Reasons and Persons

Overview

Reasons and Persons, published by Oxford's Clarendon Press in 1984, is Derek Parfit's masterpiece and one of the most important works of philosophy of the late twentieth century. The book is divided into four parts, each of which became a touchstone of its field: "Self-Defeating Theories" (on rationality and morality), "Rationality and Time" (on the rationality of self-interest), "Personal Identity" (on the reductionist view of persons), and "Future Generations" (on the ethics of population). Parfit's ambition, stated in the introduction, was nothing less than to show that "the question 'what do we have most reason to do?'" cannot be answered by ethics or by the theory of rationality alone, but requires a transformation of both — and that the transformation begins with a new understanding of what persons are.

The book's method is as distinctive as its conclusions. Parfit proceeds by argumentative example: thought experiments of extraordinary inventiveness — teletransporters, fission, fusion, the repugnant conclusion, the non-identity problem — are used to isolate intuitions and force the reader to reconsider them. The result is a book that is at once technically demanding and compulsively readable, and whose central claims — that personal identity is not what matters, that our reasons can be impersonal, that we are not the things we might think we are — have shaped the agenda of analytic ethics and philosophy of mind ever since.

Author

Derek Parfit (1942–2017) was an English philosopher who spent his career at All Souls College, Oxford. He began as a historian, with an interest in French history, before turning to philosophy in his twenties. He published relatively little during his lifetime — Reasons and Persons (1984) and On What Matters (2011) are the two great monuments — but his influence vastly exceeded his output. Parfit was famous for his intensity, his refusal of professional comforts, and his devotion to a single question: what makes life worth living, and what do we owe to one another? His second book, On What Matters, argued for a convergence between the three great traditions of normative ethics — Kantianism, consequentialism, and contractualism — and established him as one of the central figures of contemporary moral philosophy. He died in 2017, shortly after completing his final work, On What Matters, volume three.

Historical Background

Reasons and Persons was written against the background of the post-war revival of analytic moral philosophy. The 1950s and 1960s had seen the emergence of serious normative ethics after decades of metaethical formalism, and by the 1970s the field had produced the two great theories — utilitarianism in its various forms and deontology — that dominate discussion today. Parfit's intervention was to show that the debate between these theories had been conducted on a false foundation: both sides assumed a picture of the person as a unified, self-interested agent persisting through time, and both assumed that morality and rationality were separate domains. Parfit's claim is that this picture is false, and that the arguments of both sides — and of the self-interest theory that underlies much of both — are self-defeating when examined rigorously.

The book also belongs to the history of the philosophy of personal identity, which had been transformed by the thought experiments of the 1960s and 1970s. The question "what makes a person at one time the same person as a person at another time?" had been debated since Locke answered it in terms of memory; Parfit's contribution was to argue that the question, as traditionally posed, rests on a mistake, and that what matters for our concern about the future is not identity but psychological continuity and connectedness — relations that admit of degrees.

Key Ideas

Self-Defeating Theories

Part One argues that certain theories of rationality and morality are "indirectly self-defeating" — that is, they cannot be successfully followed by everyone, and the attempt to follow them undermines what they aim at. The self-interest theory of rationality holds that each person has most reason to do what is best for themselves. Parfit shows that this theory is self-defeating in the required sense: if everyone pursued their own interest, in certain conditions everyone would be worse off than if everyone pursued something else. The argument has the same structure for act-consequentialism, which holds that each person should do what has the best consequences: if everyone tried to act on this principle, the results would be worse than if people were disposed to act on other principles. Parfit's conclusion is not that these theories are false but that they must be reformulated to avoid the self-defeat — and that the reformulation requires a new account of the relation between reasons and persons.

Rationality and Time

Part Two examines the rationality of temporal preferences. The self-interest theory treats the difference between one's present self and one's future self as morally and rationally decisive. Parfit argues that this is a bias — and that it is structurally similar to the bias toward one's own interests as opposed to others'. Just as a rational person should not prefer her own good merely because it is hers, she should not prefer her present good merely because it is present. Parfit distinguishes several forms of temporal bias and argues that the most defensible view is one that gives equal weight to all times — a conclusion with direct implications for how we treat our future selves and future generations.

Personal Identity and Reductionism

Part Three is the philosophical core of the book. Parfit distinguishes two views of personal identity: the non-reductionist view, which holds that a person is a separately existing entity, a "further fact" beyond the body and the mental states; and the reductionist view, which holds that a person's existence consists in the existence of a body and the occurrence of a series of mental events, related in certain ways. Parfit defends reductionism, and he draws a striking conclusion: because identity is not the relation that matters, the question "will I survive?" is less important than the question "will there be psychological continuity between me now and whoever exists later?" What matters in survival is not identity but Relation R — psychological connectedness and/or continuity, with any cause. In the famous teletransportation example, Parfit argues that he would have "survived" even though his body was destroyed, because the psychological continuity was preserved — and that this is not a loss but a liberation.

The Non-Identity Problem and Future Generations

Part Four applies the theory to the ethics of future generations and yields the book's most disturbing arguments. The non-identity problem: many of our choices affect which people exist in the future, since different choices lead to different people being born. If a policy harms future people, but those particular people would not have existed without the policy, then the policy does not make those people worse off — they would not exist otherwise. Parfit uses this to show that the intuitive distinction between "making people worse off" and "bringing people into existence" is unstable. The book's most famous conclusion is the "repugnant conclusion": a population ethics based on total welfare implies that a huge population of people whose lives are barely worth living is better than a smaller population whose lives are excellent. Parfit's response is not to accept the conclusion but to treat it as a problem that no existing theory can solve — a challenge that has defined the field of population ethics ever since.

Important Passages

The book contains several passages that have become canonical. The introduction states its deepest ambition: "We need a theory about the nature of persons and their reasons for acting, which does not distort either the importance of morality or the nature of personal identity." The discussion of personal identity culminates in the claim that "personal identity is not what matters" — the sentence that has been quoted in thousands of discussions of the self. The account of the non-identity problem is introduced with the warning that "some of these questions are so hard that, for the first time in my life, I came to doubt whether I could make progress." And the famous opening of Part Four sets the stakes: "We are like the Titanic, heading for an iceberg we can see but not avoid."

Influence

Reasons and Persons transformed several fields at once. In the philosophy of personal identity, its reductionism and its claim that identity is not what matters remain the starting point of almost all discussion. In ethics, its arguments about self-defeating theories, rationality and time, and the non-identity problem set the agenda for consequentialism and for the ethics of future generations. In population ethics, it created the field: the repugnant conclusion and the non-identity problem are still the problems every theory must solve. Its influence extends beyond philosophy to economics (the debate about discount rates for future welfare), to environmental ethics (the ethics of population and resource use), and to the cognitive science of the self. Like the best philosophical work, it has made the questions it asks unavoidable.

Sources

• Parfit, Derek. Reasons and Persons. Oxford: Clarendon Press, 1984.
• Stanford Encyclopedia of Philosophy, "Derek Parfit" (plato.stanford.edu/entries/parfit)
• Stanford Encyclopedia of Philosophy, "Personal Identity" (plato.stanford.edu/entries/identity-personal)
• Stanford Encyclopedia of Philosophy, "The Repugnant Conclusion" (plato.stanford.edu/entries/repugnant-conclusion)