Two results follow from this peculiarity of psychological subject matter. The first is that the method of psychology differs from the methods of the physical sciences. All science demands observation, we have said; all exact science demands experiment. So far, then, all scientific method is one and the same. But the observations and experiments of physics and chemistry, physiology and zoology, are made upon material that is common scientific prop erty; the observations and experiments of psy chology are made upon private property, and, more than that, upon property which is inalien able. If we class the former all together as in spection, we may oppose the latter to them as introspection. In the physical sciences we look out upon a world that is shared by everyone alike; in psychology we look within, upon our personal world. From this difference in method it follows, in the second place, that the need of an experimental verification of results is more pressing in psychology than in any other de partment of science. If we cannot, in some way, transcend the intrinsic defect of introspec tion, its personal and individual character, we are likely to have as many psychologies as there are psychologists to introspect. In actual fact, the history of psychology records not a few cases of introspective deadlock,— of obser vation pitted against contrary observation. It was not until the introduction of the experi mental method in psychology that this danger ceased to be serious.
"But," it may be asked, "is modern psychol ogy really free from this danger? Are all psy chologists always agreed? Are there not still schools of psychology?" To answer these ques tions we must distinguish a little. In principle, modern psychology is free from the danger of introspective deadlock. Divergent observations are still made, in plenty; but psychology herself furnishes the means of reconciling the diver gence. Let us take an illustration from physics. Two competent observers may be analyzing a compound body by the spectroscopic method: the one may find the lines of a certain rare element, the other may be wholly unable to see these lines. Both analyses are published. We read them, and notice that they disagree. Do we at once lose confidence in the method? Not at all: we simply hold our judgment in suspense until further observations, by the same method, are forthcoming. We say that there must, in the one case or the other, have been some unsuspected source of error which vitiated the result; and we appeal to the method itself to indicate this source of error. More observa tions are made, with stricter regard to the con ditions of the analysis; and presently we reach a final conclusion. It is precisely the same in psychology. Experimental introspection may yield conflicting results, as does experimental inspection. But we have merely to go on ex perimenting, and the true result will ultimately emerge. In principle, then, psychology has nothing to fear from this particular danger. On the other hand, it must be frankly admitted that there are many and various schools of psy chology. Only, the points of disagreement are points that lie outside of psychology itself. Let us, again, take an illustration from the sciences of nature. Listen to a group of mathematicians discussing the character of the infinitesimal: to a group of physicists discussing the defi nition of energy: to a group of physiologists discussing the mechanics of life. To hear them, one would think that the status of their respec tive sciences was precarious in the extreme. Yet we all make use of the calculus; we build locomotives and power-plants and rely upon the balance and the thermometer; nay, we trust our actual lives to the surgeon and the physician. Moreover, the practical work of all these sciences goes on, and goes on with in creasingly fruitful result, despite the theoreti cal difficulties that lie behind it. So it is in
psychology. Psychologists are apt to dispute the greater and more fundamental issues that lie before and after their science: these issues will always be disputed, so far as we can see, while human nature remains human nature, and men are individualized by training and tem perament to envisage the universe from dif ferent points of view. In a general sketch, like the present, such differences must be baldly and plainly stated. The reader must, therefore, be warned not to lay too much stress upon them. The extreme opinions of opposing schools shade into one another by imperceptible gradations. And however extreme they may be, they have little if any bearing upon the practical work, the teaching and investigation, of mental science.
The Problem of Psychology.— We said above that the problem of a scientific psychology is to bring order into the chaos of the immedi ate experience. We may now note that, chaotic as this experience is, it neverthless is something more than chaos; it groups itself, roughly and indefinitely, no doubt, but still quite noticeably. If we reserve the wider term °mind) for the sum total of mental processes running their course between birth and death, we may say, first of all, that mind splits up into °conscious nesses, A consciousness is a mental present; a mind that has a temporal °now) stamped upon it; a bit of mind that is occupied with a single, however complicated, topic. Thus, to put the matter crudely, we begin the day with a getting-up consciousness; this is followed by a breakfast consciousness; this by a newspaper or a correspondence consciousness; this by a daily-work consciousness; this by a luncheon consciousness; and so on. The divisions are real, even if they are not very accurate or pre cise. We notice, further, that these conscious nesses themselves fall into groups. Sometimes we are stirred and moved by the topic of con sciousness: we are ill-humored, angry, anxious, pleased, relieved, aggrieved, hopeful, satisfied and what not. Sometimes we are passive, in differently taking things as a matter of course. Sometimes we are hard at work, resolute to solve a problem or to overcome a difficulty or to extricate ourselves from an embarrassing po sition, bending all our energies upon a given end. Sometimes, again, we are unable to con centrate ourselves; we are talkative, reminis cential, fanciful, dreamy, whimsical. A very little introspection of this sort will suggest the distinction of the great mental categories of memory, attention, imagination, emotion, etc. Once more, we notice that the consciousnesses which fall under these categories are complex. Take the emotion of anger. It is not a simple, unanalyzable experience, but is made up of part-processes. There is the idea of the scene or act that has called up the anger; the idea of retaliation; the feeling of injury or of wounded self-esteem; all sorts of memories of one's own or of others' conduct on similar past occasions; and all sorts of °bodily) feelings,— a choking or strangling, perhaps, or a feeling of strength and power, coming with a brace of the body and a clenching of the fist. These part-processes are readily distinguishable; and they take us a step further in the analysis of consciousness, and show us the concrete proc esses that are termed, technically, perception and idea, feeling and desire, etc. Lastly, we may notice, after a little scrutiny, that these processes in their turn are, literally, concrete: not simple, but made up of simpler elements. My idea of retaliation, for instance, is an idea of something that would take time for its ful filment, of something that would run its course in stages or phases. And it is more than prob able that each one of the stages would, under accurate observation, turn out to be a con cretion and not an elementary process.