One line of question that always interests the beginner in psychology is as to how people differ--how different people act under the same circumstances--and why; and if we watch the professional psychologist, we often find him working at just this problem. He tests a great number of individuals to see how they differ, and tries to discover on what factors their differences depend, how far on heredity, how far on environment. The "psychologist" in such a place as the children's court {3} is a specialist whose duty it is to test the delinquent children that are brought before the court, with the special object of measuring the intelligence of each individual child and of helping in other ways to understand the child's peculiar conduct and attitude.

The "psychological examiner" in the Army, during the Great War, had the same general object in view. It was desirable to measure the intelligence of each recruit as he entered the service, since military experience had shown that men of low intelligence made poor soldiers, while those of high intelligence made the best officers and non-commissioned officers, provided they also possessed good physique and certain less measureable mental qualifications, such as courage and leadership.

Applied psychology.

The Army psychologists, like the court psychologist, were engaged in applying scientific knowledge to the practical problems of life; and there are many other applications of psychology, to education, to medicine, to business and other occupations, as well as to the art of right living. Scientific knowledge enables you to predict and control. Having devised scientific tests for intelligence, you can predict of a six-year-old boy who tests low, that he will not get much good from the regular classes in school; and thus you are in a position to control the education of this boy for his own best interests. In the Army, it happened during the earlier part of the war that some companies or regiments made much slower progress in training than others; and a whole Division was delayed for months because of the backwardness of a single regiment. When the psychological tests were introduced, these slow-learning units were found to contain a disproportionate number of men of low intelligence. From that time on, it was possible by aid of the tests to equalize the intelligence of different units when first formed, and thus insure equal {4} progress in training. This was a good example of "control".

Most of us are attracted by the practical use of a science, and some have no patience with any study that does not seem immediately practical. But really any science, however much it is applied, must remain fundamentally a pure science; that is, it must seek most of all to know and understand. Practical scientific knowledge was usually first obtained without any inkling of how it might be used. The science of electricity is the most striking example of this. It began as an attempt to understand certain curious phenomena, which seemed to be nothing but curiosities; yet when the knowledge of these phenomena had progressed to a certain point, abundant use was found for it. Much the same is true of psychology, which began as a pure science and only recently has found ways of applying its discoveries to practical affairs. So the student beginning the science, though properly desirous of making practical use of what he learns, should let himself be governed for the present by the desire to know and understand, confident that the more scientific (which is to say, the more complete, systematic and reliable) his knowledge is, the more available it will be for practical application.

General psychology.

Our science is not concerned entirely with differences between people, but asks also in what ways people are alike, and this is indeed its central problem. How do "we" observe, learn, remember, imagine, think? What sensations and feelings do we have, what emotions, what instincts, what natural and acquired impulses to action? How are our natural powers and impulses developed and organized as we grow up? Psychology is concerned with the child as well as the adult, and it is even concerned with the animal. It is concerned with the abnormal as well as the normal human being. So you will find books and {5} courses on animal psychology, child psychology, abnormal psychology. Now general psychology--or just plain "psychology"--has to do with the main laws and principles that hold in all these special fields.