 Boethius’s two main authorities, Cicero and Themistius, give rather different lists of the topical differentiae, and one of the tasks of his text-book is to show that their schemes do really coincide. In his commentary on Cicero’s Topics, written shortly before, Boethius expounds the same theory, but leaves himself plenty of room for digressions on such subjects as universals, causation, free will and Stoic logic.