This paper proves a precisification of Hume’s Law—the thesis that one cannot get an ought from an is—as an instance of a more general theorem which establishes several other philosophically interesting, though less controversial, barriers to logical consequence.

The two dogmas at issue are the Humean dogma that “‘is’ statements do not imply ‘ought’ statements” and the Kantian dogma that “‘ought’ statements imply ‘can’” statements. The extant literature concludes these logically contradict each other. On the contrary, it is argued here that while there is no derivable formal contradiction, the juxtaposition of the dogmas manifests a philosophical disagreement over how to understand the logic of prescriptions. This disagreement bears on how to understand current metaethical debate between realists and (...) non-realists about morality in a way not heretofore investigated. The conclusion is that realists have the resources to account for both dogmas, while non-realists, if they strictly adhere to the “is”/“ought” gap, cannot give an adequate account of why “ought” implies “can”. (shrink)