Dynamic Thoughts on Ifs and Oughts

Iffy oughts figure prominently in a variety of paradoxes of deontic logic. A satisfying response to these paradoxes is a non-negotiable component of any adequate semantic story about conditionals and deontic modals. I demonstrate that such a story can be told but doing so requires that we supplement a semantics that pays proper attention to the sensitivity of ifs and oughts to contextual information with a dynamic conception of logical consequence. The resulting framework naturally leads to a nonmonotonic logic for conditionals and deontic modals which differs from its static alternatives in that it elegantly resolves not only Kolodny’s and MacFarlane’s recent miners paradox but also the more classical paradoxes about conditional obligations from Forrester and Chisholm.