Up to the end of the nineteenth century, the only well-known classification was that of the four temperaments made by the ancient Greeks: sanguine, phlegmatic, choleric, and melancholic, and some writers still consider this as good as any. Jastrow gives a "revised version" of it, "serviceable as a psychological clew."1 Ross2 presents four schemes of classification by as many different writers. This subject obviously belongs to physiology and psychology, and the sociologists must await the verdict of those branches of science. The sociologists, however, are at liberty to make their own needs known and to criticize the verdict when it is rendered. There is some disposition to set apart a special branch of psychology to be known as individual, differential, or variational psychology. Thorndike pronounces against the possibility of any classification that will be practically useful, because a concrete example of a particular type is rare, the persons who approximate it shading off imperceptibly into other types. This, however, though a serious objection, would not seem to be conclusive. It is useful to have names for colors even though pure colors are rarely seen. We may, therefore, still hope for a workable plan by which teachers may study individual differences and describe them when they are found.

1 Jastrow, Character and Temperament, pp. 255-263.

2 Ross, Foundations of Sociology, pp. 297-309.

. . . There is the child who excels in dealing with abstract idea. He usually has power also in dealing with the concrete, but his chief interest is in the abstract. He is the one who does splendid work in mathematics, formal grammar, the abstract phases of the sciences. Then there is the child who is a thinker too, but his best work is done when he is dealing with a concrete situation. Unusual or involved applications of principles disturb him. So long as his work is couched in terms of the concrete, he can succeed, but if that is replaced by the x, y, z elements, he is prone to fail. There is another type of child - the one who has the executive ability, the child of action. True, he thinks, too, but his forte is in control of people and of things. He is the one who manages the athletic team, runs the school paper, takes charge of the elections, and so on. For principles to be grasped he must be able to put them into practice. The fourth type is the feeling type, the child who excels in appreciative power. ... - Strayer and Norsworthy, How to Teach, p. 163.

. . . Roughly speaking, the mental tests now available for use with school children are of two sorts: first, those which aim to determine with some precision the presence or the absence or the amount of some specific mental characteristic, e.g. tests of memory-span, of quickness of learning, of pitch discrimination, of color-blindness, etc.; secondly, those which aim to determine with perhaps somewhat less precision the general status of the child's intelligence, his mental level or general all-round ability as related to that of other children of the same nationality, sex, age, and social status. . . .

. . . There is no school system of any size that does not contain dozens and scores of pupils who present special psychological problems. Examples are: pupils that cannot learn to spell, pupils that have special difficulty in committing to memory, pupils that are slow in acquiring the technique of reading, pupils that display exceptional gifts in special lines of work, pupils that seem to be tone-deaf, pupils that present peculiar and seemingly inexplicable resistance to disciplinary control, pupils that exhibit speech disorders developed from compulsory right-handedness. In fine, the painstaking scrutiny and intensive study of all individuals that exhibit striking peculiarities in their mental equipment is a form of educational research that is greatly to be desired, that some of our best-equipped school systems could readily afford, and that demands for its prosecution the application by an expert of numerous special forms of mental tests.

Tests of the second sort - test-systems designed to measure general intellectual status - have come into considerable prominence in the past decade through the interest developed by the Binet-Simon tests. These tests were first proposed in 1905 by the eminent French psychologist, Alfred Binet, and his collaborator, the physician, Dr. Simon, in response to an inquiry as to what devices might be used to segregate, for placing in special classes, pupils too defective mentally to profit by instruction in regular classes. This preliminary statement was replaced in 1908 by a more systematic formulation and this 1908 series was again replaced three years later by what is known as the 1911 revision. The extraordinary cleverness with which they were devised, the novelty of the principles they embodied, and their surprisingly satisfactory outcome from the school man's point of view, all conspired to focus upon these tests the active attention of psychologists and educators in all civilized countries. . . .

. . . Eventually, we shall undoubtedly seek to develop in all school systems at least four groups: the gifted group, the regular group, the slow group, and the group of moderately defective mentality. A fifth group - the mental defectives whose insufficiency is marked - will be relegated to special custodial institutions. ... - National Society for the Study of Education, Fifteenth Yearbook, Part 1, pp. 149, 150, 154, G. M. Whipple.

... As a matter of fact, equalizing training increases the differences. The superior man becomes more superior, the inferior is left further behind than ever. A common occurrence in school administration bears out this conclusion reached by experimental means. The child who skips a grade is ready at the end of three years to skip again, and the child who fails a grade is likely at the end of three years to fail again. ... - Strayer and Norsworthy, How to Teach, p. 159.

All this is not a school man's fancy. Intelligence tests have been put to the acid test of business efficiency, and they have stood that test. . . . For example, the American Telegraph Company found that by having candidates selected on the basis of psychological tests of their reaction time, discriminating ability, the speed and relevancy of their associations, etc., they could save the tremendous waste of the six months' training necessary under the old method before they were sure the candidate could become an efficient operator.

The courts are using psychological tests in rapidly increasing numbers. . . . The army is calling for the professional help of the psychologist. The initial, voluntary service of a number of psychologists in several training camps during the first eight months of our participation in the war was recognized by the officers in charge as of such value to them in the selection of men for particular places that the War Department has ordered psychological work put into every branch of the service. . . . - Wisconsin State Department of Education, Educational News Bulletin, May 1, 1918.