This is one of the most seminal works of Kalidas Bhattacharyya. Bhattacharyya speaks of the constant need that philosophers have felt to justify their work and their discipline. Bhattacharyya thinks that the modern defense of Philosophy is only possible through what he calls logic of alternation. Bhattacharyya’s position is that we can provide Philosophy with such a defense only by attempting a novel understanding of the knowledge-object unity. Bhattacharyya claims that this attempt is ingrained in the very being of all the important Indian systems of thought. This book is both a historical and comparative study of the basis of all Philosophy. The book has four chapters. Chapter One is on “Knowledge of Object” where the close unity of knowledge and its object is emphasized. In this connection, Bhattacharyya discusses subjective and objective attitudes and also the contradiction between subjectivity and object. Chapter Two is on “Types of Philosophy”. In this chapter, Bhattacharyya tries to show that the Unity of Knowledge and Object is Unrejectable and their unity is inevitable. Those who reject the knowledge-object unity do so because they think that such a unity would definitely lead to some kind of contradiction. But Bhattacharyya would like to show that this contradiction too is not rejectable. Actually, the Unity that he speaks of is a Disjunctive Unity. This disjunctive unity actually indicates that we have to stand alternatively on the subjective and the objective attitudes and reach a kind of dialectical unity. He then goes on to speak of the subject-object and the absolute as alternatives. In Chapter Three, “Cognition Feeling and Conation” Bhattacharyya takes up these three notions which seem to be opposed to each other. The first three chapters are analyses of these notions while the last section sees Cognition, Feeling and Conation as Alternatives. In Chapter Four Bhattacharyya considers “Further Alternatives” such as Jñāna Bhakti and Karma. He speaks of the three kinds of infinity in this chapter. The book ends with the idea of the Ultimate Alternation.