A substantially neglected major argument of Hume is that social institutions are largely unplanned, they are products of social evolution. Hume's editors do not include this idea in their indexes. In the phrase of Adam Ferguson, writing a quarter-century after Hume, many of our institutions are "the result of human action, but not the execution of any design." In the twentieth century, the strongest advocate of the thesis implicit in this phrase is F. A. Hayek with several discussions, including the paper "The Results of Human Action but not of Human Design." This principle is fundamentally important for Hume because he insists on naturalistic mechanisms against rationalist and teleological arguments for the creation of institutions of justice, the convention of promise-keeping, and the maintenance of social order, which are his three main explanatory concerns in political theory. Because there cannot be a single supreme authority making and securing all social arrangements over the centuries, the rationalist project of Bentham and others who followed Hume is misguided. Hume's theory of law begins with the world of the ordinary people he analyzes in his moral and political philosophy and it immediately proceeds to explanation. His theory is therefore more a political-sociological explanation than it is a normative theory.