Parfit argues that questions about personal identity do not necessarily have determinate answers. He does so by asking us to consider a spectrum of cases in which a person changes in a variety of ways.
Let’s call the person after the changes have been made G and the person before the changes are made Me. After considering each change, we can ask “Is G the same person as Me?” In many cases, the answer will be “yes” or it will be “no.” The conclusion Parfit hopes to establish is that there are some changes for which it is equally appropriate to say “yes” or “no” or even “yes and no.”
Parfit believes that this is a consequence of the Psychological Criterion of personal identity, the Physical Criterion of personal identity, or any combination of the two criteria. But, he believes, it is a consequence that those who propose these criteria have failed to appreciate. He is arguing that the people who hold those views are committed to a view he calls “reductionism.” Reductionism is the view that people are made up of psychological connections or physical parts and nothing else. Since the psychological connections and physical parts can continue over time to greater or lesser degrees, so can the person who is made up of those parts.
Obviously enough, Parfit is less interested in finding the true criterion of personal identity over time than he is in establishing his point about the possible indeterminacy of personal identity.
I said that I found that conclusion intolerable but, at the same time, that I could not see how to resist it. Like Williams and, I gather, Dhruv, I am stymied by the following argument.
On Parfit’s behalf, Michael insisted that this is just something we don’t understand, not something that is impossible. After all, we’re constantly finding new things that had seemed impossible. And, he said, there is nothing else for a person to be.
As I said, the reasoning is compelling, but the conclusion is very hard to understand, much less accept. What an excellent philosophical problem!