Call ‘radical moral theorizing’ the project of developing a moral theory that not only tries to conform to our existing moral judgments, but also manifests various theoretical virtues: consistency, simplicity, explanatory depth, and so on. Many moral philosophers assume that radical moral theorizing does not require any particular metaethical commitments. In this paper, I argue against this assumption. The most natural justification for radical moral theorizing presupposes moral realism, broadly construed; in contrast, there may be no justification for radical moral (...) theorizing if moral anti-realism is true. (shrink)