This thesis is an investigation into the nature of those abilities that are relevant to free will when the latter is understood as requiring the ability to do otherwise. I assume from the outset the traditional and intuitive picture that being able to do otherwise bestows a significant kind of control on an agent and I ask what kinds of ability are implicated in such control. In chapter 1 I assess the simple conditional analysis of the sense of ‘can’ relevant (...) to free will, and I agree with the consensus that this analysis fails. In chapter 2 I consider Kadri Vihvelin’s contemporary version of the conditional account, which is cast in terms of dispositions. I develop, via engagement with Vihvelin’s view, an account of how modal properties such as dispositions and abilities should be individuated. In chapter 3 I use this account to show why Vihvelin’s account of free will is unsatisfactory. I also show how it helps us to better understand a distinction that is often made in the free will literature, namely, that between some notion of ‘general’ ability on the one hand and a notion of ‘specific’ or ‘particular’ abilities on the other. I argue that there are two important distinctions, both of which are relevant to free will. In chapter 4 I consider Keith Lehrer’s analysis of ‘can’ and conclude that while it fails to achieve Lehrer’s stated aim – namely, that of demonstrating that free will is compatible with determinism – it does contain some useful insights about the kinds of ability relevant to free will. In the fifth and final chapter I switch gears somewhat; I argue that various conditions typically treated under the banner of ‘the epistemic criteria on moral responsibility’ should instead be treated as conditions on an agent’s being able to do otherwise. (shrink)