Arcesilaus

Arcesilaus was a Greek philosopher who lived from about 315 to about 240 BC and led Plato's Academy in Athens. His importance lies in steering Platonism toward skepticism: he is regarded as the founder of what is called the Middle or New Academy, the phase in which Plato's school adopted philosophical doubt as its method.

From Pitane in Aeolis, he first studied rhetoric in Athens and then followed the teaching of Theophrastus, Crantor, Polemo and Crates, becoming head of the Academy after Crates. Later sources also connect him with Timon of Phlius, a disciple of Pyrrho, whose ideas may have shaped his critical turn.

Arcesilaus committed nothing to writing, so his thought survives mainly through his opponents, above all the Stoics led by Zeno of Citium. His chief target was the 'cognitive impression' that the Stoics believed guaranteed secure knowledge. Arcesilaus argued that we cannot reliably tell a true impression from a false one, since dreams, errors of the senses and madness can produce equally vivid impressions. He therefore recommended suspending judgement, the epoche. His doubt, however, did not extend to conduct: he accepted reasonable opinions as a practical guide, which set him apart from the Pyrrhonists, whose goal was ataraxia.

His influence was considerable. Carneades and later Academics continued his critical line, and Academic skepticism became one of the most influential currents of the Hellenistic age. His method, based on dialogue and the refutation of others' claims, revived the Socratic spirit of the old Academy.