The chaotic character of psychotherapy in this first decade of the twentieth century can be easily understood. It results from the fact that in our period one great wave of civilization is sinking and a new wave rising, while the one has not entirely disappeared and the other is still far from its height. The history of civilization has shown at all times a wavelike alternation between realism and idealism, that is, between an interest in that which is, and an interest in that which ought to be. In the realistic periods, the study of facts, especially of the facts of nature, is prevalent; in idealistic periods, history and literature appeal to the world. In realistic periods, technique enjoys its triumphs; in idealistic periods, art and religion prevail. Such a realistic movement lies behind us. It began with the incomparable development of physics, chemistry, and biology, in the middle of the last century, and it brought with it the achievements of modern engineering and medicine. We are still fully under the influence of this gigantic movement and its real achievements will never leave us; and yet this realistic wave is ebbing to-day and a new period of idealism is rising. If the signs are not deceitful, this new movement may reach its historical climax a few decades hence, when new leaders may give to the idealistic view of the world the same classical expression which Darwin and others gave to the receding naturalistic age. The signs are clear indeed that the days of idealistic philosophy and of art, and of religion, are approaching; that the world is tired of merely connecting facts without asking what their ultimate meaning is. The world dimly feels again that technical civilization alone cannot make life more worth living. The aim of the last generation was to explain the world; the aim of the next generation will be to interpret the world; the one was seeking laws, the other will seek ideals. Psychotherapy stands in the service of both; it is the last word of the passing naturalistic movement, and yet in another way it tries to be the first word of the coming idealistic movement; and because it is under the influence of both, it speaks sometimes the language of the one, and sometimes the language of the other. That brings about a confusion and a disorder which must be detrimental. To transform this vagueness into clear, distinct relations is the immediate duty of science.