Chloe Armstrong

Although the philosophical systems of G. W. Leibniz and David Lewis both feature possible worlds, the ways in which their systems are similar and dissimilar are ultimately surprising. At first glance, Leibniz’s modal metaphysics might strike us as one of the most contemporarily relevant aspects of his system. But I clarify in this paper major interpretive problems that result from understanding Leibniz’s system in terms of contemporary views (like Lewis’s, for instance). Specifically, I argue that Leibniz rejects the inference that if something is possible, it therefore occurs in some possible world. This discussion highlights how Leibniz’s account of individual substance (with his strict notion of identity) constrains his modal theorizing and produces fatalistic threats. I then make an unexpected connection between Leibniz’s and Lewis’s systems by showing that Leibniz’s treatment of fatalism bears similarities to the response Lewis gives to the fatalist when considering the paradoxes of time travel.

Leibniz analyzes contingency in terms of a range of different notions: hypothetical necessity, per se contingency, infinite analysis, possible free decrees of God, and moral necessity. These have been interpreted as attempts to retreat from the neccesitarian view he adopts in his early work, but I defend the view that Leibniz’s commitment to necessitarianism—the claim that all truths are necessary—is an important and unwavering feature of his system. The core of Leibniz’s modal theory is the thesis that the denial of a necessary truth is contradictory. Leibniz thinks that if we take all necessary truths into account, including the nature of God, God’s understanding of essences, and his will to do what is best, then all things considered all truths are necessarily true. All truths are necessarily true because the denial of any truth contradicts some necessary feature of God. Instead of understanding Leibniz’s subsequent theories of contingency as abandoning necessitarianism, I treat them as attempts to account for distinctions his interlocutors draw. Rather than eschew all talk of contingency, Leibniz offers and liberally invokes proxies for this notion. I trace the development of Leibniz’s various accounts of contingency from his early to mature work in order to illustrate that they are best understood in a necessitarian framework. I develop versions of his various accounts of contingency, including per se contingency and hypothetical necessity (Chapter 1), infinite analysis and possible free decrees of God (Chapter 2), and moral necessity (Chapter 3). The outcome of my project is a systematic treatment of Leibniz’s surrogate or proxy theories of contingency within his necessitarian framework. It also establishes the character of Leibnizian possible worlds, which are key for the grounding of contingent truths in the goodness of God’s will. Instead of representing all logical space, possible worlds represent alternative plans for God’s world creation, and are thus constrained by metaphysical principles informed by God’s nature.