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

Theories

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-parfit)'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