Mechanics deals with the laws of energy and motion, physics with molecular changes of matter, but neither physics nor mechanics would have gone far, had they stopped to answer the questions as to what motion, energy, matter are in themselves. These are simply postulated, taken for granted, they are the ultimate data of these sciences. In this respect psychology does not differ from other sciences, it takes its subject matter as given and does not inquire as to what the nature of the material is in itself. The reader must remember that the question as to what things are in themselves is not at all a question of positive sciences, but of metaphysics. I do not mean in any way to detract from the dignity of metaphysics, what I wish is simply to point out the limits of positive science. The problem as to what things are in themselves does not fall within the province of science, but within the domain of metaphysical research.
The question as to the nature of consciousness, what it is in itself, may be a very important one, but it lies outside the ken of psychology, just as the laws of aesthetics do not concern the chemist, although the latter may be a great lover of beauty. In the contemplation and enjoyment of a beautiful picture he will not introduce a chemical formula, and in his chemical experiments he will not introduce aesthetic considerations. The same holds true in the case of psychology. The psychologist may be a metaphysician, but in his psychological work he must keep clear of metaphysics. Consciousness therefore is a presupposition, a postulate of psychology.
There is one more important assumption which psychology must start with in order to be a positive science at all, namely, uniformity. Under similar conditions like results follow. Suppose a geometrician should prove to you that the sum of the three angles of a triangle is equal to two right angles, suppose that some sceptic should come in and say, "Yes, that is all right in relation to the triangles in this particular space, in another portion of space, on some other star, or planet the theorem will not hold good." The only answer the geometrician could give is that we must assume that space is uniform, so that wherever we form our triangles we obtain the same results. The same is true in mechanics. The laws of motion and inertia hold good of the pebble on the roadside, of the dust grains dancing in the sunbeam, and of distant stars in the milky way. Uniformity of relations among phenomena must be postulated, if science is to be at all. If under the same conditions different results follow, science would have been an impossibility. Uniformity of nature is one of the most fundamental postulates of science. Psychology assumes uniformity; it assumes that there exist constant uniform types of mental activity with definite relations that can be formulated into psychological laws. Thus psychology at the very outset postulates consciousness and uniformity of mental phenomena.
We can now see in what relation psychology which deals with phenomena of consciousness differs from philosophy whose subject matter is also consciousness. Philosophy has no postulates, psychology, like all other sciences, must have its postulates which it cannot transcend. Philosophy deals with the ultimate in consciousness, it investigates the very postulates of conscious activity. Psychology on the contrary accepts the facts of consciousness as ultimate data.
II Physical and Psychic Facts
Psychology we said deals with facts of consciousness, but this is too broad a statement, for there are other sciences that also deal with facts of consciousness, such as ethics, aesthetics, logic. In what respect does psychology differ from these sciences? It differs in this that ethics, aesthetics and logic are normative regulative sciences; psychology is a positive natural science. Ethics deals with ideals of moral life, aesthetics with ideals of beauty, and logic with ideal ways of correct reasoning. All these sciences deal with ideals, with norms to which the matter of fact consciousness ought to conform, if it is to act rightly. They put a value on the phenomena. Psychology, however, like all other natural sciences has no other ideal than fact, it admits of no "ought." From a strictly psychological standpoint, the ugly and the beautiful, the good and the evil, the true and the false are of equal value. Psychologically they are all facts of consciousness and must be studied as such; just as the serpent and the dove are of equal interest and value to the naturalist. The ravings of a maniac are of the same psychological interest and value as the subtle reasoning of a Newton. Psychology is a positive natural science, it does not deal with the subjective evaluation of facts of consciousness, but with their objective natural existence.
Having shown in what psychology agrees with other positive natural sciences, we must now point out in what it differs from them. Psychology deals with phenomena of consciousness as facts of objective natural existence. Are these facts of the same order with those of the physical world, the subject matter of the natural physical sciences? We must answer in the negative. The objects of the natural sciences of the physical world arc of a material and spatial nature. A physical body has weight, occupies a certain portion of space, so has the molecule, the atom. Can we say the same of psychological facts? By no means. They are different in kind, and this I wish especially to impress on the mind of the reader. To realize this truth, I think it a good preliminary psychological exercise for the reader to try to find how many grams, or grains his idea of beauty weighs, how many millimeters long, wide and high his feelings of love are; let him indulge in the fancy of conceiving an engineer building a bridge with mathematical formulae as links, and his feelings of virtue and patriotism as supports. On the other hand let him think of a logician trying to fill up the defects of his train of reasoning with solid bricks, and using as connecting links bars of pig iron. In short, psychology differs from physical sciences in this, that its facts, the facts of consciousness are not of a material nature.
"Do not physical sciences it may be asked "deal with such phenomena as sound and light?" Certainly they do, but these sciences regard these phenomena from a standpoint radically different from that of psychology. Sound in physics is not the sensation sound, but the external, material vibration of air, which may or may not give rise to a sensation of hearing. The same holds true in the case of light. What physics investigates is not light as sensation, but vibrations of ether which may or may not give rise to a sensation of sight. It is, however, just such facts as sensations, facts not spatial in their nature which constitute the subject matter of psychology.
"May not facts of consciousness be some kind of matter, some form of material substance the constitution of which we do not as yet know?" Such was the question put by a medical man, when he heard me expounding the difference in kind between physical and psychical facts. "That might be" I answered, "but then substance, if it ever be discovered, will not have the properties of matter; it will be a "matter" totally different in kind from that studied by the physicist. For the "matter" of physical sciences is essentially one of extension; a matter however that occupies no space is an existence altogether different in kind from that of extended things, and is certainly no "matter" for the physicist.
The persistent antagonist may raise here a further objection. "Are not the phenomena of consciousness" he may ask "facts of activity? And is not activity, kinetic energy? And if this be the case must not the facts of consciousness be ranged along with physical phenomena, be reduced to the manifestations and transformations of kinetic energy and thus really and ultimately fall within the domain of the mechanical sciences?"
Change certainly is manifested in the mutations of states of consciousness, but this change is not the physical change of translocation. Change in the states of consciousness may no doubt, be regarded as activity, and if you please as energy, but this activity is not the energy of mechanics. Activity in mechanical or physical sciences means molar, molecular, or atomic movement of matter through space, while psychic activity is not a translation of matter through space, a thought is not a material mass having extension, weight and locomotion. This truth, simple as it may appear, cannot be too often repeated and too strongly emphasized, since one frequently meets with this fallacy of "thought-materialization" in the world of psychiatry. Words are often misleading and the metaphorical expression "mental energy" is taken in its literal meaning of mechanical energy. While I am writing these lines I find in one of the number of the Russian "Archives of Psychiatry and Neurology" edited