Bob Prokop wrote: Approximately one-twentieth of one percent of our bodies is replaced each day, through completely natural processes. At the end of 7 to 8 years, not a single atom remains in our physical selves that was there at the start of that period. Every particle of my today's physical self was either dirt, water, air, or another living organism 7 years ago. But I am demonstrably not a new person - I am the same Bob Prokop who was here eight, 10, or even 60 years ago, despite the fact that no trace of the original physical self remains. (I'd love to see someone try such a defense in court: "Your Honor, that wasn't me who committed that crime eight years ago. I wasn't even here. It was someone else with the same name!")
If that ain't proof of the existence of mind, or even of the soul, I don't know what is!
This is from an website entitled "Thought Experments on the Soul," by Kelley L. Ross.
If our concern then becomes personal identity, will the identity of material substance account for that? As I have argued, no. In physical terms alone, we know that there is a turnover of matter in our bodies. I believe that after 20 years or so, all the matter in our bodies is supposed to be different. A defendant in a legal case once even tried to argue that he was literally not the same person who had committed the crime, some twenty years plus in the past. His argument was not allowed as, indeed, we trace personal identity across that transformation. With the material objects, this can indeed produce some paradoxical results. The Stoics noticed that in their day the ship kept at Athens, which was supposed to have born Theseus to Crete, had finally been repaired so much that every single plank and other part of it was no longer original. Was it the "same" ship? In a way yes, and in a way no. One report is that this question was put to the Pythia at Delphi. With material objects, the less the original material, the less it is the original thing. There is no such ambiguity with people. And we can ask them.