Personal Identity

  • How we identify someone over time
  • Questions
    • What makes a person the same person from one moment to the next?
    • What makes us ourselves?
  • We care about numerical identity not qualitative identity


The Soul Theory

  • You are your soul
  • Two objections:
    • Asserts numerical identity over time but doesn't explain it
    • No clear identity conditions even at a given time
      • Do we really understand what makes one soul different from other souls?

Spatiotemporal Continuity Theory

  • An object is identified in terms of a continuous series of locations in space and time
  • You are something that inhabits a continuous series of locations in space and time
  • Does it really give us a philosophical account of personal identity?
  • Objection: Prince and Cobbler thought experiment
    • Brain transfer swap
      • Prince commits a crime then gets a mad scientist to swap his brain with the Cobbler's
      • Prince is now in the Cobbler's body
      • Cobbler (inside the Prince's body) is punished
    • No transfer swap
      • Same as above but the scientist just alters the existing brain's
    • John Locke concludes that personal identity follows psychological continuity, not spatiotemporal continuity
  • John Locke on personal identity
    • Personal identity consists in sameness of consciousness
      • Consciousness is inseparable from thinking
      • One distinguishes between oneself and other thinking beings via thought
    • A person's identity stretches back in time as far as one's thought extends

Brain-Based Psychological Continuity Theory

  • A past person is the same as a future person if and only if:
    • The two persons are psychologically continuous with each other
    • The brains of the two people are spatiotemporally continuous with each other

Split Brain Cases

- *X*'s brain is split into two halves
  - Two spatiotemporally distinct individuals, *Y* and *Z*, are formed
- Is *X* the same individual as *Y*, *Z*, both, or neither?
- [Derek Parfit](/second-brain/derek%20parfit)'s response
  - Something wrong with the question
  - All that really matters for personal identity is psychological continuity

David Hume on personal identity

  • Human mind is composed of a bundle of impressions in rapid succession
  • The mind is not identical over time
  • We ascribe a unified personal identity to ourselves over time as follows:
    • We form ideas of identity and diversity via actions of the imagination
    • We slide from one idea to the other, because the corresponding actions resemble each other
    • We invent the fiction of a persisting self to mask our mistake

Philosophy Identity Metaphysics