Personal Identity
Personal identity is the problem of what makes a person at time numerically identical to a person at time , i.e. the same person, not just a similar one (see the SEP entry). This is the persistence question, distinct from “are you the same kind of person you used to be” (characterization).
Why is "same person" tricky?
If “the same person” can come apart from psychological continuity, the metaphysical tag may not track the thing we actually care about.
Three main theories (per SEP):
- Psychological continuity (Locke, modern Parfit): a person is a chain of memories, beliefs, personality, intentions, causally connected mental states across time. You persist iff your psychology persists
- Animalism / biological view (Olson, van Inwagen): you are a human organism. You persist when the organism persists. Your psychology is incidental; the fetus that became you had no memories, yet it was you
- Anti-criterialism / simple view: there are no informative, non-trivial conditions for persistence. Identity is brute; continuities are evidence but not constitutive
Locke’s formulation:
A person is “a thinking intelligent being, that has reason and reflection, and can consider itself as itself, the same thinking thing, in different times and places.”
The thought experiments:
- Locke’s prince and cobbler: if the prince’s memories and personality wake up in the cobbler’s body, which person is where? Most have the intuition the prince is now in the cobbler’s body. → psychological continuity wins
- Brain transplant: your brain moves to another body. Psychological continuity says you go with the brain; animalism says you stay behind as an empty organism
- Fission (Parfit): both your cerebral hemispheres survive separately in two different bodies, each psychologically continuous with you. Both can’t be you (identity is one-to-one). So either one is arbitrarily you, or neither is
- Teletransporter (Parfit): you’re scanned, destroyed, and reconstituted atom-for-atom elsewhere. Is the arrival you? Psychological continuity says yes; intuitions wobble
- Ship of Theseus applied to persons: gradual cellular replacement. When is the organism still the same one?
Parfit's move: identity is not what matters
Parfit’s radical conclusion from fission is that what we actually care about in survival is psychological continuity itself, not identity. In fission, intuitively you care about both resulting people’s futures, but only one (or neither) can literally be you. So the thing worth caring about is the continuity, not the numerical identity tag. Consequence: the question “will I survive?” may be less determinate than we think, and for ethical purposes, less important than we think.
Key objections:
- Too-many-thinkers: if I’m a psychological continuant, my organism is also thinking my thoughts, two thinkers per head, and I can’t tell which one I am
- Fetus/corpse problem for animalism: were you the fetus? Will you be your corpse? Psychological continuity says no; animalism says yes. Neither answer is fully comfortable
- Branching / non-branching constraint: to save identity in fission, psychological-continuity theorists add that you persist only if you don’t branch. But then destroying one of two surviving hemispheres saves you, which is perverse
My take
I land closer to Parfit than I expected to. The fission case is the punch that lands: if the thing I care about (waking up tomorrow, remembering today, finishing what I started) can be entirely preserved in a process that nonetheless can’t constitute “me” under any clean logic, then “me” wasn’t doing the work I thought it was. Identity is a bookkeeping convenience over a more fundamental relation of psychological continuity.
That connects to what I wrote about determinism. The determinism bothered me until I decided it “didn’t matter” because what I cared about (agency, values, relationships) was preserved inside the deterministic picture. Parfit is making the same move about identity: the metaphysical worry doesn’t touch the thing you actually care about, so you can drop the worry without losing the thing.
The teletransporter question is the one I can’t settle. Gut says “the copy isn’t me, I died.” Reflection says “if psychological continuity is what matters, and continuity is preserved, then the question of ‘same person’ is a verbal one.” I haven’t picked a side. Simulation theory brings the same puzzle back via another door: if I’m running on a substrate, what exactly would be lost if the substrate changed?