Law as an extrinsic principle of action in Aquinas

The Secunda pars of the Summa theologiae provides Aquinas's mature and systematic account of human action. The Prima secundae represents his treatment of the moral life "in universali." After treating the end of man, and certain aspects of human action as such, he turns to what he calls the "principles of action." Well over half of the questions of the Prima secundae are devoted to these principles. The principles are divided into intrinsic and extrinsic principles, the latter being law and grace.;What does Aquinas mean when he calls law an extrinsic principle? And given that it is extrinsic, in just what sense can it be a principle of action without threatening the integrity of voluntary action?;Many writers in the broader Thomistic tradition have de-emphasized the role of law in the moral life. Others, granting law a substantial role, deny its extrinsic character. A common thread can be discerned in these two positions: namely, an unwillingness or hesitancy to grant law as an extrinsic principle a major and unique role in the moral life.;Three fundamental points concerning law as an extrinsic principle of action are central to this dissertation. First, for Aquinas law is, and always remains, essentially an extrinsic principle. Second, for Aquinas law is a foundational and essential principle of moral actions; indeed natural law provides the first principles of practical reasoning. Third, this understanding of law as an extrinsic principle does not threaten the voluntary or the profoundly personal character of human action.;After reviewing the thoughts of some contemporary writers, I examine the nature and kinds of law in Aquinas and then its extrinsic character. A treatment of just how law acts as a real principle, indeed a cause of action, where I study the relation of law and prudence, is finally followed by a consideration of the end of law.