In philosophy, the matter of personal identity[1] deals with such questions as, "What makes it true that a person at one time is the same thing as a person at another time?" or "What kinds of things are we persons?" Generally, personal identity is the unique numerical identity of a person in the course of time.[2][3] That is, 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.[a]

In philosophy, the matter of personal identity^[1] deals with such questions as, "What makes it true that a person at one time is the same thing as a person at another time?" or "What kinds of things are we persons?" Generally, personal identity is the unique numerical identity of a person in the course of time.^[2][3] That is, 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.^[a]
In contemporary metaphysics, the matter of personal identity is referred to as the diachronic problem of personal identity.^[b][4] The synchronic problem concerns the question of what features and traits characterize a person at a given time. In continental philosophy and in analytic philosophy, enquiry to the nature of Identity is common. Continental philosophy deals with conceptually maintaining identity when confronted by different philosophic propositions, postulates, and presuppositions about the world and its nature.^[5][6]