Les Deux Sources de la Morale et de la Religion is not a book to leave one indifferent. Those who are persuaded by its argument or inspired by its message are prone to manifest the same enthusiasm as Georges Cattaui who praised it as one of the greatest and wisest books conceived by philo­ sophers. Even those who take exception to the doctrine it expounds are impelled to acknowledge its significance. It was in his critique of Les Deux Sources that Jacques Maritain was moved to call the philosophy of Henri Bergson one of the most daring and profound of our time. When many years ago I opened Les Deux Sources for the first time, I turned out of curiosity to the last page and beheld these words, "l'univers ... est une machine it faire des dieux." Bergson was an evolutionist, but surely this was no ordinary evolutionist speaking, I thought. What must be the moral philosophy of a man who would write these words? When much later I undertook the present study, it was this same question which con­ cerned me.