Supervenience of the moral on the descriptive means there can be no moral difference unless there is some descriptive difference

Now, although it is an odd sentence—a very long disjunction—there is an important fact about D: it entails E and it is entailed by E. If E is true, then one of the disjuncts of D must be true, because D contains a disjunct describing every world where E is true; hence, D will be true as well. On the other hand, if D is true, then one of its disjuncts must be true, say it is Dn. E could not be false in a world described by Dn because Dn is included as a disjunct of D. Hence, if E were false in a