If your younger self were to bump into you through a time warp one day, how would he react to your current state? Would he be disappointed at your failure to adhere to nobler principles or attain a life as bright as he (and you) once envisioned? Or would he marvel with youthful romanticism at a risky route you are taking but viewing with jadedness and self-disapproval? If you have instead spent all your life ticking off the checklist of achievements prescribed for you by society, would he be mightily proud of you or sneer at the gutlessness preventing you from moving out of the comfort zone?
It is mind-blowing how the same man can act and think like vastly different persons at different ages. Nine: Nine Time Travels told the story of a 38-year-old news anchor who came across nine mysterious incense sticks after a series of family tragedies. Each time he lit up a stick, it sent him 20 years back in time, where, with the occasional help of his more innocent 18-year-old self, he tried to turn around his family’s fate. By the end of the ninth journey, at which time he found himself unable to return to the present, he realized that he himself was an incense stick, burning down each time he made a time travel such that when all his journeys were over, his life would also come to an end. So the 38-year-old time traveler died as a man stuck in the past, while the 18-year-old version of himself grew up to become him and, by imbibing the parting words of wisdom from his older self and possibly forfeiting any chances to alter time altogether, survived on to have an ostensibly happy ending. The satisfactoriness of this outcome is, however, debatable since it seems to hinge on one key question: was the 38-year-old at the end of the tale the original 38-year-old man we began with?
18-year-old Park Sun-woo growing up to see the 38-year-old self he met 20 years ago in his reflection in the new timeline.
There are many ways of defining personhood. While the most obvious would be treating the physical entity as a single unit, this overlooks the complexities of the mind and biological changes. Tying personhood to genetic constitution is also problematic since this would give twins and, in a sci-fi future, clones the same identity, notwithstanding environmental influences and individual randomness. Both approaches also present difficulties with futuristic technologies such as mind cloning, whereby an individual can have the contents of his mind recorded prior to his death and uploaded onto a new body so that he can ‘live’ on.
A more considered methodology then may be to assign personhood according to mental attributes like personality, memory or stream of consciousness. Yet none of these attributes are, in themselves, always compatible with our intuitive understanding of personhood. Chances are two individuals living together or by sheer coincidence may share the same personality and memory even though most of us consider them separate persons. Also, barring certain amnesia problems that happen in extreme scenarios, people’s memories keep changing with time, but few of us could fathom the idea of treating ourselves and those around us as different people with each passing second. Regarding someone with a continuous flow of conscious experiences as the same person may be less counter-intuitive, yet some of us cannot shake off the disturbing feeling that the sweet and demure cousin who turned aggressive and spiteful after an affliction of schizophrenia is no longer the person we knew before.
Perhaps a more accurate strategy would be to take some combination of the various attributes and set a threshold for the total magnitude of changes in them that would make an individual a different person. However, that begs the question of what weights to accord to each attribute and how high the threshold should be set. Whatever values we settle on, they will most probably appear arbitrary and thus unfair. For instance, in the case of an algorithm where, all other factors considered, a change in memory accumulation beyond 20 years would result in an assignment of a new personal identity, a 19-year-old woman would be viewed as the same person as her 39-year-old self but not her 40-year-old self, such that one year of difference disentitles the 40-year-old to the identity held by the 39-year-old.
38-year-old Park Sung-woo trying to convince his younger self that they are the same person.
This last issue of injustice reminds us that personhood is not an esoteric concept of pure academic interest. Rather, it holds real-world ramifications for ordinary men and women on the street. Perhaps then, personal identity should depend on consequences of possessing a particular identity in a particular situation.
Taking criminal responsibility and property rights for a start, a perpetrator can get off scot-free by biding his time or injuring himself if his identity changes with age or some drastic event (e.g. a brain injury that induces dramatic personality changes), whereas someone who has slogged for decades to build a sprawling villa may lose it overnight under the same condition. As such, a definition of personhood based on an individual’s discrete physical existence or, in scenarios like mind cloning, stream of consciousness may be more practicable here.
In the case of advance medical directives, though, one’s mental makeup may play a greater role in the appropriateness of outcomes. A lady, while in the pink of his health, may instruct doctors not to administer life-prolonging treatment should she need it in her old age, averring that she will never want to live in a decrepit state. As dementia creeps over her, however, she starts to adopt a child-like mindset, relishing the simple joys of life even in her ailing body. A bioethicist may thus argue that the demented woman should be regarded as a different person from the healthy woman so that the latter’s living will does not result in the senseless ‘murder’ of a perfectly happy individual.
What intrigues most people, however, must be personhood in the context of love. Very often, people discover over time flaws in their romantic partners they have either been ignorant of or did not fully appreciate. Alternatively, changes develop in their partners, turning a suave boyfriend into an alcoholic and oppressive husband or an understanding wife into a vitriol-spewing machine. Can they therefore break off their romantic bonds using the moral justification that they are now attached to someone different from the person they intended to enter a relationship with? Here, it may be suggested that some amount of change and differences from expectations are always anticipatable in individuals. Even if the changes are drastic, they may still be a natural progression of life everyone is susceptible to (e.g. cynicism, mental deterioration). Hence, if a misalignment per se in perceptions and reality were to be sufficient cause for viewing a romantic interest as a different person, no relationship would ever be safe. On the other hand, if a partner has intentionally misrepresented himself or strayed away from being the kind of (loving, faithful) person he implicitly promised to be in initiating a relationship, the discrepancies would be too unreasonable for the other party to bear.
This multitude of possibilities for defining personhood can leave an individual confused and helpless. How do we keep track of and manage the various identities we live with with respect to different matters? Is it too much to ask to hold on to a single identity all our lives? Still, although some potentially identity-changing events are unpredictable and uncontrollable (e.g. dementia in the case of the lady averse to life-prolonging treatment), so long as one has lived a life true to himself and his better sense, he would probably have minimal grounds for regret, however people define him.
The A-Philosopher's Chair 
I could not agree more fully with the issues you debate in this post. I would be fascinated to know how you learned to think this way — it is not, as I am sure you know, the thinking of the average man on the street.
I notice your “older man,” in the above fable is 38 years old. I suspect you may be of an age when that seems very mature. Or at least old. But wait until you are, like me, into your 70’s. The sense of being a different person is dramatic. I can only console myself with the knowledge that I could not possibly have acted with the knowledge and insights I have today half a century ago. In other words, the environment interacts with our genetic potential, and it’s an unending process.
Great post. I’ll be back.
Thank you for sharing your thoughts. You may enjoy watching the variety programs Granpas Over Flowers and Youths Over Flowers. Together, they explore the significance of youth and compare how people in three different age brackets (70s, 40s and 20-30s) react to similar situations. Bon appétit!