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horizon: "indefinite"horizon: "indefinite"categories: ["minds", "society"]categories: ["minds", "society"]tags: ["identity", "philosophy of mind", "parfit", "survival", "consciousness", "bioethics"]tags: ["identity", "philosophy of mind", "parfit", "survival", "consciousness", "bioethics"]summary: "The question of what makes a person at one time the same person as at another, and what — if anything — must be preserved for that person to survive."summary: "The question of what makes a person at one time the same person as at another, and what, if anything, must be preserved for that person to survive."updated: "2026-07-28"updated: "2026-10-29"------ ```infobox```infoboxlines 27–42 → 27–4213 unchanged lines not shown
**Personal identity and continuity** is the problem of what makes a person existing at one time the**Personal identity and continuity** is the problem of what makes a person existing at one time thesame person as one existing at another, and what has to be preserved for that person to survive asame person as one existing at another, and what has to be preserved for that person to survive achange. It is an old question in philosophy that acquires practical force whenever a technologychange. It is an old question in philosophy that acquires practical force whenever a technologyproposes to interrupt, copy, or reconstruct a mind — which is why it recurs acrossproposes to interrupt, copy, or reconstruct a mind, which is why it recurs across[[mind-uploading]], [[cryonics]], gradual neural replacement, and advance directives in dementia.[[mind-uploading]], [[cryonics]], gradual neural replacement, and advance directives in dementia.Nothing in neuroscience answers it, because it is not a question about what happens but about how toNothing in neuroscience answers it, because the question concerns how to describe what happens, notdescribe what happens.what happens. ## The classical positions## The classical positions John Locke separated the person from both the soul and the animal. A person, he wrote, is a thinkingJohn Locke separated the person from both the soul and the animal. A person, he wrote, is a thinkingintelligent being that can consider itself as itself across time, and personal identity extends onlyintelligent being that can consider itself as itself across time, and personal identity extends onlyas far as consciousness — effectively, memory — extends backwards.[^locke1694] The proposal explainsas far as consciousness (in effect, memory) extends backwards.[^locke1694] The proposal explainswhy a person is responsible for past acts they remember and severs identity from bodily persistence.why a person is responsible for past acts they remember and severs identity from bodily persistence. Two objections followed quickly. Joseph Butler charged the account with circularity: to rememberTwo objections followed quickly. Joseph Butler charged the account with circularity: to rememberlines 44–51 → 44–511 unchanged line not shown
than constituting it. Thomas Reid's brave officer case sharpened it: an old general remembers beingthan constituting it. Thomas Reid's brave officer case sharpened it: an old general remembers beinga young officer, the young officer remembered being a flogged schoolboy, but the general remembersa young officer, the young officer remembered being a flogged schoolboy, but the general remembersnothing of the schoolboy. Memory is not transitive; identity is. The standard repair replaces directnothing of the schoolboy. Memory is not transitive; identity is. The standard repair replaces directmemory with overlapping chains of psychological connection — *psychological continuity* — whichmemory with overlapping chains of psychological connection, called *psychological continuity*,restores transitivity at the cost of the intuitive simplicity Locke had.which restores transitivity at the cost of the intuitive simplicity Locke had. ## Parfit's reductionism## Parfit's reductionism lines 53–71 → 53–711 unchanged line not shown
not separately existing entities over and above brains, bodies, and interrelated mental events;not separately existing entities over and above brains, bodies, and interrelated mental events;personal identity consists in facts describable without presupposing it. From this he draws apersonal identity consists in facts describable without presupposing it. From this he draws aconclusion most readers find harder than the metaphysics: identity is not what matters in survival.conclusion most readers find harder than the metaphysics: identity is not what matters in survival.What matters is Relation R — psychological connectedness and continuity — and R can hold to a degree,What matters is Relation R, psychological connectedness and continuity, and R can hold to a degree,can hold with more than one future person, and can hold without identity.can hold with more than one future person, and can hold without identity. The practical upshot is that some questions have no answer because they are questions about how toOne consequence is that some questions have no answer: they ask how to describe a case, and there isdescribe a case, not about a hidden fact. Parfit's *combined spectrum* imagines a series in which oneno hidden fact for them to track. Parfit's *combined spectrum* imagines a series in which oneperson's brain and body are progressively replaced by another's; somewhere along it, asking whetherperson's brain and body are progressively replaced by another's; somewhere along it, asking whetherthe resulting person is the original is, on his view, an empty question.the resulting person is the original is, on his view, an empty question. > [!debate] Why this is the crux for uploading> [!debate] Why this is the crux for uploading> If Parfit is right, an upload that inherits full psychological continuity carries everything worth> If Parfit is right, an upload that inherits full psychological continuity carries everything worth> caring about, and its being a copy is not a further loss. If he is wrong and identity requires> caring about, and its being a copy is not a further loss. If he is wrong and identity requires> something more — a continuously running physical process, say — then destructive scanning is death> something more, such as a continuously running physical process, then destructive scanning is> with a convincing survivor. The engineering cannot decide between these. See> death with a convincing survivor. The engineering cannot decide between these. See> [[teleportation-problem]].> [[teleportation-problem]]. ## Fission and the branching problem## Fission and the branching problemlines 75–86 → 75–863 unchanged lines not shown
cannot both be the original, since they are two and identity is one-to-one. They cannot be neither,cannot both be the original, since they are two and identity is one-to-one. They cannot be neither,since each has as good a claim as an ordinary survivor. Choosing one arbitrarily is unmotivated.since each has as good a claim as an ordinary survivor. Choosing one arbitrarily is unmotivated. The available responses divide neatly. Parfit accepts that identity fails while what matters is preservedParfit accepts that identity fails here while what matters is preserved twice over. David Lewis,twice over. David Lewis, taking persons to be four-dimensional worms of person-stages, holds thattaking persons to be four-dimensional worms of person-stages, holds that two people were present alltwo people were present all along, sharing stages before the split.[^lewis1976] Robert Nozick'salong, sharing stages before the split.[^lewis1976] Robert Nozick's closest-continuer theory makesclosest-continuer theory makes identity depend on whether a candidate is the best continuer, withidentity depend on whether a candidate is the best continuer, with the awkward result that whether athe awkward result that whether a person survives can depend on what happens to someoneperson survives can depend on what happens to someone else.[^nozick1981] Every option gives upelse.[^nozick1981] Every option gives up something ordinarily assumed about persons.something ordinarily assumed about persons. Fission is not purely hypothetical. Commissurotomy patients, whose corpus callosum has been severedFission is not purely hypothetical. Commissurotomy patients, whose corpus callosum has been severedto control epilepsy, show hemispheric dissociations under controlled testing that Thomas Nagel tookto control epilepsy, show hemispheric dissociations under controlled testing that Thomas Nagel tooklines 94–101 → 94–1017 unchanged lines not shown
persists exactly as long as the organism does.[^olson1997] Its main argument is thepersists exactly as long as the organism does.[^olson1997] Its main argument is thetoo-many-thinkers problem: if a person is distinct from the animal sitting in a chair, then twotoo-many-thinkers problem: if a person is distinct from the animal sitting in a chair, then twothinkers occupy the chair. Animalism denies that psychological continuity is even necessary forthinkers occupy the chair. Animalism denies that psychological continuity is even necessary forsurvival — a patient in a persistent vegetative state is still the same animal — and denies that anysurvival, since a patient in a persistent vegetative state is still the same animal. It also deniesupload could be a person's continuation, since the animal remains behind or dies.that any upload could be a person's continuation, because the animal remains behind or dies. Narrative accounts, associated with Marya Schechtman, treat identity as constituted by an ongoingNarrative accounts, associated with Marya Schechtman, treat identity as constituted by an ongoingself-told story that organizes experience into a life.[^schechtman1996] These accounts are better atself-told story that organizes experience into a life.[^schechtman1996] These accounts are better atlines 106–117 → 106–1174 unchanged lines not shown
Experimental work suggests folk judgements track something narrower than psychological continuity inExperimental work suggests folk judgements track something narrower than psychological continuity ingeneral. Nina Strohminger and Shaun Nichols found that participants judging cases of neural changegeneral. Nina Strohminger and Shaun Nichols found that participants judging cases of neural changetreated moral traits — honesty, cruelty, compassion — as the most identity-defining part of a mind,treated moral traits such as honesty, cruelty, and compassion as the most identity-defining part ofmore so than memories or personality broadly.[^strohminger2014] Related studies find that intuitionsa mind, more so than memories or personality broadly.[^strohminger2014] Related studies find thatabout survival shift with how a case is framed, and that people give inconsistent answers tointuitions about survival shift with how a case is framed, and that people give inconsistent answersstructurally identical scenarios.to structurally identical scenarios. This is relevant to technologies that alter mental function without ending life. Reports ofThe question also bears on technologies that alter mental function without ending life. Reports ofpersonality change after [[deep-brain-stimulation]] were widely cited as an identity problem,personality change after [[deep-brain-stimulation]] were widely cited as an identity problem,though several reviews have since argued that the empirical basis is thinner than the philosophicalthough several reviews have since argued that the empirical basis is thinner than the philosophicalliterature assumed and that much of it rests on small numbers of case reports. Similar questionsliterature assumed and that much of it rests on small numbers of case reports. Similar questionslines 140–149 → 140–15022 unchanged lines not shown
continued existence taken up in [[right-to-die-and-right-to-live]].continued existence taken up in [[right-to-die-and-right-to-live]]. **Emulation and copying.** If [[substrate-independence]] holds and [[whole-brain-emulation]] works,**Emulation and copying.** If [[substrate-independence]] holds and [[whole-brain-emulation]] works,copies become cheap, and every institution built around one-person-one-body — property, criminalcopies become cheap, and every institution built around one-person-one-body (property, criminalresponsibility, voting, consent — encounters cases it was not designed for. The weak-form products marketed asresponsibility, voting, consent) encounters cases it was not designed for. The weak-form products[[digital-immortality]] raise a smaller version of the same problem now, since a convincingmarketed as [[digital-immortality]] raise a smaller version of the same problem now, since aimitation of a dead person has no continuity claim at all but is treated by users as though it did.convincing imitation of a dead person has no continuity claim at all but is treated by users asthough it did. ## Open problems## Open problems lines 151–157 → 152–1581 unchanged line not shown
measurement distinguishes a world in which Relation R is what matters from one in which strictmeasurement distinguishes a world in which Relation R is what matters from one in which strictidentity is, and no result from [[neural-correlates-of-consciousness]] research bears on it. Thatidentity is, and no result from [[neural-correlates-of-consciousness]] research bears on it. Thatleaves the question to be settled, if at all, by which set of intuitions people are willing to giveleaves the question to be settled, if at all, by which set of intuitions people are willing to giveup — and by what legal systems decide when a case arrives that cannot be postponed.up, and by what legal systems decide when a case arrives that cannot be postponed. ## See also## See also removed, struck through added, underlinedLine numbers count the serialised markdown of each revision, frontmatter included.
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