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Personal Identity & Time

A New Look At Personal Identity

Michael Allen Fox argues that old approaches to the problem don’t work.

Who am I? That’s a difficult question to tackle, and each of us must do so for him- or herself, if it is to be tackled at all. But importantly related to this question is another: Am I the same person now as I used to be? For part of the issue of personal identity is how growth, change and life experiences transform one’s self. Perhaps they alter me totally, I may think. The identity problem is compounded by asking further: Might I be a very different person in the future?

Most responses to these questions assume a substantive view of a self or person. That is, they assert that something abides through the stream of events and varying circumstances of one’s life, even in spite of them. Some call this a mind, spirit or soul; others just call it the body, or in more modern terms, the brain. The first group believes that in spite of bodily changes, the mind, spirit or soul stays the same entity, for it is ‘you’. The second group holds that the physical manifestation of ‘you’ is who you are. It is easy to locate ‘you’ or ‘me’ in the body, because this designates an easily recognized place in which personhood can reside. Less easy to imagine is how ‘you’ or ‘I’ can be found in the mind, spirit or soul, since these, not having spatial reference points, are not places where anything can be located, in the normal sense of the word. But maybe this concern merely begs the question by making the hidden supposition that for something to exist it must be locatable in space and time. Many things exist, however, that are in time but not in space, such as past events, fictional characters and worlds, and the intervals between musical notes or spoken words. (Though some might argue that they are in four-dimensional space-time, like all entities.) Could it be, then, that mind, spirit or soul can exist in time although not in space?

However attractive such a ‘magical’ possibility may be, the dominant position among philosophers today is that mind, as something independent from the brain, or spirit or soul, primarily religious concepts, either do not exist, or there is at least no good reason to maintain that they do. They hold that the world and what happens in it can be explained equally well, if not better, without appeal to any of these notions. Perhaps they are right: but this could only be established if a purely physical account of personal identity can do the job of answering our initial questions satisfactorily. Let’s see whether it can.

Historically, there has been a vigorous debate between those who argue that personal identity is established by physical continuity and those who opt instead for psychological continuity. According to the first of these views, I am the same person today that I was as a child or teenager because I have the same body, or at any rate a body that has merely changed incrementally over time. The second camp contends that it is personality traits and dispositions that carry my identity forward through time. (Note that the second view does not entail that there must be independent minds, spirits or souls; only that the story of one’s life necessarily hinges on one’s experiences, beliefs, memories, attitudes, desires, thoughts, dreams, and the like – whether these prove to be physical or non-physical in nature.)

With incremental change we encounter the ancient puzzle known as ‘The Ship of Theseus’. Theseus was a legendary king, revered as one of the founders of Athenian society. Plutarch reports that the ship in which Theseus and those under his command sailed the Aegean sea had its planks replaced one by one. Over time the entire ship was replaced, raising the question whether it remained the same ship or not, and if so, in what sense. The label ‘replacement paradox’ has been affixed to this sort of case.

Theseus’ ship appears poised to sink the physical theory of personal identity. Why? Because even though the ship has merely changed incrementally over time, overall it has changed totally, so that no part of it remains the same as at first. And if no part of an entity remains unaltered over time, can the entity itself remain?

It has been known for quite a while that incremental replacement occurs within the human body, but recent discoveries indicate more precisely the scope of this reconstruction. A technique based on carbon-14 dating devised by Swedish neurologist Jonas Frisén has led to the first accurate estimates of the amount of time it takes for various human body parts to regenerate. For example, our gut lining is replaced every five days; the skin’s outer layer every two weeks; red blood cells every 120 days; bones every ten years; and muscles between the ribs every 15.1 years. If the regeneration paradox is considered a serious worry, the bad news is that human bodily regeneration goes on relentlessly and at variable rates for different parts. The replacement paradox is further complicated by the growing practice of organ transplantation and grafting, with replacement materials supplied by living humans, cadavers and fetuses as well as by other species, and artificial prostheses. Of course, if one believes that the physical continuity criterion of identity neutralizes the paradox, then these new discoveries need not pose a threat to a body-based account of personal identity. The good news is that the cerebral cortex and visual cortex of the brain have been confirmed to be as old as we are, that is, not to regenerate. This indicates that perhaps the most important parts of us from the perspective of self-identity do not change over time – except owing to injury, disease or the effects of ageing.

It might be argued that while novel and interesting, the above biological information does not really present any kind of challenge that hasn’t been faced before in the course of the personal identity debate, so the physical continuity view can remain intact. Making sense of continuity through change is still the issue we have to deal with, and humans are only a special instance (special to us) of objects that undergo alteration yet are said to remain the same.

But unfortunately the physical continuity approach encounters another scientific hurdle, this time having to do with the very composition of our bodies. We all know that our DNA structure is unique to each of us. Philosophers who favour the physical criterion of personal identity could therefore fasten onto DNA as the source of individual continuity. They might trumpet that a scientific, physicalistic solution to the identity problem is finally at hand. Curiously, they have not thus far seized the opportunity to do so. DNA certainly seems like a tempting physical carrier for personal identity, because it’s as identifying of oneself as anything can be. (The question of how DNA translates into personhood or personality, if at all, however, is an even greater mystery than how electrical activity in the brain can do so.) But even here, hopes are dashed for identity. The human body contains between one and ten trillion cells. Red blood cells have no DNA, but all the others do. It also turns out that only ten percent of the DNA present within our bodies belongs to our own cells; the rest resides within the ten to one hundred trillion bacteria and other organisms of several hundred species which inhabit our bodies. Hence it now looks as if what counts as my body, although macroscopically quite specifiable, is, from the standpoint of genetic coding, only ten percent mine. This leaves us with the awkward conclusion (which we shall have to accept) that to be me is to cohabit my body with trillions upon trillions of other organisms, whose genetic coding radically deviates from my own DNA blueprint. My body is no longer simply my body.

Does it follow that we ought to abandon the physical continuity solution to the question of personal identity? Yes. But must we therefore return to the mind, spirit or soul approach? Not necessarily; and for many living in a scientific and secular age, in which matter and its properties make up all the universe, this would be shunned as a backward step. Perhaps a sceptical withdrawal from the whole issue is in order. But I think there is a better alternative. This is to think more carefully about the view of the self developed by existential philosophy. According to this theory, a self or person is what it does; a person is an activity, not a substance, and definitely not merely a collection of attributes, whether physical or psychological. Consciousness, that special but elusive gift we share, is for existentialists embodied and inseparable from our physical presence in the world. Here there is no question of an ‘underlying substratum’ of some kind (material or immaterial) being required to support one’s continuing identity. A person just is what he or she does in an ongoing way from day to day, reconfirming and projecting into the future, by means of choices and actions, the same individual self that existed previously. We can call this the ‘continuity of responsible action’ view of personal identity.

The advantages of fastening onto continuity of responsible action as the criterion for personal identity are several. First, it fully captures the conception we have of ourselves as self-making agents. Second, while not reducing us to mere bodies, it yet avoids forcing us to take sides between the physical and psychological continuity approaches. Third, it incorporates psychological continuity into a more holistic and intelligible picture of personhood. Fourth, it is compatible with the idea we meaningfully express when we occasionally say, “He’s (or she’s) become a completely different person of late.” (The psychological continuity view can accommodate this as well, provided a new continuity establishes itself over time; it is more difficult to see how the physical continuity view can take this into account.)

The upshot is that a person should be understood as an active process, not a thing – not even a thing that undergoes change and self-replacement during its lifetime.

Sometimes it seems as if science will bite off a piece of philosophy and possess it, as has happened often enough in the past (physics, formerly ‘natural philosophy’, went off on its own; psychology, formerly ‘mental philosophy’ followed; and so on). But the question of what makes a person, and specifically makes them the person he or she is, remains one for philosophy to investigate.

Michael Allen Fox is Emeritus Professor of Philosophy, Queen’s University, Canada, and Adjunct Professor of Social Science, University of New England, Australia. He specializes in animal ethics and environmental ethics and is the author of Deep Vegetarianism and The Accessible Hegel.