Personal identity is the unique numerical identity of persons through time. That is to say, the necessary and sufficient conditions under which a person at one time and a person at another time can be said to be the same person, persisting through time. In the modernphilosophy of mind, this concept of personal identity is sometimes referred to as the diachronic problem of personal identity. Thesynchronic problem is grounded in the question of what features or traits characterize a given person at one time.
Identity is an issue for both continental philosophy and analytic philosophy. A key question in continental philosophy is in what sense we can maintain the modern conception of identity, while realizing many of our prior assumptions about the world are incorrect.