These substantial volumes form a piece of work that was well worth doing, and is very well done. In the shape of studies of particular thinkers, they include both a history, in effect continuous, of modern theories of Cause, and an independent discussion of the scientific validity of the conception and its philosophical basis. The author, it may be noted at the outset, proclaims himself a Kantian; and being, as nearly as possible, a pure Kantian, he finds much to agree with in English experiential philosophy both before and after Kant. It is on the experiential side of Kant that he especially dwells, one of his principal results being the rejection—in reference to the conception of Cause—of philosophic rationalism. Not merely the particular phenomena that are thought of as causally connected, but the causal relation itself, is given in experience. A mental “activity” is required to turn the “given” order into a necessary connexion; but the criteria by which we know that the relation is one of cause and effect are wholly experiential. The rationalistic view of the causal sequence, the notion of the effect as deducible from its cause apart from previous experience, though not yet wholly banished from scientific thought so far as it is uninformed by philosophy, can no longer have any place in the philosophical theory of science.

The rationalistic notion of Cause, as the author begins by showing, was the predominant one at the opening of modern philosophy.