ABSTRACT
In the 17th century, Descartes, seeking a firm basis for his philosophy, wanted to ground his views in what was indisputably real. To this end, he invented the method known as Cartesian doubt, in which he resolved to make himself question everything that could possibly be doubted, to see what was left. He began with sense data; could he doubt that he was sitting by the fire in his dressing gown? Yes, he decided, because he could dream he was dressed and by the fire when he was actually naked in bed. By gradual elimination, Descartes arrived at the view that what he could not doubt was his own existence, expressed in the famous argument, cogito ergo sum:
While I wanted to think everything false, it must necessarily be that I who thought was something; and remarking that this truth, I think, therefore I am, was so solid and so certain that all the most extravagant suppositions of the sceptics were incapable of upsetting it, I judged that I could receive it without scruple as the first principle of the philosophy that I sought.
Russell (1961, p. 547)