The Relationship between the Principle of Identity of Indiscernibles and the Principle of Sufficient Reason in the Leibniz-Clarke Correspondence

Abstract

The aim of this paper is to render a detailed analysis of the correspondence with Clarke in order to shed some light in the relationship between the Principle of Identity of Indiscernibles and the Principle of Sufficient Reason. Most of the secondary literature takes for granted that Leibniz derives the Principle of Identity of Indiscernible from the Principle of Sufficient Reason in at least some parts of the correspondence. This would render the Principle of Identity of Indiscernibles a merely contingent truth and not a necessary principle. I will argue that this interpretation is misleading, and that Leibniz never abandoned the idea that the Principle of Identity of Indiscernibles is a necessary truth. Although he is continuously using the Principle of Sufficient Reason in his argumentation, he keeps in parallel a strong argumentation that entails the necessity of the Principle of Identity of Indiscernibles. To achieve this goal, it will be necessary to point out first some contextual facts that may determine a correct understanding of the correspondence. It will be also necessary to frame the discussion about the principles into the broader debate on the possibility of Newtonian space. Finally, it will be shown that the mentioned hypothesis is supported by textual evidence throughout the entire correspondence.