Deontic Modality and the Semantics of Choice
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Abstract
I propose a unified solution to two puzzles: Ross's puzzle (the apparent failure of 'ought φ' to entail 'ought [φ or ψ]') and free choice permission (the apparent fact that 'may [φ or ψ]' entails both 'may φ' and 'may ψ'). I begin with a pair of cases from the decision theory literature illustrating the phenomenon of act dependence, where what an agent ought to do depends on what she does. The notion of permissibility distilled from these cases forms the basis for my analysis of 'may' and 'ought'. This framework is then combined with a generalization of the classical semantics for disjunction — equivalent to Boolean disjunction on the diagonal, but with a different two-dimensional character — that explains the puzzling facts in terms of semantic consequence.
