  The crucial idea here is that a proposition is contingently true in this world when it is somehow dependent upon the first free decree of God, that is, when the reason for the truth of the proposition is to be located in the actualization of this particular world. There is another world, W*, existing in the infinite library of world-books, which is such that if God had brought that world, W*, into existence P would be false. In other words, a proposition is contingently true when it is true in that world and false in some other world. As mentioned above, however, Leibniz defines a possible proposition in another text from this period as a proposition which will never result in a contradiction in its analysis, and given his account of worlds, this simply means that the proposition is true in some world. Further, since necessary truths are not dependent upon the first free decree of God but are instead revealed by analysis to be identities, they are in fact propositions that are true in all possible worlds. And so, while our basic modal concepts are explained in terms of the in-esse doctrine of truth (i.e. the Predicate-in-Notion Principle) and the notion of infinite analysis (in the case of contingency), it is a not a great jump to possible-worlds semantics.