© 2007, American Catholic Philosophical Association, Proceedings of the ACPA, Vol. 80 Thomas Aquinas on Truths about Nonbeings Gloria Wasserman Abstract: In De veritate I.2, Thomas Aquinas claims that “to every true act of un- derstanding there must correspond some being and likewise to every being there corresponds a true act of understanding.” For Aquinas, the ratio of truth consists in a conformity between intellect and being. This account of truth, however, does not appear to allow for a certain class of truths, namely those that are about non- beings. Many think that it is true that ‘no chimeras exist,’ that ‘blindness can be caused by exposure to bright lights,’ and that ‘evil should be avoided.’ Yet, in each of these cases of truth, there does not appear to be a being to which the intellect conforms. In this paper, I will explore the ways in which Aquinas’s notion of truth as “conformity to being” is able to accommodate truths about nonbeings. T homas Aquinas maintains that truth is found both in the intellect and in things: primarily in the human intellect in so far as it conforms to things and secondarily, in things in so far as they are apt to produce a true apprehension of themselves in the human intellect. 1 In the De veritate, for instance, Aquinas writes: “to every true act of understanding there must correspond some being and likewise to every being there corresponds a true act of understanding.” 2 Throughout his works, he claims that the essence of truth of the human intellect consists in an adequation (or commensuration) of intellect and thing. 3 In the Com- mentary on the Sentences, Aquinas explains that, more precisely, it is the existence (esse) of a thing that enters into the relation of adequation and accordingly, causes truth to reside in the human intellect. He writes: But since in a thing there is its quiddity and its existence, truth is based more on the existence of a thing than on its quiddity, just as the name ‘being’ (entis) is derived from ‘existence’ (esse); and the relation of adequation in which the nature of truth consists is completed in the operation of the intellect which grasps the existence (esse) of a thing as it is by a certain assimilation to it. Accordingly, I say that the existence itself of a thing is the cause of truth insofar as it is in the cognition of the intellect. 4