Melissa Fusco (Columbia): “Ratifiability in Modal Semantics”

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Abstract: I propose a unified solution to two natural language modal puzzles: Ross’s puzzle (the apparent failure of Ought p to entail Ought(p or q)) and free choice permission (the apparent fact that May(p or q) entails both May p and May q.  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 the modals 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.

Melissa Fusco is an Assistant Professor at Columbia. She works in philosophy of language – especially formal semantics – decision theory, and philosophical logic.