Moral Discourse and Descriptive Properties

I discuss a strategy for grounding ethical naturalism propounded by Frank Jackson and more recently by Allan Gibbard: that the undisputed supervenience of the moral upon the natural (or descriptive) entails that moral properties are natural (or descriptive) properties. I show that this strategy falls foul of certain indubitable constraints governing natural kinds; and I then rebut some objections. The upshot is that no viable strategy for supporting ethical naturalism is to be found along these lines. This result has additional consequences, both for Jackson's attempt to accommodate ethical discourse into the natural world, and for Gibbard's purported 'meta-ethical synthesis'