摘要: We normally see self-interest and altruism as being at opposite poles. Indeed, conceptually we know what we mean by altruism only by contrasting it with self-interest. In practice, however, altruism must coincide with self-interest sufficiently to prevent the extinction of either the altruistic motive or the altruist. This essay argues that while duty and love, the two forms of altruism or unselfish motivation, are valuable in themselves, they must also be sustained by institutions or an environment that provides enough self-interested return to both motivations to prevent actions based on them from being excessively costly. Conceptually, we distinguish among motivations by opposing them one to another. We know that love or duty is at work only when an action could not possibly have been taken for reasons of self-interest. Empirically, we demonstrate that people are acting for unselfish reasons by devising situations in which they are demonstrably acting against their selfinterest. 1Yet in practice we often try hard to arrange our lives so that duty (or love) and interest coincide. Eighteenth-century writers—including Jefferson, with his remarks to his overseer on his slaves—often exaggerated the degree of coincidence. 2 Today, in the interests of a misplaced" realism," we often exaggerate in the other direction, claiming that if we can detect any self-interested reason to act in a particular way, that reason provides the only explanation we need. Self-interest does not automatically drive out duty, however, in spite of the conceptual opposition between the two. In