometimes true. The impression of truth exerts a pressure towards giving a philosophical theory of ability. It is not an option, at least at the outset, to dismiss all our talk of ability as fiction or outright falsehood. A theory of ability can be reasonably expected to say what it is to have an ability in a way that vindicates the appearance of truth. Such a theory will deserve the name ‘philosophical’ insofar as it gives an account, not of this or that range of abilities, but of abilities generally.