Pierre Duhem rejected unambiguously the strong version of realism that he believed was held by Copernicus. In fact, although Copernicus believed that his theory was clearly superior to Ptolemy's, he seems to have recognized that his theory was at best only approximately true. Accordingly, he recognized that his arguments were not demonstrative in the traditional sense but probable and persuasive. Duhem regarded even the belief in probably true explanations as misguided. Nevertheless, Duhem recognized that, even if metaphysical intuition does not enter into the content of physical theories, the rejection of hypotheses could be explained only by appeal to common sense. Hence, Duhem held a qualified instrumentalism according to which physical theories are not realist, but the terms of ordinary experience and empirical laws are realist. Accordingly, Duhem rejected the complete subordination of science to philosophy as well as the complete separation of science from philosophy. Duhem's history of cosmological doctrines reflects his belief in the origin of the subordination of science to philosophy and of the struggle to achieve the proper balance without being driven to the opposite extreme of their complete separation.