Philosophers today are typically unknown outside their discipline, but within it, Derek Parfit, who died in 2017, was considered one of the most important figures of the past fifty years. He had an extraordinary knack for revealing the hidden weaknesses of common moral theories. We may believe, for example, that an action is wrong only if it causes harm to particular individuals. But consider our relation to future generations. We might act well today to preserve the planet’s ecology or we might act very badly in this regard. In the latter case, those who are alive a couple of centuries from now will have livable but much more difficult lives. It seems we will have failed in our moral duty to them. But Parfit argues that what makes a particular self is the joining of a particular egg and sperm at a particular time. Think of all the contingencies that might have made your parents meet later and have a different child instead of you. Then consider the future individuals who live centuries from now in a world created by our resource-depleting behavior. Without that very behavior and its ramifying consequences, these particular individuals would not have been around. Much more responsible behavior on our part would have changed history enough to generate a very different cohort of individuals. The ones in our thought experiment are surely better off than if they had never existed at all, so they cannot claim that we have harmed them. In short, one common theory about what makes our current behavior wrong, though intuitively appealing, is unconvincing.
That argument is quintessential Parfit. Reactions to his work often depend on whether one finds such arguments to be disturbing threats to our moral frameworks or merely the type of puzzle that sets certain kinds of minds in pleasurable motion. To take another example, consider a utilitarian ethical theory, one aimed at producing the best ratio of pleasurable states to painful ones. It seems we could get a superior utilitarian score if we kept increasing the earth’s population to 20 or 30 billion individuals, so long as each new life added at least slightly more pleasurable states than painful ones. Such an outcome, Parfit says, is repugnant. He was interested in the kinds of actions, regarding environmental damage for example, that bring substantial benefit to an individual agent but at the same time harm millions of other people in ways that are too small to be either felt or measured. It is only when each action of this kind is combined with those of many other individual agents that the harm becomes measurable. Traditional ethical theories do not seem well designed for such cases.
Parfit did not wish to encourage moral skepticism; rather, he wanted to point the way toward a more adequate moral theory. He felt that we were just at the first stage of developing such a secular theory, now that religious and other implausible metaphysical frameworks had finally been abandoned. He was what philosophers call a non-naturalist cognitivist. That is, he believed there are ethical truths to be discovered in the way that there are mathematical truths to be discovered, but that these are not reducible to what we can learn from scientific evidence and experimentation. He felt strongly that his own life, and human life in general, would be completely meaningless if there were not such a valid ethical theory. And he believed that moral values cannot depend simply on what we happen to find ourselves valuing.
Parfit liked to use rather contrived thought experiments (cloning, teleportation, split-brain surgeries, and the like) to test our intuitions about personal identity. He concluded that personal identity has no deep basis, may depend on arbitrary choices that cultures make in the future, and in the end is not of paramount importance. We may have reason to desire the continuation of mental states that we value, but whether one’s self continues should not be a matter of overriding concern. For Parfit, the boundaries between selves were less important and less rigid than we commonly suppose, so that our concern for others is not that different in kind from our concern for ourselves. In fact, one person may identify more with another than with an earlier stage of herself, so why insist on the importance of personal identity or its continuity over time?