Identity, in philosophy, is the condition of being oneself and not another. It concerns the persistence of a thing through change and the criteria by which we say something is the same over time. The problem of personal identity asks what makes a person the same person across time and change.

Approaches include the soul theory (a persisting immaterial substance), the body theory (continuity of the same living body), the memory theory (psychological continuity, associated with Locke), and narrative theories. Identity is also discussed in logic, where the law of identity states that a thing is identical to itself.

Key points

• Being oneself and not another
• Persistence through change
• Personal identity theories: soul, body, memory, narrative
• Law of identity in logic