The Puzzle

What makes you the same person you were at age five? The cells in your body have almost completely renewed. Your beliefs, desires, and memories are radically different. Physically and psychologically — nearly everything has changed. And yet we say it is the same person. Why?

And if you suffered complete amnesia tomorrow — with no memory of today — would it still be “you”? And if your brain were divided and each half transplanted into a different body, which of the two would be you?

These questions compose the problem of personal identity — one of the most perplexing in philosophy, with implications for ethics, law, psychology, and theology.

Locke: Consciousness and Memory

John Locke (1632–1704), in the Essay Concerning Human Understanding (Book II, ch. XXVII, added in the second edition, of 1694), distinguishes three types of identity:

  • Identity of substances (the same matter)
  • Identity of living organisms (continuity of vital organization)
  • Identity of persons (consciousness and memory)

For Locke, personal identity consists in the continuity of consciousness — specifically, the capacity to extend consciousness to the past through memory. I am the same person who did X if I can remember having done X. Memory, not substance (soul or body), constitutes the person.

Moral implications: Moral responsibility follows personal identity. If a sober man cannot remember what he did while drunk, there is a sense in which they are different “persons” for purposes of responsibility — Locke does not go quite so far, but his premises lead there.

Immediate objections: Thomas Reid (1710–1796) formulated the objection of the hero and the young officer: a general who was flogged as a child no longer remembers it, but did remember it as a young officer. By Locke’s theory, general = young officer and young officer = flogged child; but if the general does not remember the child, general ≠ child. Violation of the transitivity of identity.

Hume: The Bundle of Perceptions

David Hume (1711–1776), in the Treatise of Human Nature (1739), Book I, Part IV, applies his radical empiricism to the problem of the self.

The question: what sensory impression corresponds to the “self”? When I introspect, I find only particular impressions — colors, sounds, emotions, thoughts — but never an impression of a permanent “self” underlying them. The “self” has no corresponding impression.

Bundle theory: The “mind” is not a substantial subject — it is a bundle of flowing perceptions, without any underlying unity beyond the sequence and the relations of resemblance and causation among perceptions.

Hume’s difficulty: In the Appendix to the Treatise, Hume admits he cannot satisfactorily explain what unites the perceptions in the bundle. The question remains open.

Kant: The Transcendental Unity of Apperception

Kant (1724–1804) offers a different solution in the Critique of Pure Reason. There is no observable substantial self (agreeing with Hume), but there is a formal condition of all experience: the “I think” must be able to accompany all my representations — the transcendental unity of apperception. This “self” is not an object of knowledge but the logical-formal condition of the unity of experience.

Derek Parfit: Reasons and Persons (1984)

The most radical and influential contribution. Parfit (1942–2017) defends reductionism about persons: a person is not an entity over and above their physical and mental events and relations. There is no separate “self” that persists.

What really matters: Parfit argues that personal identity is not what matters in survival. What matters is psychological continuity and connectedness — having memories, desires, and projects that develop over time. Surviving with severe amnesia (rupture of continuity) may be worse than successful brain division (two continuers with full psychological continuity).

Fission cases: If your brain were divided and each hemisphere transplanted into a distinct body, both resultants would have psychological continuity with you. But they cannot both be numerically identical to you (identity is transitive). Parfit concludes: identity is not what matters; what matters is the continuity relation, which can exist without identity.

Ethical implications: Parfit’s reductionism has consequences for distributive ethics over time and for altruism. If there is no deep self separate from one’s relations and states, the boundary between self and others is less rigid — which may favor more altruistic positions.

Buddhist connection: Parfit himself acknowledges that his conclusions have affinity with the Buddhist doctrine of anātman (no-self). The absence of a substantial, permanent self is a central Buddhist teaching. Parfit arrived at this position through independent analytic reasoning.

Narrative Identity: Ricoeur

Paul Ricoeur (1913–2005), in Oneself as Another (Soi-même comme un autre, 1990), distinguishes two types of identity:

  • Idem (sameness): the same substrate, what remains identical
  • Ipse (selfhood): identity as promise, commitment, maintaining oneself over time

Personal identity is fundamentally narrative: we are the stories we tell about ourselves — stories that integrate change and permanence, past and future projects.

Practical Implications

The problem is not merely theoretical:

  • Criminal law: Punishment presupposes identity between the offender and the convicted. If the person who committed the crime is radically different from the one who will be punished, retributive punishment loses its foundation.
  • Bioethics: Do patients with advanced dementia have the same identity as the person who signed an advance directive? Transplants, vegetative states, and advances in neurotechnology make the problem acute.
  • Immortality: If identity is psychological continuity, could one “survive” via transfer of patterns to another substrate (mind upload)? The question remains philosophically and empirically open.

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