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 and let him deceive me as much as he can, he will never bring it about that I am nothing, so long as I think that I am something. So, after considering everything very thoroughly, I must finally conclude that the proposition, "I am, I exist," is necessarily true whenever it is put forward by me or conceived in my mind. (AT VII 25; CSM II 16–17) There are three important notes to keep in mind here. First, he claims only the certainty of "his own" existence from the first-person point of view — he has not proved the existence