What principles should govern human action? As rational beings, we should act rationally. As moral beings, we should act morally. What, in each case, are the principles involved? What is it to act rationally, or morally? It is often thought, or said, that philosophers are preeminently the people who have (and have neglected) a moral obligation to apply their rational skills to these great questions. Derek Parfit, fellow of All Souls at Oxford, is a philosopher who does exactly this. He marshals the most immediately obvious and plausible principles of rational, and of moral, action; he submits them, with great dialectical skill, to patient and thorough analysis and criticism; he tests the results against our intuitions, and draws the consequences.

He does more. One of the metaphysical questions that have engaged the attention of philosophers, at least from Descartes onward, is that of the nature of personal identity. Most of us are greatly concerned with our survival in this life as just the person that each of us is. Parfit argues that this concern with identity is misplaced; that what really does, or should, matter to us is something else, something that is indeed, in some degree, an element in such survival, but is, nevertheless, to be distinguished from the preservation of personal identity. And he argues further that once this truth is appreciated, and our ordinary beliefs revised accordingly, not only will our understanding of the principles of rational and moral action be modified, but the result will be, in certain additional ways, better for us. At least, he claims, it is better for him. But he admits that there are great obstacles in the way of our appreciating this truth.

Parfit delays consideration of this thesis until he has examined and criticized certain immediately obvious candidates for the status of acceptable general principles of rational, or of moral, action. One venerable theory about rationality is the “self-interest theory” which has been elaborated by philosophers since Hobbes. This is the view that each person should, if he is to act rationally, always act in such a way as to secure the best results for himself throughout his entire life; to secure, that is, that his life goes, as a whole, as well as possible. A rival to this view is the “present-aim theory”; according to this, it is rational for each person always to act in the way that will best achieve his current aims, as distinguished from the goals he may have in later life. Evidently either theory allows for great variation in content, depending on different conceptions of self-interest. I may believe, for example, that my self-interest is in a life of pleasure or that it is in a life in which my abilities are fully developed; my “present aims” may similarly differ.

Trivially and uninterestingly, the two theories might even coincide: e.g., if an agent’s sole present aim were to achieve the goal of the self-interest theorist. But generally, and more interestingly, they will be opposed; and in two ways. A person’s current aims may include aims, rational in themselves, that are impersonal and altruistic and the pursuit of which he knows to be against his personal interest. If my personal interest is in accumulating wealth, then giving money to the poor may run against it. Similarly the pursuit of a person’s self-regarding present aims may run counter to his long-term interest. If I seek a life of pleasurable sensations, the current pleasures of taking heroin may foreclose this long-term interest. A strict follower of the self-interest theory, on the other hand, will always regard it as rational to put his long-term personal interest first.

In the case of morality, as in that of rationality, two theories, or groups of theories, immediately present themselves as candidates for acceptable principles of action. One is the group of theories that can be characterized, in virtue of their common character, as “consequentialist”: each of us individually ought to do whatever would, so far as consequences are concerned, achieve the best overall outcome. Consequentialist theories again can vary widely in substantive content, depending on what are regarded as morally good or bad outcomes. Utilitarianism is only the simplest and most familiar of such theories, holding that the best outcome is the one that, as Parfit puts it, “gives to people the greatest net sum of benefits.” This is a standard often used by those who make public policy. What most of us, most of the time, accept, however, and, insofar as we are moral, are governed by, is not consequentialism, but some version of what Parfit calls “common sense morality,” an unsystematic assemblage of special and general obligations and prohibitions, whose validity does not necessarily depend on the consequences of observing them. We accept prohibitions of certain kinds of harmful or dishonorable actions (such as breaking promises, for example); and we accept obligations to people to whom we stand in certain special relations (children, parents, clients, colleagues, etc.), or to strangers in extreme and obvious distress.


With much subtlety and skill, by a combination of close reasoning and vivid example, Parfit exposes the flaws in unreconstructed versions of three of the four positions which have been distinguished. Individual attempts directly to follow the dictates either of self-interest or of consequentialism may be self-defeating. Parfit gives an example of a young woman who strives so hard to achieve her long-term interest of becoming a good writer that she collapses with exhaustion; as a consequence she can no longer write. Self-interest may be better served, or a morally better outcome achieved, by the development of dispositions to act in ways that, by the standards of these theories themselves, would, at least superficially, seem to count as irrational or wrong. (Parfit’s writer might have done better to cease writing for a while.) This does not by itself show these theories to be mistaken; but it does induce initial uneasiness.

More seriously, to make such individual attempts general throughout a given community may be similarly self-frustrating. It may, for example, be greatly to the disadvantage of every member of the community if each of them attempts to secure the maximum advantage for himself; and it may secure what is, from the moral point of view, a far worse outcome if each does all that either consequentialism of the special obligations of common sense morality would seem to require of him than if each does less. To cite one of Parfit’s examples, when the land is overcrowded in a peasant society, “it can be better for each if he or she has more children, worse for each if all do.” That these three types of theory—self-interest, consequentialism, and common sense morality—are, as Parfit puts it, self-defeating for groups when followed by each member may perhaps leave one of them, the self-interest theory of rationality, damaged but still standing; but it seems fatal to the two types of theory of morality. This is because a moral theory must be a theory about how we all should act, whereas a self-interest theory is simply a theory about individual rationality.

In the end, however, the outlook is less bleak for the two types of moral theory than it is for the self-interest theory. For the two former theories can be modified and refined in such a way as to come closer to each other and to meet the objections mentioned above. Thus a consequentialist can acknowledge the value of the dispositions and the force of obligations that are honored by common sense morality; and a common sense moralist can recognize the need to subordinate those special obligations to the common or general good when a certain threshold of cooperation is in prospect.

On the other hand, the self-interest theory, with its insistence on putting long-term personal self-interest first, faces, and succumbs to, a challenge from an alliance of common sense morality with the present-aim theory. Present aims, as I have already remarked, may rationally include aims congenial to the moralist, such as helping people in distress. Some may object to the present-aim theorist that he displays a bias toward the present or the near future that is irrational because the pursuit of present aims, or the fulfillment of present desires, may frustrate the fulfillment of aims or desires that we may have in the future. But the present-aim theorist and the moralist can respond that it is inconsistent, hence irrational, for the advocate of self-interest to insist on impartiality between the present and the future while also rejecting impartiality between persons.

Parfit acknowledges that the self-interest theory of rationality has, nonetheless, a continuing strong intuitive appeal. He suggests that this can be attributed in part to the long history of a false belief in a future life of rewards and punishments, for example in the prospect of heaven or hell. As long as it was believed that morality and self-interest would coincide in this all-important long-term way, the self-interest theory was a useful tool, not to be readily discarded, in the hands of those concerned with promoting morality.

Parfit’s arguments on these points extend over nearly two hundred pages of reasoning, both cogent and subtle, of which it has not been possible to give more than a selective outline. In the next long section of the book Parfit develops his avowedly unorthodox views on the nature, and on the importance, of personal identity—both being matters on which, he believes, our ordinary beliefs are mistaken. It is this section of the book that those philosophers who tend, regrettably, to ignore fundamental ethical questions are likely to find the most absorbing, and the most controversial.


It is well to be clear, first, which of our ordinary beliefs concerning personal identity Parfit would not dispute. These beliefs include the following: it is a matter of fact that the lives of most ordinary human beings exhibit both physical and psychological continuity. Their lives exhibit physical continuity in that each such person possesses one unique body and one unique brain from the beginning of his life to the end of it; and they exhibit psychological continuity in that earlier and later phases of such lives are continuously linked by overlapping memories, by the forming and execution of intentions, by the persistence or overlapping modifications of dispositions, beliefs, and desires; and these psychological continuities are made possible by the combination of external stimuli on the unique brain and body and the persistence of that unique brain and body.

It is implicit in Parfit’s position that he would accept this statement of the conditions normally satisfied in the case of an ordinary human life. It is also implicit in his position that he would declare the satisfaction of these conditions to be logically sufficient (and more than sufficient) to guarantee personal identity. In his commitment to this further step he sees himself as contradicting one generally held view: the view, namely, that so far from these being sufficient conditions of personal identity, the satisfaction of the condition of psychological continuity is, at best, a mere consequence of something else, which constitutes the real essence of personal identity and consists in the persistence of a unique separate entity, a soul-substance or Cartesian Ego. This is believed to animate the unique body and is the subject of the mental states we attribute to the man or woman.

It is not clear how far the “separate entity” view is in fact now generally held. It is rejected by most philosophers, though some still adhere to it; and I suspect it would now be rejected by many nonphilosophers as well. Parfit does not reject the view on the ground that it is incoherent or absurd, as some have plausibly done; he simply, and reasonably, observes that there is no convincing evidence in its favor and much evidence against it. The importance of the rejection, for him, and for us, is that it frees him to argue that survival in this life as the identical creatures that we are does not really have, for any of us, the importance that we are naturally disposed to attach to it; that what really matters is something else, related, indeed, to such survival, but distinguishable from it. In arguing this, Parfit undoubtedly is disputing a view that is generally and unreflectively held.

The burden of the argument is carried by a rich variety of imagined examples, vividly described, intellectually delightful to read and contemplate, and often, in a certain measure, convincing. It is no objection that the cases offered as examples are imaginary, and for the most part (at least at present) technically, though not logically, impossible; for it is a laudable and necessary procedure, if we wish to clarify our ideas, to submit them to all the strains that imagination, so long as it does not cross the bounds of logical coherence, can suggest. We should test our concepts to the point of near destruction.

The imaginary cases of one central class exhibit a common feature: in these cases the ascription of a single identity in the case of an earlier and a later person is either excluded by the facts of the case or is questionable or, at best, is arbitrary; yet there holds—not fortuitously—between the earlier and the later person the relation of psychological continuity.

The simplest case is the following. Although the two hemispheres of the brain are generally thought to support quite different abilities, we can suppose that I am one of the minority with two exactly similar hemispheres. If from my damaged body one hemisphere of my brain were successfully transplanted into, and connected with, another similar, undamaged body, I would survive. If, however, both halves were successfully transplanted into different, but similar bodies, there would be two resultant and similar persons, both psychologically continuous with me. Only a believer in the indivisible Cartesian Ego could believe that I am identical with just one of the two—and such a view is evidently implausible. And since they are not identical with each other it follows, by the logic of identity, that I am identical with neither. But, Parfit asks triumphantly, how can a “double success” be a failure? Another question follows. If one of the two immediately suffers a fatal accident, the original “I” does not thereby become identical with the survivor. That would be nonsense. But is not the result as good for me as if I had survived in the full, and indeed the only, sense of continuing to be the same person I was?

Parfit wishes to draw the conclusion that what really matters to us is not the prolonging of personal existence (identity) but the prolonging of psychological continuity, or, more importantly, of those direct connections between phases of a mental life the overlappings of which yield, in an ordinary life, the psychological continuity that characterizes it from beginning to end. We may grant to his examples the power of showing that this connectedness-and-continuity, though normally a feature of continued identity, is theoretically separable from it; and we may concede that it is perhaps, of all the features of continued identity, the one that matters most to us. Yet doubts and difficulties arise; and though Parfit is not unaware of them, he gives them less weight than they seem to deserve; and the fact that he does so is partly owing (paradoxically enough, given his concern to move away from preoccupation with the self) to the fact that he treats the issue almost exclusively from the point of view of the person whose continuity is in question, paying relatively little attention to that person’s place in society or his relation to others.

To illustrate. If I am the same person as X, then all X’s rights and duties and other social relations are mine: his property is mine, his wife and children, his office, his status, and his friends. But what if I am divided up, on the model of Parfit’s “double success”? No doubt an equitable arrangement could be arrived at in some cases. Property can be divided. Families present more difficulty. And which of my two “psychological inheritors,” if either, will command my regiment? Or present himself, with a reasonable hope of welcome, at the door of my lover, if I have one? Perhaps the two should fight a duel about it. If only one of them survives, that would ease this particular problem. Ease it, but not solve it. Though he ascribes overwhelming importance to psychological continuity and connectedness, Parfit allows that physical continuity, or at least physical similarity, may have “some slight importance.” Only slight importance? In the eyes of parents, spouse, or lover? And what if I am a heavyweight boxer? or a celebrated film actor?

There are other reasons for doubt, more general though perhaps less weighty. Whatever imagination may suggest as logically possible, the natural fact of the matter, as things stand (and are likely to continue to stand), is that the preservation of those relations of psychological continuity and connectedness, to which Parfit attaches overriding importance, is causally dependent on the continued existence (identity) of the individual person. Given this fact, Parfit’s concern with the preservation of those relations is in practice inseparable from our natural concern with the preservation of personal identity. No invocation of the false belief in a Cartesian ego is required to underpin that concern. At times Parfit suggests that our natural concern with our personal futures, as just the identical individuals that we are, can be ascribed to biological or evolutionary causes; and, he adds, the fact that a deep-rooted natural attitude has such a source does not show it to be rationally justified. To this it may be replied that human reason is also a product of nature and evolution and can operate efficaciously only within the limits that nature sets.

These last points, however, are not really damaging; for it is open to Parfit to recast his thesis, not as a thesis to the effect that personal identity is not what matters, but rather as a thesis concerning what it is precisely about personal identity that matters. Suppose we accept, in either its revised or its unrevised form, the thesis that it is psychological connectedness and continuity that matter. What consequences follow? Parfit points out (and illustrates the point with engaging illustrations from Proust and Solzhenitsyn) that between earlier and later phases of the same life there may be little or no direct psychological connectedness, even though psychological continuity is secured by, for example, overlapping memories.

Since connectedness matters more to us than bare continuity, we should, and shall, care less about our remoter future. “Suppose,” Parfit writes, “that I shall have a day of pain both tomorrow and in forty years. I am strongly psychologically connected to myself tomorrow. There will be much less connectedness between me now and myself in forty years. Since connectedness is one of my two reasons for caring about my future [the other being continuity], it cannot be irrational for me to care less when there will be much less connectedness.” On this argument, we can contemplate with greater equanimity the ultimate prospect of our death. (The reasoning here, it may be noted, works better in the case of those for whom that prospect is remote than in the case of those for whom it is imminent.)

In the conclusion that our remoter future should be of less personal concern to us, Parfit sees the final defeat of the classical self-interest theory which represents it as irrational not to have equal concern for all parts of our future lives. Not that imprudence is condoned by this defeat. For Parfit, morality takes over from self-interest: imprudence is morally condemned because if it is wrong to impose suffering on anyone, it is also wrong to impose it on one’s future self. (Parfit gives the example of a “boy who starts to smoke, knowing and hardly caring that this may cause him to suffer greatly fifty years later.”) The personal concern we ought to have for our future selves coincides with the impersonal concerns of morality. The principle of benevolence, which is impartial between people, including future selves, comes to the fore. And thus it is that Parfit claims for the true view the power to make one less enclosed, more open to others.

Other consequences follow. Where there is zero, minimal, or reduced connectedness, the fact will bear, in obvious ways, on controversial questions concerning the beginning of life, its end, and the diminution of responsibility with time. Parfit further argues that while the scope of distributive principles is widened to take account of the different stages of an individual’s life, or different lives, the weight of those principles is reduced, as against that of utilitarian principles, which are simply concerned with “maximizing” the net amounts of benefits, however distributed.

Many of these conclusions seem acceptable. But Parfit has not finished. Because social and economic policy is among the important determinants both of the composition and size of future generations and of the distribution of benefits and harms between, and within, them, we need a theory of rational beneficence to decide what outcomes of social policy are desirable or morally unwelcome. These questions occupy the long last section of his book, and are treated with a remarkable combination of imaginative fertility and argumentative power. A multitude of possibilities—too great an array to be summarized here—are considered and compared with respect to their morally desirable and undesirable features. Parfit shuns the “elitism” that would favor a relatively small population with a high quality of life over a very much larger population with lives that, though of much lower quality, would be rated as well worth living by those who lived them. He shrinks equally from the conclusion that the best outcome of all would be the largest possible population of lives that were just worth living.

Unable to produce decisive arguments against either conclusion, or in favor of any alternative, he concludes that he has not found the theory we need. But he does not despair of its being found. On the contrary. He points out that, if we do not destroy mankind by nuclear war, it is reasonable to suppose that many millions of years of human existence on earth lie before us. In that long perspective, civilized human life has only just begun; and the systematic study of ethics, unhampered by belief in God or gods, is younger still. Though we cannot know how nonreligious ethics will develop, “it is not irrational to have high hopes.”

The upbeat ending is well earned; and it shows an engaging modesty. Very few works in the subject can compare with Parfit’s in scope, fertility, imaginative resource, and cogency of reasoning. In the seventeenth century that enlightened statesman, the Marquess of Halifax, wrote: “The Government of the World is a great thing; but it is a very coarse one too, compared with the Fineness of Speculative Knowledge.” It is perhaps too much to hope that the finer thing will have much direct influence on the coarser; or even on the attitudes and behavior of more than a few individual human beings. But an indirect influence there can be. So Parfit’s book, besides contributing, as it certainly does, intellectual illumination and delight, may possibly do more: it may point the way to the emergence of a satisfactory theory of rational beneficence, and this might, in the long run, be capable of influencing political behavior. That is evidently his hope. It would be churlish not to share it.

This Issue

June 14, 1984