Megarians also called Megarics, a loose-knit group of Greek philosophers active in the fourth and early third centuries B.C., whose work in logic profoundly influenced the course of ancient philosophy. The name derives from that of Megara, the hometown of Euclid (died c.365 . .; unrelated to the later mathematician), who was an avid companion of Socrates and author of (lost) Socratic dialogues. Little is recorded about his views, and his legacy rests with his philosophical heirs. Most prominent of these was Eubulides, a contemporary and critic of Aristotle; he devised a host of logical paradoxes, including the liar and the sorites or heap paradoxes. To many this ingenuity seemed sheer eristic, a label some applied to him. One of his associates, Alexinus, was a leading critic of Zeno, the founder of Stoicism, whose arguments he twitted in incisive parodies. Stilpo (c.380–c.300 B.C.), a native of Megara, was also famous for disputation but best known for his apatheia (impassivity). Rivaling the Cynics as a preacher of self-reliance, he once insisted, after his city and home were plundered, that he lost nothing of his own since he retained his knowledge and virtue. Zeno the Stoic was one of many followers he attracted. Most brilliant of the Megarians was Diodorus, nicknamed Cronus or ‘Old Fogey’ (fl. 300 B.C.), who had an enormous impact on Stoicism and the skeptical Academy. Among the first explorers of propositional logic, he and his associates were called ‘the dialecticians,’ a label that referred not to an organized school or set of doctrines but simply to their highly original forms of reasoning. Diodorus defined the possible narrowly as what either is or will be true, and the necessary broadly as what is true and will not be false. Against his associate Philo, the first proponent of material implication, he maintained that a conditional is true if and only if it is never the case that its antecedent is true and its consequent false. He argued that matter is atomic and that time and motion are likewise discrete. With an exhibitionist’s flair, he demonstrated that meaning is conventional by naming his servants ‘But’ and ‘However.’ Most celebrated is his Master (or Ruling) Argument, which turns on three propositions: (1) Every truth about the past is necessary; (2) nothing impossible follows from something possible; and (3) some things are possible that neither are nor will be true. His aim was apparently to establish his definition of possibility by showing that its negation in (3) is inconsistent with (1) and (2), which he regarded as obvious. Various Stoics, objecting to the implication of determinism here, sought to uphold a wider form of possibility by overturning (1) or (2). Diodorus’s fame made him a target of satire by eminent poets, and it is said that he expired from shame after failing to solve on the spot a puzzle Stilpo posed at a party. See also ACADEMY , ARISTOTLE , CYNICS, SOCRATES , SORITES PARADOX , STOICIS. S.A.W.