 The view of identity just put forward (henceforth “the classical view”) characterises it as the equivalence relation which everything has to itself and to nothing else and which satisfies Leibniz’s Law. These formal properties ensure that, within any theory expressible by means of a fixed stock of one- or many-place predicates, quantifiers and truth-functional connectives, any two predicates which can be regarded as expressing identity (i.e., any predicates satisfying the two schemata “for all x, Rxx” and “for all x, for all y, Rxy → (Fx → Fy)” for any one-place predicate in place of “F”) will be extensionally equivalent. They do not, however, ensure that any two-place predicate does express identity within a particular theory, for it may simply be that the descriptive resources of the theory are insufficiently rich to distinguish items between which the equivalence relation expressed by the predicate holds (“Identity” in Geach 1972).