This feeling makes us strive to bridge over this opposition, and ultimately the whole spiritual striving of mankind is nothing but the bridging of this opposition. The history of our spiritual life is a continuous seeking after union between ourselves and the world. Religion, Art, and Science follow, one and all, this goal. The religious man seeks in the revelation, which God grants him, the solution of the world problem, which his Self, dissatisfied with the world of mere phenomena, sets him as a task. The artist seeks to embody in his material the ideas which are his Self, that he may thus reconcile the spirit which lives within him and the outer world. He, too, feels dissatisfied with the world of mere appearances, and seeks to mould into it that something more which his Self supplies and which transcends appearances. The thinker searches for the laws of phenomena. He strives to master by thought what he experiences by observation. Only when we have transformed the world-content into our thought-content do we recapture the connection which we had ourselves broken off. We shall see later that this goal can be reached only if we penetrate much more deeply than is often done into the nature of the scientist's problem. The whole situation, as I have here stated it, meets us, on the stage of history, in the conflict between the one-world theory, or Monism, and the two-world theory, or Dualism. Dualism pays attention only to the separation between the Self and the World, which the consciousness of man has brought about. All its efforts consist in a vain struggle to reconcile these opposites, which it calls now Mind and Matter, now Subject and Object, now Thought and Appearance. The Dualist feels that there must be a bridge between the two worlds, but is not able to find it. In so far as man is aware of himself as "I," he cannot but put down this "I" in thought on the side of Spirit; and in opposing to this "I" the world, he is bound to reckon on the world's side the realm of percepts given to the senses, i.e., the Material World. In doing so, man assigns a position to himself within this very antithesis of Spirit and Matter. He is the more compelled to do so because his own body belongs to the Material World. Thus the "I," or Ego, belongs as a part to the realm of Spirit; the material objects and processes which are perceived by the senses belong to the "World." All the riddles which belong to Spirit and Matter, man must inevitably rediscover in the fundamental riddle of his own nature. Monism pays attention only to the unity and tries either to deny or to slur over the opposites, present though they are. Neither of these two points of view can satisfy us, for they do not do justice to the facts. The Dualist sees in Mind (Self) and Matter (World) two essentially different entities, and cannot therefore understand how they can interact with one another. How should Mind be aware of what goes on in Matter,