 It is customary to distinguish identity at a time from identity across time. An example of an identity holding at a single time is: the table in the next room is (now) identical with my favorite table. An example of an identity holding across different times is: The table in the next room is identical with the one you purchased last year. Diachronic identities pose some of the most intractable problems about identity. Before looking at those problems, and some of the most frequently proposed solutions to them, let us ask whether there is anything that distinguishes identity from other relations.