Turning now to the alleged obscurities, fallacies, and difficulties of introspection, we may note at the outset that these do not exist when the questions which it has to answer are made sufficiently broad and simple. There is no fallacy, obscurity, or ambiguity in the statement that when I have toothache I dislike it very much, or that I was afraid when I saw a white figure in a churchyard. There is no fallacy or ambiguity in the statement that feeling pleased is different from feeling displeased, or that when we are fully convinced that an action is totally impossible, we cannot voluntarily determine to perform it. Facts of this kind can be observed with ease and certainty by everyone. Now if introspection could only supply us witli such simple and obvious data, it would none the less be of essential value. It would supply us with the general terms in which to describe mental process. The more precise determination of such process in detail might be hypothetical, and dependent on other data as the ultimate test of its correctness. To a large extent this is the case. In this respect psychology is on a footing with other sciences. If we ask for the actual observations of the process of natural selection on which the Darwinian theory is based, we find what appear very slender foundations of fact for a very large superstructure. There are the experiences of the breeder, and very little more. The real data which support the weight of the theory consist in the nature of the actual products which the process is assumed to explain,—the actual constitution of animal and vegetable species in their higher and lower forms.

The deliverances of introspection are not, however, limited to such simple and obvious issues as we have mentioned. Like all other modes of observation, it is capable of being immensely improved by systematic training and practice. The plain man, as Dr. Sidgwick calls him, has, as a rule, no permanent and absorbing interest in the workings of his own mind. His attention is mainly engrossed by other objects. Thus, the introspective attitude is unfamiliar to him. This unfamiliarity is the chief reason why he seems so helpless when called on to observe the finer details of his own mental operations. Like a person passing from full illumination into a dimlylighted room, he can at first discern little; but in time his power of discrimination may increase. By repeating his observations again and again, and comparing them with each other, he makes gradual progress. The result of previous observation becomes the basis of a new advance. This is of course in no way peculiar to introspection. A man who is only beginning to observe in a systematic way fine distinctions between tastes, smells, and colours, shows at first the same helplessness. Advance is made as the cumulative result of a series of successive efforts of attention, each paving the way for the next. It is indeed a commonplace that the practised observer notices at once what the untrained fail to see even when it is pointed out. But besides individual practice there is yet another element in the training of the introspective psychologist. He derives immense help from the work of his predecessors. They teach him what to look for, and how and where to look for it. Thus what the introspection of one generation has achieved becomes the startingpoint for fresh progress in the introspection of the next. The advance that has actually been made in this way is immense, as at once appears on comparing from this point of view the work, let us say, of Aristotle, with that of William James.

Nevertheless, it must be admitted that there are certain drawbacks attaching to the introspective process which cannot wholly be overcome even by sustained practice and systematic training. The most important drawback is that the mind in watching its own workings must necessarily have its attention divided between two objects,—on the one hand, the mental operation itself which is to be observed, and on the other, the object to which this mental operation is directed. If I observe the process of seeing, I must attend at once to what is seen, and to the seeing of it. If I observe what takes place in attending, I must first attend to something, and then to the process of attention. Thus if the introspective effort is sustained and strenuous, it is apt to destroy the very object which it is examining. For by concentrating attention on the mental process, we withdraw it from the object of that process, and so arrest the process itself. Thus, introspection, when it is directly concerned with, a mental operation that is in itself more or less absorbing, can only proceed by taking a series of transient sideglimpses. This difficulty is, however, not so serious as it appears; for, in the first place, retrospection is to a large extent free from it. By calling up a process in memory immediately after it is over we are often able to notice much that escaped us when it was actually going on. In like manner the astronomer can call up in memory the image of a star which has just passed before his vision; and can then notice details which had escaped him at the moment of its actual appearance. In the next place, we must bear in mind that it is not the isolated observation which is of importance in introspective psychology, but rather the accumulation of a vast number of observations, each helping the others. Thus, what is important is to acquire a general habit of alertness, a perpetual readiness to attend to the workings of our own minds whenever opportunity presents itself; and it must be noted that opportunities are constantly presenting themselves; the subjectmatter which we have to observe is perpetually with us. This may be set down as a grand advantage of introspection, compensating in a high degree for its drawbacks. Finally, introspection, to be effective for the advancement of science, must, like other modes of observation, be carried on by a number of experts in cooperation. Each must communicate to the rest his own results, for confirmation or rejection. Thus, it is an essential part of his business to state his results in such a form that they can be tested by others. He must be able to point out to others exactly where and how to look for what he himself has observed. This is most easy when the method of experiment, as distinguished from mere observation, is followed, and constitutes one of the main advantages of that method. Of course, what is true of one individual, A, may not hold good of another, B; but B's inability to confirm A by his own experience should deter A from setting down as true for all men, or most men, what holds good only for some persons, possibly only for himself.