Abstract:

We consider a paradox involving indicative conditionals ("ifs") and deontic modals ("oughts"). After considering and rejecting several standard options for resolving the paradox--including rejecting various premises, positing an ambiguity or hidden contextual sensitivity, and positing a non-obvious logical form--we offer a semantics for deontic modals and indicative conditionals that resolves the paradox by making modus ponens invalid. We argue that this is a result to be welcomed on independent grounds, and we show that rejecting the general validity of modus ponens is compatible with vindicating most ordinary uses of modus ponens in reasoning. (This is joint work with Niko Kolodny.)