20. How can you teach children what it is to concentrate their attention and the value of concentrated attention? * * * * * IV. THE FORMATION OF HABITS Habit in its simplest form is the tendency to do, think, or act as one has done, thought, or acted in the past. It is the tendency to repeat activities of all kinds. It is the tendency which makes one inclined to do the familiar action rather than a new one. In a broader sense, habit formation means learning. It is a statement of the fact that conduct _is_ modifiable and that such modifications may become permanent. The fact of learning depends physiologically on the plasticity of the nervous system. The neurones, particularly those concerned with intellectual life, are not only sensitive to nerve currents but are modified by them. The point where the greatest change seems to take place is at the synapses, but what this modification is, no one knows. There are several theories offered as explanations of what happens, but no one of them has been generally accepted, although the theory of chemical change seems to be receiving the strongest support at present. There can be no disagreement, however, as to the effects of this change, whatever it may be. Currents originally passing with difficulty over a certain conduction unit later pass with greater and greater ease. The resistance which seems at first to be present gradually disappears, and to that extent is the conduct modified. This same element of plasticity accounts for the breaking of habits. In this case the action is double, for it implies the disuse of certain connections which have been made and the forming of others; for the breaking of a bad habit means the beginning of a good one. The plasticity of neurone groups seems to vary in two respects--as to modifiability and as to power to hold modifications. The neurone groups controlling the reflex and physiological operations are least easily modified, while those controlling the higher mental processes are most easily modified. The neurone groups controlling the instincts hold a middle place. So far as permanence goes, connections between sensorimotor neurone groups seem to hold modifications longer than do connections between either associative-motor or associative-association. It is probably because of this fact that habit in the minds of so many people refers to some physical activity. Of course this is a misconception. Wherever the nervous system is employed, habits are formed. There are intellectual, moral, emotional, temperamental habits, just as truly as physical habits. In the intellectual field every operation that involves association or memory also involves habits. Good temper, or the reverse, truthfulness, patriotism, thoughtfulness for others, open-mindedness, are as much matters of learning and of habit as talking or skating or sewing. Habit is found in all three lines of mental development: intellect, character, and skill.