First published in 1956, Frederick Wilhelmsen's Man's Knowledge of Reality remains a classic study in Thomistic epistemology. Wilhelmsen begins with an examination of what he refers to as Descartes' "critical problem"; namely, the supposed inability of philosophy to procure what Descartes calls "certain knowledge." Using Descartes' argument as a starting point, he then launches into a comprehensive examination of Thomistic Metaphysical Realism, focusing on our primal experience of being as the self-evident truth upon which we can order our experience of reality. Building upon this first principle of being, Wilhelmsen proceeds to examine the natures of existence, knowledge, and judgement, and how they shape our experience of reality. Despite the intellectuality inherent in such a work, Wilhelmsen proves his merit as both a philosopher and a teacher by never straying far from the practical implications of such ideas, incisively demonstrating how the theories of Descartes and others have resulted in a loss of the unity and integrity of being, leading to the many false dualisms of the modern world.