パーフィットの功利主義擁護論 (完) : 人格論からのアプローチ

Abstract

This paper deals with Derek Parfit's theory of personal identity, and with its bearing on utilitarianism. He is known as a 'defender' of utilitarianism, but we must ascertain in which sense he is so, and how we, following him, can defend utilitarianism. Utilitarianism has often been criticized that it does not take seriously the distinction between persons. For example, Rawls and Nozick criticized utilitarianism precisely on that ground, and Williams attacked utilitarianism by saying that it neglects the integrity of a person. But what is a person? What does 'personal identity' mean? In order to give a satisfactory reply to these criticisms, one must look to the theory of persons and personal identity. Hence, we begin by expounding Parfit's arguments on these topics in his Reasons and Persons (Part Three). First, introducing the concepts of person and personal identity, Parfit proposes two kinds of criteria for personal identity, i. e. the Physical and the Psychological. Then, he contrasts two views on the nature of a person, one (1) that a person's existence over time can be reduced into physical and psychological events and their interrelations (Reductionist), and another (2) which denies this (Non-Reductionist). Parfit advocates the former. And, as he propounds the arguments for Reductionism, which are at first sight extraordinary, but surely persuasive in the light of the knowledge of modern science, there emerges a consequence that some of our ordinary beliefs ―― that identity is crucial and it must be determinate ―― should be denied. If we accept this consequence, the criticism that utilitarianism does not take seriously the distinction between persons can be alleviated, because the utilitarian's point is that our concrete experiences are more fundamental than our personal identity. One of the effects of this result is that the anti-utilitarian views concerning the treatment of persons come to be re-examined. Roughly speaking, we should reconsider the following points : (1) the claim of inviolability of a person; (2) the objection to the 'balancing the gains and losses of different persons', the claim that 'someone's burden cannot be compensated by benefits to someone else', and distributive justice; and (3) the claim about desert and commitments. It will be shown that these points are bound either to be rejected or at least questioned, or to become much similar to, and almost substantially the same as, the utilitarian claims that the anti-utilitarians try to refute. In this sense, Parfit's theory surely serves as an indirect defence of utilitarianism. Besides this, it would be valuable to suggest that Parfit's insights also give us better understanding of R. M. Hare's moves for utilitarian theory, e.g. treatment of prudence, integrity, or knowledge of others' preferences. Thus, by our analyses, we can conclude that utilitarianism, especially Hare's, is well supported by Parfit's reflections on persons and personal identity.