Possible worlds can be understood in terms of individual essences. A possible world is a maximally consistent combination of co-exemplifiable individual essences. A particular exists in a possible world w if and only if the actuality of w entails that the corresponding individual essence is exemplified, which is to say that a particular exists if and only if its individual essence is exemplified. Proper names express, and at the same time refer to, individual essences. This account helped dispose of the problem about singular propositions mentioning non-existing particulars. Yet there is another important metaphysical question we have to deal with. What exactly does the actuality of a possible world consist in? What is it that makes a certain possible world the actual world?¹