"In his masterpiece, The Essence of Thomism, Gallus Manser succeeded in the difficult challenge of presenting St. Thomas and Thomism in a way that is both systematic and historical. The work is systematic since it identifies the composition of act and potency as the key theoretical principle that informs Aquinas's major theses, yet historical since it places St. Thomas and his disciples in the debates of their own time. At a time when philosophers and theologians are showing a growing interest in the resources of thought offered by the Thomist tradition, it was imperative to make this monument of twentieth-century Thomism accessible to a wider English-speaking audience."

"The Essence of Thomism impresses by its crystalline clarity and its iron consistency. The extensive work is the answer to a single fundamental question and the broad demonstration of a single thesis. It is no exaggeration to claim that The Essence of Thomism is the most important German-language comprehensive presentation of Thomistic philosophy in the first half of the twentieth century."

"It must be welcomed, not only by the adherents of 'strict' Thomism but even more so by everyone else, when a leading representative of this school undertakes to present its very essence. We may thus hope to be instructed from the best source on the ultimate foundations and supporting pillars of this system. Manser's book serves this purpose."

"Father Manser chose the duality of act and potency as the deep intuition that guided the elaboration of Thomism. He also sees it as the keystone of the system. It is always somewhat precarious to want to reduce the theses of an entire body of knowledge to a single and very simple vision of reality. But, unless further evidence is brought forward, one can admit that the doctrine of act and potency, as St. Thomas understood it, was the living force—or, if you will, the guiding idea—of his metaphysical thought. From this angle, one can only rejoice that Father Manser's book is once again accessible to students of Thomistic philosophy. Everything that a logical and comparative analysis of St. Thomas's principal texts can yield as an immanent interpretation of his thought may be found in this book."

"At the heart of Thomist metaphysics lies the real distinction between act and potency in every created being. This foundational principle illuminates all other aspects of the science and gives metaphysics its proper unity as a discipline. Long unknown to English-speaking readers, Manser's Das Wesen des Thomismus is now, happily, available in English. May it help form the minds of contemporary metaphysicians in the pursuit of true sapiential unity."