‘Contested Concepts: Plutarch’s On Common Conceptions’ by Thomas Bénatouïl addresses the question of how ordinary concepts, for instance a layman’s concept of a spider, intersect with a zoologist’s concept of that insect. While from the epistemological point of view the latter’s concept should be allowed to prevail, from the point of view of semantics and the philosophy of mind it is not at all obvious that the scientific concept of spider should be allowed to rule over the corresponding lay concept, nor is it obvious that there is only one concept of spider whose content can be fixed for every context. Clearly, the Academics and the Stoics were aware of the importance of this and related problems. Plutarch’s dialogue On Common Conceptions, subtitled Against the Stoics, is a representative text of these schools’ respective stances, and its study by Thomas Bénatouïl aims to bring out both its historical significance and systematic interest.