Monday, January 15, 2024

Phil 417 - Personal Identity

 Questions on Personal Identity

In our modern society, many transactions are based on an individual’s identity. To apply for a car loan, one must provide a social security number, date of birth, mailing address, and other bits of data, all to indicate the identity of a person. Unfortunately, a person’s identity could be stolen and while the actual person would not open a credit line at the local Best Buy, someone else with that data actually could and could commit theft. As frustrating as this can be to a person, other people suffer from a different identity crisis in the form of dissociative identity disorder (DID), which is defined as a person whose identity is disrupted by “two or more distinct personality states” (American Psychiatric Association, 2022, p. 330). One of the most vivid examples of someone who experienced DID was Chris Sizemore, who possessed over twenty different personalities throughout her life (Costner Sizemore & Huber, 1988). These personalities were so fundamentally different from each other that they had differing IQs, tastes, mannerisms, memories, and even religions. After resolving these personalities into a unified self, in a question-and-answer session she said of herself, “On an intellectual level, I am fully aware that I am all of these personalities and that they are me, but on an emotional level, it is as though 22 women used my body for a period of 40 years” (p 59).

What are we to make of these examples of identity? When each of us is asked the question, “Who are you?” how are we to respond? On what basis can we answer such a seemingly basic question, when we are confronted with bewildering examples of people who suffer from mental disorders such as DID? Is our identity related to our body, our memories, our experiences, our survival, or other things? While there are many theories on personal identity, this paper will only review a handful: physical persistence, psychological continuity, and what ultimately matters (Olsen, 2002). After reviewing a few theories, I’ll discuss my opinions on the subject and conclude that there may not be a problem or definition of personal identity, but rather the idea of a personal identity does not exist, or at the very least, there is no simple, straight-forward essence of personal identity.

Physical Persistence

Perhaps the simplest theory of personal identity is to plainly state a person is their body. Certainly, a person is conceived, grouped as cells into an organism, is born and continues to grow and evolve, and then dies. As long as the body is viable, the person’s identity is tied to that body until death, upon which the identity ceases to exist as well. A. J. Ayer asserts this point in his book Language, Truth and Logic (2001), by contending a person may survive a loss of memory or even experience a change in character and survive as the same person, but if he were to lose his body to death, it would be a contradiction to state he survived his death. In sum, Ayer and others who hold to the physical persistence theory of personal identity would state that the defining, consistent feature of a person’s identity is the body. Ayer would state that Chris Sizemore is not multiple identities, but one.

However, while Ayer states that surviving one’s death is contradictory, there is some evidence supporting the claim that an identity does survive a bodily death. Since many have discounted the idea of reincarnation, one doctor decided to apply strict scientific methods to determine the validity of claims of an identity surviving death. Through the course of his lifetime and career, Dr. Ian Stevenson racked up roughly 3000 detailed cases of people who possessed evidence that they had lived a previous life and thus survived death (Bering, 2013). His most detailed work is captured in his book describing cases and analyses of children who make claims of living a previous life (Stevenson, 2016). The common theme in many of these cases is that an identity of a person indeed survives death and lives on in another body. While there is no explanation for how this is possible, there is evidence it does occur.

Psychological Continuity

Another theory of personal identity relates to a person’s ability to retain a memory from moment to moment. As a person is born, grows and experiences life, assuming they have a working memory, they collect sensual and mental states of mind. And while a person’s environment and circumstances and judgements change from moment to moment, there is a causal link between their mental states, such that they are able to have a continuous psychological identity (Olsen, 2002).

To make this theory even clearer, Sydney Shoemaker (2004) proposed a thought experiment in which two people, named Brown and Robinson, underwent operations for brain tumor removals, in which the entire brain of each patient had to be removed from the skull. However, when the time came to re-insert the patients’ brains, by a procedural error, Brown’s brain was placed in Robinson’s skull. The resulting person was dubbed Brownson and retained all of Brown’s memories and mental, psychological states. Upon waking from the surgery, Brown would continue to be Brown. As long as there remains a causal link from one moment to the next, the personal identity of an individual is retained.

Olsen (2002) wonders if personal identity is retained if this thought experiment were slightly changed. Instead of moving the physical brain plus its contents from one skull to another, what if only the mental contents of person 1 were copied, like bits of data, into the brain of person 2 and the original mental contents of person 2 were erased - would this retain the qualifications of psychological continuity? The neural links and aspects of the physical brain would be the same from one moment to the next, but only the mental contents would be different. Interestingly, Olsen notes that some psychological continuity theorists say yes, while others say no. This gray area in the psychological continuity theory leads to a related concern for personal identity: personal survival.

What Matters

One dissertation took a deeper dive into personal identity by reviewing Derek Parfit’s work on this topic. Gromak (2015) summarizes Parfit’s theory by stating identity is not what truly matters, but rather what the individual deeply and ultimately cares about is what matters. More specifically, while Parfit’s theory states that identity does matter to some extent, what genuinely matters for an individual is psychological continuity and connectedness (p. 100). In other words, an individual’s ultimate concern is to simply persist and continue in some form or fashion.

Gromak covers many variations of thought experiments in his paper, but there is one that seems to grasp the subtle nuance of the matter regarding a choice an individual could make about remaining a specific identity or persisting in some form or fashion. A person steps into a machine, pushes a button, after which the machine scans him and creates a replica. During the process, the original person’s heart is damaged and will die in a few days, while the replica version lives. Gromak further elaborates on this thought experiment by changing one factor: the original person will live for 10 years, while the replica version will live for 11 years. In this case, Gromak contends the rational choice is to not push the button and remain as that identity, but Parfit would contend the rational choice is to push the button, die after 10 years, and persist in the replica for an additional year, thus placing emphasis on what truly matters: survival.

Discussion on Personal Identity

Besides those reviewed in this essay, there are many other questions and possible answers surrounding personal identity. As such, I do not think personal identity can be reduced to one or a few factors such as physical persistence or some aspect of psychological continuity. It seems as if every attempt to define personal identity is met with some challenge and therefore perhaps personal identity is undefinable, or perhaps “there are no philosophical problems about identity” (Noonan & Curtis, 2004). An individual person is not an island. He is born into a network, community and social structure. Most people live in an interconnected society and complex ecosystem. To attempt to define the essence of a personal identity is to ignore hundreds, if not thousands of other variables which could define who a person is. While not in the analytical philosophical realm, Buddhism goes so far as to state there is no self and no identity (see section on Non-Self in Siderits, 2011).

If I were to attempt some definition of personal identity, I would argue that every human being is unique and connected with others and his environment at the same time. The thousands of variables that constitute an identity of a person would not be the same from one identity to another. For example, the physical persistence and/or a causal link of psychological continuity of a person could apply and be one or two of the variables in defining personal identity, or not. I would even contend there could be overlapping factors of identities which could account for multiple personalities and reincarnation, which further underscores that personal identity is difficult to reduce to one or two factors.

In sum, while the physical persistence and psychological continuity explanations have merit, I don’t think either one adequately explains any essence of personal identity. I tend to lean towards the concept of a person simply being a part of a whole, not dissimilar to how an aspen tree is a part of a grove; and even that analogy is somewhat inadequate.


In conclusion, this essay briefly reviewed three considerations regarding personal identity: physical persistence, psychological continuity, and the idea that what truly matters is not personal identity, but that a person persists in some form or fashion. While I find these ideas useful in exploring the topic, I lean towards the idea that there is no philosophical problem to solve with personal identity, and if there could be an answer, no definitive, single essence of personal identity could be denoted. 


American Psychiatric Association. (2022). Diagnostic and statistical manual of mental disorders, text revision DSM-5-TR. (5th ed.). American Psychiatric Association

Ayer, A. J. (2001). Language, Truth And Logic. (eBook). Penguin Books. (Original work published 1936)

Bering, J. (2013, November 2). Ian Stevenson’s Case for the Afterlife: Are We “Skeptics” Really Just Cynics? Scientific American Blog Network. 

Costner Sizemore, C., & Huber, R. J. (1988). The Twenty-Two Faces of Eve. Individual Psychology, 44(1), 53-.

Gromak, J. A. (2015). Personal identity, survival and what matters. ProQuest Dissertations Publishing.

Olson, E. T. (2002, August 20). Personal Identity (Stanford Encyclopedia of Philosophy).

Noonan, H., & Curtis, B. (2004, December 15). Identity (Stanford Encyclopedia of Philosophy).  

Shoemaker, S. (2004). Brown-Brownson Revisited. The Monist, 87(4), 573–593.

Siderits, M. (2011). Buddha (Stanford Encyclopedia of Philosophy). 

Stevenson, I. (2016). Children Who Remember Previous Lives. McFarland.

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