Theories of Actuality

The problem which I wish to discuss can be introduced by the following presumptuous exercise in imagination. Let us imagine ourselves in the position of Leibniz's God. In His infinite understanding, He has a perfect knowledge of infinitely many possible worlds, each of them completely determinate (presumably in infinite detail). One of them is the single world on which He has conferred actuality: the actual world. But what is it that He has conferred on that world in actualizing it? What does that world have by virtue of being actual that the other possible worlds do not have? In what does the actuality of the actual world consist? My purpose here is to consider critically the principal solutions which have been suggested for this problem, and to try to find the best one. Most of the theories to be discussed are at least suggested by things that Leibniz says. (This is not an issue on which he held consistently to one settled view.) I shall not begin by assuming any one theory about what a possible world is or what it is for there to be a plurality of possible worlds, because we shall see that a disagreement on this issue underlies some of the diversity of theories of actuality. I shall normally assume, however, that there is a plurality of completely determinate possible worlds. In saying that the possible worlds which we discuss are completely determinate, I mean to imply at least the following two claims. (1) For every possible world, w, and every pair of contradictory propositions, one member of the pair is true in w and the other member is false in w. (2) Each possible world, if temporally ordered at all, is a complete world history and not a momentary stage of one. The actual world, therefore, includes what has