Derek Parfit is a philosopher writing on issues of personal identity, rationality, and ethics, and his work "Reasons and Persons" was published in 1984. Although it expands broadly on issues concerning the nature of reasons and the values and obligations of persons, the book's primary focus is Parfit's fundamental critique of some traditional views of personal identity. This critique is of tremendous importance, not just for its implications for philosophical debates but for its potential to shape the direction of moral theory for years to come.
At the core of Parfit's account of personal identity is his claim that identity is an unnecessary concept. He argues that it is not necessary to think of people existing throughout time as “the same” person, and instead identifies two distinct notions of personal identity: psychological and physical. Parfit argues that at any one given time, a person is identical to them-self psychologically in terms of memory and character. However, he claims that over time, changes to the body and the mind, as well as our changing beliefs about who we are, make it impossible for us to remain physically identical over time.
In terms of moral concern, Parfit argues that our ultimate interest, regardless of whether we are the same person over time or not, lies in our psychological continuity. That is, we must consider the consequences that our actions have not just on the people in the past, present, and future who are endowed with some degree of psychological relatedness to us, but also on everyone else who might be affected. Parfit argues that this view has important implications for our obligations. In particular, it means that a person's own interests can be tempered and even secondary to the interests of other persons.
Parfit's book also critiques traditional rationalist approaches to ethics, arguing that we should reject the view that all meaningful moral claims are grounded in rationality or logic. While this may still be true in certain cases and with certain values, Parfit points out that in many cases, moral decisions are contingent on the experiences, desires, and decisions of individuals and that rationalism is not an appropriate basis for making moral judgments.
Parfit's work has been extremely influential in shaping philosophical debates both directly and indirectly. It significantly changed the landscape of moral theory and has had a profound impact on our conception of personal identity. His ideas are also applicable to more everyday issues, such as our own personal values and beliefs, and have taken hold in areas such as social responsibility, distributive justice, and animal rights. In summation, Reasons and Persons is a powerful and important book that is well worth the time and attention that it deserves.
