This book is the result of a project that I started work on a decade ago but later laid aside for several years. At the time I began my study of the deontologists it was my impression that the movement was virtually ended, with only a historical interest for ethicists. Since then, I have revised my opinion. Although few writers today can be called followers of the deontologists, much that is being written, even by those who reject the deontologists' basic assumptions, bears witness of their influence. The continuing vitality of deontological ethics, it seems to me, rests mainly on the deontologists' profound respect for the concrete facts of man's moral life. In evaluating any ethical theory, the question they ask is not, Is the theory neat and simple? but rather, Does it accurately reflect our deepest moral convictions? In its persistent attempt to do justice to the facts, even if this means abandoning the major tradition in the history of Western ethics, lies the main strength of the deontologists' position. Whatever the fate of their own theory may be, the deontologists have, in their real concern for the facts, made a significant and, I think, lasting contribution to ethical thought. Many people - far too many to mention here - have helped in one way or another with the production of this book.