If we cannot regard the brain and the mind as two independent entities, scarcely any other conception of them is possible except as a single entity of which we may obtain knowledge in two ways, an objective and a subjective way. _Mind_ knows itself directly, without mediation of any kind, as a complex of sense impressions, thoughts, feelings, wishes, ideals, and endeavors, non-spatial, incessantly changing, yet to some extent also permanent. But _mind_ may also be known by other minds through all kinds of mediations, visual, tactual, and other sense organs, microscopes and other instruments. When thus known by other minds, mind appears as something spatial, soft, made up of convolutions, wonderfully built out of millions of elements, that is, as brain, as nervous system. By mind and brain we mean the same entity, viewed now in the aspect in which mind knows itself, now in the aspect in which it is known by other minds. Suppose a person is asked a question and after some hesitation replies. In so far as this act is seen, heard, and otherwise perceived (or imagined as seen, heard, or otherwise perceived), it is a chain of physical, chemical, neurological, etc., processes, of material processes as we may say. But that part of the chain of material processes which occurs in the nervous system may not only be known by others, but may know itself directly, as a transformation of perceptual consciousness into thought, feeling, willing. The links of these two chains of material processes in the brain and of mental states should not be conceived as intermixed and thus forming one new chain, but rather as running parallel--still better as being link for link identical. The illusion that one of these chains brings forth the other is caused by the fortuitous circumstance that they do not both become conscious at once. He who thinks and feels cannot at the same time experience through his sense organs the nervous processes as which these thoughts and feelings are objectively perceptible. He who observes nervous processes cannot at the same time have the thoughts and feelings as which these processes know themselves. Those objective processes, however, which go on outside of the nervous system, in particular those outside of the experiencing organism, in the external world, precede or follow mental states as causes generally precede their effects and effects follow their causes. There is no objection to speaking of a causal relation between material processes of this kind and mental states. Whatever explanation of the functional relation between brain and mind a person may accept, he need not constantly be on his guard lest he be inconsistent. We speak of the rising and setting sun without meaning that the earth is the center of the universe and that the sun moves around it. So we may also continue to speak quite generally of the material world as influencing our mind, and of the mind as bringing about changes in the material world.