We shall regard these abstract and general ideas as the products of an intentional purpose directed to the special end of isolating the one and of classifying the other; we shall reserve the term _rational_ for the conduct which is guided in accordance with an ideal scheme or deliberate plan of action; while for behaviour to the guidance of which no such reflection and deliberation seems to have contributed we shall reserve the term _intelligent_. If, for example, the rejection of a cinnabar caterpillar by the chick is the direct result of experience through the re-presentation in the new situation of certain elements introduced during the development of a like situation, we shall call it an intelligent act. But if we have grounds for supposing that the situation is reflectively considered by the chick in relation to an ideal and more or less definitely conceived plan of action which is (perhaps dimly) taking form in its mind, we shall regard it as so far rational. And so, too, in other cases of animal behaviour. Now, with regard to the control through which consciousness is effective in the guidance of behaviour, it is necessary, in view of these considerations, to distinguish its intelligent from its rational exercise. And this is of importance since we generally speak of control in the latter sense in reference to human conduct. Intelligent control (on the perceptual plane) is due to the direct operation of the results of experience without the intervention of any generalized conception or ideal. In rational control (on the ideational plane), such conceptions and ideals exert a controlling influence. If, to prevent a boy sucking his thumb we administer bitter aloes, we trust to intelligent control through the immediate effects of experience; but if he be induced to give up the habit because it is babyish, he so far exercises rational control. What we call self-control is of this type. Only one more distinction need be drawn. Intelligent behaviour, founded on direct association gained through previous experience, we shall attribute to _impulse_; but for rational conduct, the outcome of reflection and deliberation, we seek to ascertain the _motive_. In human affairs our motives are referred to certain categories each of which presupposes an ideal scheme, prudential, æsthetic, ethical, or other. To act from motive and not from impulse is to act deliberately, because we judge the action to be expedient, seemly, or right, as the case may be. If, then, we contrast the lower perceptual stages of mental evolution with the higher ideational phases, the former includes behaviour due to impulse; but from it conduct due to motive is excluded. IV.--THE EVOLUTION OF CONSCIOUSNESS