Earlier quoted context omitted.
In context of the thought experiment there can be more than one person with equal claim to be the person that you believe yourself to be. For example, given the postulated copying technology there could be Two or ten or a hundred people with the same claim 91 you to be today's version of who you remember yourself to be. The only thing that makes one person's claim better than another's is a perceived continuity of ph…
My argument is that you don't really know other people, you only know yourself. Clones don't even have to be physical replicas of people, they need only be entities or systems which can pass the Turing test. The fact that a clone may think it is me makes zero difference to my friends who have no way of knowing and it makes zero difference to me because I can clearly see that it is a separate person from me. Now, you…
In fact, we do know that human memory is spectacularly unreliable, and, moreover, that it is a virtuoso liar, very accomplished at convincing us that we vividly remember things that never actually happened. It's proficient at rearranging memories and sensory impressions into ad hoc stories that we uncritically accept as true records of events.
From this point of view it seems a little over optimistic to me to say that we know ourselves, or to say that I know that the me of today is "the same person" (whatever I might mean by that) as the me of yesterday or last week or 1965.