  Frank Jackson’s Moral Functionalism is the most influential contemporary version of analytic naturalism. (Finlay (2014) endorses another version of analytic naturalism.) Jackson believes that ethical properties are natural properties or, as he prefers to say in this context, descriptive properties. His argument for this appeals to the supervenience of the moral on the descriptive. This is the claim that no two completely specified situations that differ in their ethical properties can be exactly alike in their descriptive properties. Supervenience entails that no two worlds that are exactly like each other descriptively can differ ethically, which means that ethical properties and descriptive properties are necessarily coextensive. And Jackson does not believe there are any necessarily coextensive but distinct properties. If two properties not only coincide in the actual world but could not fail to coincide we have, he contends, not two properties but one. Thus, Supervenience entails that ethical properties are descriptive.