Thought Experiments in Personal Identity
Fission, teletransportation, and body-swap scenarios are the imaginative cases used to test theories of personal identity.
Definition
Thought experiments in personal identity are hypothetical scenarios, such as splitting a person or duplicating them by teletransporter, designed to test which criterion of identity our intuitions support and whether identity is what matters.
Scope
This topic covers the principal thought experiments in the personal identity debate: brain transplants and body swaps, fission and the combined spectrum, and teletransportation. It examines how these cases are used to elicit intuitions and to argue that identity is not what matters in survival.
Core questions
- What do our reactions to body-swap cases reveal about identity?
- If a person fissions into two, what happens to their identity?
- Does surviving as a duplicate preserve what matters even without identity?
- Can intuitions about fictional cases settle metaphysical questions?
Key concepts
- fission
- teletransportation
- brain transplant
- combined spectrum
- what matters in survival
- branching
Key theories
- Fission and what matters
- If a person divides into two equally continuous successors, identity cannot hold with both, suggesting that what matters in survival is continuity rather than identity.
- Asymmetry of body-swap intuitions
- Described one way a brain swap looks like a change of body, but described another it looks like torture of oneself, revealing instability in our intuitions.
History
Williams (1970) used reduplication and body-swap cases to defend bodily intuitions and question psychological criteria. Parfit (1971, 1984) deployed fission, spectra, and teletransportation to argue that personal identity is indeterminate and not what matters, reshaping the field around the notion of survival.
Debates
- Reliability of intuitions
- Whether intuitive responses to bizarre cases are evidence about the nature of identity or artifacts of how the cases are described.
- Identity versus survival
- Whether fission cases show that what matters in survival can be present without identity.
Key figures
- Derek Parfit
- Bernard Williams
- Sydney Shoemaker
Related topics
Seminal works
- parfit1971
- williams1970
- parfit1984
Frequently asked questions
- What is the fission case?
- It imagines a person's brain hemispheres each transplanted into a different body, yielding two people equally continuous with the original, which challenges the idea that identity tracks what matters.