Pitane, 315 -  241 B.C.

He was born in the Pitani region of Aeolia. It belongs to the period of the Academy which is called "sceptic or middle Academy". In 268 BC he succeeded the leader of the oldest Academy, Kratita. Initially he was a student of the mathematician Autolycus, with whom he stayed for a while in Sardis. Then he came to Athens and became a student of Theophrastus, who was a close friend, colleague and successor of the work of Aristotle. Crador, however, lured him to the Academy, where he met Polemon and Cratias, who taught there. Arcesilaus was greatly influenced by Pyrrho. He was famous for his wit, ironic manner and oratorical skill. None of his works have survived to this day. We learn his teaching from Diogenes Laertius, Cicero and Sextus Empiricus.

Arcesilaus fully accepts the theory of Pyrrho without changing it. Also, as he is a follower of the Academy, he studies the philosophy of Plato and tries to prove the rational aspects of the Socratic teaching. Socrates always maintained that he knew nothing. In his speeches he never asserted anything and made his interlocutor assert himself. And then, by certain questions and objections, he made him confess that he knew nothing. We find this method mainly in young Plato's dialogues. According to Arcesilaus, this way is an expression of the skeptical principle that "we can support with evidence, for and against, every claim". Both proofs will have the same validity. Arcesilaus already uses the same method in his discussions, but not like Socrates, with the aim of pushing his interlocutor to think and draw his own conclusion, but on the contrary, with the aim of persuading him to support the skeptical view. In this way, the skepticism of the Academy was linked to the argumentative and elenctic dialectic of the Megarians, as formulated by Diodorus.

Arcesilaus is known for his epistemology, which is diametrically opposed to that of Zeno of Elea. According to the Stoics, true knowledge rests on the senses. The source of knowledge is sensation. Correct knowledge, however, is not ensured by all the senses, but only by "perceptive imaginations". Apprehension is the measure of right knowledge. To this theory Arcesilaus reacts as follows: there is no such measure to judge whether knowledge is right or wrong, that is, it corresponds to something existent or non-existent. In the case of mental disturbances, dreams, or false information of the sense organs, the "perceptual imagination" may appear clear and intelligible, and yet in fact be false. And this proves that we can never know if a perception is false or not. Moreover, there are gradations between perceptual and non-perceptual representations, just as there are gradations between the clarity of knowledge and its validity. For this reason, the Stoic criterion for ascertaining correct knowledge is of no use. Arcesilaus' epistemology concludes with this criticism against the Stoics.