abstract. Each so-called type of intelligence involves the presence in a high degree of a group of different traits.

Individual differences are seen not simply as differences with respect to given mental traits, but differences as to general mental capacity ranging from idiocy to genius, the largest number of individuals being normal or average. The size of the group diminishes according to deviation from the average in either direction.

It should be noted that the existence of special differences does not of itself imply general superiority or inferiority. It merely implies a difference with respect to the performance of a particular type of work (10,11,12,13). It is the business of scientific psychology to note individual differences, the specific demands work makes upon certain capacities, and to endeavor to select and direct individuals according to their capacity, talents, interests, and training.

1. Individual Differences and Their Causes [THORNDIKE, E. L., Education, pp. 67-70. Copyright, 1912, by the Macmillan Co.] (Adapted.)

Behavior is due in part to original individual differences. Individual differences are due to sex, remote ancestry, near ancestry, chance variation, and to maturity and previous education. The sex of the child determines, in part, the way he reacts to certain situations. The remote ancestry determines many characteristics, as the color of skin. The differences between the races are probably more due to social heredity than to physical inheritance from remote ancestors. The racial differences are sufficiently real, however, that they need to be taken into account. Near ancestry plays a much more noticeable part in the behavior of children. They resemble more or less the one or the other of the parents or possibly both in some respects. Children "take after" their parents in energy, ability to learn, and other mental traits in much the same way as they do in physical traits. Individuals may differ also because of chance variations in the germ cells. Not all of these cells are alike in potentiality although they come from the same individual. Chance variations may account for new species as well as individuals.

Education is furthermore concerned with individual differences due to different degrees of maturity or growth, and those which previous education and training have caused. Children of four differ from those of fourteen, primarily on account of the maturity and previous experience factors. In teaching, the instructor needs to take all of the causes of the differences into account. Educational situations must be set up within the reach of the understanding of the child. Both subject matter and methods must be adapted to individual needs and requirements.

2. The Difference Between the Child and Adult Mind [MARTIN, Herbert, Formative Factors in Character, pp. 12-20. New York, Longmans, Green & Co., 1925.]

The world of the child is a different world from that of the adult. The child lives in a world of persons and objects more or less unrelated. His is a perceptual rather than a conceptual world, a world of concrete rather than of abstract realities, a sense world rather than a rational world. Abstract thinking, so difficult for many adults, is practically impossible for him. Our abstractions do not exist for him. The word must become flesh and dwell with him and he with it. He must see and hear and taste and smell and handle. His life is absorbed in things more or less connected with his needs and satisfactions. . . . The writer was asked to speak on a Sunday morning in a local pulpit. Having decided, as his theme, to utter a protest against the din and stress of our increasingly complex life, he felt that the employment of the traditional text would give definition and strengthen his presentation. On being introduced by the resident minister the speaker announced, without preliminary, as his text, "Be still and know that I am God." The minister's little daughter, about five or six years old, doubtless not having noticed the stranger until he rose to speak, on hearing these words nudged her mother and whispered, "Mother, is that God?” Such mistaken identity expresses the concrete quality of the child's verbal imagery. . . . The specific and immediate character of the child's mind we may think of negatively as the absence or lack of that sense of relation between facts that characterizes the normal adult mind. . . . The child world consists mainly of isolated, independent realities. He is a realist without limitation. For him things are, events happen. He is not

obsessed with the "linkage of facts." The fact of relationship is not appreciated. Causes and consequences, as such, receive little consideration. "You look horrid," uttered by the child, is merely a statement of fact. Spoken by the adult it is, in addition, an unpardonable discourtesy. . . . The child mind differs from the adult mind in the degree of its organization. The adult mind is highly integrated, the child mind is loosely organized. The order and system that mark the mature mind are absent in the immature mind. If we may speak of the structure of the mind, the child mind is simple in its structure while the adult mind is highly complex. . . . Mental maturity is marked by inner control, by a certain independence of circumstance. In less degree does the immature mind enjoy this freedom. The child lives in an external world. There his interest and satisfactions are found. . . . A further difference, and very important here, between the child and adult is the fact that the same situation may convey very different meanings to the two. . . Fullness of meaning involves a complex, a totality of situation and conditions impossible to the child mind. His meanings are partial and fragmentary, due to the limited forms and range of his experience. . . .

FIG. 6. A NORMAL FREQUENCY SURFACE, SHOWING A NORMAL DISTRIBUTION OF TRAITS WHEN A LARGE NUMBER OF CASES ARE CONSIDERED.

FIG. 7. SAMPLES OF THE FORMS OF DISTRIBUTION FOUND IN MENTAL

TRAITS.

A. Reaction time: 252 college freshmen.

B. Memory of digits: 123 women students.

C. Efficiency in marking A's on a sheet of printed capitals: 312 boys from 12 years 0 months to 13 years 0 months.

D. Efficiency in giving the opposites of words: 239 boys from 12 years 0 months to 13 years 0 months.

E. Accuracy in drawing lines to equal a 100 mm. line: 153 girls from 13 years 0 months to 16 years 0 months.

F. Efficiency in marking words containing each the two letters a and t: 312 boys from 12 years 0 months to 13 years 0 months.

In all six cases the left end of the scale represents the lowest abilities that is, the longest times in A, the fewest digits in B, etc. The continuous lines give the distributions. The broken lines are to be disregarded for the present. (E. L. Thorndike, Educational Psychology, Briefer Course, p. 405.)

FIG. 8. GRAPHS SHOWING DISTRIBUTION OF INTELLIGENCE RATINGS IN TYPICAL ARMY GROUPS.

The literate groups were given Army Alpha, and illiterate groups Army Beta. (Army Mental Test, Washington, D. C., 1918.)

FIG. 9.

SCORES- 5 6 7 8 9 10 11 1240VER

DIAGRAM A SHOWING THE DISTRIBUTION OF MENTAL AGES, AND B, SHOWING THE DISTRIBUTION OF SCORES IN THE DEARBORN GROUP INTELLIGENCE TESTS, SERIES I.