The moral supervenes on the descriptive: things can’t differ morally without differing in some descriptive way. The connection is a necessary one, so it needs an explanation, and non-naturalist realism cannot provide any, while other theories can; non-naturalist realism is in this way worse at explaining than rival theories.

This argument, endorsed in some form by Simon Blackburn and R. M. Hare among others, has been popular for a long time, but recently some philosophers have doubted its cogency. I survey these doubts and conclude that the argument is a sound one.

The doubts I canvas include: that the moral does not supervene on the descriptive; that it does but only in a trivial way that is easy to account for; that the necessary connection is conceptual rather than metaphysical and so cannot be a particular problem for any metaphysical view; that the necessary connection is normative and needs a normative rather than metaphysical explanation.