Personal identity asks what makes a person at one time the same person at another time. This essay will compare Parfit’s psychological continuity theory with Shoemaker’s account of personal identity. I will argue that Shoemaker is more convincing because, while Parfit explains survival and psychological concern well, he inherently weakens the concept of personal identity. Shoemaker provides the stronger view because he preserves psychological continuity while also explaining memory, non-branching identity, and moral responsibility more securely.
Parfit’s theory is first of all reductionist; he rejects the idea that there must be an immaterial soul or metaphysical substance that makes one identical with the future self, and personal identity consists in more basic psychological and physical facts. He argues the two thing that links a person’s life is psychological connectedness and continuity. Psychological connectedness refers to direct mental links, such as memory, belief, character, or desire of a person. Psychological continuity refers to overlapping chains of such connections over time. Parfit defines this as “Relation R”, meaning the psychological connectedness and continuity with the right kind of causal relation. Parfit’s thought experiment of fission illustrates this view. Suppose one person’s brain is divided, and each hemisphere is transplanted into a different body. Both future people are psychologically continuous with the original person, because they remember his life, continue his projects, and possess his character. However, the original person cannot be numerically identical with both future people, because identity is one-one. Identity is also transitive, meaning that if A is identical with B and A is identical with C, then B must be identical with C. But the two future persons are clearly distinct. Parfit concludes that identity is not what matters in this case. Even if strict identity fails, the original person may still survive in the sense that matters, because Relation R continues. Thus, Parfit makes a clear distinction between survival and numerical identity. Parfit therefore argues that personal identity is less important than we normally believe.
The first weakness of Parfit’s theory equivocation, because h changes the subject from identity to survival. The question of personal identity asks what makes one person the same person over time. Parfit’s answer is that sameness may not matter as long as psychological continuity continues, but this means his theory becomes less an account of identity and more an account of what we should care about. This is especially problematic because numerical identity cannot simply replace our intuitions of psychological importance. Saying that two future people are both psychologically continuous with me does not answer whether either of them is me. Therefore, Parfit’s theory is weaker as a direct answer to the metaphysical question of personal identity.
The second weakness is that Parfit’s theory makes identity too dependent on degree. Psychological connectedness is rather vague in its strength: I remember what happened yesterday clearly, childhood memories faintly, and infant experiences not at all. My desires, values, and character also change greatly as I grow up and become more mature. Parfit partly explains this by saying that connectedness comes in degrees, but personal identity does not work in exactly the same way. In ordinary life, I am either numerically the same person who made a promise yesterday, or I am not. If identity is reduced to gradual psychological relations, it becomes unclear when identity begins or ends. This creates vagueness in cases where practical and moral judgment require clearer criteria.
The third weakness is that Parfit’s theory struggles to preserve moral responsibility. Responsibility depends on whether the person now is the same agent who acted in the past. If a person commits a crime, regrets a past action, or keeps a promise, we assume diachronic identity: the same person persists through time. Parfit can say that responsibility follows psychological connectedness, but this makes responsibility a matter of degree. A person with weak memory or a transformed character might become less connected with their past self, yet we would not usually say they are literally a different person. Therefore, Parfit’s view risks weakening the basis of forensic identity, which makes it difficult for laws to praise or punish an individual.
On the other hand, Shoemaker’s account also begins from a similar rejection of a purely bodily theory, believing that psychological continuity is central to personal identity. He imagines that if Brown’s brain is transplanted into Robinson’s body, and the resulting person has Brown’s memories, beliefs, character, and intentions, we are inclined to say that Brown survives in Robinson’s body. This suggests that personal identity follows psychological continuity rather than bodily sameness. Shoemaker further defines a quasi-memory to distinguish the right kind of causal continuity between mental states. Locke’s identity theory says that I am the same person as a past person if I remember that person’s experiences. However, this faces a circularity objection: if I assume that past memories belong to me, then I am already presupposing that I am identical to the past self, because I can only truly remember doing something if I was the one who did it. Therefore, memory cannot define identity. Shoemaker solves this problem by introducing quasi-memory, which has the same internal character as memory and is caused in the right way by a past experience, but does not logically presuppose that the rememberer is identical with the original experiencer. This allows Shoemaker to use memory-like psychological continuity as evidence for identity without arguing in a circle.
Shoemaker’s first strength is that he gives a more precise account of why memory matters. This directly answers a weakness in Parfit. Parfit treats memory as one part of psychological connectedness, but his reductionism makes memory mainly one relation among many. Shoemaker, by contrast, explains the special role of first-person memory in personal identity. Quasi-memory shows how a present person can be linked to a past experience through the right causal relation without already assuming identity. This is a unique strength because it avoids both extremes: it does not reduce identity to mere bodily sameness, but it also does not dissolve identity into loose psychological resemblance. It explains why genuine memory-like continuity supports identity, while false memory, delusion, or accidental similarity does not.
Shoemaker’s second strength is that his theory preserves the logical structure of numerical identity better than Parfit’s. Parfit’s fission case is powerful because it shows that psychological continuity can branch. While Parfit responds by saying identity is not what matters, Shoemaker’s approach is stronger because it can accept that branching cases create a failure or indeterminacy of identity without abandoning identity itself. Since numerical identity must be one-one, a theory of personal identity should not allow one original person to become two numerically identical future persons. Shoemaker’s account is therefore more logically disciplined, as it treats non-branching causal psychological continuity as crucial.
Shoemaker’s third strength is that his account better supports moral responsibility and practical self-concern. Parfit’s theory shows that we care about future psychological continuers. However, responsibility requires more than survival-like continuity. Shoemaker can explain why a later person is responsible for an earlier action: the later person is connected to the earlier agent through the right causal chain of memory, intention, character, and agency. This makes responsibility neither purely bodily nor merely a matter of similarity. It also avoids making responsibility too vague. For example, even if I forget some details of a promise, I may still be the same person because enough of my agency and psychological structure continues. Shoemaker therefore gives a more stable foundation for ordinary practices of blame, regret, punishment, and commitment.
In conclusion, Shoemaker’s account is more convincing than Parfit’s to a large extent. Although Parfit offers a powerful reductionist theory that explains psychological survival and challenges the assumption that identity is always what matters, his view has three major weaknesses. Shoemaker avoids these problems by using quasi-memory to solve the circularity problem, preserving the one-one structure of numerical identity, and grounding responsibility in causal psychological continuity.