The object of metaphysics is being, which is to say "that whose act is to exist (esse)." But being is also the object of our intellect. Thus, a Thomist epistemology begins with this fundamental: that the object of metaphysics corresponds to the object of the intellect. To accept this proposition is to take one's stand on the side of what has come to be known as philosophical realism. The metaphysics of St. Thomas, as for that matter almost all the great systems of antiquity, is a realist metaphysics. In a realist world the intellect meets things existing independently of it but which, in being known, measure and determine it. More simply, in a realist world there are things and we can know them.1
This thesis - that the mind knows things other than itself, or that the intellect is measured and determined by its object, and not vice versa - this is axiomatic in a realist philosophy. It is also in accord with the deepest instinct of the human mind; we have, and we cannot escape, the impression that we know things "out there," apart from us and our minds, and that merely to know them makes no difference - to things. And yet from the beginning or nearly so, philosophy has had to contend, within its own ranks, with such as questioned or denied the validity of this fundamental experience. Aristotle had already to cope with them, as when he was impelled to defend the very principle on which all certitude rests, that of contradiction (or noncontradiction); this had come under fire from the Sophists, the "subjectivist phenomenalists" of the time. Later came the Skeptics, who admitted nothing to be true, devising to their purpose no end of specious arguments.
As for modern thought, it has consistently bent its efforts against realism, and this among its leading representatives, Descartes being but the first of many. Inevitably, the renuntiation of realism in knowledge carried over to metaphysics, so that pitted against traditional metaphysics, which rested on the premise that being is prior to and determines thought, were now various systems which stood on the primacy of thought over being, which is to say, on the general assumption that what we know first and last and always is a thought, never a thing.
The epistemological problem thus lies at the heart of modern (if not contemporary) philosophy. Nothing else has so preoccupied it, and again the question comes up to which we addressed ourselves briefly in the introductory chapter: Can metaphysics be solidly established without first inquiring into the validity of human knowledge? We thought it not only possible but that the normal life of the intellect indicates and justifies such a procedure. This granted, it should nevertheless be evident that philosophical positions as important as the ones adverted to above cannot be simply ignored. Besides, the question of human knowledge poses serious problems to the realist as well as to the nonrealist or idealist. Accordingly, having but touched on it in our introductory chapter, we shall now make a more extensive study of the problem of knowledge, more often and perhaps more formally named the "critical problem." In this, as indicated, we have the precedent of Aristotle, who also considers the arguments that had been raised against the validity of knowledge, and right after he has set forth the object of metaphysics.
The discussion to follow will deal only with the fundamental
aspects of the problem at hand. Primarily, these are
1) the realism, or objectivity, of the first object of the intellect
and 2) the validity of the principles, commonly
called first, which flow immediately from the first object.
Before discussing these cardinal points, however, it will be
necessary to trace the critical problem to its roots and to
attend to the difficulties, real or alleged, which begot it.
Altogether, then, we have four principal headings:
I. Critique of Realism
II. Starting Point of a Thomist Epistemology
III. Concerning the Foundation of Realism
IV. First Principles