Let us say that two or more substances are compossible if and only if there is no contradiction between the predicates derivable from their CICs.For example, consider the two individuals, Don and Ron.When Leibniz speaks of a , on the other hand, is simply that set of finite things that is instantiated by God, because it is greatest in goodness, reality and perfection. Now, given that Leibniz's safe claim is that “[t]here are as many possible worlds as there are series of things that can be conceived that do not imply a contradiction,” (Grua 390) it might still be the case that there is only possible world – only one set of essences that implies no contradiction.Naturally, the fact that we are here experiencing this world – the actual world – means that there is at least one possible world. If we accept the claim that a possible world is simply any set of compossible individuals (i.e.
Certainly, Don and Ron cannot be said to be members of the same world if Don perceives the moon landing of Apollo 11 on July 20, 1969 and Ron does not (or would not)—and not simply because he does not have a television set, but because on July 20, 1969, there is no United States of America, let alone a space program.For not even God can bring into existence a world in which there is some contradiction among its members or their properties. 40 dating Langeland But this opens up the question: Just what is meant by a contradiction in the case of the members of a world?(A VI iv 1540/AG 41) (CIC), which contains (or from which are deducible) all predicates true of it past, present, and future.Leibniz asks his reader to consider the case of Alexander the Great.
From this, it should also be clear that the compossibility of substances in a world is another manifestation of Leibniz's thesis of the universal harmony of perceptions of substances.A possible world, however, is not simply a set of compossible individuals.Individual substances, of course, are parts of, or rather, members of a world.In other words, a , a world is a “collection of finite things.” (G VII 302/AG 149) More specifically, Leibniz tells Bourguet, “the universe is only a certain kind of collection of compossibles; and the actual universe is the collection of all possible existents, that is, of those things that form the richest composite.” (G III 573) In saying that a world is a set of compossible things, however, Leibniz is saying that a world is a kind of collection of things that God bring into existence.(The issue is, in fact, vexed; for insightful presentations of views rivaling that presented here, see Sleigh 1990 or Cover and Hawthorne 1999.) Further, according to Leibniz, one of the consequences of this view of the nature of an individual substance is that no two substances can be qualitatively identical and differ numerically.
In other words, the Principle of the Identity of Indiscernibles (PII) follows from this conception of the nature of substance, and PII entails that, for any possible world, there is at most one instance of a CIC.In the course of his writings, Leibniz developed an approach to questions of modality—necessity, possibility, contingency—that not only served an important function within his general metaphysics, epistemology, and philosophical theology but also has continuing interest today.Indeed, it has been suggested that 20 In order to explain Leibniz's modal metaphysics—the metaphysics of necessity, contingency, and possibility—we must look first at the foundation of Leibniz's system more generally: his conception of an The nature of an individual substance or of a complete being is to have a notion so complete that it is sufficient to contain and to allow us to deduce from it all the predicates of the subject to which this notion is attributed.One of Don's properties is and be members of the same world.Now in Leibniz's fully developed metaphysics this example might not be considered a good one, since it is most likely the case that Leibnizian individuals are not to be thought of as constituted by such relational properties.