The aim of this inquiry was, as said at the outset, neither a comprehensive history of metaphysics nor the establishment of new metaphysical ideas. In order to get a concept of metaphysics common to all sides in disputes on the subject, the author has tried to investigate some representative historical usages of the word "metaphysics." This special purpose has restricted the subject and forced him to exclude many great metaphysical theories. The inquiry has been confined to some important philosophers who made metaphysics the subject of their inquiries. Even when those philosophers were also great metaphysicians as in most cases they were, the contents of the metaphysical theories themselves were set aside. If this aim is understood, it will be admitted that it would be unreasonable to demand as the conclusion of this book the author's own metaphysical theory or even a new definition of the concept of metaphysics. Such a problem is of great importance, especially for the author, who is in various ways interested in metaphysics. But it must be reserved for another enterprise. The assessment of modern metaphysicians was generally unfavourable, so that the reader might suppose that the denial of metaphysics was the final outcome of his inquiry. But the rule that the criticism of contemporaries is generally strict must be taken into account. Moreover suspicion of the new metaphysics may sometimes tend towards defence of the old, as in the case of the Thomists. The only idea in conflict with the possibility of such a conservative attempt is the idea of progress, but philosophy can even doubt the validity of this faith.