 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 world described by Dn it would be possible for there to be two worlds that were exactly alike in all descriptive respects with the moral statement E being true in one of these worlds but false in the other. The supervenience of the moral on the descriptive tells us that this cannot happen—there can be no moral difference unless there is some descriptive difference. So D entails E.