Indiana University Bloomington

The Physicality of Psychology 
in Personal Identity

John Grady

Written for PHIL-P300


Throughout the discussion on the nature of personal identity, many arguments have been made as to the conditions necessary to confirm its presence. These arguments tend to circulate around the idea that personal identity is associated with either a continuity of psychology or body. In the dialogue of Identity, bodily and psychological conditions for continuity of identity seem to be considered as two separate criteria. I would suggest, however, that while psychological continuity in some form is what we seem to see as important in reference to sameness of person, that it is purely derived from bodily continuity. In the intent to measure personal identity through psychology, we are in actuality mistaking psychological continuity for symptoms of a specific form of physical continuity as evidence by the direct interactions between the state of the body and state of mind. I think it is not only possible, but pertinent and necessary to describe psychological continuity as a facet and subset of bodily continuity rather than as a separate and competing criteria.

History of the Discussion

In order to fully understand the gravity of this assertion, one must first understand the background on which this assertion rests as a destination cannot be fully comprehended without understanding the starting point.

The history of modern ideas on the nature of Personal Identity can be said to start with John Locke’s essay, “Of Identity and Diversity”. This would become the groundwork for the conversation on identity of what it takes for personhood to exist and be sustained over the course of time. In his essay, he asserts what he believes to be sufficient for objects to be identical over time, be it inanimate matter, unthinking organisms, animals, or humans. He is also the first to make use of concepts of body, mind, the thinking substance, and consciousness. Locke’s essay stands as an attempt to quantify personhood and the requirements for personal identity over time. Locke himself asserts that personal identity consist in consciousness, but the benchmark set through his work would give rise to a much larger dialogue on the subject. The development of the discussion will be broken down by criteria for personal identity, their history, evolution, and problems each face.

Consciousness, Memory, and Psychological Continuity

The concept of psychological continuity as a criterion for personal identity is an extension of John Locke’s original criteria for personal identity. This is the belief that sameness of conscious psychological experience is what is necessary and sufficient for sameness of person over time. It can be reduced roughly to the idea that personhood can be extended only into areas that one can remember. According to these views, if I cannot remember past actions or experiences as my own, then I am not the person who did or experienced those things. Problems arise with this criterion for personal identity in the way of circularity; consciousness presupposes personal identity and seems to demonstrate self-affirming characteristics as a result. The following statement is an example of this issue:

“I am the same person if and only if I can [remember/be conscious/conceive] of past actions as my own”

The problems of circularity lie in the fact that this statement necessitates the existence of personal identity even before it requires memory or consciousness to confirm its presence. By asserting that “I” am the same person as “I” was if “I” can conceive of “my” past actions, we are making personal identity the metric of itself rather than consciousness or memory. Many have addressed this circularity by asserting causal relationship between past and future selves:

“I am the same person if and only if my [memory/ consciousness/ conception] of past actions creates a causal relation between my current self and a past entity”

Or even, famously, by attempting to remove the idea of “self,” and the concept of identity entirely, from the very act of consciousness and memory as Derek Parfit did in his essay, “Personal Identity.” Parfit uses memory in a way that forgoes the assumption that one’s memories belong to their own experience in an attempt to break the circularity inherent in memory based criteria for personal identity called q-memory. His assertion is as follows:

I have a belief that possesses the following characteristics (q-memory):

  • The belief feels like a memory
  • Somebody (not necessarily the person recalling the event) experienced the event that the belief is related to
  • This belief was directly caused by the brain storing information of the experience

I am the same person if and only if my q-memory of an event connects my current self to a past entity.

The practical outcome of this is that Parfit has created a criteria for personal identity through psychological continuity that does not fall prey to circularity by removing the self as the entity that must have experienced and remembered past events recalled by the consciousness.

Physical Continuity as Criteria for Personal Identity

Physical continuity as criteria for personal identity also stems fundamentally from John Locke’s ideas on what it means for an object, animal, or man to be the same over time. Very simply, an object is the same if it composed of the exact amount and arrangement of matter over time. Plants and animal (and subsequently humans) can lose and gain matter constantly over the course of their lifetime, but so long as the movement of matter supports the existence of a single organism, it can be considered to be the same over time. In short:

 “I am the same person over time if there is a continuity of organism”

This view is known as Animalism and is the idea that people are entirely constituted by their bodies. It is controversial within the philosophical community and is widely criticized on the grounds that, according to this simple model of personal identity, a person should be considered to remain with their body in situations where the brain is removed or transplanted. Despite this, its simplicity and accurate real-world applicability make it an attractive perspective for many.

More specific views of physical continuity tend to revolve around the brain. These ideas reason that the brain is particular facet of the body that effects personal identity. To some, this idea seems more intuitive than brute-animalism as it places more weight on the fact that not all matter in body is equally important to continuity of identity. In fact, most theories of brain-based bodily continuity even disregard the rest of the body entirely, asserting:

 “I am the same person over time if there is a continuity of brain”

This, much like brute-animalism, serves to create simple and easily analyzable criteria for personal identity, but this view suffers much in the same way that views of psychological continuity does in that it can be argued that continuity of the brain does not necessarily encompass everything that we care about in terms of persons or identity. For example, an opponent of brain-based bodily continuity might suggest that in the case of two individuals switching brains, an individual’s loved ones might experience hardship and confusion dealing with the this event. Important aspects of a person they care about have been divided, separated, and diluted by aspects of a separate identity (in this case, mind and body) and, as a result, it is unclear how one should logically feel or react in this situation, showing that there may be something more at play than what brain-based bodily continuity theories can account for.

The Interactions Between Body and Mind

The general dialogue between these two criteria for personal identity tends to form a pattern of proponents of one school of thought claiming that the other is unable to encompass the full scope of the issue. In light of the large amount of logical insight given by each side, it would seem to make it very difficult to definitively claim that any theory of bodily or psychological continuity is sufficient to accurately represent the behavior of personal identity. This leads many to suggest that each are inaccurate and do not effectively describe what it means to be the same person over time, and that personal identity is ultimate and unanalyzable. While I think it is correct to say that neither of these views adequately represent the solution to the questions that personal identity presents, I also don’t believe that both are wrong. In fact, I would argue, despite the seemingly contradictory dialogue, that each of these views is, to an extent, correct. The only thing they are missing is each other.

As a result of this view of mind-body connectedness, we must assume, if there is nothing outside of the realm of the body and resultant psychology that is important to us in terms of personal identity, that the body encompasses all that we should be concerned with. We must then come to the conclusion that having the same body is necessary and sufficient for sameness of person. To assert this connectedness and its implications, we will observe a series of cases in which the body can be said to comprise and have an effect on areas of concern in views of psychological continuity.


Starting on a relatively small scale, the first case examined will be that of hormones. Hormones are chemicals that the body excretes internally into the blood stream in response to changing environments. This can be due to exposure to stress, temperature, or even diet. These chemicals flow throughout the circulatory system causing change all over the body. One organ that is affected by this system is the brain. The presence of certain chemicals amongst the nerve cells causes alteration in circuitry and even structure of the brain with extremely consistent effects. It has been observed that the release of these chemicals into the body can exhibit a change on the brain and psychology. For example, sex stimulating hormones FSH and LH show comprehensive effects on many aspects of mental states, such as attention, motor control, mood, and memory. This would seem to confirm the statement that there is, in fact, a relationship present between alterations of psychology and alteration of body, specifically alteration of the brain. Furthermore, it would seem that alteration of brain and brain function result in alterations in psychology. Because of this, we must reason that psychological aspects of person such as consciousness and memory can be altered through physical changes in the body.

External Substances

Having examined a situation in which the body is internally influenced by chemicals, let us shift focus to external influence from chemicals as a parallel event. The mechanisms of change in this case will not be drastically changed from the last involving hormones. External chemicals influence the body and brain in much the same way, but what will be a notable difference in this example will be the scope and intensity of alterations to psychology and mental states.

A commonly understood example in this case are the effects of alcohol on the body, brain, and mind. The consumption of alcohol results in a physiological state known as drunkenness. This is primarily a result of the depressive effects that ethanol exhibits on the central nervous system and causes progressive impairment in motor function, coordination, balance, decision making ability, and even memory and consciousness of action. These are important examples because, under a strict psychological criteria for personal identity, this change of body has the capacity to erase continuity of memory and consciousness. This would be sufficient to deem the sober and drunk person as distinct individuals, but I think this brings up some complications in what we deem the drunk and sober person responsible for in this case. Should the sober man be held accountable for an assault he committed or a traffic collision the drunk man caused if he is “not the same person,” but share a body? By understanding this change in psychological continuity to be linked to a change in the brain, however, we see the advantages of a criteria for personal identity that parallels the body. Because he is the same organism (albeit one with a slightly altered physiology) we must say that the sober man and the drunk man are the same person regardless of the lack of memory or consciousness connecting the two.

Medicinal Physical Alteration

Both previous mechanisms of internal and external chemical alteration of the mind are what could be called indirect means of investigating the relationship between mind and body. They make good case studies for their commonality and applicability to real-world situations, but to truly observe the relationship in its most basic form, attention must be payed to the unusual circumstances that surround direct alterations to the brain. For this example, we look to Laura Klaming and Pim Haselager’s essay on neuroethics, “Did My Brain Implant Make Me Do It? Questions Raised by DBS Regarding Psychological Continuity, Responsibility for Action and Mental Competence.” In their work, the authors examine a medical procedure meant to treat patients suffering from a handful of neurological or psychiatric conditions through a procedure known as Deep Brain Stimulus. DBS is a non-invasive method of disabling parts of the brain without needing to physically destroy them in order to treat diseases derived from degradation of the brain. This is accomplished by applying small shocks to localized areas in the brain. It has proven markedly effective in many areas including treatment of alcohol dependency and reduction of aggressive behavior, but has occasionally shown complex side effects in some patients, significantly altering their psychology. The authors seek to examine “whether the use of DBS does, or could under certain circumstances, affect the psychological continuity standardly taken to be characteristic of personal identity.” They attempt this through the case study of a Tourette’s syndrome patient treated with DBS.

At the age of 43, an individual suffering from uncontrollable tics began DBS treatment as a last resort for his Tourette’s syndrome. The treatment was administered incrementally over a 12 month period. Eventually though, with increased intensity of stimulation, the patient began to develop a dissociative response to the treatment. This offered the treating physicians a unique opportunity to observe the correlation between the amplitude of cranial stimulation and extent of the patient’s dissociative episodes. What was discovered was that as the amplitude of brain stimulation was increased, the patient was reduced to a state of irrational fear and childish disposition. He would hide in the corner of the hospital room, speaking nonsensically in a childish pitch, and even violently kick and resist if approached by the physicians. As soon as the amplitude of the treatment was reduced or removed, he would revert to his traditionally characteristic behavior, but would report having being overcome by negative childhood memories. What the physicians were observing in this reaction could be said to be nothing other than the neurological basis of psychology. Obviously this man’s character and personality are important to us and if for some reason this patients mind were to become stuck as that of a terrified child, we would consider it a tragedy. But do we then treat this 43 year old man as a child? Ethically, I feel that to do so is to ignore his dignity as an elder and a human being. After all, this change was only brought about by a fairly small physical alteration to the organ is responsible for creating his experience. The actual physical change could certainly be said to be less severe than, say, losing a limb, and I don’t think this change in body (even taking into the account the drastic change in mental state) is sufficient to assert a change in this person’s identity. This would also extend to individuals suffering from conditions that severely affect memory and even those in vegetative states. Although their mind may not be connected to their past, either in part or in whole, their loved ones still care about them. We have laws in place to protect them, and we continue to treat them with the respect we afford to those who have these faculties. I believe the reason for this is because we do hold a fundamental belief that identity follows the body in some regard.

Real-World Examples

The cases we have observed so far have gradually progressed our question on the nature of the relationship between bodily and psychological continuity. With hormones, we establish that there is, in fact, a relationship between the states of the body and states of mind. With alcohol and external chemicals, we find that the body-mind relationship is something that we can influence externally, and that the path of influence seems to be primarily body to psychology rather than psychology to body, or bidirectional. Cases of Deep Brain Stimulus further confirm the nature of the aforementioned relationship by explicitly altering the brain to the effect of a direct change in psychology and psychological continuity. This also shows us that it must be the brain that is responsible for the creation of the experience of consciousness. All these cases are clinical in nature for the purpose of establishing a base of understanding through a logical progression, but now that the thesis has been established, we can examine many real world examples that support our model that psychology is influenced by the body.

For this purpose, we shall examine the bizarre case of Phineas Gage. 25 years old at the time of the incident, Gage was a foreman managing the construction of a railway in the UK. On the 21st of September, 1848, he was packing clay into a blasting site with an iron rod to concentrate the force of a future demolition when the powder ignited, causing an explosion. The premature detonation took the rod into the left side of Gage’s face, up and behind his left eye, and out the top of his cranium. Far from being killed, Gage didn’t even lose consciousness from the incident and, after a lengthy stay at a hospital, even recovered enough to return to work after losing at least a teacup’s worth of brain matter from his prefrontal cortex. During his recovery, however, complications began to arise. A former favorite among his peers, Phineas suffered significant character alterations as result of the accident. Once a hardworking and interpersonal employee, Phineas had undergone a transformation to a much more profane, impulsive, and irreverent, shadow of his past self to the point that his employers were unable to allow him to maintain his position as Forman. His physician wrote this on Gage following his return to health:

The equilibrium or balance, so to speak, between his intellectual faculties and animal propensities, seems to have been destroyed. He is fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom), manifesting but little deference for his fellows, impatient of restraint or advice when it conflicts with his desires, at times pertinaciously obstinate, yet capricious and vacillating, devising many plans of future operation, which are no sooner arranged than they are abandoned in turn for others appearing more feasible. A child in his intellectual capacity and manifestations, he has the animal passions of a strong man. Previous to his injury, though untrained in the schools, he possessed a well-balanced mind, and was looked upon by those who knew him as a shrewd, smart business man, very energetic and persistent in executing all his plans of operation. In this regard his mind was radically changed, so decidedly that his friends and acquaintances said he was “no longer Gage.”

This is a popular case in the discussion of psychology as a facet of the physical realm, but its infamy tends to obscure the fact that there exist so many parallel situations. While they may not all include a tamping-rod lobotomy, what Neuroscientist David Eagleman describes as “nature’s tragic experiments” are great in number. Over the past 143 years, we have observed degeneration, strokes, and tumors change persons on fundamental levels all over the world. After noting these cases and their importance to our understanding of people, David has this to say on the brain and mind:

“The brain is a system whose operation is governed by the laws of chemistry and physics—with the end result that all of your thoughts, emotions, and decisions are produced by natural reactions following local laws to lowest potential energy. We are our brain and its chemicals, and any dialing of the knobs of your neural system changes who you are…”

“Consider the powerful effects of the small molecules we call narcotics. These molecules alter consciousness, affect cognition, and navigate behavior. We are slave to these molecules. Tobacco, alcohol, and cocaine are self-administered universally for the purpose of mood changing. If we knew nothing else about neurobiology, the mere existence of narcotics would give us all the evidence we require that our behavior and psychology can be commandeered at the molecular level.”

If anything can be said for these cases it is certainly that psychology seems to exist as a symptom of the brain and body. This would initially appear to support ideas of animalism in which persons are considered entirely their bodies, and while theories of mind-body connectedness would agree, animalism does not account for the importance that we also place on psychology. We care, I think, deeply about psychological continuity. It is why it’s loss in situations like Phineas Gage’s and patients of Alzheimer’s are mourned among loved ones and not dismissed as simply arbitrary changes of arbitrary and unimportant component of personhood. I would say that the importance we place on psychological continuity is the very reason why we seek so fervently to treat brain disease and conditions. But where brute animalism would disregard the importance we place in continuity of mind, views of pure psychological continuity would take that importance to the extent that we lose sight of other aspects that we see as contributing to personhood. The theory of mind-body connectedness, however, finds a suitable middle ground between these two by describing the vital cooperation and relations that they hold to one another.

Objections and Problems in Application

The Richness of the Human Experience

The middle ground created by this relation may still leave something to be desired among those that see psychological continuity as something that cannot be reduced to such base origins. Marya Schechtman, for example, writes in her essay, “Personhood and Personal Identity,” against Parfit and his ideas of q-memories. She claims that to reflect on a memory and remove the concept of self from it is impossible as there is a certain richness of experience that accompanies recollection of lived events. Schechtman might also say that reductionist views of psychological continuity such as we have created here are unable to account for the rich and full nature of experience, and she would be right in a sense. Neuroscience can’t account for the complexity and depth of the human experience. But by recognizing both its existence and its origin, I think the mind-body connectedness view comes closer than any other criteria for personal identity to accounting for it.

When psychology is reduced to a byproduct of the makeup of the body, it is easy to jump to the conclusion that the body is all that matters to us in the realm of personhood. One might argue that we don’t interact with a brain or a body, we interact with a person. That is to say, we interact with their character and memories and experience, but if all these things are produced directly by the brain, even if we can’t quantify how they are produced, aren’t we, in a way, interacting with both? Yes, there is a certain intangibility in the realm of human experience that cannot be explained by a reductionist point of view, but reductionism certainly does not discount its presence or its magnitude. Our view of mind-body connectedness simply seeks to take a look under the hood, so to speak, at the mechanisms behind the incredible intricacies that constitute the mind. I would even go so far as to argue that not only does mind-body connectedness account for the richness of the human experience, but that to assert a criterion for personhood that is based on this richness, yet fails to encompass the roll of the body in its influence, is in actuality the view that least accounts for the depth of experience. Much like clockwork to a clock, we can observe the effects without understanding the inner workings, but to at least understand that there are inner workings in no way discounts the product they orchestrate. To at least understand where our experience is born from in no way discounts the phenomenon that it manifests as.


A second, more abstract objection that could be proposed to the theory of mind-body connectedness is that that criteria of physical and psychological continuity simply aren’t what we should be concerned about in questions of identity. This carries the discussion outside a realm that our theory can respond to. While most views tend to deal with one or the other and thus fit the suggested model in one way or another, Derek Parfit discusses survival as a metric of personal relation over time. With this  Derek Parfit seems to forgo the notion of personal identity entirely. Discussing reactions to objections of circularity, Parfit states:

“Certain important questions do presuppose a question about personal identity. But they can be freed of this presupposition. And when they are, the question about identity holds no importance.”

Because he believes criteria involving personal identity must be inherently circular or meaningless, he introduces his parallel notion of survival. Survival, according to Parfit, is a gradient relationship that can be held between two entities over time. For example, Parfit explains a case in which a man, like an amoeba, divides into two parts, each sharing half of a divided brain. From here, there can be three outcomes:

  1. The original individual has died as a result of the division
  2. The original man survives as only one of these halves
  3. The original man survives as both of the resultant individuals.

Some might assert that the first scenario is what we should consider to happen, but Parfit asserts that (and I think that this is pertinent) it would be counterintuitive to see this as “death,” or “not survival”. The second situation doesn’t seem to be correct either. If each half is “exactly similar,” to assert that the outcomes must be different per each individual undergoing the exact same process also seems to be counterintuitive. So either they both must or must not be considered to survive the original individual, and, as discussed in the first case, it seems inappropriate to consider that the original person does not survive. As such, we come to the conclusion that both these new beings “survive” the original. This notion is extended to many situations in which a person can be divided. These seem to be situations that notions of personal identity (either of psychology or body) would have a difficult time accounting for, but survival, as a separate notion, seems to be able to explain the cases simply and effectively.

Survival, according to Parfit, seems to be, at its core, a notion of causal relation. It avoids the circularity present in notions of personal identity by simply avoiding the notion of personal identity altogether. I believe Parfit would assert that survival is useful as a metric for (or, rather, an equivalent to) personal identity, giving evidence for identity overtime without possessing self-affirming characteristics exhibited by other methods of measuring personhood overtime. It is this appeal, however, that is also its greatest shortcoming.

Survival as a measure of causal relation between two (or more) individuals over time seems to encompass aspects of what we care about in reference to identity in some respects, but according to this model, survival can be extended to many relationships that identity would never conceivably connect. One’s children could be considered to be connected in Parfit’s survival relation for example. As an extension, so would grandchildren, great grandchildren, etc. Additionally, Given Parfit’s potential outcomes in situations of fission, there are some issues that arise. I agree that the situation in which a person is divided into two does not seem to represent death, and that it is pertinent to say that the original individual “survives” as two products, but if survival is a matter of degree (and I think that the situation involving a parent and their relation to their children and grandchildren perfectly represents the gradient nature or survival that Parfit suggests), then I think it stands that the relationship would be much weaker than Parfit seems to propose. I feel that it stands to reason, therefore, that degree of survival may be an indicator of sameness of person, but that it fails be an exact or precise metric with which to gauge the aspects that we care about in reference to personhood itself such as responsibility, liability, and recognizing distinctness among other individuals. Because of this, I believe that while survival may be a measure of something, that it is not an adequate measure of what we care about in relation to personhood and therefor is not an acceptable replacement for our model of physical continuity as a criterion for personal identity.

The Soul

A second objection that would extend beyond the matters that are covered by the thesis would be matters of the soul. This is an interesting argument in that it adds little in substance to the discussion of personal identity while also being impossible to prove or disprove as a result of using the natural world as evidence. As a result, it is a criterion for personal identity that lies outside of what the combination of physical and psychological continuity encompass and must be discussed for its implications in our theory.

John Locke makes mention of the soul and its function in identity. In his essay, “On Identity and Diversity,” Locke postulates on how a soul-based criteria for personal identity would operate. Using this model, sameness or continuity of soul would equate to sameness of person. The soul is said to exist as separate from, yet within the body and mind. It is because of this that it should be considered as a competing criteria for personal identity. While a soul based criteria for personal identity is simple, it carries with it some major complications. Locke discusses these, bringing to light the fact that if my soul were taken by God overnight, I would wake in the morning and not be the same person. The primary issue being that nobody, including myself, would be aware that I am not the same person as the one that went to sleep in my body, with my mind. I would think that I was the same person, but according to a soul based criteria for personal identity, I would be wrong; the person that went to bed that night would be dead. Even more complicated still, there would be no way to tell. As such, how do I know that this didn’t happen last night? An hour ago? How do I even know that it is not happening now as I write this? There is no way to observe or account for states of the soul or the change in identity that it might affect. This creates uncertainty in an area of life and death. If my soul (which may only persist for a short time) changes, the person that I used to be is simply dead. Furthermore, how does one know this doesn’t happen frequently, on the hour even? People could conceivably only “last” minutes.

It is important to note here that there is nothing that would “disprove” the existence of the soul. I feel that to argue against something so intangible would be gainless. Rather, I think it is important to realize that whether or not the soul does exist, it is not what we should be concerned about it terms of our identity. Arguments for the importance of the soul in identity are very simplistic, but carry with them some troubling implications in their application. It would seem unwise to base our criteria of personal identity at all on a notion that is unobservable and as a result leave us fundamentally in the dark about our own identity. As mentioned before, the difficulty in addressing concepts of the soul is that these notions are very difficult to dispel or ratify. As such, instead of fighting to assert that the soul does not exist, it is more pertinent to show here that even if souls do exist, they may not be the key to personal identity.


This essay has sought to establish that the mind resides within the body and that psychological continuity is a symptom of physical continuity. Furthermore, given the evidence, it seems pertinent to assert that physical continuity (especially but not limited to the aspects that constitute psychology) are and should be what people are concerned about in cases of personal identity. Its simplicity deals extremely well in conventional application much like animalism, but the additional emphasis that mind-body connectedness places on psychological continuity also accounts for the brain and the importance it plays in the creation of consciousness and the human experience. This avoids some of the issues of over-simplicity faced by pure animalism while still maintaining a high degree of integrity and clarity. In matters where physical and psychological states are concerned, this is an excellent model of how we should measure personal identity. In theoretical situations, it may lead to less conclusive answers, but I feel that theoretically practicality, while important, should come second to applicability in the world we live in. Perhaps, in a future time when the soul can be located, brains can be transplanted, or people can be fragmented, other more comprehensive solutions may be needed. Until then, our body is all that we have to our name and is thus all that we have to measure our names by.


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