Amidst the broad divergence in opinion of philosophers and scientists at understanding reality that has lent character to the historical epochs of the Philosophical enterprise, the crucial realization has always been, of the necessity of Epistemology in our entire program of making inquiry into ‘What Is’. This realization seems born out of the erstwhile problem of knowing. Epistemology, which investigates the nature, sources, limitations and validating of knowledge, offers a striking challenge here. Since we have no direct access to our (...) world around us, outside of the subjective experience offered us by our senses, we are handicapped at making comparisons of our beliefs with a concrete world, out there, or with elements of the world. Our statements about the world seem to stand alone, buffeted against the intimidating tide of possible contradicting circumstances. Our putative claims to knowledge, therefore, face the exigency of justification. Ayer, expressing the urgency of resolving this persisting lacuna, provides an alternative criterion of knowing, as ‘having the right to be sure’. Thus, it is this deep-seated concern that has evolved, over time, to become the primary thrust of the project of Epistemology, raising the controversy over which, of Epistemology or Metaphysics, is to be accorded the prime status of first philosophy. However, Aquinas is wise to build his epistemological premise on a firm metaphysical support, clarifying the needed development from being to knowledge. For, being has to first exist to constitute the object of perception, belief, and knowledge. Accordingly, our exposition of Aquinas’ epistemology will first take a cursory look at the theoretical and historical background to Aquinas’ Philosophy, before offering a general characterization of his theory of knowledge. Then, the paper will discuss his concept of sense perception as a basis for all knowing, followed closely by an analysis of cognition and Scientia. (shrink)