The most persistent objection to Locke is that memory seems too narrow to do the work assigned to it. Joseph Butler, in his 1736 essay “Of Personal Identity,” presses a devastating point: memory presupposes identity rather than constituting it. I can remember only if I am already the one who had the earlier experience. So if identity rests on memory, and memory rests on identity, the theory appears circular. Locke had tried to ground personhood in consciousness, but Butler insists that consciousness is a mode of relation to oneself, not the ultimate ground of sameness.
This objection has bite because it preserves what Locke wanted to explain while denying his analysis of it. In ordinary life, we do not treat memory as a magical bridge that creates the past; we treat it as access to a past already ours. Butler’s challenge therefore protects common sense. But it also raises a deeper issue: if identity cannot be analyzed through memory, what can explain our strongest sense of ownership over the past?
A second line of critique comes from Thomas Reid, whose “Brave Officer” example shows how memory can be transitive without identity being transitive in the way Locke needs. The boy is flogged, the young officer remembers the flogging, and the old general remembers the battle. Yet if the old general no longer remembers the flogging directly, Locke’s criterion seems to imply that the general is not the same person as the boy, even though he is linked through a chain of remembered experience. The example is elegant because it exploits a familiar fact: memory can be partial and overlapping while life remains continuous.
Reid’s point exposes a weakness in any strict memory criterion. If identity requires direct memory, it excludes too much. If it allows indirect links, it begins to look like psychological continuity more broadly, not memory alone. That is one reason later theories shift from episodic recollection to overlapping chains of mental connection. The critic is not merely being pedantic; he is showing that the self is not recovered by a single bright line.
A third challenge comes from the possibility of duplication, later dramatized in modern thought experiments. Suppose my psychological life could be copied into two future beings, each equally continuous with me. Locke’s framework, taken literally, has trouble saying which is me, or whether both are. Identity, after all, is one-to-one. But psychological continuity can branch. The theory then seems to fit survival only in cases where no branching occurs, which is a severe limitation once we imagine advanced technologies or divided mental states.
This is not merely science fiction. Split-brain cases in neuroscience raise related worries about whether unified consciousness is as simple as common sense suggests. If a single organism can exhibit partially independent streams of awareness, then the relation between consciousness and personhood is less tidy than Locke hoped. The body may stay one; the person may not. Yet if personhood can divide, then perhaps the criteria of identity must be plural rather than singular.
The bodily and animalist objection is even more straightforward. On this view, developed in various forms by later philosophers, a person just is a human animal, and the persistence of the person is the persistence of the organism. This avoids the puzzles of memory loss and duplication by placing identity where biology places it. It also better matches our everyday practice of tracking people by bodies, names, and legal records. The cost is that it seems to ignore the intuition that what matters in survival is not merely that this animal continues, but that consciousness continues.
The tension here is sharp. If I wake after total amnesia in the same body, most of us feel that some important continuity remains, yet not enough perhaps for the full moral weight of my past. If, conversely, my memories and character were transferred elsewhere, many would hesitate to call that survival even if psychology seemed preserved. The debate survives because each side captures something true and leaves something out.
Locke’s account also strains under the weight of ethical practice. Courts and communities often hold people responsible not only for what they explicitly remember, but for what they have done, endorsed, or become. Habit, character, and social role matter. A purely episodic model of selfhood can make the person look too fragmentary to sustain the continuity that moral life requires. At the same time, a purely bodily model can make responsibility too crude, as if the flesh itself could deserve blame.
This is where the philosophical debate becomes humanly costly. If personal identity is too thin, responsibility may dissolve; if it is too thick, we may punish the wrong subject. Dementia, severe trauma, and coma sharpen the pain of the issue. The question is not academic when a family asks whether the person they love is still there. A theory that handles teletransportation but cannot speak to grief has not solved the problem; it has only moved it.
The strongest defenders of Locke respond by broadening the idea of psychological continuity or by separating strict identity from what matters in survival. But that move itself concedes an important point: perhaps sameness of person and concern for one’s future are not identical questions. The theory is tested most severely when we realize that survival may come in degrees, while identity, if it holds at all, does not. That pressure opens the way to a new phase of the debate.
Once the classical objections have done their work, the question is no longer whether personal identity has a single essence. It is whether the puzzle itself has taught us to think differently about what a person is.