Greece & Rome · c. 279–206 BCE
Chrysippus
Third head of the Stoa, its great systematiser and logician
Built Stoicism into a rigorous system, including an early propositional logic and a theory of fate compatible with moral responsibility. Ancients said, “Without Chrysippus there would be no Stoa.” Of his reported 700-plus books, only fragments survive.
Life and thought
Chrysippus came from Soli in Cilicia, on the south coast of Asia Minor, and moved to Athens, where he studied with Cleanthes, Zeno’s successor, and probably also with the sceptics of the Academy. Around 230 BCE he became the third head of the Stoa and rebuilt its doctrines against the Academics’ attacks. Ancient sources credit him with more than 700 books; none survives whole, and we know him through quotations, often by opponents.
His greatest achievement was logic. Where Aristotle’s logic dealt with terms such as “all men”, Chrysippus worked out a logic of whole propositions joined by “if”, “and” and “or”, with rules such as: if the first, then the second; the first; therefore the second. It was largely forgotten until modern logicians recognised it. He also defended fate: everything happens through a chain of causes, yet our assent depends on our own character, as a cylinder rolls because it is pushed but rolls because of its shape. “Without Chrysippus there would be no Stoa,” the ancients said.