Personal Identity Over Time (SACE Stage 2 Philosophy)

What this dot point is asking

You need to set out the rival criteria of identity, apply them to the standard puzzle cases, and evaluate which theory best survives them.

The bodily criterion

The simplest view is that a person is identical to a living human body, or more plausibly to a functioning brain. You are the same person tomorrow because the same organism persists, with continuous physical and biological processes. This view is grounded in ordinary practice: we re-identify people by their bodies and faces, and the law treats bodily continuity as decisive.

The challenge comes from imagined cases of brain or body swaps. If your psychology, including all your memories and your personality, were transferred into another body, most people judge that you would go with your mind, not stay with your old body. That intuition pulls against the bodily criterion and toward a psychological one. The brain-only version handles some cases but is itself strained by hemisphere-division scenarios.

The psychological criterion

John Locke argued that personal identity consists in continuity of consciousness, especially memory. A person is a thinking, reflective being that can consider itself as the same over time, and identity reaches back as far as memory reaches. On this view, the prince whose memories enter the cobbler's body is the prince, because the person goes where the psychology goes.

Locke's view faces the circularity objection, raised by Joseph Butler: memory presupposes identity, since to genuinely remember an experience is already to have been the one who had it, so memory cannot define identity without circularity. Thomas Reid's brave-officer case adds a transitivity problem: an old general remembers being a young officer, who remembered being a flogged boy, but the general does not remember being the boy, so identity comes out both holding and not holding. Modern psychological theorists answer by appealing to overlapping chains of psychological connectedness rather than direct memory.

The no-self view and Parfit

David Hume denied there is any enduring self to be found. Introspection reveals only a bundle of perceptions in constant flux, never a simple self that has them. Derek Parfit developed this into an influential modern position: what matters in survival is not identity, a yes-or-no relation, but psychological continuity and connectedness, which come in degrees. In a teleporter case that creates an exact replica while destroying the original, Parfit argues the question whether the replica is really you may have no determinate answer, and that identity is not what we should care about anyway.

Evaluation

The standard method is to test each theory against puzzle cases and see which best preserves our considered judgements while remaining coherent. The bodily theory is concrete but clashes with the strong intuition that we follow our minds. The psychological theory honours that intuition but faces circularity, transitivity and duplication problems. Parfit's reductionism handles the puzzle cases elegantly but at the cost of the deeply held belief that there is a determinate fact about whether you survive. A good answer recognises that the puzzle cases may be revealing the limits of the concept of identity itself rather than simply deciding between theories.