20.11.03 · philosophy / metaphysics

Personal identity: Parfit, fission, teleportation, and the reductionist view of the self

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Anchor (Master): Locke 1694 Essay 2.27; Butler 1736 (circularity); Reid 1785 (gallant officer); Hume 1739 (bundle theory); Williams 1970; Shoemaker 1963; Lewis 1976 'Survival and Identity'; Nagel 1971 'Brain Bisection'; Parfit 1984 Reasons and Persons; Unger 1990; Olson 1997 The Human Animal (animalism); Parfit 2011 On What Matters; Schechtman 1996/2014 (narrative)

Intuition Beginner

What makes you the same person you were at age ten? Three candidates dominate the philosophical tradition. Your body, which has changed almost every atom but kept a continuous biological organisation. Your memories, which link today's thinking self to the child who once had them. Your brain, the physical organ that carries both. None of these is plainly correct, and the choice between them is not a matter of taste.

Consider teleportation. A machine in New York scans your body, destroys it, and transmits the blueprint to Paris, where an exact copy is built atom by atom. The person in Paris wakes up remembering your life, finishing your sentences, holding your opinions. Did you travel, or did you die and a stranger wake up wearing your mind? The question is not about future technology. It is a magnifying glass for a question that already presses in ordinary life.

Derek Parfit (1934-2017), working at Oxford through the 1970s and 1980s, argued that the question is malformed. There is no deep fact of personal identity over and above the underlying physical and psychological continuities. The self is not a thing riding on top of these processes; it is the pattern they compose. This is the reductionist view. Its consequence, Parfit reported, was personal: he became less afraid of his own death.

Visual Beginner

The picture traces the principal theories of personal identity from Locke's founding statement to the late twentieth-century debates.

The timeline shows the lineage Parfit inherited and the alternatives his reductionism provoked. Locke's memory criterion is the seed; the fission case is the test Parfit used to push it past its limits.

Worked example Beginner

The fission case. A surgeon removes your brain, splits it into left and right hemispheres (each independently sufficient for thought), and transplants each hemisphere into a different empty body. Call the two resulting people Lefty and Righty. Both wake up remembering your childhood, your name, your plans; both finish the sentence you were saying when you went under anaesthesia.

Step 1. Assume the psychological-continuity view: a person at one time is identical to a later person if and only if their psychologies are appropriately continuous (memory, character, intention).

Step 2. Apply it. Lefty is psychologically continuous with you, so Lefty is you. Righty is psychologically continuous with you, so Righty is you.

Step 3. Count. There are now two distinct people (Lefty and Righty) in two rooms. They will go on to live different lives, marry different people, die in different years.

Step 4. Reach the contradiction. Identity is one-to-one: if A is identical to B and A is identical to C, then B is identical to C. But Lefty is not identical to Righty. So at least one of the identities "Lefty is you" and "Righty is you" is false.

What this tells us: in fission, identity ceases — you do not survive as Lefty, and you do not survive as Righty. But on Parfit's view, what matters (psychological continuity) survives in both.

Check your understanding Beginner

Exercise (easy, multiple choice).

On Parfit's reductionist view, personal identity over time consists in:

A. The persistence of an immaterial soul B. Biological (bodily) continuity alone C. Psychological continuity (memory, character, intention), with no further fact of identity over and above it D. A deep further fact beyond all physical and psychological continuities

Hint

Reductionism is the view that the self is reducible to underlying continuities and is not a thing in addition to them.

Answer

C. Parfit's reductionism holds that personal identity consists in psychological continuity (relation R) and that there is no further deep metaphysical fact. In ordinary (non-branching) cases, identity tracks R; in branching cases like fission, identity ceases while R is preserved in each branch. Options A and D are forms of the "further fact" view that reductionism denies; option B is the animalist alternative (Olson 1997).

Exercise (easy, multiple choice).

John Locke (1694, Essay 2.27) held that personal identity over time consists in:

A. Sameness of material substance (the body) B. Sameness of consciousness (memory) C. Sameness of an immaterial soul D. Biological continuity of the human organism

Hint

Locke's criterion displaced the Scholastic identification of the person with a substantial soul and made personal identity turn on consciousness.

Answer

B. Locke's Essay Concerning Human Understanding, book 2 chapter 27: "as far as consciousness can be extended backwards to any past action, so far reaches the identity of that person." Personal identity is sameness of consciousness, not sameness of substance — Locke explicitly allowed that the same person could be hosted by different substances over time.

Formal definition Intermediate+

The vocabulary of personal identity over time is light on notation and heavy on conceptual distinctions. The load-bearing relation is R — Parfit's name for the psychological-connectedness-and-continuity relation.

Definition (personal identity over time). Let x be a person existing at time t and y a person existing at time t′ with t < t′. Then x is identical to y iff x = y. Identity is one-to-one, transitive, and obeys Leibniz's law: if x = y and x has property F, then y has F.

Definition (psychological connectedness and continuity, relation R). A person-stage x at t is psychologically connected to a person-stage y at t′ iff there are psychological bonds (memories, intentions, beliefs, character traits, desires) between x and y with sufficient overlap. Person-stages x and y are psychologically continuous (x R y) iff there is an overlapping chain of psychologically connected stages between x and y. R is a matter of degree, can take any cause, and can hold one-to-many.

Definition (the psychological-continuity criterion of personal identity). x at t is identical to y at t′ iff x R y and no other person-stage z at t′ is such that x R z (the "no-branching" or "no competitors" clause). Without the clause, the criterion fails in fission; with the clause, identity tracks R only in the non-branching cases.

Definition (reductionism about personal identity). Personal identity over time consists entirely in physical and/or psychological continuities — there is no further fact (a "deep further fact" of the self) in which personal identity consists. On the strong reductionist form, identity is not what matters; what matters is R, which comes in degrees and can survive where identity does not.

Counterexamples to common slips Intermediate+

Slip: "memory = personal identity." The bare memory criterion (Locke) fails Butler's circularity objection (memory presupposes identity — you can remember only your own experiences) and Reid's transitivity objection (the gallant officer). The modern criterion uses quasi-memory — remembering an experience without the remembering being constitutive of identity with the original experiencer — to escape circularity, and appeals to overlapping chains of psychological connections rather than direct memory alone.
Slip: "personal identity = brain identity." A brain can be split and transplanted into two bodies (the fission case); both survivors inherit brain tissue, yet they are two. Brain identity is one-to-one like personal identity and meets the same fission problem.
Slip: "Parfit proved there is no such thing as personal identity." Parfit argued that personal identity is reducible to underlying physical and psychological continuities, not that the concept is empty. The everyday notion survives for ordinary (non-branching) cases; what it is not is a deep further fact over and above the continuities.
Slip: "biological continuity suffices for personal identity." Animalism (Olson 1997) defends biological continuity as the criterion, but it faces the brain-transplant case: if your brain is transplanted into a new body and the rest is destroyed, the resulting person seems to be you — not a different human animal that has merely acquired a new brain. The persistence of the organism and the persistence of the person pull apart in just the cases that press the question.
Slip: "the fission case is unrealistic." Real cases approximate it: split-brain patients (Nagel 1971) and dissociative identity disorder exhibit the same branching structure in less dramatic form. Thought experiments probe our concepts; the empirical analogues confirm that the structure they isolate is not a fantasy.

Key argument: Parfit's reductionism and psychological continuity Intermediate+

Argument (the fission argument for reductionism, after Parfit 1984).

Premise (the live options are psychological or biological). Either personal identity over time is grounded in psychological continuity (relation R), in biological continuity, or in a further fact. Substance-dualist and soul theories lack independent support; the serious debate is between the first two and the further-fact view.
Premise (fission defeats the bare identity=R criterion). In the fission case, two later people (Lefty, Righty) each stand in R to the original pre-fission person. If identity = R without qualification, identity would be one-to-two, which is impossible because identity is one-to-one.
Intermediate conclusion. Identity is not identical to bare R. The defender of identity must add a no-branching clause (identity = R + no competitors), or abandon identity as the load-bearing relation.
Premise (the no-branching clause is implausible). On the no-branching view, whether you survive an operation depends on whether the surgeon transplants one hemisphere or two — even though the psychology of the resulting person(s) is identical in either case. A metaphysical fact whose obtaining depends on a fact wholly extrinsic to your psychology cannot be what matters to you.
Conclusion (reductionism). What matters is not identity but R. Identity is a useful everyday concept (it works in the non-branching cases that fill ordinary life), but it is not a further fact over and above the physical and psychological continuities that constitute R. In fission, identity ceases; what matters survives in both branches.

Reconstruction. The argument is a dilemma pressed by the fission case. Fission is a logical microscope: it isolates the structural feature (branching) that distinguishes identity from continuity, and shows that identity — being one-to-one — cannot be what we care about. We care about R; R is preserved in each branch. Parfit reports that the discovery was personal: his fear of his own death diminished, and his concern for his future selves became no different in kind from his concern for the future selves of others.

Bridge. The fission argument builds toward 20.11.02 metaphysics-depth, where the same one-to-one versus one-to-many structural distinction reappears in Leibniz's law and the problem of temporary intrinsics, and appears again in 20.06.04 neuroscience of consciousness, where the split-brain patients of Nagel 1971 supply an empirical instance of the same branching structure that fission dramatises. The foundational reason the argument works is that identity is a logical relation with formal constraints (one-to-one, transitive) that psychological continuity does not share, and this is exactly the structure that identifies what we care about (survival, R) with something other than identity. The bridge is from the everyday concept of personal identity to its reductionist replacement, and the central insight is that what matters comes in degrees while identity does not — a pattern that generalises across the metaphysics of persistence (the endurance/perdurance debate of 20.11.02) and puts the fission case in the same family as the statue-and-lump.

Exercises Intermediate+

Exercise 1 (easy, multiple choice).

Butler 1736 objected to Locke's memory criterion on the grounds that:

A. Memory is unreliable B. To remember an experience as one's own already presupposes that the experience was one's own, so memory cannot constitute identity C. Memory cannot survive sleep D. Locke confused identity with similarity

Hint

The circularity objection: whatever makes a memory yours cannot itself be the memory.

Answer

B. Butler's circularity objection (1736, Analogy of Religion, Dissertation I) holds that "one should really think it were evident that personal identity is presupposed in memory, and therefore cannot be constituted by it." The criterion is circular because the ownership of the remembered experience (its being my experience) is what makes it a memory, and identity with the original experiencer is presupposed rather than established.

Exercise 2 (easy, multiple choice).

Reid 1785 used the "gallant officer" case to argue that Locke's memory criterion violates:

A. The principle of individuation B. The transitivity of identity C. The law of non-contradiction D. The principle of sufficient reason

Hint

The general remembers being the brave young officer; the brave officer remembers being the apple-stealing boy; the general does not remember being the boy. What goes wrong?

Answer

B. The gallant officer: the boy who stole apples later became the brave young officer; the officer later became the aged general. The general remembers being the officer, so general = officer. The officer remembers being the boy, so officer = boy. The general does not remember being the boy (the memory has faded), so general ≠ boy. Identity must be transitive (if general = officer and officer = boy then general = boy); the bare memory criterion yields a contradiction. Reid's objection presses Locke on transitivity.

Exercise 3 (medium, multiple choice).

In Lewis 1976 counterpart theory, the relationship between survival and identity over time is:

A. They are the same relation B. Survival comes in degrees; identity does not C. Identity comes in degrees; survival does not D. Both are one-to-one

Hint

Identity is a logical relation with fixed formal properties. Survival is what we care about when we care about our own future.

Answer

B. On Lewis's counterpart-theoretic treatment, a person at one time can stand in the counterpart relation to multiple later people, with varying degrees of psychological and physical continuity. The counterpart relation (survival) is a matter of degree and can be one-to-many; identity is a logical relation — one-to-one, transitive — and does not come in degrees. The asymmetry is the load-bearing structural fact: what we care about is the counterpart relation, not identity.

Exercise 4 (medium, short answer).

In three or four sentences, explain why Parfit introduces the relation R in addition to psychological continuity, and why R does not require a "no-branching" clause.

Hint

R is meant to capture what we should care about in survival. Identity is one-to-one; what we care about may not be.

Answer

R is psychological connectedness and/or continuity with the right kind of cause (Parfit ultimately allows "any cause" in the broadest form); it is meant to capture what we should care about when we care about our own future. Identity, by contrast, is a one-to-one logical relation that fails in branching cases like fission. By separating R (which can be one-to-many and come in degrees) from identity, Parfit preserves what matters while admitting that identity ceases in fission. R needs no no-branching clause precisely because R is not identity; one can be R-related to two later people without contradiction.

Exercise 5 (medium, multiple choice).

Olson 1997's animalism holds that:

A. We are essentially persons, and personhood is a psychological kind B. We are biological human animals, and our identity over time is biological continuity C. We are immaterial mental substances D. We are narrative constructs

Hint

Animalism takes the persistence of the organism, not the persistence of the psychology, as primitive.

Answer

B. Olson's The Human Animal (1997) defends animalism: each of us is identical to a biological human animal, and our identity over time consists in the biological continuity of that animal (the persistence of the organism, not the persistence of the psychology). The view resists the brain-transplant intuition (where the post-transplant person seems to be you) by holding that a human animal whose brain has been removed and replaced is no longer numerically the same animal.

Exercise 6 (medium, multiple choice).

The "no-branching" clause added to the psychological-continuity criterion holds that:

A. Personal identity requires branching B. Personal identity requires that there be exactly one psychological successor C. Branching creates two identities D. The clause is required by animalism

Hint

Without the clause, identity = R and fission makes one person identical to two. The clause restores one-to-one-ness.

Answer

B. The no-branching clause holds that x at t is identical to y at t′ iff x R y and no other z at t′ is such that x R z — that is, the psychological continuity must be unique. In fission, where two later people each stand in R to the original, the clause makes identity fail for both. The clause restores the formal properties of identity (one-to-one, transitive) but at the cost of making whether you survive depend on whether the surgeon transplants one hemisphere or two — Parfit's principal objection.

Exercise 7 (hard, short answer).

In four or five sentences, reconstruct Parfit's argument that the no-branching clause is implausible. Why does the implausibility of the clause support reductionism?

Hint

Consider two operations: in one, only the left hemisphere is transplanted; in the other, both hemispheres are transplanted into two bodies. The psychology of the single survivor in operation one is identical to the psychology of Lefty in operation two. Does it make sense for whether you survive to depend on the second transplant?

Answer

The no-branching clause holds that you survive an operation only if exactly one person is R-related to your pre-operation self. But whether the surgeon transplants one hemisphere or two has no effect on the psychology of the resulting person(s); the difference is wholly extrinsic to your psychology. If personal identity is what matters, then whether you survive should depend on intrinsic facts about you, not on whether a second person is also created in another room. Since the clause makes survival depend on an extrinsic fact, identity cannot be what we care about. The reductionist conclusion follows: what matters is R (which is preserved in each branch), not identity (which is not).

Exercise 8 (hard, numeric).

Consider three person-stages: A (the boy at age 5), B (the brave officer at age 30), C (the aged general at age 80). On Locke's bare memory criterion (read literally, requiring direct memory), B is identical to A and C is identical to B, but C is not identical to A (the general no longer remembers the boy). Treating each "is identical to" relation as a separate identity edge in the graph on {A, B, C}, how many identity edges does the bare memory criterion assert?

Hint

Count the pairs (X, Y) for which the criterion asserts X = Y. The criterion asserts B = A (officer remembers boy) and C = B (general remembers officer). It does not assert C = A.

Answer

2. The bare memory criterion asserts two identity edges: B = A (officer remembers boy) and C = B (general remembers officer). It does not assert C = A because the general does not remember the boy. But identity is necessarily transitive — if B = A and C = B, then C = A must hold. The criterion's two edges generate a contradiction with the transitivity of identity (the third edge must hold but the criterion denies it). This is Reid's gallant-officer paradox: the bare memory criterion generates a graph whose edges cannot all be true simultaneously. Modern psychological-continuity views repair the criterion by replacing direct memory with overlapping chains, recovering C = A.

Interpretive debates Master

Five live positions structure the modern personal-identity literature. None commands consensus; each is a standing interpretive option.

Debate 1: Lockean psychological continuity versus animalism. The longest-running divide. The Lockean tradition (Locke 1694, Shoemaker 1963, Parfit 1984) makes personal identity consist in psychological continuity; animalism (Olson 1997, Snowdon 2014) makes personal identity consist in biological continuity. The decisive cases are the brain transplant and the locked-in patient. The Lockean says the post-transplant person is you (your psychology went with the brain); the animalist says a different human animal was created and the original died. Each side charges the other with confusing the person with the human animal.

Debate 2: The branching problem — no-branching, reductionism, counterpart theory. Three responses to the fission case are live. The no-branching view (Shoemaker, Wiggins) adds a "no competitors" clause to identity = R. The reductionist view (Parfit) separates identity from what matters: identity ceases in fission but R survives. Lewis's counterpart theory (1976) replaces identity-over-time with a counterpart relation that can be one-to-many. Each preserves a different piece of common sense; none preserves all of it.

Debate 3: Reductionism versus the "further fact" view. Parfit's reductionism denies any further fact of personal identity beyond physical and psychological continuity. The opposing view — defended in variant forms by Swinburne, Chisholm, and Madell — holds that there is a further fact (a Cartesian ego, a bare thisness, a substantial self) that grounds identity over and above the continuities. Parfit's fission argument is the principal evidence against the further-fact view: in fission, two later people have equal claim to be you, and no further fact could settle which (if either) is identical to you without arbitrariness.

Debate 4: Narrative identity as a third path. Schechtman (1996, 2014) argues that personal identity is constituted by a self-telling narrative — a person is identical to the protagonist of the story they tell about their life. The view handles the standard cases elegantly and connects personal identity to ethics and to psychopathology. Critics press on false narratives (a person can be mistaken about their past), imposed narratives (a story told by others), and the case of advanced dementia (where the narrative unravels).

Debate 5: The empirical turn. Metzinger (2003), Blanke and colleagues, and the cognitive-science tradition press the question empirically. What neural mechanisms support the unified self-model whose breakdown — in schizophrenia, in out-of-body experiences, in Cotard's delusion, in dissociative identity disorder — can now be observed? The empirical turn does not dissolve the philosophical question but constrains it: any viable theory of personal identity must be consistent with the empirical facts of self-representation and its pathologies.

Synthesis. The five debates build toward 20.13.01 philosophy of mind, where the unity of consciousness and the self-model are first-class explanatory targets, and appear again in 20.06.04 neuroscience of consciousness, where split-brain patients and disorders of self supply the empirical data against which each theory is tested. The foundational reason the debates persist is that personal identity sits at the intersection of three different conceptual constraints — logical (identity is one-to-one and transitive), biological (organisms persist by continuous life), and psychological (memory and intention bind a life into a single stream) — and the central insight of Parfit's reductionism is that these constraints come apart in the hard cases. This is exactly the structure that identifies the fission case as the load-bearing thought experiment, and the bridge is from the everyday concept of personal identity to its decomposition into the underlying continuities. The pattern generalises across the metaphysics of persistence (endurance, perdurance, stage theory of 20.11.02) and across the philosophy of mind (the bundle theory of Hume, the narrative self of Schechtman, the extended self of Clark and Chalmers), putting personal identity in the same family as the statue-and-lump and the ship-of-Theseus problems: ordinary concepts whose joint deliverances fail under controlled stress.

Full argument set Master

Proposition (transitivity of identity). If x is identical to y and y is identical to z, then x is identical to z.

Proof. Identity is the relation $=$ defined by the axioms of first-order logic with identity: reflexivity $(\forall x) (x = x)$ and Leibniz's-law substitutivity $(\forall x) (\forall y) ((x = y \land F (x)) \to F (y))$ for every predicate $F$ . Taking $F$ to be the predicate "is identical to $x$ " (so $F (y)$ is $y = x$ ), reflexivity gives $x = x$ , and substitutivity with $x = y$ yields $y = x$ — symmetry. Taking $F$ to be the predicate "is identical to $z$ " (so $F (x)$ is $x = z$ ), substitutivity with $y = x$ and the premise $x = z$ gives $y = z$ — which, combined with the premise $x = y$ and another application of substitutivity on the predicate "is identical to $y$ " with $y = z$ , yields $x = z$ . $□$

Proposition (Reid's gallant officer: the bare memory criterion violates transitivity). Suppose personal identity over time consists in direct memory (Locke's bare criterion). Then there exist person-stages A, B, C such that the criterion asserts A = B and B = C but not A = C, contradicting the transitivity of identity.

Proof. Let A be the boy who stole apples, B the brave young officer, C the aged general. By construction, B remembers being A (the officer remembers the apple-theft), so the criterion asserts B = A. By construction, C remembers being B (the general remembers the military decoration), so the criterion asserts C = B. By construction, C does not remember being A (the memory of the apple-theft has faded in old age), so the criterion does not assert C = A. By the previous proposition, if B = A and C = B then C = A — but the criterion denies C = A. The criterion's verdicts are jointly inconsistent with the formal properties of identity. The modern repair replaces direct memory with overlapping chains: B = A by direct memory, C = B by direct memory, and C = A by transitive closure through B. $□$

Proposition (the fission argument). If personal identity over time consists in psychological continuity (relation R) without a no-branching clause, then in the fission case the pre-fission person is identical to two distinct post-fission people, contradicting the one-to-one-ness of identity. Therefore either a no-branching clause must be added (and identity is not what matters) or identity is not what matters.

Proof. Let P be the pre-fission person, and let L (Lefty) and R (Righty) be the two post-fission people. By construction, L is psychologically continuous with P and R is psychologically continuous with P. Suppose identity = R without qualification. Then P = L and P = R. By transitivity (previous proposition), L = R. But L and R are distinct people in distinct rooms (they will be in different places tomorrow), so $L \neq = R$ by the identity-of-indiscernibles reading of distinctness. Contradiction. Therefore the supposition is false: at least one of P = L or P = R fails. The no-branching reply adds the clause "and no other person stands in R to P," restoring one-to-one-ness; the reductionist reply accepts that both fail and identifies what matters (R) as surviving in both branches. The further-fact reply holds that there is a further fact that settles which survivor (if either) is P; Parfit's objection is that no such fact is available without arbitrariness. $□$

Connections Master

Metaphysics — foundations 20.11.01. The foundations unit introduces the modal and persistence notions (identity, modality, Leibniz's law, the identity-of-indiscernibles) that personal identity presupposes. The fission argument is an application of the foundations framework to the special case of persons: identity is one-to-one and transitive, and the philosophical task is to decide whether psychological continuity — which is neither — can ground personal identity.
Metaphysics — depth: grounding, persistence, possible worlds 20.11.02. The persistence debate (endurance versus perdurance versus stage theory) applies to persons as a special case; Parfit's reductionism is structurally a stage-theoretic view of persons. The fission argument has the same logical shape as the statue-and-lump: an ordinary concept of identity generates contradictions under controlled variation, and the philosophical task is to diagnose which concept must give way.
Neuroscience of consciousness 20.06.04. The split-brain patients of Sperry and Gazzaniga, discussed by Nagel (1971) and Parfit (1984), supply an empirical instance of the fission structure that the thought experiment dramatises. When the corpus callosum is severed, the two cerebral hemispheres process information independently, raising the question whether one person has become two. The empirical case constrains the philosophical theories and shows that fission is not a fantasy.
Philosophy of mind — foundations 20.13.01. Personal identity is partly a philosophy-of-mind concept: the unity of consciousness, the self-model, and the subject of experience all bear on it. The reductionist view is in tension with the substantive-self tradition (Descartes, Kant's transcendental unity of apperception) and in alignment with the bundle theory (Hume 1739) and the modern self-model theories (Metzinger). The philosophy-of-mind unit develops the upstream concepts that personal identity takes as load-bearing.

Historical & philosophical context Master

John Locke introduced the modern problem of personal identity in the 1694 second edition of the Essay Concerning Human Understanding ^[Locke1694], book 2 chapter 27 "Of Identity and Diversity": personal identity consists in "sameness of a rational being" and extends "as far as consciousness can be extended backwards to any past action." Locke's criterion displaced the Scholastic identification of the person with a substantial soul and made the question turn on consciousness rather than substance. The criterion attracted immediate objections. Joseph Butler, in the 1736 Analogy of Religion, charged that memory presupposes personal identity rather than constituting it — one can remember only one's own experiences, so memory cannot be what makes those experiences one's own ^[Butler1736]. Thomas Reid, in the 1785 Essays on the Intellectual Powers of Man, pressed the transitivity objection with the gallant-officer case: if memory is identity, then identity fails to be transitive, which is impossible ^[Reid1785].

The modern tradition reshaped Locke's criterion in response. David Hume's Treatise of Human Nature (1739), book 1 part 4 section 6, had already proposed a bundle theory of the self, denying any substantial ego; Parfit acknowledged Hume as the ancestor of his reductionism. Sydney Shoemaker's Self-Knowledge and Self-Identity (1963) replaced direct memory with overlapping chains of psychological connections (memory, character, intention) and introduced the notion of quasi-memory to escape Butler's circularity ^{[Shoemaker1963]}. Bernard Williams's "The Self and the Future" (1970) framed the contest between psychological and bodily continuity through torture thought experiments. David Lewis's "Survival and Identity" (1976) offered counterpart theory as a way to make survival come in degrees while preserving identity. Derek Parfit's Reasons and Persons (1984) drew these threads together into the reductionist view: personal identity consists in psychological continuity (relation R), identity is not what matters, and what matters comes in degrees ^[Parfit1984]. Eric Olson's The Human Animal (1997) mounted the principal contemporary counter-attack, defending animalism — the thesis that we are biological human animals whose identity is biological, not psychological ^[Olson1997]. Parfit's On What Matters (2011) extended the reductionist program into metaethics.

Bibliography Master

Locke, John. An Essay Concerning Human Understanding. 2nd ed. London, 1694. Book 2, chapter 27, "Of Identity and Diversity."
Butler, Joseph. The Analogy of Religion, Natural and Revealed, to the Constitution and Course of Nature. London, 1736. Dissertation I, "Of Personal Identity."
Reid, Thomas. Essays on the Intellectual Powers of Man. Edinburgh, 1785. Essay III, chapter 4, "Of Mr. Locke's Account of the Identity of Persons."
Hume, David. A Treatise of Human Nature. London, 1739. Book 1, part 4, section 6, "Of personal identity."
Williams, Bernard. "The Self and the Future." Philosophical Review 79, no. 2 (1970): 161-180.
Shoemaker, Sydney. Self-Knowledge and Self-Identity. Ithaca, NY: Cornell University Press, 1963.
Wiggins, David. Identity and Spatio-Temporal Continuity. Oxford: Blackwell, 1967.
Perry, John, editor. Personal Identity. Berkeley: University of California Press, 1975.
Lewis, David. "Survival and Identity." In The Identities of Persons, edited by Amélie Oksenberg Rorty, 17-40. Berkeley: University of California Press, 1976.
Nagel, Thomas. "Brain Bisection and the Unity of Consciousness." Synthese 22, no. 3-4 (1971): 396-413.
Parfit, Derek. "Personal Identity." Philosophical Review 80, no. 1 (1971): 3-27.
Parfit, Derek. Reasons and Persons. Oxford: Oxford University Press, 1984. Parts I-III.
Unger, Peter. Identity, Consciousness and Value. New York: Oxford University Press, 1990.
Olson, Eric T. The Human Animal: Personal Identity Without Psychology. New York: Oxford University Press, 1997.
Schechtman, Marya. The Constitution of Selves. Ithaca, NY: Cornell University Press, 1996.
Schechtman, Marya. Staying Alive: Personal Identity, Practical Concerns, and the Unity of a Life. New York: Oxford University Press, 2014.
Parfit, Derek. On What Matters. Edited by Samuel Scheffler. 2 vols. Oxford: Oxford University Press, 2011.
Metzinger, Thomas. Being No One: The Self-Model Theory of Subjectivity. Cambridge, MA: MIT Press, 2003.

Prerequisites

20.11.01

Tier anchors

beginner: Parfit — Reasons and Persons (Oxford 1984), accessible chapters; Edmonds — Would You Kill the Fat Man? (Princeton 2013) for the popular register
intermediate: Shoemaker — Self-Knowledge and Self-Identity (Cornell 1963); Parfit — Reasons and Persons (Oxford 1984) Parts I-III; Olson — The Human Animal (Oxford 1997)
master: Locke 1694 Essay 2.27; Butler 1736 (circularity); Reid 1785 (gallant officer); Hume 1739 (bundle theory); Williams 1970; Shoemaker 1963; Lewis 1976 'Survival and Identity'; Nagel 1971 'Brain Bisection'; Parfit 1984 Reasons and Persons; Unger 1990; Olson 1997 The Human Animal (animalism); Parfit 2011 On What Matters; Schechtman 1996/2014 (narrative)

References

Locke — An Essay Concerning Human Understanding (2nd edition 1694) · Book 2, chapter 27 'Of Identity and Diversity'; the founding statement of the memory criterion
Butler — The Analogy of Religion (1736) · Dissertation I 'Of Personal Identity'; the circularity objection to Locke
Reid — Essays on the Intellectual Powers of Man (1785) · Essay III chapter 4 'Of Mr. Locke's Account of Identity'; the gallant-officer transitivity paradox
Shoemaker — Self-Knowledge and Self-Identity (Cornell University Press 1963) · Chapters 2-3; the modern psychological-continuity view and quasi-memory
Parfit — Reasons and Persons (Oxford University Press 1984) · Parts I-III (the reductionist view); the fission argument; the玻璃-tunnel passage at p. 281
Olson — The Human Animal: Personal Identity Without Psychology (Oxford University Press 1997) · Chapters 1-3, 7; the animalist critique of psychological views

Estimated time

beginner: 25m
intermediate: 50m
master: 85m