mean the same by our ideas, but I can never have your perception and you can never have my perception. My ideas are enclosed in my mind. I may awaken in your mind ideas which have the same purpose and meaning, but they are new copies in your mind. We both may be angry, but your anger can never be my anger, and your volitions can never enter my mind. Every possible psychical fact thus exists in one consciousness only, while every physical fact exists for every possible consciousness.

The psychologist's final task is to explain the appearance and disappearance, the connections and sequences of these mental objects, the contents of consciousness. But before he can start on explanation of the facts, he has to describe them, and describing means analyzing them into their elements and fixating those elements and their combinations for an exact report. Such descriptive work is in a way preparatory for the further task of real explanation; yet it is in itself important, complicated, and difficult. Of course, it may be easy to separate the complex content into some big groups of facts, to point out that this is a memory idea and this an imaginative idea and the other an abstract idea, and this a perception and that a feeling, this an emotion and that a volition. But such clumsy first discrimination does not go further, perhaps, than does the naturalist's, who tells us that this is a mountain and that a tree, this a pond and that a bird. The real description would demand, of course, an exact measurement of the height of the mountain and the geological analysis of its structure, or an exact classification of the tree and the bird, with a complete description of their organs, and in each organ the various tissues have to be described, and in each tissue the various cells, and the microscopist goes further and describes the structure of the cell. Certainly in the same way the psychologist has to go on to resolve every one of those complex structures; he has to examine the mental tissues and the mental cells of which a volition or a memory idea or a perception are composed. And while he cannot use a microscope for these mental elements, yet his studies may cause elements to appear which the naïve observation remains entirely unaware of.

Perhaps he finds in his consciousness the perception of the table before him which lingers for a little while in his mind. He finds no difficulty in analyzing it into color sensations and tactual sensations; and yet he is aware of so much more in it. The table, for instance, has form for him and he may find that these form perceptions involve the sensations of the eye movements which he makes from one corner of the table to the other; he may find that if the idea lasts in him, he becomes aware of the time by sensations of tension; he finds that in his perception of the table lies an idea of its use, and he discovers that that is made up of elements which are partly memory reproductions of earlier impressions, partly sensations of movement impulses; he also finds that the table feels smooth, and he discovers by his analysis that this impression of smoothness results from a special combination of tactual sensations and movement sensations; and again those movement sensations he analyzes further into sensations of muscle contraction and sensations of pressure in the joints and sensations of tension in the tendons. Before a zoölogist has completed his description of a bird in the landscape, he has given account of hundreds of thousands of things; but before the psychologist would complete the enumeration of the mental elements which enter into the seeing of the table, he would have to give account of by far more psychical elements. Every point in the surface of the table has its own light value, perhaps different in its quality and intensity and saturation, in its hue and tint and shade from the next one, and at whatever point of the table's edge our attention is directed, each one involves numberless shades in the vividness of all the other points and numberless mental relations of space perception among the various parts of the table. In the thorough analysis of the describing psychologist, every single idea, and in the same way, every single emotion or feeling or judgment becomes complex like a living organism, an aggregate of thousands of mental tissues, and yet made up from "the stuff that dreams are made of."

But there is one particular difficulty which makes the psychological description so much harder than that of the physicist, and which gives rise to many disagreements and discussions in psychological literature. The psychologist has not only to tear the complex into pieces and thus to seek the elements, but he has to fixate those elements for the purpose of communication, as, of course, a scientific description demands that he be able to give account to others of what he experiences. The physicist has no difficulty whatever in that line because, as we saw, the world of physical things is the world which all men are sharing together. Every element which I find in it, I can show to every other person, and if I cannot show that particular thing, because I cannot yet carry the mountain to another place, then I can at least measure it, as we share those standards of space. Thus natural science has in its objective measurements the possibility of describing every part of the physical world. The psychical world, on the other hand, is as we saw, the world which is private property. Every effort at description is thus entirely in vain as long as our mental facts cannot somehow be linked with physical happenings. If I say that I have in my mind sweetness or sourness, or bitterness or saltness, I cannot carry any understanding to anyone else and therefore cannot give any description until I have agreed that I mean by sweetness the sensation which sugar gives me, and by saltness the sensation of salt. The sugar and salt I can point out to my neighbor and only in that way I understand what he means if he says that he tastes salt and sweet; otherwise I should have no means whatever to discriminate whether that which he calls a sweet taste sensation is not just what I call headache. Where no such direct relation for a physical thing is known, description of the mental element would remain impossible. Of course, everyperception of the outer world, all our seeing and hearing, and touching and tasting, offers us at once such definite connection between the inner experience and a piece of the physical universe. Our own organism is also such a piece of physical nature: just as I describe my tasting or touching, I may describe the perception of my arms and legs or my inner organs. Thus everything which is material of perception gives us a handle for a real psychological description. Psychology usually calls the elements of these perceptions sensations. Whatever is composed of sensations is thus describable.

On the other hand, no other way of description is open. If there were mental states which are composed of other elements than sensations, they would necessarily remain indescribable; we could not grasp them because they would not have any definite relation to the common physical world. We might say, for instance, that our mental content is made up of sensations and feelings, but if such feelings were really entirely different from sensations, they would have to remain for all time mysterious and unknown. We could not compare notes. The feeling which I call joy may feel just like the one which you call despair. The consistent development of modern psychology and its emancipation from vagueness and superficial analysis became possible only through the fact that such recourse to indescribable elements has become unnecessary. Modern psychology has been able to demonstrate more and more that the same elements which constitute our perceptions are also the