Nihil Obstat: Lewis's Compatibilist Account of Abilities

In an outline of a paper found amongst his philosophical papers and correspondence after his untimely death in 2001-"Nihil Obstat: An Analysis of Ability,"reproduced in this volume-David Lewis sketched a new compatibilist account of abilities, according to which someone is able to A if and only if there is no obstacle to their A-ing, where an obstacle is a 'robust preventer' of their A-ing. In this paper, we provide some background context for Lewis's outline, a section-by-section commentary, and a general discussion of the account's main features.