 Much of the account of common natures can be found in nuce in Aquinas’s De ente et essentia. But Scotus’s account is usually thought to diverge from Aquinas’s in at least one crucial way. According to both Scotus and Aquinas – following some suggestions in Avicenna – it is possible to consider a nature in itself, abstracting both from its existence as a universal concept and as the particulars into which it is divided. (Hence Avicenna’s famous slogan “equinity is just equinity”: Avicenna, Liber de scientia divina, V, c. 1 (Avicenna [LPP], 2:228–229).) Aquinas is clear that this bare nature lacks numerical unity (see Aquinas, De ente et essentia, c. 3 (Aquinas [DEE], 24–25)), and it seems that it lacks any kind of entity too. So where Scotus ascribes to the nature a kind of entity, and unity short of numerical unity, Aquinas does neither. It is perhaps worth noting, in passing, that a plausible case can be made for tracing this moderate sort of realism on the question of universals to the Aristotelian tradition (specifically, Alexander of Aphrodisias: see Tweedale [1993]). One might also argue, as his famous commentator Cajetan did, that Aquinas would be willing to attribute some sort of unity and proportionally some sort of being to the absolutely considered nature. For Cajetan’s exposition of the issue, carefully distinguishing Aquinas’s from Scotus’s position, and for useful references to both authors, see Cajetan [CBE], c. 4 (nn. 55–62), pp. 134–155. Scotus, while clearly in this same tradition, evidently considers the sort of account found in Aquinas to be insufficient, and thus is more clearly to be placed in the realist camp than Aquinas on this question. Far from holding that the nature in itself lacks any kind of reality, Scotus holds that the primary reality of the nature belongs to the nature in itself.