Stuart Rachels

Derek Parfit's combined-spectrum argument seems to conflict with epistemicism, a viable theory of vagueness. While Parfit argues for the indeterminacy of personhood, epistemicism denies indeterminacy. But, we argue, the linguistically based determinacy that epistemicism supports lacks the sort of normative or ontological significance that concerns Parfit. Thus, we reformulate his argument to make it consistent with epistemicism. We also dispute Roy Sorensen's suggestion that Parfit's argument relies on an assumption that fuels resistance to epistemicism, namely, that 'the magnitude of a modification must be proportional to its effect.'

Would it be good, other things being equal, for additional people to exist whose lives would be worth living? I examine and reject several arguments for the answer that it would not be good; then I offer opposing arguments that I believe are more successful. Thus, I agree with utilitarians who say that it is better for there to be more happy people. Next I argue for the stronger claim that the happiness of potential people is as important as that of adults. Potential quality of life, then, matters in a host of bioethical issues: abortion, commercial surrogacy, the treatment of defective newborns, and so on. What is the practical upshot of all this? I reject the idea that we must do whatever is necessary to prolong life worth living. But I also reject the view that the side‐effects of overpopulation always outweigh the value of realizing potential happiness. So I advocate a middle position, which I do not identify precisely. Even from this middle position, however, potential happiness is more important than is commonly assumed in bioethics.