It depends on how you define the "I". Two identical computers - down to the arrangements of individual atoms and quarks - might operate in exactly the same way. But they would be two distinct computers. Or do you think that they are somehow the same? The difference therefore, one could argue, is in the potential that each offer: they each offer the potential to be in different places, to experience different things. And this makes them distinct. They might operate (up to that point of difference) in exactly the same way based on the identical wiring and experiences, but they would be different due to all those factors: place, time etc. It is not the physical matter per se... but the arrangement and movement of matter... the pattern that the matter adopts and acts in. And each pattern is unique due, in part, to being located in different places / times. If you replace all your atoms with identical ones, you would still be you because the arrangement and movement of the matter remains the same. The pattern constantly changes, to a degree (more so if there is damage) sure, but our memories then root our current pattern to the one of a moment before, to provide that sense of it being a continuous "I". At least that is how I see it. In many regards people who knew the original "you", as well as the "you" in the new body, would all think that the new "you" is the same as the old "you". And there is nothing to say that it isn't... and to all intents and purposes it is. I have no qualms with that. Any issue would only arise with there being multiple copies at the same time - and I do not think that they would all be the same "you"... i.e. there would be no communal sense of "I" - each would have their own. It is up to observers (including ourselves) to judge who "you" are. The only thing the individual can say is that they are themselves, and their memories provide internal consistency to that claim. And it is an unscientific claim that, while possibly offering comfort to individuals who wish to believe it, is to others a pointless venture into wishful thinking. It's an idea, sure. I just question the point of it... like stating that the universe sits in a bowl of custard. Science does not discount the possibility. But it is not something that science can feasibly prove - unless it can monitor all people at all time - which it can't - and thus it is unfalsifiable. That it doesn't happen (the claim made by science) IS a scientific claim as it can be falsified by the simple occurrence of a single case of duplication. The default for science is the one without redundancy, and the one with the fewer unknowns - the one that would satisfy Occam's Razor. That we merely cease to exist after death is thus the default. No need to invoke any further complexity into the default unless demonstrably necessary. I would say that "my body" is the one in which the sense of "I" can confirm it is operating within. If "I" ask my hand to lift and it does, and I can "feel" and see it does, it gives me comfort that it is "my" body. And of course it will (hopefully) match the body of my memories. You're almost slipping into solipsism with that train of thought. I'm not sure I follow it fully, though. It might well depend on what you mean by an "unphysical entity"... one could call the motion of the sea an "unphysical" entity that applies itself to the physical water. If that is the type of thing you are referring to then I do not see this as unphysical - it is merely a pattern of activity of the physical. But if you see the "unphysical entity" as something more then I do not agree... it is a possibility, sure, but so is the possibility that a planet can exist made out of pure milk. Your last sentence is meaningless, simply because "We" didn't exist with which to have no differing qualities. It is therefore meaningless to say "we had..." when there was no "we" to have anything. What is simpler than the sense of "I" being solely due to the physical... i.e. a pattern of activity within our biological body, requiring no proven "unphysical entity"? What problem do you have with such a view?