A certain conception of epistemology is often seen, by historians of philosophy, as definitive of the modern period in philosophy. This conception structures the epistemological task by a contrast between our privileged or certain knowledge of our own minds and our problematic knowledge of the external world. With this contrast in mind, our knowledge of the external world seems either impossible or inadequate. Even epistemologies which try to take our knowledge of our minds as a foundation for knowledge of the world fail to bestow upon the latter the certainties of the former, because the bridging principles are tentative or probabilistic.