CHAPTER XVII

        With all other sciences psychology must postulate the existence of an external material world of space, time, and objects. Psychology does not inquire into the nature of these objects, as to what they are in themselves. This as we pointed out is the business of metaphysics, not of science. Psychology however does ask how we come to know the outside world; it inquires as to the process by which external reality comes to be presented in consciousness.

        The fact that psychology postulates an external material world and studies it in so far as it comes to be reflected in consciousness, points to another postulate which psychology must assume in addition, namely, the existence of an inner world consciousness. This postulate is peculiar to psychology, no other of the descriptive and objective sciences have to assume it. Although it is quite clear that without mind there can possibly be no study, no science, still this is but an indirect reflection which none of the concrete sciences have to take into consideration. Of course, a chemist is required for chemistry, a physicist for physics, a physiologist for physiology, and so on, but the chemist, the physicist, the physiologist do not introduce themselves into their science. In all concrete sciences the mind is entirely projected into its object, it is the external object itself that has to be taken into consideration. In concrete science consciousness is drowned in the object, in psychology, on the contrary, the object is drowned in consciousness. The chemist, the physicist, who will turn his attention to consciousness and introduce his psychic states, his moods, dispositions, and intentions as elements into his investigations will hardly be an exact scientist. Not so with the psychologist, he must take the inner world into account, he must deal with consciousness, with moods, with feelings. It is true that he must treat them as objects, but these objects, unlike those of other positive sciences, are after all of the inner subjective world of consciousness. For the very essence of psychology is the taking account of phenomena of consciousness.

        In our last statement that psychology deals with the objective external world as reflected in consciousness another postulate is implied. Besides the external and internal worlds, psychology also postulates the interrelation of the two.

        This interrelation is not direct, it is not one of antecedent, and consequent, but that of coexistence; for as we have already pointed out, the two series of phenomena, the mental and the physiological, must be assumed as concomitant, as running parallel to each other. If, however, by "the external world" we understand the universe of objects exclusive of the functioning psycho-physiological processes then we may say that it stands to the phenomena of consciousness in relation both of sequence and coexistence.

        The objective external world enters into relation with consciousness only through the intermediacy of physiological nervous processes. Only on this condition can the external world enter into relation with consciousness, and under special conditions become its dire object. I take a dose of opium, mescal, or cannabis Indica, and have different hallucinations and illusions, mental activity is stimulated. The mind teems with sensations, images, ideas, feelings, emotion moods; now the whole organism is pierced by sharp pain, now it tingles with indescribable acute pleasure; now a charming vision appears, a beautiful scenery unrolls before the mind's eye, a feeling of perfect heavenly bliss diffuses itself all over our conscious being; now a disgusting, ugly figure presents itself, a horrible scene is witnessed that plunges the mind into an abyss of misery. The current of consciousness is accelerated and it drives its waves with more vigor than ever.

        Instead of being accelerated, the current may be depressed and retarded even to such a degree as to plunge the mind into a deep sleep. Such retardation we find under the influence of bromides, or of anaesthetics, such as ether, chloroform, of hypnotics, such as sulfonal, chloral and others. We have here the action of a drug, of an external object on the physiological nervous processes with their psychic concomitants. In this case, however, the drug itself does not become the direct object of consciousness. Through the mere absorption of opium, cannabis or belladonna, we can know nothing of their constitution, we can know nothing of their color, of their size, of their weight, specific gravity and so on, we cannot possibly perceive them as objects. The states of consciousness which cannabis, for instance, gives rise to affords no knowledge of the external objective nature of the drug itself.

        A direct knowledge of an external object is acquired through the special senses. Yonder is an object, an inkstand. It stimulates the peripheral sense organ, the eye, the retina, the physiological processes aroused in the rods and cones are transmitted by the optic nerve and by the optic tracts to the visual centres of the occipital lobes, the functioning of which is accompanied by sensations of sight. The wave of stimulation spreads from the visual centres to other centres closely associated with them. They too begin to function with more or less intensity, accompanied by images, ideas, thought, which constitute the perception of the inkstand yonder. The combined activity, or function of a whole system of centres gives rise to the percept inkstand along with its psychic fringe, with the stream of consciousness in which it is bathed. We see and know the inkstand.

        From a psychological standpoint the mode of action of the inkstand differs radically from that of the opium. The latter may be characterized as psycho-physiological, or even purely physiological, the former may be termed psycho-physical or psychological, perceptual. The one gives rise to perception, to knowledge of the external object, while the other does not. Both, however, agree in this that they can enter into relations with consciousness only through the intermediacy of physiological nervous processes. The two modes of action and their relation to consciousness may be represented by the following diagrams:

         I. Psycho-physical or perceptual relation.

         II. Psycho-physiological relation.

         In fig. I, Ob. is the object stimulating S. the organ of special sense, giving rise to physiological nervous processes with their concomitant psychic states constituting the subjective object which is objectified in the object yonder. In Fig. II, D is the drug acting directly on the nervous centre the stimulated activity of which gives rise to the perception of an external object Ob. Thus we find that external physical and physiological processes are causally related, or stand to each other in relation of invariable or necessary sequence while the physiological and psychic processes stand in relation of coexistence. What the nature of this inter-relation is and how it is possible are problems for epistemology and metaphysics. Psychology must assume this interrelation as its postulate.

        If psychology is to be a science at all, it must postulate the uniformity of the phenomena with which it deals. This we have pointed out in our second chapter when we discussed the subject matter of psychology. We turn to it again in order to realize clearly its full meaning in psychology. Psychology, as we know, in addition to the external world of physical sciences, also postulates consciousness. Its postulate of uniformity is, therefore, far more complex than in other positive sciences. With physical science psychology must postulate uniformity of the external world, because it presupposes the physical sciences, and because the external world forms the content and object of consciousness. This, however, is not sufficient. Psychology must also postulate the uniformity in the inner world of psycho-physiological, or mental phenomena. Were there no uniformity in the phenomena of consciousness, psychology, as a science would have been an impossibility.

        This, however, is not all. Psychology must also postulate the uniformity of relationship between the phenomena of the external and inner worlds. Definite physical processes must be concomitant with certain well defined psychic states. Were this otherwise, the two series, the mental and the physical, would be out of joint, the relations of coexistence would no longer be obtained, and the two series would stand to each other in no relation at all; thus noise, for instance, would sometimes be smelled, sometimes tasted, and sometimes seen. Psychology as a science that deals with general laws, would certainly have been impossible. We would neither have been able to express to others our states of consciousness in uniform definite movements, nor would it have been possible for others to understand us, nor would it have been possible to call forth in others certain desired states of consciousness; in short, not only psychology would have been an impossibility, but also all human intercourse. The myth of the tower of Babel would have been fully realized. Psychology must postulate uniformity of interrelation of physical, physiological, and psychic processes.