The best summary of this book is in the author's foreword: "It is the proper aim and scope of the present book to show that the history of philosophy makes philosophical sense, and to define its meaning in regard to the nature of philosophical knowledge itself. For that reason, the various doctrines, as well as the definite parts of these doctrines, which have been taken into account in this volume, should not be considered as arbitrarily selected fragments from some abridged description of medieval and modern philosophy, but as a series of concrete philosophical experiments especially chosen for their dogmatic significance. Each of them represents a definite attempt to deal with philosophical knowledge according to a certain method, and all of them, taken together, make up a philosophical experience. The fact that all those experiments have yielded the same result will, as I hope, justify the common conclusion... that there is a centuries long experience of what philosophical knowledge is - and that such an experience exhibits a remarkable unity."