While the nature of legal systems is a perpetually contested question, it is fairly uncontroversial that each must contain certain essential characteristics. First, each must suppose some picture of the appropriate way for human beings subject to it to live together in society. Second, to secure that proper arrangement, each must employ, to a greater or lesser degree, the device of general rules of conduct. Finally, in all but the simplest systems, the effectiveness of those rules must be guaranteed by some process of adjudication. The relationships among these three factors – social values, legal rules and judging – comprise much of our study of jurisprudence. In this essay, I want to reprise that theme, paying particular attention to the mutual tensions these elements create in the practical operation of a legal system. I want, that is, to review the difficulties inherent in the use of abstract rules to vindicate social policies in concrete cases.