  The extent to which law can actually guide behavior by providing its subjects with reasons for action has been questioned by a very influential group of legal scholars in the first half of the 20th century, called the Legal Realism school. American Legal Realists claimed that our ability to predict the outcomes of legal cases on the basis of the rules of law is rather limited. In the more difficult cases which tend to be adjudicated in the appellate courts, legal rules, by themselves, are radically indeterminate as to the outcome of the cases. The Legal Realists thought that lawyers who are interested in the predictive question of what the courts will actually decide in difficult cases need to engage in sociological and psychological research, striving to develop theoretical tools that would enable us to predict legal outcomes. Thus Legal Realism was mainly an attempt to introduce the social sciences into the domain of jurisprudence for predictive purposes. To what extent this scientific project succeeded is a matter of controversy. Be this as it may, Legal Realism paid very little attention to the question of the normativity of law, that is, to the question of how the law does guide behavior in those cases in which it seems to be determinate enough.