This article deals with the doctrine of knowledge developed by Reginald Garrigou-Lagrange, the Dominican and a prominent Catholic thinker of the first quarter of the 20^th century. It shows that Garrigou-Lagrange provides grounds for the realistic variant of epistemology and follows the category of "common sense", but understands this category as a classical lumen naturale. This allows one to examine the relation of the "natural reason" and the external world and substantiate the fundamental logical principles of cognition on the one hand and to determine the boundary of "common sense" and outline its direction towards the "supernatural" as its aim on the other hand. Garrigou-Lagrange attributes the main significance to the metaphysical interpretation of principles of being which guarantee its objectivity and cognoscibility. Following the assumption about the primordial act of grasping (apprehension) being as a fact of existence, Garrigou-Lagrange then deduces the main ontological and epistemological categories that describe reality and make up the foundation of the reasonability of reality and intellect (adaequatio rei et intellectus), of which speaks the Thomist understanding of verity. According to the Dominican thinker, this definition is based on logical categories of identity, contradiction, substabce, sufficient ground, causality, and finiteness. This being said, the category of finiteness is no less important and fundamental than the initial category of identity, from which one deduces the ontological definitions of possibility and reality, cause and effect, etc. The finiteness makes up the foudation of existence of the living unity of reality both in nature and in human spirit. Moreover, it makes up the foundation for the spirit's transcending beyound its limits, to what is supernatural and superessential, to God as the ultimate aim of all. This allows one to describe the interpretation of problems of cognition given by Garrigou-Lagrange as a significant step in the development of Neo-Thomist gnoseology that overcomes the psychologism of Leuven dchool, and also as a starting point for a number of alternative epistemological projects, i.e. J. Marshal's transcendental Neo-Thomism, J. Maritain's critical realism, and E. Gilson's immediate realism.