The prestige of the mathematical and physical sciences is great, and properly so. But the difference between facts which are what they are independent of human desire and endeavor and facts which are to some extent what they are because of human interest and purpose, and which alter with alteration in the latter, cannot be got rid of by any methodology. The more sincerely we appeal to facts, the greater is the importance of the distinction between facts which condition human activity and facts which are conditioned by human activity. In the degree which we ignore this difference, social science becomes pseudo-science. Jeffersonian and Hamiltonian political ideas are not merely theories dwelling in the human mind remote from facts of American political behavior. They are expressions of chosen phases and factors among those facts, but they are also something more: namely, forces which have shaped those facts and which are still contending to shape them in the future this way and that. There is more than a speculative difference between a theory of the state which regards it as an instrument in protecting individuals in the rights they already have, and one which conceives its function to be the effecting of a more equitable distribution of rights among individuals. For the theories are held and applied by legislators in congress and by judges on the bench and make a difference in the subsequent facts themselves. I make no doubt that the practical influence of the political philosophies of Aristotle, the Stoics, St. Thomas, Locke, Rousseau, Kant and Hegel has often been exaggerated in comparison with the influence of circumstances. But a due measure of efficacy cannot be denied them on the ground which is sometimes proffered; it cannot be denied on the ground that ideas are without potency. For ideas belong to human beings who have bodies, and there is no separation between the structures and processes of the part of the body that entertains the ideas and the part that performs acts. Brain and muscles work together, and the brains of men are much more important data for social science than are their muscular system and their sense organs.