Metaphysics
Personal Identity
What makes you "you" over time? — psychological vs physical continuity
Personal identity is the question of what makes someone the same person over time. You at 5 years old vs you now: different cells, different memories, different beliefs — yet "same person." Why? Major theories: (1) Body theory — same physical body. (2) Brain theory — same brain. (3) Memory theory (Locke) — connected memories. (4) Psychological continuity theory — connected mental states. (5) Narrative identity — coherent self-story. (6) Bundle theory (Hume) — no enduring self; just succession of experiences. Thought experiments (teleporters, brain transplants, ship of Theseus) probe intuitions.
- QuestionWhat makes you "you" over time?
- Body theorySame body across time
- Brain theorySame brain across time
- Memory theoryLocke; connected memories
- Bundle theoryHume; no enduring self
- Famous thought experimentsTeleporter, brain transplant, ship of Theseus
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Why personal identity matters
- Ethics. Responsibility over time.
- Law. Criminal liability years later.
- Medicine. Brain damage; advanced directives.
- Religion. Soul, afterlife, reincarnation.
- AI. Identity of digital copies.
- Cryonics. Same person after revival?
- Personal meaning. Continuity of self.
Common misconceptions
- Identity is obvious. Surprisingly hard to specify.
- Body settles it. Bodies change; intuitions resist.
- Memory settles it. Reid's case shows problems.
- Identity is all-or-nothing. Could be matter of degree (Parfit).
- Same person = same self. Different concepts.
- One theory must be right. Many defensible.
Frequently asked questions
What's the personal identity problem?
How does same person persist over time despite changes? Body changes (cells, organs). Mind changes (memories, beliefs, personality). Yet there's intuition: same person. What grounds this? Different theories give different answers. Practical implications: criminal responsibility (am I same person who committed crime years ago?), medical decisions, religious continuity, contracts, etc.
What's Locke's memory theory?
John Locke (1690): person is same if connected by memory. I am same as 10-year-old me because I remember being 10. Person who can't remember a past act: not responsible for it. Limits: (1) Forgetting old things — am I still same person? (2) False memories. (3) Reid's brave officer case: officer remembers boy who stole apples; old general remembers being officer; doesn't remember boy. By Locke's logic: officer = boy, general = officer, but general ≠ boy. Memory not transitive.
What's psychological continuity?
Modern descendant of Locke. Person same if connected by overlapping psychological states (memories, beliefs, personality, intentions). Doesn't require direct memory of every previous state — chain of overlapping connections. Like rope: many fibers; not one runs full length. Each fiber connects across time; rope continuous. Derek Parfit: most influential modern advocate.
What's bundle theory?
David Hume (1739). No enduring self; just bundle of perceptions. "When I enter most intimately into what I call myself, I always stumble on some particular perception." No "I" beyond experiences. Counterintuitive but defensible. Buddhist anatta (no-self) similar. Modern eliminativists (Parfit's later view): self is constructed; not metaphysically real.
What's the teleporter thought experiment?
Star Trek-style teleporter. Body destroyed at point A; reconstituted at point B. Same person? Intuitions vary. Versions. (1) Original destroyed, copy created: same person? (2) Original survives, copy created: which one is you? (3) Multiple copies: what about identity? Tests intuitions about body vs psychological continuity. Parfit famous discussion in "Reasons and Persons" (1984).
What's narrative identity?
Identity grounded in coherent self-story. We're the protagonist of our own narrative. Unifying story across time, despite changes. Common in modern philosophy (Charles Taylor, Paul Ricoeur), psychology (Dan McAdams). Strengths: captures meaning-making. Critiques: too simple narratives; some lives lack clear narrative; just-so stories.
What does Parfit conclude?
Derek Parfit (1984): personal identity less important than we think. What matters is psychological continuity, not strict identity. In some teleporter cases, no clear answer to "is it you?" — but what matters (psychological connections) preserved. Implications: less self-interested rationality; less concern for distant future self. Influential in ethics and philosophy of mind.