Several features of St Thomas’s commentary on the De hebdomadibus suggest that he was taking quite seriously Boethius’s view concerning the fundamental harmony between the philosophies of Plato and Aristotle. The paper focuses on the commentary’s treatment of the doctrine of participation in being (esse). There are several places where St Thomas seems to be working quietly to bring the doctrine in line with aristotelian ontology. These have a bearing on the much disputed question of the relation between St Thomas and Boethius on the distinction between esse and id quod est.