2. A major criticism is that environment and heredity are so intimately interwoven that it is impossible to tease them apart. All I.Q. tests make use in part of skills and information previously acquired through contact with the environment; how can we ever hope to equalise these contacts? The problem is similar to that encountered by Newton in putting forward his laws of motion; these laws only apply properly in a complete vacuum, and cannot be tested anywhere on earth, where friction and air resistance are ever present (even in the most perfect vacuum we can produce nowadays). There are many ways out of this difficulty. We can calculate the effects of air resistance; or we can measure the fall of different type body in different vacua, forming a mathematical equation and calculating the effect on having a complete vacuum. Similarly, in psychology we can construct tests depending to a greater or lesser extent on environmental factors. We assume that tests which are least dependent on such factors, easier something nearest to the innate intelligence.
3. Another type of criticism is often directed at the format of test items: they are all ‘convergent’ in other words, the correct solution is unique and completely prescribed by the relations obtaining between the parts of the problem. It is sometimes suggested that ‘divergent’ tests might give a better indication of a person’s originality and creativeness – such test are scored in terms of how many solutions to a problem the subject cam put forward. A typical problem might be: think of as many as possible uses of a brick. It has been suggested that such tests measure something entirely different from I.Q., but this is not true; correlations between the two types of tests are in fact quite high. Nor is there any evidence that truly creative people do any better on ‘divergent’ tests than on ‘convergent’ tests. There is some evidence that extroverts do better on divergent tests; this is probably due to the fact that introverts are more critical of their solutions and suppress the sillier ones. Solutions are evaluated in terms of quantity, not quality; hence such reticence is penalised. School children who go in for science tend to do better on convergent tests, those who go in for arts on divergent tests; this may be related to extrovert introvert distinction. On the whole the available evidence does not suggest that divergent tests would add anything of lasting value to I.Q. measurements, although further research may unearth something of importance.
4. Another criticism which is often raised against I.Q. test suggests that there is much arbitrariness about the selection of items. This, actually is not so. Test items are selected in accordance with certain objective principles; they are retained in the tests only if they continually prove faithful to these principles. In short, item selection is not an arbitrary business which has become prevalent by design or accident, but a lawful procedure, the results of which have scientific meaning.
5. One last point may be worth making it is often objected that intelligence tests are not a measure of a man’s worth; this is obviously true, but then no psychologist has ever suggested that intelligence has any such wise-ranging function. Science, as we have seen previously, always abstracts from the rich web of experience; only in this way can we carry out measurement at all. We can isolate a certain class of invariant features which we label ‘intelligence’ this class of features is not identical with the other classes of features. There are many desirable virtues; intelligence is only one among many, and a person possessing high intelligence can of course be lacking in any or all of the other virtues. Very intelligent men have been cowards, self-seekers, criminals, hypocrites, and every bad thing you conjure up in the imagination; I.Q. test have nothing to say about these other aspects of personality all that a high I.Q. score mean is that the person in question has a marked ability to solve problems, think abstractly, and generally act intelligently. He may not always be able to employ his high gifts to the best advantage; many neurotics are intelligent, but their emotional problems interfere with the proper exercise of their ability. It is easy to exaggerate the importance of this abstracts ability we call ‘intelligence’; it is equally easy to underrate its value. Intelligence is not all there is to man; nevertheless, intelligence is an important, and socially extremely useful part of man. Our ability on measure this human characteristic with some degree of precision means that we can control it and use it to the general advantage of society.