In a 1687 letter to Arnauld, Leibniz draws on an argument against mind-body causation that is reminiscent of one from Spinoza’s Ethics. According to this argument, mind-body causation is impossible because of the lack of proportion between thoughts and motions. This paper aims to shed light on Leibniz’s use of Spinoza’s argument by reconstructing both its internal structure and its development in Leibniz’s later works. In particular, the reconstruction focuses on the new version of this argument that Leibniz adopts against Stahl’s vitalism as well as on the change that this new version reveals in Leibniz’s attitude towards occasionalism. The possible influence of Cordemoy is also taken into consideration. The epistemological and metaphysical issues surrounding this argument are an essential part of the history of Leibniz’s psycho-physical parallelism.

To explain why God is not the author of sin, despite grounding all features of the world, the early Leibniz marginalized the divine will and defined existence as harmony. These moves support each other. It is easier to nearly eliminate the divine will from creation if existence itself is something wholly intelligible, and easier to identify existence with an internal feature of the possibles if the divine will is not responsible for creation. Both moves, however, commit Leibniz to a necessitarianism that is stronger than what prominent interpreters such as Robert Sleigh and Mogens Lærke have found in the early Leibniz, and stronger than the necessitarianism that threatens his later philosophy. I defend this reading of Leibniz and propose that some features of Leibniz’s later metaphysics, including his “striving possibles” doctrine, are an artifact of the effort to rescue the early theodicy from its unwelcome implications.

This paper focuses on Leibniz’s engagement with Thomas Hobbes’s political anthropology in the Mainz-period writings, and demonstrates that Leibniz tried to construct an alternative to the English philosopher by conceiving of a physically- and ontologically-grounded psychology of actions. I provide textual evidence of this attempt, and account for Leibniz’s rejection of Hobbes’s political theory and anthropological assumptions. In doing so, I refer to diverse aspects of Leibniz’s work, thereby highlighting his aspiration to congruity and consistency between different areas of investigation. Furthermore, Leibniz’s political writings and letters will reveal another—sometimes neglected—aspect of the issue: his concern to defend and legitimize the existence of pluralist and collective constitutional political systems like the Holy Roman Empire by providing the theoretical ground of their ability to last.