 So far it has been assumed that (non-trivial) necessary and sufficient conditions for transworld identity with a given object would involve the possession, by that object, of an individual essence: a set of properties that it carries with it in every possible world in which it exists. But one might wonder why we should make this assumption. Those who believe that there are (non-trivial) necessary and sufficient conditions for identity over time need not, and almost universally do not, believe that these conditions consist in the possession, by an object, of some ‘omnitemporal core’ (to use a phrase suggested by Harold Noonan) that it has at every time in its existence. So why should things be different in the modal case?