Leibniz's Definitions of an Individual Substance: “Complete Concept” and/ or “Law of the Series.” Replacement, Development, or Complementarity?

Throughout his career, Leibniz defines individual substances in different ways. In the 1680s, especially in the Discourse on Metaphysics, Leibniz develops an original definition of substance through the complete concept of an individual (CCI). Most commentators hold that the CCI fades out in Leibniz's later philosophy. Others argue that the “law of the series” (LoS) replaces the definition of an individual substance through the CCI. We argue that these definitions are complementary. Early versions of the LoS inform the development of the CCI in the 1680s and are clearly pronounced in Leibniz's later texts. We discuss several often-neglected texts that show that the CCI is still present in Leibniz's late writings. We support the complementarity thesis by suggesting that the CCI primarily characterizes possible individuals, whereas the LoS characterizes actual individuals. As such, the LoS is especially apt to highlight the dynamic traits that Leibniz ascribes to individual substances from the 1690s.