The Human Condition (book) but the self, Descartes and other moderns thought, could be known. Though his cogito ergo sum was anticipated by Augustine, his dubito ergo sum is original and a hallmark of modernity: beginning from doubt. The notion of common sense as a sense in which the other five were fitted to a common world ceded to a conception of common sense as an inner faculty with no relationship to the world, and the assumption that all humans had faculties like this in common became necessary to get theories going, but without the assumption of a common world, the assumption of faculties
Cogito, ergo sum itself is good and pleasant (...) and if one who sees is conscious that he sees, one who hears that he hears, one who walks that he walks and similarly for all the other human activities there is a faculty that is conscious of their exercise, so that whenever we perceive, we are conscious that we perceive, and whenever we think, we are conscious that we think, and to be conscious that we are perceiving or thinking is to be conscious that we exist... ("Nicomachean Ethics", 1170a25 ff.) Augustine of Hippo in "De Civitate Dei" writes "Si […] fallor, sum"