In answering question 24759, Michael Cholbi writes: "It's important not to confuse the facts by which others know or identify a person and the facts that constitute his or her identity as a person. The way you and I think about Nelson is in terms of social facts about him (his accomplishments, etc.). If I were struggling to remember who was South Africa's first post-apartheid leader, you'd naturally tell me, "Don't you remember? It was Nelson Mandela."" Professor Cholbi intended that as an argument in favour of the theory that "He's not Mandela unless he has that genetic constitution." But suppose we are extremely well informed geneticists and you were struggling to remember who was the person who had the unique sequence of nucleotides CTAG repeated for 999 times between locations 1A237C and 1A324A. I would also tell you: "Don't you remember? It was Nelson Mandela." What is the difference between the genetic and the social fact? Or the difference between genetic constitution and whatever events that...

Thanks for following up. You're asking about a number of issues at once, so let's see if we can distill them out. First, you wonder why people must have "essences" at all. That's a big question -- Hume is a well-known philosopher who can be read at suggesting that persons or selves don't exist. That 'no self'' position is a minority view within philosophy, but is arguably the position espoused by Buddha and has some affinities with the 'eliminative materialism' defended by Paul and Patricia Churchland. I'd encourage you to explore those views further. Second, in my earlier response, the point that we might identify someone on the basis of social facts about him or her was not an argument for genetic facts being essential to a person. Rather, my purpose in making that point is to illustrate how this line of reasoning is invalid: Whether a is F can be reliably determined by whether a is G. Therefore, G is a's essence. To see why, suppose (again) that the way we would normally identify Mandela is by...

I have been reading Stanford Encyclopedia's article on the "non-identity problem". I find it very interesting, but in the whole article it is assumed that one person is the same person in two alternative realities if and only if he or she came out of the same egg (genetically and perhaps atom by atom) produced by her biological parents. I find this idea very wrong. Consider an alternative reality where a man named Nelson Mandela did the same important things that Nelson Mandela did in our reality, but who was conceived and born two months later than our Nelson Mandela. Does it make any sense to say that he would not have been Nelson Mandela? It doesn't, it makes sense only for philosophers who don't want things to make sense at all.... And what if the same egg produced a person completely different from our Nelson Mandela and with a different name? Would that person be Nelson Mandela? I am sure he wouldn't, for no reason, except if you *stipulate* that it has to be that way. Now you may ask: where do you...

I'm pretty confident philosophers do want to make sense of personal identity. But you are taking issue — not unreasonably, in my estimation — with a claim many philosophers make in motivating the non-identity problem. Let's review the reasoning that's supposed to generate this problem. Let's imagine Nelson is brought into existence in circumstances C1. In order for Nelson to have been harmed by being brought into existence in C1, then there must be some other circumstance C2 in which Nelson could have been brought into existence which would have been better for Nelson. But (the reasoning goes) in any circumstance beside C1, the individual brought into existence would not have the same genetic constitution, and so would not have the same identity, as Nelson. Hence, there is no other circumstance into which Nelson could have been brought into existence, and so Nelson could not have been harmed by being brought into existence at C1. (And the point generalizes: No one is ever harmed — or benefitted — by...