Kevin Tobia in Aeon:
What does it take to be the same person over time? This question has vexed philosophers for millennia. If an individual’s character changes enough, can this disrupt identity to such an extent that it no longer makes sense to say that we are dealing with the same person? That seems a reasonable conclusion to draw when the change is extreme. But I wanted to explore whether there might be more going on than this, and specifically whether the direction of change, not just the magnitude of change, might be a key factor.
In order to explore this question, I presented participants (Aeon readers who responded to a survey) with one of two different scenarios. The two scenarios expressed different versions of a classic thought experiment. They were based on the well-known story of Phineas Gage: a 19th-century railroad worker who had an unfortunate accident in which a tamping rod went right through his skull; he survived, but underwent a major character transformation as a result of brain damage – or so the story goes. Consider a vignette based on the myth of Gage:
Phineas is extremely kind; he really enjoys helping people. He is also employed as a railroad worker. One day at work, a railroad explosion causes a large iron spike to fly out and into his head, and he is immediately taken for emergency surgery. The doctors manage to remove the iron spike and their patient is fortunate to survive. However, in some ways this man after the accident is remarkably different from Phineas before the accident. Phineas before the accident was extremely kind and enjoyed helping people, but the man after the accident is now extremely cruel; he even enjoys harming people.
Gage’s friends and family were inclined to regard the man after the accident as ‘no longer Gage’. This case study is often taken to show that some substantial changes of character can disrupt personal identity to the extent that it seems reasonable to say that this is a different person in an important sense. However, in this case, the accident involved not just a large change, but specifically a deterioration: the man after the accident is seen as worse than Gage before the accident. The typical interpretation of this case is that sufficient magnitude of character transformation disrupts identity. But might this other feature, the direction of change (‘improvement’ or ‘deterioration’) be partly responsible for judgments about identity?
More here.