In Athens Arcesilaus interacted with the Pyrrhonist philosopher, Timon of Phlius,[3] whose philosophy appears to have influenced Arcesilaus to become the first Academic to adopt a position of philosophical skepticism, that is, he doubted the ability of the senses to discover truth about the world, although he may have continued to believe in the existence of truth itself.

His chief opponent was his contemporary, Zeno of Citium, the founder of Stoicism, whose dogma of katalepsis (i.e., that reality could be comprehended with certainty) Arcesilaus denied.

[5] He subsequently became intimate with Polemo and Crates of Athens, who made Arcesilaus his successor as scholarch (head) of the Platonic Academy.

[6] Diogenes Laërtius says that, like his successor Lacydes, Arcesilaus died of excessive drinking, but the testimony of others (e.g. Cleanthes, who said that he lived a dutiful life) and his own precepts discredit the story.

[10] Eusebius, probably quoting Aristocles of Messene, reported that Arcesilaus studied in Pyrrho's school and adhered, except in name, to Pyrrhonism.

[13] On the one hand, Arcesilaus professed to be no innovator, but a reviver of the dogma-free dialectic that had characterized the academy under Plato.

He attacked their dogma of katalêptikê phantasia (i.e., a convincing conception) as understood to be a mean between episteme (knowledge) and doxa (opinion).

It involved a contradiction in terms, as the very idea of phantasia implied the possibility of false as well as true conceptions of the same object.