Oliver Wendell Holmes and the realists alike rejected Langdell’s idea that law is principled and coherent. They broke with the natural-law tradition in American common law. Legal rules—however well wrought in reason, or even pedigreed by precedent—underdetermine the results of judicial cases. Instead, legislative might or social convention, said Holmes, or sociology or psychology, said the realists, are the deciding factors, whatever the details of legal rules might say. To speak of “law,” then, is to speak solely of specific legal decisions, not a principled body of doctrine. Legal decisions may be predicted, they say, but through attention to societal mores and contemporary common sense, not the exercise of internal legal reasoning. Holmes and the realists, nonetheless, differed on the basic question of what the law is for. Holmes’s skepticism was thoroughgoing: extending beyond the law to morality, even truth. Law, for Holmes, channels the will of the strong, albeit with the helpful benefits of monopolizing legitimate violence and organizing human affairs. Law, for the realists, is a principal tool of social engineering, a means to bring about a fairer more humane society. One significant realist legacy, accordingly, is to teach law interwoven with social policy, even desired social progress. Whereas Langdell sought value-free science, following the realists, twentieth-century American law schools were increasingly values-driven. Unlike a Blackstone or a Story, however, these values, whatever their flavor, were no longer seen as co-constituted by the common law, but specified from without.