It is inconceivable how we can hope to explain a feeling by the laws of motion; and so the fond hope of explaining the problems of the nature of the soul by mechanics is preposterous. No objection can be made to the possibility of explaining the delicate motions in the nervous substance of the brain by the laws of molar or molecular mechanics. But these explanations would throw no light upon the causation that takes place in the mind. The properly psychical phenomena, the properly intelligent action of thought, could not be explained in this way. For the world of mentality introduces quite a new factor into the sphere of being. What is this new factor? The nature of mental activity consists in the symbolism of feelings. Feelings, being different under different conditions and the same under same conditions, become representative of their corresponding causes, and thus the objects of experience are depicted in feeling symbols. Representativeness, accordingly, is the nature of mind. The question, How certain brain-structures operate, is a question of the mechanics of nervous substance, and further, the question, How thought-operations take place, is a question, so to say, of logical mechanics. But the question, Why a certain idea responds to certain stimuli and not to others, does not admit of a mechanical explanation or formulation. The answer to this question will be a description of the nature of the idea; and the nature of the idea is not a motion: it is the meaning of which the idea is possessed. The action of a mind depends upon the meaning of certain symbols. A written or spoken word has a special meaning, and this meaning becomes the determinant factor of mind action. The meaning of a word is not a piece of matter, neither is it a motion. It is something _sui generis_. I do not say that there is any inexplicable mystery connected with it. On the contrary, wonderful as the fact is, it is not mysterious; it does not stand in contradiction to any other fact of nature. Symbols stand for something; they indicate, denote, or signify something. This significance is called their meaning; and mind is a system of symbols in states of awareness. Now, neither states of awareness are mechanical, nor is the meaning of words anything mechanical. How can we hope for a mechanical explanation either of the soul or the mind or of any mental action?