logical system. To learn the fundamental truths of education through a direct, comprehensive, systematic study of them and thereby to satisfy a serious need for which other subject matter does not provide, - this is the essential reason for the study of the principles of education. II - Since human development is explained in terms of both efficient and final causation, a simple basis for organizing the principles of education is possible only when the principles of education revealed from these two points of view are reduced to a common denomina tor. In seeking a simple basis on which to organize the principles of education for systematic study, we meet a difficulty in the fact that a human being may be regarded in two very different ways, and that various special studies of human life, whatever the minor differences among them may be, take one or the other of these general points of view. Since man has a body and is, therefore, a part of the physical world, such natural sciences as biology undertake to describe and explain his nature and behavior in a materialistic way as controlled by physical causes only; since he has a spirit and is, therefore, a free moral personality, teleological studies, such as logic, ethics, and history, regard him as controlled by purposes and ideas. A simple basis on which to organize the principles of education apparent from these two widely different points of view, which we shall explain more fully, is possible only if the principles can be reduced to a common denominator. In order to find this common denominator, this simple basis for bringing together and organizing educational principles, it will be necessary first to consider more fully the point of view of natural science, which may be called physical, or materialistic, and the point of view of teleology, which may be called ethical, or idealistic. III Natural science describes and explains man as a psychophysical organism controlled by physical causation only, and accounts for purposes and ideas as mere accompaniments of changes in the brain, thus making the body appear to be master of the mind. Natural science, since it is the science of the physical world, must base its explanations upon physical causes. This method of explanation is the only one that it ever uses, the only one that it knows anything about. Primitive man, with his superstitious belief in animism, attempted to explain changes in the physical world by attributing them to spiritual forces; the modern scientist - never! Imagine the futility of trying to convince a physicist that, when the throttle is open, the steam locomotive moves as the result of some spirit inherent in the mechanism! The physical structure of the locomotive and the physical conditions under which it is placed are sufficient for a complete explanation. These, in turn, are traced to their physical causes. The locomotive was produced by whirring machinery in the factory, and the machinery was the product of previous mechanical action. One condition for the movement of the engine is coal, which was made by physical forces geological ages ago. Indeed, every factor in the movement of the locomotive may be traced backward, theoretically at least, from physical effect to physical cause, until the chain of connection is lost in primeval chaos. Nowhere, absolutely nowhere, does natural science recognize a spirit link in this chain. But did not men work in making the locomotive? Did they not with physical hands guide the iron and steel through the machines and swing the hammers in assembling the parts? And did they not do this because they had desires to earn wages and to construct, and had ideas that guided their movements? According to the view of natural science, they did not do this because they had desires and ideas. Natural science cannot recognize feelings and ideas as having any part whatever in the causal chain. Conservation of energy, a fundamental assumption of science, forbids it, because force can be attributed with scientific accuracy to physical objects only. According to this assumption, the total amount of force in the universe is always the same; it never increases or diminishes. If this assumption is true, energy, when not manifesting itself, must be considered as latent, or stored away. For example, when a clock spring is wound, energy is stored in it to be given off gradually in the running of the clock during the flight of hours. When a wagon is drawn up hill, the force applied to it that is not turned into heat by the friction of the running parts, is stored up in it and is given out again when the wagon runs down hill. Energy from the sun is stored in the coal and may be released to warm our houses, cook our food, or run our factories. But how could energy be stored in a mere idea or feeling, neither of which has a body or, except during its momentary appearance in consciousness, even exists? When the workman is asleep, when on a holiday he is thinking about social pleasures, the ideas and feelings that appear in the factory are not in his consciousness; they do not exist. How, then, could there be stored in them forces which contribute to the construction of the locomotive? How could there be stored in them the force necessary even to modify the engineer's brain and nerves so as to make his muscles open the throttle, when the locomotive, under a full head of steam, is ready to run? According to natural science, so long as it holds to the fundamental assumption of the conservation of energy, purposes and ideas cannot have even an infinitesimal amount of force; they cannot add to or in any way change physical forces. It is true that feelings and ideas may with correctness be spoken of as causes of physical actions. We may say that a man eats because he feels hungry or because he has the idea of strengthening his body. But in this case the materialistic point of view is not taken, and physical, or efficient, cause is not meant. What is meant is explained in the discussion of the teleological view of man. So far as natural science is concerned, to speak of feelings and ideas as causes of physical action is to use a metaphor that has no foundation in fact. The idea of the locomotive and the warmth of constructive interest, according to the explanation of natural science, can no more cause movements of the physical body of the workman than a bright idea can reflect sunshine into the factory, sharp wit cut the tempered steel, or the heat of desire kindle the forge. Since man's body is a part of the physical world, natural science has a right to explain his actions in its own way as the result of physical causes. Just as the movements of the locomotive are considered the result of its structure and of the physical environment, such as coal, air, and water, acting upon it, so the actions of man, whether they be breathing, walking, painting a picture, or composing a poem, may be explained as the result of his bodily structure and of the stimuli coming from its physical environment. And just as the structure of the locomotive is the result of physical causes, so the structure of the human being is the result of physical heredity, variation, and natural selection in the great factory of the material world. Natural science, equipped with its materialistic methods of description and explanation, did not stop with the conquest of the physical world. Flushed with victory in this conquest, it invaded the realm of mind and attempted to explain the nature of consciousness. But here, at the very outset, it met a serious difficulty, because natural science was developed to explain the physical world and knows of no basis for explanation except physical causation. Since, as has been shown, physical energy cannot be stored in ideas and feelings, the mind is not subject to the kind of causal relations to which natural science is limited in its explanations. A way to overcome this difficulty, however, was invented. It was known that lesions in the brain are accompanied by changes in the character of consciousness, that certain drugs taken into the body affect the ideas and feelings, that stimuli applied to nerves leading to the brain are followed by corresponding sensations. These and many other similar facts were made the basis for the assumption that every mental change is paralleled by a corresponding physical change in the brain. This assumption, which is called psychophysical parallelism, opened the way for natural science in the explanation and control of mental life. If every idea and feeling is chained in some mysterious way to a physical partner in the brain, natural science, although it cannot lay hands directly upon ideas and feelings, can do what is for practical purposes the same thing; it can substitute for the direct explanation of ideas and feelings an explanation of the physical partners which they invariably accompany. It can account for the sensation of light as the accompaniment of the stimulation of certain |