In this final revision of the classic work, the author has produced the fullest and most sophisticated account of this influential theoretical model. Here, he makes clear that morality is an informal system that does not provide unique answers to every moral question but does always limit the range of morally acceptable options, and so explains why some moral disagreements cannot be resolved. The importance placed on the moral ideals also makes clear that the moral rules are only one part of the moral system. A chapter that is devoted to justifying violations of the rules illustrates how the moral rules are embedded in the system and cannot be adequately understood independently of it. The chapter on reasons includes a new account of what makes one reason better than another and elucidates the complex hybrid nature of rationality.