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"Intelligence" and Intellectual Power

We must sharply distinguish between intelligence, which refers to native capacity, and intellectual power which depends in part upon experience.

Behavior is always the result of the reaction of experience upon this native capacity or intelligence. This is true of the idiot as of the genius. Native capacity or intelligence is almost entirely latent at birth and develops slowly with years; the extent of its development is relatively independent of the particular kinds of experience with which it interacts. Intellectual power, on the other hand, is strictly a function of two variables; the native intelligence and the number an quality of the experiences enjoyed.

The intelligence of the idiot ceases to develop at or before the level reached by normal children of three. With such an equipment, development in intellectual power is painfully slow and strictly limited in extent. The intelligence of the moron continues to develop to the level reached by normal children of seven to thirteen years. A considerable development in intellectual power is possible after the maximum development in intelligence has been attained but the extent is still strictly limited. The intelligence of the average normal person does not develop much beyond the level of the higher grade morons, but, present evidence sets no limit to the extent to which such an average person may continue to develop in intellectual power. William James thought that few such persons grew much after their twenty-fifth year and to the intuition of James we must give some weight; but experimental evidence we have none. The superior person and the genius continue to develop in intelligence for longer periods and in intellectual power indefinitely. (James himself to the time of his death was evidence that not all persons cease to grow at twenty-five.) The accompanying graph fails to show the relative speed with which the developments in both the vertical and horizontal directions take place; in general the speed increases as we pass from idiot through moron and average to superior and genius.

Once the distinction between intelligence (which is measured by tests) and intellectual power is grasped, we see that Mencken's statement that half the draft were not the intellectual equals of a thirteen year school-girl is almost a self reducing absurdity.

It is as inaccurate to say that fifty per cent of all American men are intellectually thirteen as that Mencken himself, with all his great gifts, is intellectually an adolescent eighteen; yet it is at this point, apparently, that the superior man who falls short of genius ceases to gain in intelligence.

But the contention that half of our population is feeble-minded is supposed to be based upon the official report to the Surgeon General of the army. Let us see. "If this definition," says the official report, referring to a widely current but tentative definition of feeble-mindedness, "can be interpreted as meaning any adult below the mental age of thirteen, almost half the white draft, 47.3 per cent, would have been classed as morons." (See Memoirs of the National Academy of Sciences, xv, 789.) The little word "if" has been pretty consistently overlooked. Of course such a result as this merely reduces to absurdity the proposed definition of feeble-mindedness and was recognized as doing so even by those who had originally proposed it. It is not for mere psychologists, at any rate, to indict half a nation.

How Many Are Feeble-minded?

If the feeble-minded do not number 47 per cent, how many do we have? The answer is peculiarly hard to give. The whole question of the definition of feeble-mindedness is in the melting pot as never before. Hereditary mental deficiency is universally recognized as the basic fact, but the general tendency at present seems to be to supplement purely psychological considerations with sociological, to revert somewhat to the familiar definition of the English Royal Commission which stressed the "inability to manage one's affairs with ordinary prudence."

Whatever the definition of feeble-mindedness, there is fair agreement that its diagnosis remains an art -- a matter of intuitive judgment, based upon a wide variety of factors, by a trained and qualified examiner. This it was impossible, for various reasons, to get under army conditions, and we have consequently no secure official basis upon which to estimate the number of mentally deficient in the country.

The discharges and rejections avowedly cover only a small per cent of the total. The instructions of the Provost Marshal General relative to rejection prior to muster provided, in effect, for the rejection of only the imbecile and idiot, that is, of the second and third degrees of feeblemindedness. The result was a large mass of unteachable soldiers who had, after considerable time and money had been spent on them, to be discharged.

The writer's own experience in supervising the examination of all low grade recruits who reached one large camp, confirmed by informal discussions with others who had like opportunity for observation, leads him to estimate that less than six or seven per cent of the adults of the country are definitely feeble-minded. Certainly no competent student would place the number at less than four per cent and few would place it at more than ten.