 There is a surprising disconnect between the way abilities have been discussed in the philosophical literature in the tradition of Hume and the way that they have been approached in more recent work in logic and linguistics. Here, ability claims are understood as categorical possibility claims: claims about what some agent does in some non-actual state of affairs (or ‘possible world’). Let a modal theory of ability be any theory on which claims about an agent’s abilities are understood in terms of claims about what that agent in fact does at some possible world (or set of worlds). The idea that some such modal theory of ability must be true is a presumption of much formal work on ability and ability-ascriptions. Yet there are serious challenges to the idea that ability is in this sense a modality.