Locke's memory theory has real philosophical power. It explains our moral and legal practices: we punish people for crimes they remember committing because they identify with the self who committed them. We don't punish someone who genuinely cannot remember, through amnesia or radical psychological change, because the connection that grounds responsibility is severed. It also explains the phenomenology of personal identity: the sense that you are the one who had those experiences in childhood is constituted by memory-access, not by any mystical soul-substance.
But the theory faces several powerful objections.
Thomas Reid's Brave Officer paradox (1786): An old general remembers, as a young officer, receiving a medal for bravery. But as a young officer, he remembered being flogged as a boy for stealing from an orchard. By the time he is an old general, he has entirely forgotten the flogging. Therefore:
- The old general is the same person as the young officer (by memory)
- The young officer is the same person as the boy (by memory)
- But the old general is not the same person as the boy (no memory)
This violates the transitivity of identity: if A=B and B=C, then A=C. Locke's memory theory violates this basic logical property.
The response is to invoke overlapping chains of memory (a refinement by later philosophers like Sydney Shoemaker): identity is constituted not by direct memory but by overlapping chains of psychological connectedness, each stage remembers enough of the previous stage, even if the first and last stages share no direct memory. But this raises new questions about how much overlap is required, and whether identity is really a matter of degree.
Circularity: Locke says personal identity consists in memory. But memory is always memory as oneself, when you remember running as a child, you remember yourself running, not just that some child ran. So memory already presupposes personal identity in its very structure. The identity explains the memory; the memory can't therefore explain the identity without circularity.
The self-continuity problem: Locke's theory requires that only memories of your own first-person experiences constitute your identity. But what about personality, character, values, skills, all the things that make you recognizably you, which are not explicitly remembered experiences but deeply embedded dispositions? Derek Parfit's later work (Reasons and Persons, 1984) extended Locke's framework to include all forms of psychological continuity: not just memory but continuity of beliefs, desires, intentions, and character. Parfit's radical conclusion: personal identity is not what matters. What matters is psychological continuity, and that is a matter of degree, not all-or-nothing. The question "is this the same person?" is no more deep than the question "is this the same nation?", it is a question about how to apply a concept, not a discovery about metaphysical fact.
Parfit's view leads to a startling ethical consequence: if you are not a separate, discrete entity persisting through time but rather a series of overlapping psychological states, then the special concern you have for your future self loses some of its special status, your future self is no more intimately connected to you than a very close friend. This has implications for personal prudence, for how we think about long-term obligations, and, Parfit argued, for our duties to future generations.