S Stoic accounts of oikeiōsis—appropriation, as I will translate it—are marked by two features: they begin with the apparently descriptive claim that the complex, seemingly purposeful behaviour all animals display in relation to their environment depends on a sophisticated capacity for self-perception. They conclude, on the other hand, with the normative thesis that the human good consists in a life regulated by reason or, as the Stoics sometimes describe it, in a life lived according to nature. This account is central to three of the fullest surviving presentations of Stoic ethics, and sources report that the Stoics appealed to it to defend their conception of the human good in general and their account of justice in particular. Since Pohlenz, most commentators have regarded the oikeiōsis doctrine as substantially Stoic in origin and important, one way or another, to Stoic ethical theory. But they