Book excerpt: First published in 1924, this book examines one of the main philosophical debates of the period. Focusing on Kant’s proof of causality, A.C. Ewing promotes its validity not only for the physical but also for the "psychological" sphere. The subject is of importance, for the problem of causality for Kant constituted the crucial test of his philosophy, the most significant of the Kantian categories. The author believes that Kant’s statement of his proof, while too much bound up with other parts of his particular system of philosophy, may be restated "in a form which it can stand by itself and make a good claim for acceptance on all schools of thought".