  The founder of the Stoa, Zeno of Citium (335–263 BCE), studied with Diodorus. His successor Cleanthes (331–232) tried to solve the Master Argument by denying that every past truth is necessary and wrote books—now lost—on paradoxes, dialectics, argument modes and predicates. Both philosophers considered knowledge of logic as a virtue and held it in high esteem, but they seem not to have been creative logicians. By contrast, Cleanthes’ successor Chrysippus of Soli (c. 280–207) is without doubt the second great logician in the history of logic. It was said of him that if the gods used any logic, it would be that of Chrysippus (D. L. 7.180), and his reputation as a brilliant logician is amply attested. Chrysippus wrote over 300 books on logic, on virtually every topic logic today concerns itself with, including speech act theory, sentence analysis, singular and plural expressions, types of predicates, indexicals, existential propositions, sentential connectives, negations, disjunctions, conditionals, logical consequence, valid argument forms, theory of deduction, propositional logic, modal logic, tense logic, epistemic logic, logic of suppositions, logic of imperatives, ambiguity and logical paradoxes, in particular the Liar and the Sorites (D. L. 7.189–199). Of all these, only two badly damaged papyri have survived, luckily supplemented by a considerable number of fragments and testimonies in later texts, in particular in Diogenes Laertius (D. L.) book 7, sections 55–83, and Sextus Empiricus Outlines of Pyrrhonism (S. E. PH) book 2 and Against the Mathematicians (S. E. M) book 8. Chrysippus’ successors, including Diogenes of Babylon (c. 240–152) and Antipater of Tarsus (2nd cent. BCE), appear to have systematized and simplified some of his ideas, but their original contributions to logic seem small. Many testimonies of Stoic logic do not name any particular Stoic. Hence the following paragraphs simply talk about ‘the Stoics’ in general; but we can be confident that a large part of what has survived goes back to Chrysippus.