Philosophy

That is a really huge question and I am tempted to pull out a bunch of philosophy books to remind me of the arguments so I can sound clever but that would be cheating! There is very good evidence that your mind doesn't actually forget anything and that we retain all of the information we receive through our senses, what is happening when we seem to forget is just an inability to recall that information but we have all experienced remembering something that we had previously forgotten so it is all available to us given the right triggers. When I say we retain all information there are obviously exceptions when parts of the brain are damaged or deteriorate as in amnesia and alzheimers. I would say that whether atoms change or not is fairly irrelevant since atoms are pretty uniform and one is much the same as the next, the structure in which the atoms place themselves as determined by our DNA is what determines our physical make-up and although our appearance does change over time, we change in a relatively predictable direction, as demonstrated by computer programs that can artificially age you so that you can see how you are likely to look in the future. Having said this, my personal feeling is that identity has little to do with appearance or physical form since I would still feel like me if I were a brain in a vat. You mentioned memory and that is something which could be argued to define us since our experiences shape our feel for the world, the way we perceive it including what we value, what we do and don't pay attention to and how we behave. I still don't feel this defines identity though. Whilst memory and its effects on our personality and physical appearance both give us consistency, provide us with points of reference and play a large part in defining our identity to others, the part which I call me is the consciousness which persists in my head. This is quite a nebulous concept since I cannot define the feeling of veing me or distinguish it from the feeling of being you. It is not constant because, although it persists in dreams, in the non-dreaming part of sleep, when under anaesthetic or if blacked out or unconscious for any other reason, that part of me ceases temporarily or rather, my awareness of Self is temporarily absent. I have read the argument that identity can be defined by consistency over time. That is, if you follow a person around over any length of time and no apparent change occurs then they must be the same person at the end of this period as at the start. I find this a somewhat materialist view though. It suggests that identity is observable. What happens if the person that we are following has multiple personality disorder or dissociative identity disorder as it is now called? They may show no outward sign that the personality in control of the body has changed but internally their Self is felt to be different. I think that the only way that a really acceptable answer to this question can be found will be by having a definitive idea of what consciousness is and how it works. As yet there is no sign of this happening. As I mentioned before, the difficulty with objective experience is that we can't compare our experience with that of another so, whilst I assume that there is a qualitative difference between the experience of being me and the experience of being you, we cannot know for sure that if we were swapped around in our sleep so that I woke up in your body with your memories (and so believing that I was you) and vice versa, we would sense any difference in the subjective quality of being one person rather than another.