I will begin by saying that I am persuaded by most of Derek's claims and arguments. That may tend to make for rather uninteresting commentary, but I shall try to find something to say. I shall offer only one criticism of the main part of Derek's paper, and then I shall discuss at somewhat greater length the questions he raises in the last section of his paper. In the main body of the paper, Derek attempts to prove that if we accept what he calls the Complex View of personal identity, then we must abandon what he calls the Equal Concern Claim of Classical Prudence. The basic argument is simple. On the Complex View, personal identity is a matter of degree. But it is not irrational to think that a fact which is a matter of degree is of lesser importance when it holds to a lesser degree. Therefore, it is not irrational to think that one's identity with oneself in the distant future may be of lesser importance than one's identity with oneself in the near future. It follows that it is not irrational to give greater weight to one's interests in the near future. Classical Prudence is not a requirement of rationality.
Regan, Donald H. "Comments on Parfit." Synthèse 53 (1982): 245-9.