Stardate 20040612.1757

(Captain's log): In response to my musings about the conceptual and ethical problems of different concepts of identity, I received a couple of letters which inspired long answers, and I thought those answers might be interesting to other people.

In Chess, there's what is known as a discovered check. That happens when one of your pieces would be able to check the opposing king, but the line is blocked by another of your pieces, and you move the intervening piece. So if the opposing king would be in check from your rook were it not for the bishop which is in between them, then if you move that bishop you would "discover" the check, and it would not be the piece that you moved which checked the opposing king.

In examining some kinds of philosophical questions, there's what one might call a discovered dilemma. You may be presented with a question, and it might not seem difficult to answer it. But if you explore the consequences of your answer, it might lead you into dilemmas or unpalatable conclusions. In my previous article, I included this thought experiment regarding Christian beliefs about human souls:

One can propose thought experiments which such believers might find troubling. For instance, suppose that a mad scientist kidnaps a pair of identical twins and performs a mutual brain cross-transplant, moving the brain of each into the body of the other. Then assume that one of them is hit by a bus and dies. Presumably someone's soul went to heaven, but whose soul was it? Was it the soul which was originally associated with the body, or the soul originally associated with the brain? A different way to ask the question is this: During the mad scientist's operation, when the brains were moved, did the souls move with them? What part of the body is the soul actually hooked to?

In that article I didn't want to explore that further, since that article was about problems faced by atheists, not about problems faced by Christians. So I didn't really make clear that this was a case of discovered dilemma. It's not so much that those questions themselves are troubling, as that every answer to them implies other things which are troubling.

Dick wrote:

I don't see the problem inherent in the twins with the brain exchange. The brain is the seat of the individual and the individual is where the soul is attached.

Is it the brain? or the behavior of the brain? It's true that the brain is the seat of the individual, but what if they're not inseparable?

The detailed physical structure of the brains of identical twins will not be identical, because it's not totally genetically determined. But it will be much more similar than for fraternal twins or for two people who are not closely related. The difference will be quite small, and clinical evidence (e.g. performance on various kinds of tests) suggests that the computational properties of the brains of identical twins are extremely similar – close enough to be considered essentially identical, for our purposes in consideration of ethical thought problems.

Dick didn't think the first question was hard to answer. But let's look at some of the implications of the answer by considering variations in the thought experiment.

Suppose that instead of swapping the brains, the mad scientist copied and somehow stored Alan's memories, copied and stored Bob's memories, wiped clean all the memories in both brains, and then copied Alan's memories into Bob's brain and copied Bob's memories into Alan's brain. The only thing moved would be information; no tissue would be transplanted.

Afterwards, Alan would "remember" being Bob, but would not in any way remember being Alan. Likewise, Bob would "remember" being Alan, but not remember being Bob. And Alan would thereafter act pretty much the way Bob previously had, and vice versa.

If the individual is the identity – the memory, the perception of self, the characteristic behavior – then the individual which used to occupy the body named "Bob" now occupies the body named "Alan", and vice versa. In a sense, Alan became Bob and Bob became Alan. But the original brains would remain in each body.

Did the souls move when the memories were transferred? The body which previously had been Alan now thinks of himself as "Bob", and carries Bob's memories, and acts the way Bob had acted. If that person is hit by a bus, who died? Which soul goes to heaven?

Suppose that the mad scientist copied Alan's memory, wiped Bob's memories clean, and then copied Alan's memories into Bob's brain. Upon awakening, Alan and Bob both remember being Alan and will act as Alan had acted. Neither of them remembers being Bob or will act as Bob had acted.

The individual we knew of as "Bob" is gone. Does that mean Bob is dead? In a sense, yes. Did his soul go to heaven? If not, then it means that the soul isn't really attached to the individual as Dick contended; since Bob's body retained its soul even though it became a different individual.

But if, on the other hand, Bob's soul did go to heaven when Bob the individual was destroyed and replaced, then we are left with two bodies both of whom seem to be the individual named "Alan", and only one soul between them. Does each one get half? Does one get the soul, and does the other live without having a soul at all?

Or if we decide there reall