If you are familiar with Koestler's The Yogi and the Commissar and his Dialogue with Death (and not solely with his fiction) you will be not unprepared for this scholarly psychological treatise which deals with the inner man and his relation, as part of the evolutionary process, to the world about him. The author's contention is that all of the creative activities of man are based on a common pattern, and he then proceeds to trace this pattern as a unifying theory through three chosen fields, humor, art, and discovery. By the use of three ad hoc hypotheses, he develops a system of ethics, neither utilitarian nor dogmatic, which is derived from the same integrative tendency in the evolutionary process to which the creative activities of art and discovery are traced. His habit of contrasting and explaining his terminologies in terms of those of other writers in the same field is helpful and illuminating. Part I examines the geometry of the creative mental processes, approaching through the comic; Part II examines the qualities of the emotions and stresses as well the tragic; Part III relates Part I to Part II; Part IV analyzes the emotive arts. The theories of Freud and Bergson and others are examined. The book is a tour de force of planning and presentation. The appendices and bibliography are a valuable contribution in themselves. Juicy meat for the expert on matters psychological, and no barrier to interested laymen...Koestler's name will carry this well beyond the obvious market.