The Logic of Being in Thomas Aquinas
Being acquainted with the familiar distinction between the “is” of existence, the “is” of predication, and the “is” of identity, which Hintikka has labeled “the Frege trichotomy” (pp. 433f), a modern student of Thomas Aquinas's doctrine of being cannot fail to realize that this distinction, though it seems not to have been ignored by Aquinas, is overshadowed in his writings byanother distinction between two semanticallydifferent uses of the verb “be”, which he borrows from Aristotle. Myaim in this paper is, first, to examine how the two distinctions are related to one another; secondly, to show that Aquinas, though drawing these distinctions, does not commit himself to the assumption that the verb “be” is genuinelyambiguous 1 and, finally, to elucidate how Aquinas avoids such a commitment.
Since it is an ontological and to a certain extent even a theological rather than a logical point of view from which Aquinas approaches the problem of the semanticallydifferent uses of the verb “be”, what he has to sayconcerning the logic of being is split up into a lot of scattered remarks, mainly the by-product of metaphysical reflections, from the larger context of which theyhave to be gathered and put together like the pieces of a jigsaw puzzle. In view of this, not a few of the moves I shall make in myfollowing attempt to trace a coherent picture of Aquinas's logical treatment of the verb “be” will be little more than conjectural.
The distinction which plays the predominant role in Aquinas's theory of being is twofold rather than threefold and has indeed been called “a fundamental ontological dichotomyin Thomas Aquinas's thought” In accordance with this dichotomy, for which he invokes the authority of Aristotle (Metaph.