Many of you are probably familiar with the story of Phineas Gage. He was widely regarded as a kind and generous man, but he suffered from a freak accident during his work on a railroad, and the result was that a railroad spike ended up entering his brain. After the accident was over, the person who remained was not a kind or generous man. He was impulsive, callous, and clearly lacked all of the moral virtues that Phineas had previously shown.
Now, let's consider this case as a problem of personal identity. In particular, let's ask yourself whether the following sentence is correct:
- The original man named Phineas does not exist anymore; the man after the accident is a different person.
Many people have the intuition that this sentence is correct. It might seem, then, that our intuitions conform to an approach to personal identity that emphasizes psychological similarity. Since the man after the accident is not sufficiently similar to the original Phineas, we conclude that they are not the same person.
In a new paper in Analysis, Kevin Tobia make an incisive criticism of this interpretation. As he points out, it is indeed the case that the man after the accident is dissimilar in certain respects from the original Phineas, but there is also another quite salient fact about him. Specifically, he is morally worse than the original Phineas. That is, it is not just that he differs psychologically in some way; he specifically differs by lacking some of the original Phineas's moral virtues. Might that be the explanation of our intuitions here?
To find out, Tobia conducted a simple and elegant experiment. Some participants received the actual historical story of Phineas Gage. Then other participants received a version that was tweaked in one important respect. In particular, they received a 'reverse Phineas Gage case.' That is, these participants were told that Phineas started out as a person who was callous and impulsive, then suffered from an accident, after which there remained a person who was kind and generous. In other words, all participants received a case in which the people before and after the accident are highly dissimilar, but some received a case in which the person after the accident is morally worse while others received a case in which the person after the accident is morally better.
All of these participants then received the question posed above. They were asked whether it was right to say that the original man named Phineas doesn't exist anymore, and the person after the accident is actually a different person.
Confirming numerous claims from the existing literature, participants who received the story of the actual historical Phineas Gage tended to say that the person after the accident was a different person. But those participants who got the reverse Phineas Gage case said just the opposite! They tended to say that the kind and generous person after the accident truly was still Phineas Gage. As Tobia points out, this result suggests that people's intuitions about personal identity are determined not only by the degree of psychological dissimilarity but by a moral question, namely, whether it is a case in which moral virtues are gained or lost.
The full text of Tobia's forthcoming paper is available online, but please do feel free to comment even if you haven't read the paper. I'm very curious to hear any thoughts people might have about how to explain these results or what implications they might have for larger philosophical problems.