"The first article republished in Studies in Philosophy, Politics and Economics, "Degrees of Explanation," originally published in 1955, was largely consistent with Popper's methodology. Hayek embraced Popper's "hypothetico-deductive" approach to science: "The conception of science as a hypothetico-deductive system has been expounded by Karl Popper in a manner which brings out clearly some very important points." Here, as elsewhere in his work, Hayek distinguished between the facts of the natural and social sciences primarily on the basis of their complexity."