From ‘Is’ to ‘Ought’ in Moral Epistemology

Abstract

Many philosophers claim that no formally valid argument can have purely non-normative premises and a normative or moral conclusion that occurs essentially. Mark Nelson recently proposed a new counterexample to this Humean doctrine:

All of Dahlia's beliefs are true.

Dahlia believes that Bertie morally ought to marry Madeleine.

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∴ Bertie morally ought to marry Madeleine.

I argue that Nelson's universal premise has no normative content, that Nelson's argument is valid formally, and that Nelson's moral conclusion occurs essentially and not vacuously. Nonetheless, I show that Nelson's argument faces a more fundamental problem if it is used in moral epistemology. An argument that appeals to a moral authority, such as Dahlia, might justify some moral belief out of a contrast class that does not include extreme views like moral nihilism; but it begs the question against moral nihilism, since one cannot be adequately justified in believing the conjunction of its premises without depending on assumptions that moral nihilists would deny. Thus, arguments like Nelson's can accomplish something important in moral epistemology, but their use is strictly limited.