Simplicity and Substantiality:The Development of ‘Simple Substance’ as a Key Notion in Leibniz’s Philosophy

摘要

In this thesis, I will argue that there are various considerations which drove Leibniz to the adoption of simplicity as a fundamental criterion for substantiality. ‘Simplicity’ seems to be a deceivingly obvious term, but on closer inspection it turns out to be nonetheless in need of further explanation. Leibniz’s definition as that which is ‘without parts’ does not lead us to an understanding unless it is clearly set out what ‘being a part’ entails and whether simplicity goes beyond indivisibility. The reconstruction of such considerations will be of help in carving out a more determinate content of this notion as it features in Leibniz’s metaphysical system, and will explain how it came to be assigned a core function in his philosophy. Various undertakings throughout his lifetime about activity, unity, indivisibility and impredicability finally culminate in the notion of simplicity. Within this overall development, several different areas of science and philosophy have taken influence on Leibniz’s considerations. There is, obviously, an overreaching metaphysical strand, which tries to account for a notion of substance that is in accordance with the requirements from other, more specific strands. Some demands derive from Leibniz’s reflections on physics, most importantly the notion of force, and from logical considerations concerning the concept of substance. Equally important are theological considerations concerning the simplicity of God, and thus the hierarchy of monads and their similarity with God. Part of the answer as to what to regard and not to regard as partless, i.e. simple, can also be found in Leibniz’s mathematical writings. First and foremost it is mereology that occupies itself with the notions of parts and wholes and will thus give clues as to how to understand the terms explicitly involved in the definition of ‘simplicity’. But Leibniz also frequently feels the need to resort to mathematics and the notions of ‘point’ and ‘function’ in order to illuminate the notion of a simple substance. Bringing all these strands together will finally give a clearer picture of what it means to be a Leibnizian simple substance.