Thomas Aquinas on the perpetual truth of essential propositions

Abstract

It is well known that Thomas Aquinas thought that creaturely es sences did not exist apart from the individual creatures to which they belonged. Aquinas writes in his Commentary on the Sentences that nature has being except for in its supposit. Indeed human ity is not able to exist unless in a man.1 It is also well known that Aquinas thought that the truth of a proposition depends on a corre sponding being to which it conforms. In the De veritate, for instance, he writes, To every true act of understanding there must correspond some being.2 While both Aquinas's understanding of essences and his conception of truth have received much scholarly attention, his thought on a certain implication of these two views has yet to be explored. A significant philosophical difficulty arises when one couples the view that essences depend on their subjects for their existence with the view that true propositions depend on a corresponding being for their truth. If essences perish with the substances to which they belong, then it seems that nothing remains to ground the truth of essential proposi tions about subjects that no longer exist. If the essences of dinosaurs, for example, perish with the dinosaurs themselves, to what being can the proposition dinosaurs are sentient correspond?3 Although Aquinas himself never discussed this difficulty, later Scholastics viewed it as quite a significant problem. The great historian of medieval philosophy Francisco Su?rez wrote, [I]f the essence perishes when the existence of the substance is taken away, then those propositions in which essential attributes are predicated of a thing are not necessary or perpetually true.. . . [A] 11 truths about creatures would be contingent and accord ingly, a science of creatures would not be possible since science regards only necessary truths.4