The Perils of Rejecting the Parity Argument

Many moral error theorists reject moral realism on the grounds that moral realism implies the existence of categorical normativity, yet categorical normativity does not exist. Call this the Metaphysical Argument. In response, some moral realists have emphasized a parity between moral normativity and epistemic normativity. They argue that if one kind of normativity is rejected, then both must be rejected. Therefore, one cannot be a moral error theorist without also being an epistemic error theorist. Call this the Parity Argument. In this paper, we address three possible responses to the Parity Argument from moral error theorists: (1) accept the parity but still reject epistemic error theory, (2) reject the parity, (3) accept the parity and defend epistemic error theory. We argue that there are problems with each of these responses, so the Parity Argument stands as a strong counterargument to the Metaphysical Argument. We conclude by drawing some lessons for any future challenges to the Parity Argument