Derek Parfit (born December 11, 1942) is a British philosopher who specializes in problems of personal identity, rationality and ethics, and the relations between them. His 1984 book, Reasons and Persons (described by Alan Ryan in The Sunday Times as "something close to a work of genius") has been very influential. He has worked at Oxford for the whole of his academic career, and is presently a Senior Research Fellow at All Souls College, Oxford. He is also a Visiting Professor of Philosophy at New York University, Harvard University, and Rutgers University. Between 1965-66 he was Harkness Fellow at Columbia University and Harvard University .
Reasons and Persons is a four-part work, each successive section building on the last. Parfit believes that non-religious ethics is a young and fertile field of inquiry. In many ways, he serves as a foil to Wittgenstein, directing his study inwards to address the everyday mechanics of moral problems. He asks questions about which actions are right or wrong, and shies away from meta-ethics which focuses more on logic and language.
In Part I of Reasons and Persons Parfit discusses "self-defeating theories", namely the self interest theory of rationality (S) and two ethical frameworks: common sense morality (CSM) and consequentialism (C). He posited that the S has been dominant in Western culture for over two millennia, often making bedfellows with religious doctrine, which united self interest and morality. Because S demands that we always make self interest our supreme rational concern and instructs us to ensure that our whole life goes as well as possible, S makes temporally neutral requirements. Thus it would be irrational to act in ways that we know we would prefer later to undo.
As an example, it is irrational for a 14-year-old to listen to loud music or get arrested for vandalism if he knows such actions would detract significantly from his future well-being and goals (such as an academic career in philosophy or having good hearing).
Most notably, the self-interest theory holds that it is irrational to make any acts of self-denial or to act on desires that negatively affect our well-being. One may consider an aspiring author whose strongest desire is to write an award-winning novel. However, in doing so, she suffers due to lack of sleep and depression. Parfit holds that it is plausible that we have such desires outside our own well-being, and that it is not irrational to act to fulfill these desires.
Aside from the initial appeal to plausibility of desires that do not directly contribute to one's life going well, Parfit contrives situations where S is indirectly self-defeating. That is, it makes demands that it initially posits as irrational. It does not fail on its own terms, but it does recommend adoption of an alternative framework of rationality. For instance, it might be in my own self interest to become trustworthy in order to participate in mutually beneficial agreements, despite the fact that in maintaining the agreement I will be doing, ceteris paribus, what will be worse for me. In many cases S instructs us precisely not to follow S, thus fitting the definition of an indirectly self-defeating theory.
Parfit contends that to be indirectly individually self-defeating and directly collectively self defeating is not fatally damaging for S. To further bury S, Parfit exploits its partial relativity, juxtaposing temporally neutral demands against agent centered demands. The appeal to full relativity raises the question whether a theory can be consistently neutral in one sphere of actualization but entirely partial in another. Stripped of its commonly accepted shrouds of plausibility that can be shown to be inconsistent, S can be judged on its own (lacking) merits. While Parfit cannot offer an argument to dismiss S outright, his exposition lays S bare and allows its own failings to show through. It is defensible but the defender must bite so many bullets that he might lose his credibility in the process. This is clearly undesirable thus we need to search for a new theory of rationality. Parfit offers the Critical Present Aim Theory (CP), a broad catch-all that can be formulated to accommodate any competing theory. Parfit constructs CP to exclude self interest as our over-riding rational concern and to allow the time of action to become critically important. He leaves the question open, however, whether it should include "to avoid acting wrongly" as our highest concern. Such an inclusion would pave the way for ethics. Henry Sidgwick longed for the fusion of ethics and rationality and, while Parfit admits that many would more ardently avoid acting irrationally as opposed to immorally, he cannot construct an argument that adequately unites the two.
S is not the only self-defeating theory however. Where S puts too much emphasis on the separateness of persons, C fails to recognize the importance of bonds and emotional responses that comes from allowing some people privileged positions in one's life. If we were all pure do-gooders, perhaps following Sidgwick, that would not constitute the outcome that would maximize happiness. It would be better if a small percentage of the population were pure do-gooders, but others acted out of love, etc. Thus C too makes demands of agents that it initially deemed immoral; it fails not on its own terms, for it still demands the outcome that maximizes total happiness, but does demand that each agent not always act as impartial happiness promoters. C thus needs to be revised as well.
S and C fail indirectly, while CSM is directly collectively self-defeating. (So is S but S is an individual theory.) Parfit shows, using interesting examples and borrowing from Nashian games, that it would often be better for us all if we did not put the welfare of our loved ones before all else. For example, we should care not only about our kids, but everyone's kids.
Parfit often poses more questions than he answers. In ethics, he points to a need for a dynamic framework that combines CSM and C but does not offer any specific solution. Such an attitude tracks his stance that non-religious ethics is a young, fertile field.
Parfit uses many examples seemingly inspired by Star Trek and other science fiction, such as the teletransporter, to explore emotions and feelings regarding self-identity. He is a reductionist, believing that self-identity can be reduced to a set of criteria that need not suppose that people do exist. To Parfit, identity can be fully described impersonally: there need not be a determinate answer to the question "Will the person that continues to exist remain to be me?" We could know all the facts about an entity's continued existence and not be able to answer the question of whether or not the persisting person possesses a continual identity. He concludes that we are mistaken in assuming that personal identity is what matters; what matters is rather Relation R: psychological connectedness (namely, of memory and character) and continuity (overlapping chains of strong connectedness).
On Parfit's account, individuals are nothing more than our brains and our bodies, but identity cannot be reduced to either, for identity, in the classical sense, is not what matters. Rather, Relation R is the point around which Parfit's theories turn. Parfit concedes that his theories rarely conflict with rival Reductionist theories in everyday life, and are only brought to blows by the introduction of extraordinary examples. However, he defends their usage in that they seem to arouse genuine and strong feelings in many of us. Identity is not as determinate as we often suppose it is, but instead, such determinacy arises mainly from the way we talk. People exist in the same way that nations or clubs exist (which may be raised as support for the existence of corporations and corporate law).
A key Parfitian question is: given the choice to maintain your personal identity or your psychological continuity, which would you choose? Would one prefer to die (a loss of character but a persistence of personal identity), or instead have one's personal identity fragmented, but retain one's personality?
Parfit's most famous postulations come in Part IV of Reasons and Persons where he discusses possible futures for the world. He shows that, in the discussion of possible futures, both average and total utilitarian standards lead to unwelcome conclusions. Applying total utilitarian standards (absolute total happiness) to possible growth paths of population and welfare leads one to what he calls the Repugnant Conclusion. Parfit illustrates this with a simple thought experiment. Imagine a choice between possible futures, in A 10 billion people would live during the next generation all having extremely happy lives, lives far happier than anyone lives today. In B, there are 20 billion people all living lives, while slightly less happy than those in A, are still very happy. Under total utility maximization we would prefer B to A, and through a regressive process of population increases and happiness decreases (in each the happiness decrease is more than outweighed by the population increase) we are forced to prefer Z, a world of 100's of billion people all living lives barely worth living, over A. Even if we do not hold that coming to exist can benefit someone, we still must at least admit that Z is no worse than A.
Parfit makes a similar argument against average utilitarian standards. If all we care about is average happiness, we would be forced to conclude that an extremely small population, say 10 people, over the course of human history is the best outcome if we assume that these first 10 people (Adam and Eve et al.) had lives happier than we could ever imagine. Then consider the case of American immigration. Presumably alien welfare is less than American, but the would-be alien benefits tremendously from moving from his homeland. Assume also that Americans benefit from immigration (at least in small doses) because they get cheap labor, etc. Under immigration both groups are better off, but if this increase is offset by increase in the population, then average welfare is lower. Thus although everyone is better off, this is not the preferred outcome. Parfit asserts that this is simply absurd.
Parfit then moves to discuss the identity of future generations. He first posits that one's existence is intimately related to the time and conditions of conception. I would not be me if my parents waited 2 more years to have a child. While they would still have had a child, it would certainly be another being; even if it were still their first born son, it would not be me.
Study of weather patterns and other physical phenomena in the 20th century has shown that very minor changes in the initial conditions at time T, have drastic effects at all points after T. Compare this to the romantic involvement of future childbearing partners. By this we can see that any actions taken today, at time T, will affect the resulting people that exist after only a few generations. For instance, a significant change in global environmental policy would shift the initial conditions of the conception process so much that after 300 years none of the same people that would have been born are in fact born. Different couples meet each other and conceive at different times—different people exist. This is known as the 'non-identity problem.'
We could therefore craft disastrous policies that would be worse for nobody, because none of the same people exist under the different policies. If we consider the moral ramifications of potential policies in person-affecting terms, then we will have no reason to prefer a sound policy over an unsound one provided that its effects are not felt for a few generations. This is the non-identity crisis in its purest form: the identity of future generations is causally dependent, in a very sensitive way, on the actions of the present generations. So much so that they effectively have no identity if one looks as little as a half century into the future. Philosophers have long ignored this problem and have devised systems of ethics that are powerless to argue against our temporally biased policies.
Parfit has now made available on-line a large (650+ pages) draft manuscript of a forthcoming work on ethics, initially entitled Climbing The Mountain but now called On What Matters.