The Dumbest Man Alive: Arcesilaus

"Up to Arcesilaus, the Academy accepted the principle of finding a general unity in all things, by the aid of which a principle of certainty might be found. Arcesilaus, however, broke new ground by attacking the very possibility of certainty. Socrates had said, 'This alone I know, that I know nothing.' But Arcesilaus went farther and denied the possibility of even the Socratic minimum of certainty: 'I cannot know even whether I know or not.' Thus from the dogmatism of the master the Academy plunged into the extremes of agnostic criticism." (Encyclopædia Britannica [11th ed.]. Cambridge University Press. 1911. 105–106.)