A Necessary Defense of the Principle of the Identity of Indiscernibles in the Metaphysics of Leibniz

Abstract

Today, studies on Leibniz’s views on metaphysics and its relation to his theology do not address his metaphysical principles, especially the principle of sufficient-reason and the identity of indiscernibles, in a holistic manner. These principles are sometimes discussed on their own in contemporary philosophical debates and sometimes independently of Leibniz’s theological assumptions. The main reason for this is the interpretation of Leibniz’s logic as prioritising his metaphysics. The main purpose of this article is to interpret Leibniz’s metaphysics and theology in a way that prioritises his logic in order to deal with the principle of the identity of the indiscernibles. Leibniz’s doctrine of monads proposed in his adulthood and his metaphysical and theological debates with Samuel Clarke suggest that the possibility of a priorist interpretation of Leibniz’s metaphysics. According to Leibniz’s principle of the identity of the indiscernnibles (PII), if two things are similar in all their properties,  they  are identical. Accordingly, Leibniz first asserts this principle in a theological way and extends it to the logical and empirical domain. The aim of this study is to analyse Leibniz’s PII in this way and to examine in detail the metaphysical necessity of the principle and its relation with his theology. As a result, we obtain a version of Leibniz’s PII derived from the principle of sufficient cause  (PSR). We conclude that, taken together with PSR, the PII can be grounded in a non-trivial way that is consistent with Leibniz’s metaphysics.