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Noah Harris says Descartes failed to find absolute foundations for knowledge.
Cogito ergo sum: ‘I think, therefore I am.’ This statement by René Descartes, which has become known as ‘the Cogito’, is perhaps the most famous phrase in all of philosophy. It summarises his argument that one’s own existence is the only thing one can never be mistaken about. In his Meditations on First Philosophy (1641), he argues that with every other proposition – even those of basic mathematics – it may be that every time I think them, an all-powerful demon interferes with my mind and deceives me, leading me to be mistaken. For example, every time I think about 2+3, this demon may be interfering to make me believe the total is 5, when actually it’s something else.