The demarcation of personal identity

Any way you define what a person is is fraught with problems. These are problems of demarcation, of deciding where a person's identity begins and where that identity ends. In my three previous Monday posts, I described three of these problems: resurrection, duplication, and replacement. Those are abstract, science-fiction-like problems we don't encounter in the real world, but some problems with personal identity are practical. If you want a reminder of one of these real-world problems, try loudly proclaiming in a large group of mixed company your opinions about abortion. Even if that group has only a few outspoken people who disagree with you, you'll soon remember which of your beloved assumptions regarding personal identity are not shared by everyone. In particular: when does life begin?

If you've ever debated the ethics of abortion, you've run into this question. And you discovered—hopefully quickly and without losing friends—that no matter what you believe about when life begins, there's no fact that irrefutably backs up what you're saying. There are some facts, and they each give some credit to various claims, but there's no ace of spades that trumps all other facts. Ultimately the question "When does life begin?" is decided by the arbitrariness of choosing a definition—Life begins at X. Given such a definition, the best you can do is to be consistent with how you apply that definition to your other beliefs.

There's also the practical problem of when life ends. Just as with determining when life begins, there's no irrefutable fact that forces one answer to this question. And if you doubt the importance of determining life's terminus regarding real-world scenarios, try returning to that large group of mixed company and loudly proclaiming your opinions about euthanasia.

So personal identity suffers from problems of demarcation, of identifying an exact boundary around what at first glance seems obvious. We're all in agreement that healthy thirty-year-olds are alive—the middle cases are easy. It's the border cases that give way to differing beliefs and attitudes and fail to satisfy all our intuitions.

These problems of demarcation are symptoms of a greater problem. They suggest that personal identity is a leaky abstraction.