Cognitive partitions are useful. The notion of numerical identity helps us induce them. Consider, for instance, the role of identity in representing an equivalence relation like taking the same train. This expressive function of identity has been largely overlooked. Other possible functions of the concept have been over-emphasized. It is not clear that we use identity to represent individual objects or quantify over collections of them. Understanding what the concept is good for looks especially urgent in light of the fact (...) that numerical identities themselves are tangibly trifling. (shrink)