The differences in both vocabulary and concepts between social science and the law reflect differences in thought processes which prevent the effective use of social science research in the courts. Social scientists pursue principle-guided, autonomous inquiry, while lawyers concentrate on rule-guided work. Moreover, social scientists tend to understand and predict behavior in the aggregate, rather than the exceptions to the rules which are often the case in legal situations. Conclusiveness simply does not fit the paradigm of social science, but in the law a decision is required on the basis of whatever evidence is available. The distinction between social science research data and the law must also take into consideration the different types of law, such as statutes, litigation, academics, jurisprudence, and judicial opinions. During the first third of the 20th century, the legal realists shattered the notion that decisional law was determined by scientific principle, but this notion has not been replaced with any rigorous conception of what a judge actually does in writing opinions. The historical response to the legal realists has been the legal process school; that is, the idea that judicial opinions should legitimate the resolution of certain social disputes. Since the fifties, the nature of litigation in this country has undergone a vast transformation, and the courts have become tools to effectuate public policy. These two functions, legitimizing and effecting social policy, have two different ways of discovering, appreciating, and assimilating facts. Some of the apparent misuse and nonuse of social science is traceable to these alternative legal agendas. A discussion follows, along with notes and 24 references.