The Identity of Indiscernibles

The Identity of Indiscernibles is a principle of analytic ontology first explicitly formulated by Wilhelm Gottfried Leibniz in his 'Discourse on Metaphysics', Section 9 (Loemker 1969: 308). It states that no two distinct things exactly resemble each other. This is often referred to as 'Leibniz's Law' and is typically understood to mean that no two objects have exactly the same properties. The Identity of Indiscernibles is of interest because it raises questions about the factors which individuate qualitatively identical objects. Recent work on the interpretation of quantum mechanics suggests that the principle fails in the quantum domain (see French 2006).