particles composing a stream be re-collected and made to pass a given point in its course in precisely the same order and relation to one another as before. This means, then, that we can never have precisely the same mental state twice; that the thought of the moment cannot have the same associates that it had the first time; that the thought of this moment will never be ours again; that all we can know of our minds at any one time is the part of the process present in consciousness at that moment.
The Wave in the Stream of Consciousness.—The surface of our mental stream is not level, but is broken by a wave which stands above the rest; which is but another way of saying that some one thing is always more prominent in our thought than the rest. Only when we are in a sleepy reverie, or not thinking about much of anything, does the stream approximate a level. At all other times some one object occupies the highest point in our thought, to the more or less complete exclusion of other things which we might think about. A thousand and one objects are possible to our thought at any moment, but all except one thing occupy a secondary place, or are not present to our consciousness at all. They exist on the margin, or else are clear off the edge of consciousness, while the one thing occupies the center. We may be reading a fascinating book late at night in a cold room. The charm of the writer, the beauty of the heroine, or the bravery of the hero so occupies the mind that the weary eyes and chattering teeth are unnoticed. Consciousness has piled up in a high wave on the points of interest in the book, and the bodily sensations are for the moment on a much lower level. But let the book grow dull for a moment, and the make-up of the stream changes in a flash. Hero, heroine, or literary style no longer occupies the wave. They forfeit their place, the wave is taken by the bodily sensations, and we are conscious of the smarting eyes and shivering body, while these in turn give way to the next object which occupies the wave. Figs. 1–3 illustrate these changes.
Consciousness Likened to a Field.—The consciousness of any moment has been less happily likened to a field, in the center of which there is an elevation higher than the surrounding level. This center is where consciousness is piled up on the object which is for the moment foremost in our thought. The other objects of our consciousness are on the margin of the field for the time being, but any of them may the next moment claim the center and drive the former object to the margin, or it may drop entirely out of consciousness. This moment a noble resolve may occupy the center of the field, while a troublesome tooth begets sensations of discomfort which linger dimly on the outskirts of our consciousness; but a shooting pain from the tooth or a random thought crossing the mind, and lo! the tooth holds sway, and the resolve dimly fades to the margin of our consciousness and is gone.
The "Piling Up" of Consciousness is Attention.—This figure is not so true as the one which likens our mind to a stream with its ever onward current answering to the flow of our thought; but whichever figure we employ, the truth remains the same. Our mental energy is always piled up higher at one point than at others. Either because our interest leads us, or because the will dictates, the mind is withdrawn from the thousand and one things we might think about, and directed to this one thing, which for the time occupies chief place. In other words, we attend; for this piling up of consciousness is nothing, after all, but attention.
3. CONTENT OF THE MENTAL STREAM
We have seen that our mental life may be likened to a stream flowing now faster, now slower, ever shifting, never ceasing. We have yet to inquire what constitutes the material of the stream, or what is the stuff that makes up the current of our thought—what is the content of consciousness? The question cannot be fully answered at this point, but a general notion can be gained which will be of service.
Why We Need Minds.—Let us first of all ask what mind is for, why do animals, including men, have minds? The biologist would say, in order that they may adapt themselves to their environment. Each individual from mollusc to man needs the amount and type of mind that serves to fit its possessor into its particular world of activity. Too little mind leaves the animal helpless in the struggle for existence. On the other hand a mind far above its possessor's station would prove useless if not a handicap; a mollusc could not use the mind of a man.
Content of Consciousness Determined by Function.—How much mind does man need? What range and type of consciousness will best serve to adjust us to our world of opportunity and responsibility? First of all we must know our world, hence, our mind must be capable of gathering knowledge. Second, we must be able to feel its values and respond to the great motives for action arising from the emotions. Third, we must have the power to exert self-compulsion, which is to say that we possess a will to control our acts. These three sets of processes, knowing, feeling, and willing, we shall, therefore, expect to find making up the content of our mental stream.
Let us proceed at once to test our conclusion by introspection. If we are sitting at our study table puzzling over a difficult problem in geometry, reasoning forms the wave in the stream of consciousness—the center of the field. It is the chief thing in our thinking. The fringe of our consciousness is made up of various sensations of the light from the lamp, the contact of our clothing, the sounds going on in the next room, some bit of memory seeking recognition, a "tramp" thought which comes along, and a dozen other experiences not strong enough to occupy the center of the field.
But instead of the study table and the problem, give us a bright fireside, an easy-chair, and nothing to do. If we are aged, memories—images from out the past—will probably come thronging in and occupy the field to such extent that the fire burns low and the room grows cold, but still the forms from the past hold sway. If we are young, visions of the future may crowd everything else to the margin of the field, while the "castles in Spain" occupy the center.
Our memories may also be accompanied by emotions—sorrow, love, anger, hate, envy, joy. And, indeed, these emotions may so completely occupy the field that the images themselves are for the time driven to the margin, and the mind is occupied with its sorrow, its love, or its joy.
Once more, instead of the problem or the memories or the "castles in Spain," give us the necessity of making some decision, great or small, where contending motives are pulling us now in this direction, now in that, so that the question finally has to be settled by a supreme effort summed up in the words, I will. This is the struggle of the will which each one knows for himself; for who has not had a raging battle of motives occupy the center of the field while all else, even the sense of time, place and existence, gave way in the face of this conflict! This struggle continues until the decision is made, when suddenly all the stress and strain drop out and other objects may again have place in consciousness.
The Three Fundamental Phases of Consciousness.—Thus we see that if we could cut the stream of consciousness across as we might cut a stream of water from bank to bank with a huge knife, and then look at the cut-off section, we should find very different constituents in the stream at different times. We should at one time find the mind manifesting itself in perceiving, remembering, imagining, discriminating, comparing, judging, reasoning, or the acts by which we gain our knowledge; at another in fearing, loving, hating, sorrowing, enjoying, or the acts of feeling; at still another in choosing, or the act of the will. These processes would make up the stream, or, in other words, these are the acts which the mind performs in doing its work. We should never find a time when the stream consists of but one of the processes, or when all these modes of mental
