Personal Identity Over Time
What makes a person at one time the very same person who existed years earlier, despite changes in body, memory, and character? This topic studies the conditions for the diachronic identity of persons.
Definition
Personal identity over time concerns the conditions under which a person existing at one time is numerically identical to a person existing at another.
Scope
Covers psychological-continuity theories, the bodily and biological (animalist) criteria, Parfit's reductionism and the claim that identity is not what matters in survival, and thought experiments such as teleportation and fission.
Core questions
- What makes a later person the same as an earlier one?
- Is psychological continuity or bodily continuity the criterion?
- Is identity what matters in survival?
- How should fission and duplication cases be handled?
Key concepts
- Psychological continuity
- Memory criterion
- Bodily criterion
- Animalism
- Fission
- What matters in survival
Key theories
- Psychological continuity theory
- Originating with Locke's memory criterion, this view holds that personal identity consists in overlapping chains of psychological connections such as memory, intention, and character.
- Reductionism and what matters
- Parfit argues that personal identity just consists in physical and psychological continuity, that it can be indeterminate, and that what matters in survival is continuity rather than identity itself.
- Animalism (biological criterion)
- Olson argues that we are human animals and that our persistence conditions are those of organisms, so personal identity is a matter of biological continuity rather than psychology.
History
Locke introduced the memory-based account in 1690, against substance-based views. Bernard Williams pressed bodily-continuity intuitions through thought experiments. Parfit's Reasons and Persons reframed the field with reductionism and fission cases, prompting animalist responses such as Olson's biological criterion.
Debates
- Psychological versus biological criteria
- Psychological-continuity theorists tie identity to mental connections; animalists object via cases such as the persistence of a person in a vegetative state and the 'too many thinkers' problem, arguing biological continuity is what persists.
- Is identity what matters?
- Parfit argues that in fission cases identity fails yet what we care about in survival is preserved, so identity is not what fundamentally matters; critics defend the prudential significance of identity.
Key figures
- John Locke
- Joseph Butler
- Bernard Williams
- Derek Parfit
- Eric Olson
Related topics
Seminal works
- locke1690
- parfit1984
Frequently asked questions
- Why do philosophers use teleportation and fission thought experiments?
- These cases probe our criteria of identity by separating factors that normally go together, such as psychological and bodily continuity. They test whether identity tracks the mind, the body, or neither, and whether identity is really what matters in survival.