Scepticism

Ancient Scepticism took two forms. The Pyrrhonists, following Pyrrho of Elis, sought to suspend judgment (epochē) on all matters beyond appearances, holding that for every argument an equal and opposite one can be found; from this suspension, they claimed, comes ataraxia, untroubled calm. The fullest account survives in Sextus Empiricus.

The other form arose within Plato's own Academy: under Arcesilaus and Carneades, the 'New Academy' turned Socratic questioning into a sustained assault on the Stoic claim to certain knowledge, arguing that nothing can be securely known and that the wise will live by what is merely probable.

By denying that knowledge is possible, Scepticism posed the deepest challenge to every dogmatic school — a challenge that opinion without certainty might be all that is left to us.