This book is a product of militant common-sense; and common-sense, in logic as in fiction, has little use for the neutral grays of everyday life; it likes its villains to be real angels of darkness. The fiend in human form who dominates this story is the logician. With a stupidity which quite achieves the level of malice, the logician since the days of Mill has involved every phase of causation in chaos and dark night, until in despair the author had to let in the light himself. The logician can hardly be expected to admit that this portrait is a true likeness, but if he is blessed with a sense of humor, he may be content to leave his revenge to nemesis. Perhaps he will be satisfied when he finds the light-bringer deriving cause from the fact that we cannot imagine a change to be 'produced' without action upon the thing changed (p. 43). While he is struggling to set the bounds to what we can imagine, the logic