Suppose that you’re just an ordinary person, with an ordinary person’s personality, habits, and idiosyncrasies. Then, somehow, you come to find out that your personality, habits, and idiosyncrasies are all caused by the fact that there’s not enough iron in your blood, or some of the proteins in your brain are misbehaving, and you fix the problem, causing your personality, habits, and idiosyncrasies to be erased and replaced with something else. Maybe you’re happier and also more skilled as a result. But what part of you has been preserved?
Suppose that you’re just an ordinary person, with an ordinary person’s personality, habits, and idiosyncrasies. Then, somehow, you come to find out that your personality, habits, and idiosyncrasies are all caused by the fact that there’s not enough iron in your blood, or some of the proteins in your brain are misbehaving, and you fix the problem, causing your personality, habits, and idiosyncrasies to be erased and replaced with something else. Maybe you’re happier and also more skilled as a result. But what part of you has been preserved?
My feeling of existence.
What if I just replaced you with a copy of, I dunno, my high school English teacher? You would still have a feeling of existence if I did that.
If you did that gradually, maybe.