The Principle of Double Effect (hereafter PDE) has long been a mainstay of Catholic moral thinking.' In recent years, however, the use and discussion of this doctrine have not been limited to Catholics or to theologians.' The PDE, or propositions closely related to it, have come up for considerable discussion by English-speaking philosophers.3 In spite of this discussion, however, the PDE remains something of a mystery. As I hope to show, its purpose, its essential claims, and its presuppositions are not adequately understood. This lack of understanding is due both to the difficulties and ambiguities in traditional formulations of the PDE and to the fact that its central conceptions are either foreign or contrary to much of contemporary ethics and action theory.4 The purpose of this paper, therefore, is to state plainly the propositions involved in the PDE and at least some of the propositions concern-