Reasons, identity, and future people › The book begins with self-defeating theories

Suppose you could prevent a future hardship only by changing which child will be born. Waiting would lead to a different conception and a different person. The child who actually arrives has a life worth living, although the alternative child would have had a better start. Something about choosing the worse future seems open to criticism, yet the familiar complaint that we made this particular child worse off becomes difficult to state.

Derek Parfit develops this difficulty in Reasons and Persons, first published in 1984. The book also examines self-interest, attitudes toward time and personal identity. These subjects are connected by questions about what we have reason to do, but they are not all solved by a single theory of the self. The population problems remain problems even after Parfit's account of personal identity is understood.

The value of reading the book lies partly in learning to keep these questions apart. A theory of what makes someone the same person does not automatically determine how much concern that person deserves. A judgment that a future is worse does not always identify someone for whom it is worse. Following those distinctions reveals why several ordinary ways of justifying conduct need more careful support.

Reasons and Persons has four parts. The first examines theories that can be self-defeating. The second concerns rationality and time. The third investigates personal identity. The fourth addresses future generations and population ethics. Beginning with the personal-identity thought experiments is possible, but it can conceal the earlier question about how theories of reasons should guide conduct.

A theory can tell us to pursue an aim while a particular way of following it frustrates that aim. Parfit distinguishes different forms of this problem. A theory's recommended dispositions or methods of deliberation can have poor results even when its criterion for assessing outcomes remains defensible. Consequently, identifying a self-defeating pattern does not always establish that the theory should be abandoned.

Consider a hypothetical friendship conducted through constant calculations of personal advantage. Someone may monitor every conversation for a better return and thereby undermine the trust they hoped would benefit them. This is an illustration of a possible tension between an aim and a way of pursuing it. It is not an empirical finding that every deliberate attempt to promote one's welfare damages friendship.

Parfit calls the Self-interest Theory S. As a theory of rationality, it gives each person the aim of making their own life go as well as possible. This differs from psychological egoism, the claim that people always act from self-interested motives. A normative theory can tell someone what to aim at while recognizing that they frequently want or do something else.

It also differs from a theory of well-being. To apply the self-interest aim, we need an account of what makes a life go well for the person living it. Parfit distinguishes hedonistic, desire-fulfillment and objective-list accounts. These locate well-being, respectively, in happiness or pleasure, fulfillment of relevant desires, and goods whose value need not depend on being desired. Rejecting one account of well-being would not by itself refute every form of self-interest reasoning.

The broader lesson is about levels of explanation. A criterion of rational action, an account of welfare and a recommended motive answer different questions. They may constrain one another, but we should not move between them unnoticed. An argument against constantly calculating personal advantage is not yet an argument that one's own welfare has no importance.