Chrysippus and the Action Theory of Aristo of Chios

Aristo of Chios’ total denial of moral value to objects intermediate between virtue and vice prevents selection or rejection of indifferents from being a basis for rational action. Moral action appears arbitrary, irrational and incomprehensible, as Cicero concludes (Fin. IV.43). A testimony of Plutarch (Stoic Self-refutations, ch. 23) suggests that Chrysippus too was compelled to take in consideration the notion of indifferent as ‘that by which impulse or rejection is moved no more in one direction than another’ (Sextus Empiricus M XI 60), showing that not only Aristo, but the whole Stoa, had this problem. To confront this difficulty, Chrysippus tried to harmonize the Stoic notion of indifference with rational action. He used Aristo’s theory of rational behavior as a possible answer for his school.