Only recently have philosophers begun to discuss the question of whether we can meaningfully speak of distant peoples and future generations as having rights against us or of our having corresponding obligations to them. Answering this question with respect to distant peoples is much easier than answering it with respect to future generations. Few philosophers have thought that the mere fact that people are at a distance from us precludes our having any obligations to them or their having any rights against us. Some philosophers, however, have argued that our ignorance of the specific membership of the class of distant peoples does rule out these moral relationships. Yet this cannot be right, given that in other contexts we recognize obligations to indeterminate classes of people, such as a police officer's obligation to help people in distress or the obligation of...