The prevalence of philosophical appeals to universal agreement in ancient thought indicates that a limited notion of ‘common sense’ was around, at least implicitly, from the fourth century bc. But, despite the partial justification Aristotle gave for such appeals, a developed theory of common sense was not possible until the Socratic insight that rationality is in some sense constitutive of all adult human beings was adapted and elaborated by the Stoics. In this paper, I argue that the earliest theory of common sense in the ancient world was not this Stoic doctrine – the theory of the ‘common conceptions’ – but a transformation of it found in Cicero's later rhetorical works.

This transformation is part of a broader series of developments, from the Stoic understanding of common conceptions, and in the direction of ‘common sense’, in a variety of later philosophical and rhetorical traditions ranging from Carneades in the second century bc to Simplicius in the sixth century ad. Some of the earlier stages of this process seem relatively clear. Carneades initiated a sceptical attack on Chrysippus' theory of common conceptions, by reducing them to common-sense beliefs, and showing how the Stoics' doctrines conflict with those beliefs. And in the hands of his more dogmatic Academic successors (Philo, Cicero, Plutarch), this form of argument acquired a more positive role, parallel to that of the various traditional arguments from consensus omnium of the Hellenistic schools, with the result that, rather than merely showing the inconsistency of the Stoics, it was taken to show the falsity of their basic doctrines.