From 1870 to 1940, the principal motivation for most theorists was to make scholarly work in law scientific. Early American scholars attempted to construct a respectable discipline along two quite different lines. Some sought to ground legal scholarship in an analytical science built in definition and classification. Others sought to base legal knowledge in history with principles of legal evolution as the guide to understanding. In each case, the primary purpose of developing theoretical explanations was to demonstrate that the study of law involved much more than the mere systemization of professional practices and that it required sophisticated learning and intellectual skill. Dissatisfaction with the existing legal system was a motivating force in producing legal theory from 1930 to 1970. American legal realists during this period made negative criticism central to their efforts. They attacked the premises of the dominant expository paradigm and cast serious doubts about its validity by demonstrating that formal rules of law were highly ambiguous and often contradictory. In contrast to the realists, the evolutionists attempted to explain law as a historical product. Additional schools of legal thought included the Poundians and the Thomists. The author discusses the social science of law, natural law, and the contributions of migrant scholars. Supplemental legal history information is appended. References and notes