Beginning from that stage of evolution where inhibition intervenes, reflex action loses the character of an automatic response to impulse and becomes disciplined. Inhibition tries to suppress reflex action. Its success is more or less complete according to the sensitiveness and life energy of the tissue receiving the stimulus and the degree to which the mechanism of inhibition is developed. The organism retains its tension, remains charged with energy, and is able to carry out work for definite purposes. In place of anarchistic reflex action which occurs regardless of the needs of the organism, we find economy of energy, co-ordination of effort, movement directed to a profitable end. It is only inhibition which can raise the organism from its state of passivity, its helpless dependence upon tropism, to a being in which a will is beginning to dawn and which by its will becomes self-determinative. Inhibition is a function of the will; it is the will's tool. Even Plato dimly perceived this, and he expresses it in the metaphorical language peculiar to himself, when, in the "Republic," he compares a human being to a creature made up of three animals: a hundred-headed sea-serpent which must at one and the same time be fed and tamed, a blind lion, and a man who tames the serpent by means of the lion. These three animals are desire ([Greek: epithumia]), courage ([Greek: thumos]), and mind ([Greek: nous]). We say in biological language, reflex action, inhibition, and will or volitional reason.