Carneades was head of the Platonic Academy in the 2nd century BCE. As a fierce academic skeptic, he was a strong critic of other schools, especially the Stoics, who vigorously attacked his academic skepticism. Carneades also attacked the Epicureans, challenging the value of the "swerve" of the atoms proposed by Epicurus as necessary to break the "fate" or necessity implicit in the determinism of the atomist Democritus. Following his predecessor Arcesilaus, Carneades mitigated his skepticism. He knew his claim that "knowledge is impossible" is itself a knowledge claim. He denied the Academy's founder Plato's definition of certain knowledge as - "justified true belief" - but he believed that we can acquire enough probable and fallible knowledge to lead a good life. We know Carneades from Cicero's De Fato, where Cicero attacks the absurdity of the Epicurean swerve as an explanation for human freedom using Carneades as the spokesman for academic skepticism. Although they say the swerve itself is unintelligible, Cicero and Carneades strongly defend chance as adequate to deny the causal determinism and fate that worried the Epicureans. Carneades said that Epicurus would have done better to give the mind a special non-causal voluntary power than to claim the atoms had a special power to swerve uncaused.
(Cicero, De Fato, XI) Although Carneades was a skeptic and had no positive positions of his own, this suggestion perhaps makes him the first "agent-causal" thinker, although Alexander of Aphrodisias argued that Aristotle believed that the mind had powers that were unaffected by physical determinism.