It’s your 100th birthday but barring some extraordinary luck, you are dead. Most likely you’ve been dead for thirty-forty years already; ten-twenty years if you’re lucky. Your remains, if one might use the word ‘your’, have been converted into a million different chemicals. Of course, you never had any fixed set of atoms anyway, your body had been replacing its atoms every x months (details don’t matter anyway, you’re dead). So who were you?? Who the hell were you??
One would be tempted to start answering the question by first narrowing down the range of possibilities, that is to say by first eliminating stuff which is definitely NOT you. Start with the limbs – oh so important, yet practically useless (in today’s day anyhow) appendages for survival, unless you belong to one of the few hunter gatherer tribes left. Remember, we’re trying to find a definition for ‘you’, so one might go ahead and claim, without much controversy that your hands and feet definitely don’t define you. You’d still be the same (or would you??) being if you had a hook instead of a right hand.
Similar logic would lead any logical person to conclude the same is true for hair, eyes, kidneys, liver, blood, heart, genitals, nails, etc. Though some of them are vital for your survival, strictly speaking they’re not necessary in the sense that a replacement from a proper donor would get the job done as well. Continuing, one would ultimately be left with the few cubic inches of space inside your skull.
So, now we’re left with the brain. One would be tempted to proceed further with the same principle. So let’s start taking apart bits of your brain little by little. Now though, it’s no longer obvious what effects one might observe – they would invariably depend on the part of the brain chosen and the effects would also vary depending on the individual. However, some insight into the effects can be found by construing the impact of Alzheimer upon its patients. In the first day, once the symptoms start appearing, most people will agree that by and large the patients are still themselves. But fast forward a few years to the time when they can no longer remember their loved ones, and it would be debatable if they are really ‘them’ in a colloquial sense of the word. This observation hints that there is a spectrum in the development of the disease. At the beginning you really were you, almost everyone would agree. On the other end your Alzheimer has progressed so far that you barely recognize your daughter/son. Somewhere in between you’ve ceased to be you.
That hypothetical point (say, D Day) HAS to be arbitrary and subjective. For one day before the point, one would conclude you are yourself while one day later you are no longer you. This seems, and most definitely IS absurd because it is certain that most people would not be able to recognize you in D Day from D+1 or D-1. The above reasoning shows that any attempt at defining who YOU are is certain to fail, for any such definition would be arbitrary and worse, subjective. And all that is before asking questions about the legitimacy of taking a person’s ability to recognize his loved ones as the basis of defining him/her.