Carneades

Carneades was a Greek philosopher and orator, born in Cyrene, a Greek colony in North Africa, around 214 or 213 BC. He led Plato's Academy and is regarded as the most prominent figure of the so-called Third Academy, which took a skeptical direction. He matters because he was one of the most effective critics of the dogmatism of his time, especially of Stoicism.

As a young man he moved to Athens, where he attended Stoic lectures and learned logic from Diogenes of Babylon. He later turned against the Stoics and joined the Academy, which had suffered their attacks. After the death of Hegesinus of Pergamon he was chosen head of the school. In 155 BC he was part of an embassy to Rome seeking to reduce a fine imposed on Athens. There he gave two speeches on justice, one in praise and one against it, which led Cato the Elder to urge his return to Athens. He left no writings; his ideas survive mainly through his pupil Clitomachus, as well as through Cicero and Sextus Empiricus.

His central thesis was that nothing can be asserted with certainty, not even that nothing can be asserted, and that we can speak only of degrees of plausibility. He proposed judging impressions by their persuasive force, their consistency with other impressions, and careful examination of the circumstances, which is enough to act in everyday life without claiming absolute truth. He also held that rules of justice are useful conventions for living together rather than natural laws. His influence reached Cicero and the later Academy, and Augustine engaged with his ideas, though he questioned their consequences.