This history of political theory is written in the light of the hypothesis that theories of politics are themselves a part of politics. In other words, they do not refer to an external reality but are produced as a normal part of the social milieu in which politics itself has its being. The reflection upon the ends of political action, upon the means of achieving them, upon the possibilities and necessities of political situations, and upon the obligations that political purposes impose, is an intrinsic element of the whole political process. Such thought evolves along with the institutions, the agencies of government, the moral and physical stresses to which it refers and which - one likes at least to believe - it, in some degree, controls.