All of his life, Kant wrestled with the possibility that ideas are either mostly affected by sensory input or by an over-active imagination. He struggled to understand how thoughts could be described as logical, rooted in the nature of things and the only correct way to think. The book is designed writes the author in his preface, to do the general reader a service and, of course, his demands concern the larger sweep of Kant’s thought rather than the minute details of the Critical Philosophy.