Does the individual consciousness depend on the actual atoms or only on the configuration of the atoms? Suppose we have mastered cryo-freezing and atom-manipulation technology. We can freeze and unfreeze people at will. We freeze Sarah. We replace Sarah's atoms one by one. With all atoms replaced, we wake her up. Is it the "same" Sarah? (the same to herself, not just to us). Thanks, Mario

If one thinks of 'atoms' as ultimate constituents of matter, indistinguishable apart from their spatial and temporal position, then it is hard to see how changing them for identical duplicates at the same location could make a difference. (I'm interpreting the experiment as replacing every atom with an identical duplicate: same atomic weight, same charge, etc.) After the experiment, one would have replaced every atom with a partner with exactly same causal powers at the same location, and it is hard to see how this could effect an overall difference in her consciousness. The only difference between Sarah before and after the operation is an historical one: the atoms in Sarah after the operation would have a different history to those in Sarah before the operation. But it is difficult to see how this difference could make a difference to Sarah's consciousness. (Going through a freezing process might make a difference to her consciousness though!)

Let's call the being that results from all this replacement Sarah2. We can ask a pair of questions that seem different. One is whether Sarah2's conscious states will be like Sarah's. I agree with Mark that the answer to that question is yes; at least, it's hard to see why it would be no. But we can ask another question that seems to a different one: is Sarah2 the same person as Sarah? That's a lot more controversial.

A comparison, based on an example by Peter van Inwagen: Suppose little Johnny builds a house from a small number of blocks and leaves it in the middle of the floor. And suppose that I come in and clumsily kick the house over. If I re-arrange the blocks in exactly the same way, then the house I assemble will be indistinguishable from the one Johnny built, but it's not so clear that it's literally the same house. And if I actually replace the blocks with new ones that are just like the old ones, then it's even less clear.

So if we cryo-freeze Sarah, interrupting her normal biological and psychological processes, and then perform this massive replacement, there's at least room to wonder whether it's literally the same person. Sarah2 will no doubt think she's Sarah, but she could be wrong for all that.

This is part of a big debate, of course. One good collection that provides a wide range of background readings with a nice historical introduction is Raymond Martin and John Barresi's anthology Personal Identity, published by Blackwell.

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