Logical Principles and Moral Principles: The Identity of Indiscernibles

Abstract

The logical status of the identity of indiscernibles is considered in the context of Principia Mathematica’s definition of identity and in reference to the Leibniz-Clarke polemics. In his defence Leibniz distinguishes between logical and moral necessity and relates the latter to existence, jure divino, and the principle of sufficient reason. In Wittgenstein’s Tractatus Russell is criticised in the same terms that Clarke used against Leibniz, but Wittgenstein also talks about the ‘experience’ that something is, necessary to understand logic, and points out that logic could be prior to the question ‘How?’, but not to the question ‘What?’ From this a parallel is suggested between Wittgenstein’s position and Leibniz’s distinction which could be used to rethink in Leibnizian terms logic’s radical independence.