QuestionsWho am I, really?The teletransporter: identity is not what matters
Who am I, really?No fixed self

The teletransporter: identity is not what matters

Parfit's teletransporter

Derek Parfit 1942 · 2017Asks what really matters, and seeks to reconcile Kant, contract and consequences.
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What it claims

Identity is not what matters. What matters is relation R: psychological connectedness and continuity, with the right kind of cause. And in borderline cases (copy, fission), the question "is it still me?" is "empty": we can know all the facts without answering it, and choosing an answer is only choosing a word.

Why

If the copy and the original lived at once they would be two people, yet the copy has all my memories: identity is not what matters.

The same idea through history
John Locke1694For Locke, what makes the same person is the continuity of consciousness and memory, not the body. Parfit keeps this idea, but measures it in degrees and detaches it from identity.
David Hume1739Hume finds only perceptions in himself and never a "self" that would carry them. Parfit draws from this the idea that a person is nothing over and above the chain of her physical and mental states (the "Reductionist" view).
David Wiggins1967In Identity and Spatio-Temporal Continuity, Wiggins imagines a person who divides like an amoeba: each half of the brain is grafted into a different body. Parfit makes it the core of his argument.
Derek Parfit1984Reasons and Persons, Part III (ch. 10 to 12): the teletransporter, the branch line and division show that what matters is relation R, not identity.
In short

"The teletransporter: identity is not what matters" is an argument by Derek Parfit (Reasons and Persons, 1984, Part III, 1984) on the question "Who am I, really?" (answer: no fixed self). Its claim: Identity is not what matters. What matters is relation R: psychological connectedness and continuity, with the right kind of cause. And in borderline cases (copy, fission), the question "is it still me?" is "empty": we can know all the facts without answering it, and choosing an answer is only choosing a word. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P4). AskPhilosophy presents 4 objections, 4 of them with a documented reply, and the original text behind each premise, checked word for word.

Reasons and Persons, 1984, Part III
Valid with an implicit premise

You step into a booth. A machine destroys your body on Earth, reads each of your cells and sends the blueprint by radio. On Mars, another machine builds a body and brain exactly like yours, with all your memories. You wake up there. Did you arrive on Mars, or did you die on Earth, replaced by a copy? Parfit starts from this scenario (Reasons and Persons, 1984) to defend a disturbing idea: the question "is it still me?" may have no answer, and that is not so bad, because what matters is not identity but the continuity of our memories, character and projects (he calls it "relation R").

P1The branch-line case: if the old body survives a few days after the copy, I can talk to my double on Mars. We are two people, so he is not me. Yet he has all my memories, my character and my intentions: relation R (psychological continuity) is fully there.
P2The fission case (Wiggins): if my brain is divided and each half is grafted into a different body, each of the two people who wake up is linked to me by relation R. But identity is a "one to one" relation: I cannot be two people at once. Nothing says it is one rather than the other. Neither is therefore strictly me (or the question has no answer): identity is absent while R is present.
P3Yet my relation to each of the two results contains everything needed for me to survive: I would survive if only one of them existed (people can survive with half a brain). Nothing is missing. All that is wrong is that there are two. Division and copying are thus about as good as ordinary survival.
P4 · implicit premiseWhat matters in my survival depends on the nature of my relation to the future person, not on whether someone else is also related to me in the same way. If identity really mattered, a case without identity would be worth less than ordinary survival.
Therefore identity is not what matters. What matters is relation R: psychological connectedness and continuity, with the right kind of cause. And in borderline cases (copy, fission), the question "is it still me?" is "empty": we can know all the facts without answering it, and choosing an answer is only choosing a word.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P4, the computer finds a case where R is present, identity is absent and the relation is as good as survival, but identity still matters (it would add value on top). The premises are true, the conclusion false.
The argument is valid with P4. Without it, nothing prevents identity from mattering anyway: one could accept P1 to P3 and say that identity is valuable on top of relation R. P4 says that uniqueness (the fact that only one person is related to me) does not change the value of the relation. The second half of the conclusion (R is what matters) rests on P3, which states that R alone is enough.
Analogy. A piece of music recorded on a disc, then copied to another: there are two discs, so only one is "the original". But what matters to the listener is the music, not the disc. Parfit says the same of us: what matters is the music (the continuity of our mental life), not the disc (strict identity).

Objections

4

Each objection is a conversation: click to see who replies and where the debate stands.

Bernard Williams 1970 · attacks premise 3

Summary, after Parfit's simplified version: a surgeon announces that he will make you suffer, after wiping your memory and then giving you a false character and false memories. This gives you no reason to think the pain will stop: you still fear for the body that will suffer. Fear follows the body, not psychological continuity, and relation R is not enough for survival.

Parfit replies
Derek Parfit Parfit's reply (the psychological spectrum)
Parfit replaces Williams's single case with a series of cases, each very close to the next, covering every possible amount of psychological change. If identity were what matters, a sharp line would have to be drawn somewhere between "it is me" and "it is not me". That line would be arbitrary, and one cannot believe that it has importance in itself.
Where the debate stands (our summary)Both camps agree on one point: fear for one's future does not vanish when psychology changes. The basic disagreement is about the conclusion: for Williams, bodily continuity explains this fear; for Parfit, the fear remains, but it does not prove that strict identity is what matters (our summary).
Joseph Butler 1736 · attacks the conclusion

Summary: for Butler, self-consciousness already presupposes personal identity: it cannot constitute it. Applied to Parfit: to remember is to remember one's own experiences, so the continuity of memories (relation R) already presupposes identity instead of explaining it.

Parfit replies
Parfit Parfit's reply (quasi-memory)
Parfit answers that a wider concept can be defined, "quasi-memory": one has a quasi-memory of an experience if one seems to remember it, someone did have it, and the memory depends on it in the right way. Ordinary memories are quasi-memories of our own experiences. Relation R can therefore be defined without presupposing identity.
Where the debate stands (our summary)Quasi-memory removes the circle from a logical point of view. Some critics nonetheless find it artificial, since we have no experience of memories coming from another person (our summary).
Thomas Reid 1785 · attacks premise 2

Summary: for Reid, a person's identity is perfect and simple: a person is an indivisible thing, which can have neither parts nor degrees. For every case there is therefore an answer: it is me, or it is not me. The idea of an "empty" question makes no sense.

Parfit replies
see the argument
Parfit Parfit's reply
Parfit describes this position (our identity is always "yes" or "no") as a "further fact" that nothing in the observable facts shows, and he concludes that we have enough reason to reject the view that we are entities existing separately from our brain and body.
Where the debate stands (our summary)Basic disagreement: for Reid, personal identity is a simple fact without degrees; for Parfit, there is nothing more in a life than the relations between its states. Each finds the other contrary to experience: Reid because we feel ourselves to be a whole, Parfit because nothing proves it (our summary).
David Lewis 1976 · attacks the conclusion

Summary: in "Survival and Identity", Lewis argues that fission does not set identity against what matters. Before the division there were already two people sharing the same body and memories; each therefore survives as one of the two people after the division. Identity and relation R coincide, and identity is what matters.

Parfit replies
Parfit Parfit, on a neighbouring objection
Parfit writes before Lewis publishes his revised version, and does not answer him directly. He answers a neighbouring objection: identity would be what matters because it adds to R the fact of being "unique". For him, whether R is unique makes no difference to the nature of the relation, which is what matters most.
Where the debate stands (our summary)The disagreement is largely about how to count persons: for Parfit, fission yields two persons after the division and neither is identical to the original; for Lewis, there were already two before. Both agree on what to feel about fission: dread is not justified (our summary).