If you take on of the ready-made tests of intelligence and try it on a very
large number of persons, you will find that they succeed with it in very
different degrees. Repeat the test, and you will find that they cannon, with
the best will in the world to do well, alter their scores very greatly. Then
give the same group another test, and you will discover that the difference
among individuals are approximately, although not exactly, the same. And you
can go on. You will find that an adult, after continued exposure to his
social and educational environment, does not greatly alter his score on a
given test; that children, however, do steadily improve their performances
until somewhere between ten and twenty years old; that the average age at
which improvement stops is about 14 years; but that children while improving
tend to maintain the same individual differences, so that in a given group
every child would keep about the same rank within the group. These are basic
observational facts of the psychology of intelligence. What do they mean?

What the Tests Test

They mean in the first place that intelligence as a measurable capacity must
at the start be defined as the capacity to do well in an intelligence test.
Intelligence is what the tests test. This is a narrow definition, but it is
the only point of departure for a rigorous discussion of the tests. It would
be better if the psychologists could have used some other and more technical
term, since the ordinary connotation of intelligence is much broader. The
damage is done, however, and no harm need result if we but remember that
measurable intelligence is simply what the tests of intelligence test, until
further scientific observation allows us to extend the definition.

An observational method for extending knowledge of intelligence as the tests
test it is the method of statistical correlation. The relation to
intelligence of any measurable capacity at all can be determined by
comparing the relative performances of a large number of persons in an
intelligence test with their achievement in the measure of capacity in
question. If the correlation is considerable, yet not perfect, say 60
percent, we say that the particular capacity is partly dependent upon
intelligence and partly independent of it. We shall not be far wrong if we
think of such a capacity as complex, involving 60 percent of intelligence
and 40 percent of some special ability that is not intelligence.

The method of correlation gives us at once some insight into the nature of
intelligence as the tests test it. No satisfactory intelligence test exists
at present which employs a single type of mental operation. Most tests for
intelligence, like the army tests, consist of batteries of single tests,
every one of which appears, on inspection, to test some special ability,
like arithmetical ability, or an appreciation of verbal relations or of
logical relations. When one obtains the correlations among the different
tests that make up the battery called an intelligence test, one finds that
the separate tests do not correlate with one another so very highly - not so
highly as a rule as does one combined intelligence test with another. These
results are explained by saying that the separate tests are really tests of
separate abilities; and that each of these abilities involves, in part,
intelligence, which is a factor common to all the tests, and in part a
special ability, which is not intelligence and which therefore explains the
failure of the tests to correlate very highly. When the separate tests are
combined in a total score, the special abilities being unrelated, are
supposed to cancel out, leaving the score to represent the "common factor,"
intelligence.

Thus we see that there is no such thing as a test for pure intelligence.
Intelligence is not demonstrable except in connection with some special
ability. it would never have been thought of as a separate entity had it not
seemed that very different mental abilities had something in common, a
"common factor."

A Confusion of Meanings

One of the most frequent reasons for the misunderstanding of the tests is
the fact that the existence and importance of these special abilities are
usually lost sight of. The psychologists themselves are very apt to forget
them and it is no wonder that their lay audiences are scarcely aware of
them. Yet it is not even possible to understand the nature of tested
intelligence without considering them. They are forgotten in part because
the "common factor" has seemed especially important and the interest of the
testers in the last decade has centred on it. Words, however, have also
helped to obscure their existence. The tested intelligence of an individual
is often called his "mental age": the increase of intelligence in childhood
is generally called "mental growth." In this way psychologists have
inadvertently equated the "intelligent" to the "mental,' overlooking in
their terminology the vast number of special abilities that help to make up
the "mind." It is high time for a change of words here. The present usage
requires us to say that the average adult has a "mental age" of

--------------------------------------------------------------------------------

( 35) about fourteen and that "mental growth" on the average stops at
fourteen. Nothing could be more untrue. The statement can be true only of
intelligence as the tests test it. The special abilities, which make up
skill and knowledge, continue to cumulate presumably throughout all adult
life.

A very useful conception of intelligence, and one that is approximately
correct in the light of our present knowledge, is that intelligence is like
"power" as the physicist uses the word: the amount of work that can be done
in a given time. All intelligence tests involve the maintenance of
time-limits to some extent, and most tests are "speed" tests where all the
work is performed against time. We may think, then, of intelligence as power
and of a special ability as a machine that utilizes the power for a
particular purpose. No machine can operate without power, and power is
actually demonstrable only when it has a machine through which to operate.
It is idle to speculate as to which is the more important, the power or the
adaptive device for the utilization of the power; and it is folly to bet
one's fortune on the power, forgetting the machine.

Up the Hill on Low

A frequent complaint made of the tests is that they place too much emphasis
upon speed. it is argued that some people, who do poorly in the intelligence
tests, are persons who naturally work slowly but very accurately, and that
the test penalize them unfairly. If, however, intelligence is like power,
this contention in not an argument. If these people have less power, they
have to go up the hill on low gear and it takes them longer; that is all. Of
course they "get there" just the same, but when they "get there" their
powerful rivals are on and somewhere else. If they ride more smoothly as
they go, that is an entirely different matter from the one under discussion;
they have a special ability which is not intelligence as the tests test it.
They probably never would have complained at all if they had not been misled
into thinking that the intelligence-rating characterized their entire mental
make-up. There were, for instance, competent surgeons in the army who rated
low in the tests. There was no question about their value to the army; they
had the requisite knowledge and skill. The conception of intelligence as
power implies merely that they had gained their professional competence
relatively late.

There has been much public concern since the war over the discovery of the
army psychologists that the average "mental age" of Americans is about
fourteen years. This concern is founded on ignorance, although it must be
admitted that some psychologists have shared it. Before the war less
adequate investigations had led the psychologists to suppose that the
average "mental age" was about sixteen. No one was concerned on account of
this tenet, largely because it did not get public attention. Now the army
results correct the earlier finding, and everyone exclaims: "We are a nation
of fourteen-year-olds!" Well, with respect to stature we are a nation of
twenty-year-olds. There is no reason for concern because it is discovered
that a given mental capacity, intelligence, attains its maximal development
in adolescence. If there were some reason to believe that we ought to be
sixteen or that other nations are on the average sixteen, there might be
some cause for alarm, but there is not. We ought to be congratulating
ourselves that we now have a more accurate knowledge concerning one mental
capacity, and hoping that success in the field of intelligence promises
eventually a detailed knowledge of the special abilities, which are equally
important factors in mental life and in the value of the individual to
American civilization.

The place where observation often yields too readily to inference is in the
answer to the question : Is intelligence inherited ? Psychological belief
has been that it is, though recently some psychologists have been doubting.
The question cannot be answered with assurance until there are observational
correlations between parents and their offspring. It may well be that only a
tendency toward intelligence is inherited, just as a tendency toward some
diseases is inherited, and in such a case we should need to state, in terms
of a correlation, the strength of the tendency. Experiments upon animals are
in progress, but the results can hardly settle the problem for human beings.
The test of intelligence in an animal is a maze to learn or a puzzle-box to
open. Such a performance measures a special ability along with the "common
factor," and it cannot be considered a test of intelligence, as we have been
using the word, unless observational correlation establishes a relationship.
The positive answer therefore lies in the future, and the person who states
dogmatically that the man who consistently scores low in intelligence test
has only his ancestors to blame is not stating an irrefutable fact.

Intelligence is Largely Predetermined at Five

It is obvious, however, that the intelligence which the tests test is at
some time predetermined. If it stops developing in adolescence, it is
predetermined for the adult as much as is stature, and no man by taking
thought can add ten percent to his intelligence quotient. The intelligence
test begin to be fairly accurate at about five years of age, and we have
seen that the child's relative position in intelligence with respect to
other children of his age does not alter greatly as he grows up. This fact
is expressed by saving that the intelligence-quotient of the child (the
ratio of his tested intelligence to his physical age) does not usually vary
greatly. It would seem then that intelligence is predetermined at five years
of age.

--------------------------------------------------------------------------------

( 37)

We are left with several possibilities. The actual time of the
predetermination may be in infancy, in utero, or in the germ plasm. The
Freudians have shown the importance of infantile life in its effect upon
adult life, and it might not seem strange if the predetermination occurred
then. Psychologists, however, do not generally regard this argument
seriously because the Freudian mechanisms are all of the order of special
abilities. Almost nothing is known about prenatal determinants, but one
psychologist has recently suggested them as accounting for his seeming
failure to obtain high correlations between the intelligences of children in
the same family. Predetermination by inheritance is supported most strongly
by the family histories of the feeble-minded: the Jukes, the Kallikaks, and
similar studies. These cases, however, are not conclusive against
environment in infancy as a determiner. Degenerate strains naturally grow up
in an environment of degeneracy. Strangely enough the argument from
correlation is sometimes inverted. Bright parents have a stupid son, and it
is suggested that this is just what would sometimes happen if a Mendelian
law applied to intelligence. There is no doubt that the argument from
authority is for the inheritance of intelligence. It is better, however, to
wait upon more research.

If we agree, then, to define intelligence as what the tests of intelligence
test, there is a good deal that we can say about it. We can say that it is a
"common factor" in many abilities, that it is something like power, that it
can be measured roughly although not very finely, that it is only one factor
among many in the mental life that it develops mostly in childhood, that it
develops little or not at all in adult life, and that it is large
predetermined at five years of age. Only with more observation and less
inference shall we eventually know much more about both intelligence and
special abilities.

Edwin G. Boring.

http://www.brocku.ca/MeadProject/sup/Boring_1923.html