European journal of analytic philosophy

Abstract

I show that intuitive and logical considerations do not justifyintroducing Leibniz’s Law of the Indiscernibility of Identicals inmore than a limited form, as applying to atomic formulas. Once thisis accepted, it follows that Leibniz’s Law generalises to all formulasof the first-order Predicate Calculus but not to modal formulas.Among other things, identity turns out to be logically contingent