Metaphysics, formerly the queen of science, fell into oblivion under the onslaught of empiricism and positivism and its very possibllity came to be denied. Professor Elders traces the history of this process and shows how St. Thomas innovated in determining both the subject of metaphysics and the manner in which one enters this science, particularly in the framework of his Aristotle commentaries.The work then considers being and its properties, its divisions into being in act and being in potency, into the act of being essence, and into substance and the accidents. Finally the causes of being are considered. The work also introduces and surveys the extensive literature of Thomas interpretation of the past 50 years.