13 December 2019, joint EXPRESS-DiP Colloquium, Melissa Fusco
The Free Choice effect—whereby ♢(p or q) seems to entail both ♢p and ♢q—has long been described as a phenomenon affecting the deontic modal “may”. This paper presents an extension of the semantic account of deontic free choice defended in Fusco 2015 to the agentive modal “can”, the “can” which, intuitively, describes an agent’s powers.
I begin by sketching a model of inexact ability, which grounds a modal approach to agency (Belnap & Perloff, 1998; Belnap et al., 2001) in a Williamson (1992, 2014)-style margin of error. A classical propositional semantics combined with this framework can reflect the intuitions highlighted by Kenny (1976)’s much-discussed dartboard cases, as well as the counterexamples to simple conditional views recently discussed by Mandelkern et al. (2017). In §3, I substitute for classical disjunction an independently motivated generalization of Boolean join—one which makes the two diagonally, but not generally, equivalent—and show how it extends free choice inferences into a simple object language.