This is the 58th post in my Theories of Knowledge and Reality series. The last post looked at bodily accounts of personal identity. As a quick refresher, here is that post's summary of the personal identity views up to this point:
According to the dualist account of personal identity, being the same person is having the same immaterial mind or soul. According to the psychological account of personal identity, being the same person is having a continuation of the same set of psychological properties such as memories, desires, beliefs, personality traits, moral character, and so on. The main contender to those two approaches would be biological accounts, which base personal identity in some biological facts. The most common versions of biological accounts are the bodily account and the brain account. The bodily account takes someone to be the same person just in case they have same continuing body.The brain view, like the bodily view, looks to biological continuity but not of the entire body, just the brain. One major advantage of this view is that it fits better with the intuition a lot of people have that a brain transplant is not really a brain transplant but a body transplant. If my brain got put into your body, a lot of people would take the resulting person to be me in your body, not you with my brain. A psychological view would give the same result, but psychological views face duplication problems too easily. You can have two candidates for who it is to be me if you continue my memory and personality in two different places, and in certain cases it's too hard to find a decent answer as to why one or the other is a better candidate for being me (such as a Star Trek transporter accident using new matter to reconstruct me, but it creates two of me, and each duplicate is intrinsically just like the other).
It seems at first glance as if the duplication problem doesn't occur quite so easily with the biological views. After all, only one body could plausibly be mine, and only one brain could plausibly be mine. If you put my brain in a new body, the bodily view would say the resulting person is not me, because it's not my original body. If you put my memories and personality in a new brain, the brain view would say it's not me, because it's not my continuing brain.
But John Perry presents a case that makes brain views seem odd too. Suppose I'm dying of brain cancer, and medical technology progresses to the point where you could produce an exact duplicate of my brain except for the brain cancer and then transplant it into my head. They call it brain rejuvenation. I get a new brain, but I seem to continue. A bodily view would be fine with that description of the case, as would a psychological view. But the brain view would say that I die, and someone new but just like me continues on in my body. Many people find such a conclusion at odds with how we would intuitively think about such a case.
A further difficulty for the brain view is that the first-glance sense of no duplication problems turns out to be wrong. You can present duplication problems for the brain. If brain cancer required removing one of my brain hemispheres, but the other one remained healthy, it would seem that I continue to exist in the same body with one-half of my brain. This would be true whether it's the left hemisphere or the right. But what would happen if you transplanted half my brain into a new body while leaving the other in my body? Many would be inclined to say I'm still with the original body, but that would mean the brain view is false, since my continuing body plays a role in determining where I am. But remove that possibility altogether. Just remove both hemispheres and put them both in new bodies. If either brain hemisphere would be me in the absence of the other, and neither body has more right to counting as me than the other, then the duplication problem arises again. Perhaps you could favor the dominant hemisphere, but person with the other hemisphere would certainly wonder why he is less a candidate for being me. He'd wonder why the other guy got to remain married to my wife and remain the father of my children. He'd wonder why all my worldly goods would belong to the other guy. It does seem arbitrary to deny the second hemisphere the rights to something you clearly give to the other, just on the ground that it was the dominant hemisphere when both hemispheres were fully half of me. Each hemisphere would take itself to be me, and it does seem that on the brain view they both have the right to such a claim.
So those are the main views on personal identity. A number of philosophers have been frustrated enough with the difficulties of these views that they have turned to more unconventional approaches to solve the problem. The next post will look at the temporal parts or (four-dimensionalist) solution.