§ 2. Introspection.—To introspect is to attend to the workings of one's own mind. When instead of asking what we perceive or will, we inquire how we perceive or will, or how we come to perceive or will, the answer, so far as it can be obtained by direct observation, depends on introspection. Thus, to take once more the case of the stereoscope. Because the solid object is not physically present, someone may say that its presence is merely inferred. From a purely logical point of view, this may be true. If a man, deceived by the stereoscopic appearance, were called upon to define his reasons for believing the solid object to be physically present, he would no doubt say that it looks solid, just as if it were really so. He would then be assigning a peculiar visible appearance as a reason for assuming a physical fact. But if it is meant that the actual visible presentation of solidity is itself an inference, appeal must be made to introspection. Inferring is a mental process with which we are familiar. In it we proceed to a conclusion, which is mentally distinguished or distinguishable from its premises. But in the stereoscopic illusion there is no distinguishing between premises and conclusion, or transition between them. On the evidence of introspection, therefore, we say that inference as a psychological process is not present. Take another example. A man shows us a pretty chess problem and its solution. Neither his mental attitude nor ours is introspective while he is telling us about the problem. But suppose that he goes on to describe how he came to invent the problem, or how he came to discover its solution; he will then be describing the workings of his own mind. He will speak of his disappointment and perplexity, his renewed hopes, his despair when all possible ways appeared futile. He will perhaps tell us how the understanding of the whole problem flashed upon him suddenly with the keymove, every element in it then assuming its right place, so that his subsequent mental activity became smooth and easy. All this is introspection. Consider next an example from the sphere of practice. A general gives an important order, or a responsible statesman puts before the world a scheme of policy. Neither the general's order nor the statesman's scheme directly expresses psychical facts; but if the general begins to tell us how he was led to give the order, he will, in all probability, describe the process of his own consciousness. He may tell us that his mind for a time oscillated between alternative lines of conduct; now one appearing better, and now the other. He may tell us that the state of indecision, where there was need for prompt action, became unbearable; and that he suddenly put an end to it by fixing on one definite decision, without any real conviction that it was the best. Or again, he may describe how the decision emerged gradually out of his previous hesitation, so that he awoke one morning with a clear conviction that a certain course was the right one.

Much has been written about the difficulty and untrustworthiness of introspection. It is often urged that psychology, in so far as it rests on an introspective basis, must always be in an unsatisfactory condition. But it must be remembered that quite apart from any aid which he may receive from physiology, the psychologist has at his command a vast mass of data which are not due to introspection. This we have brought out in the preceding section on presented objects as data for psychology. It is conceivable that this class of data alone would serve as the basis of hypotheses explanatory of the development of mind. Thus we might have a kind of psychology without introspection, and yet quite distinct from physiology. What introspection does is to supply us with a direct instead of a hypothetical knowledge of mental process. It thus forms a source of psychological material which is invaluable and unattainable by any other means. But the ultimate test of psychological theories is their power to explain how the world comes to exist for the individual mind. The ultimate data of the science are therefore objects as presented to the individual mind, in successive phases, and under varying conditions of its development.