Mereological Nihilism: Substance and Matter in Leibniz's Metaphysics

Central to Leibniz's philosophical system is his view that substances must have genuine unity, that they must be simple or indivisible. In this dissertation, I argue that Leibniz's well-known view that substances must be simple, i.e. without parts, follows from his commitment to mereological nihilism--the view that nothing with a plurality of parts is truly one being. I begin by offering a detailed analysis of Leibniz's view that matter or body is inherently plural. I argue that the reasons for this view have not been fully understood, and are rooted in Leibniz's claim that matter is discrete. I then defend Leibniz's commitment to the plurality of matter against what I call the 'Spinozistic Challenge' according to which the entire physical world is a single substance, a view sometimes attributed to Descartes. This challenge alleges that since the physical world is a plenum, the parts of matter can't exist without the entire physical world, and as such the physical world is really one thing, not many things. I argue that, for Leibniz, the sort of dependence involved here does not undermine the plurality of matter. After establishing the reasons for Leibniz's view that matter is inherently plural, I turn to Leibniz's frequent talk of composite, corporeal substances. How can Leibniz account for such substances given his views that matter is inherently plural and that no substance--no true unity--has a plurality of parts? I first examine Leibniz's view that composite substances have bodies that are actually infinitely divided. It seems that this view conflicts with Leibniz's explicit rejection of infinite number. I defend the claim that Leibniz can accept infinite pluralities without accepting infinite number. Finally, I analyze Leibniz's attempt to reconcile the existence of composite substances with his view that no substance has parts. Ultimately, I argue, this attempt fails to offer a real account of the per se unity of composite substances, and this leads Leibniz to a theory where only monads are genuine substances.Ph