Aristo of Chios was a disciple of Zeno of Citium, the founder of Stoicism. The scant biographical information that exists, from Diogenes Laertius (VII 160–64), describes him as an unorthodox Stoic, who later abandoned the school to found one of his own. There is some question in Diogenes' sources as to whether works ascribed to him are genuine or belong to the peripatetic Aristo of Ceos. But there are difficulties about his views as well. Like Zeno, he accepted the Socratic and cynic principle that virtue was sufficient for happiness. But whereas Zeno identified this with "living consistently," Aristo understood it as an internal consistency, where one behaved indifferently toward anything that was not virtue or vice (adiaphoria). At the core of his philosophy is the view that moral values are absolute: Only virtue is good and only vice...