The Binet scale is made up of an extended series of tests in the nature of “stunts,” or problems, success in which demands the exercise of intelligence. As left by Binet, the scale consists of 54tests, so graded in difficulty that the easiest lie well within the range of normal 3-year-old children, while the hardest tax the intelligence of the average adult. The problems are designed primarily to test native intelligence, not school knowledge or home training. They try to answer the question “How intelligent is this child?” How much the child has learned is of significance only in so far as it throws light on his ability to learn more.

Binet fully appreciated the fact that intelligence is not homogeneous, that it has many aspects, and that no one kind of test will display it adequately. He therefore assembled for his intelligence scale tests of many different types, some of them designed to display differences of memory, others differences in power to reason, ability to compare, power of comprehension, time orientation, facility in the use of number concepts, power to combine ideas into a meaningful whole, the maturity of apperception, wealth of ideas, knowledge of common objects, etc.

How the scale was derived.

The tests were arranged in order of difficulty, as found by trying them upon some 200 normal children of different ages from 3to15years. It was found, for illustration, that a certain test was passed by only a very small proportion of the younger children, say the 5-year-olds, and that the number passing this test increased rapidly in the succeeding years until by the age of 7or8years, let us say, practically all the children were successful. If, in our supposed case, the test was passed by about two thirds to three fourths of the normal children aged 7years, it was considered by Binet a test of 7-year intelligence. In like manner, a test passed by 65to75percent of the normal 9-year-olds was considered a test of 9-year intelligence, and so on. By trying out many different tests in this way it was possible to secure five tests to represent each age from 3to10years (excepting age4, which has only four tests), five for age12, five for 15, and five for adults, making 54tests in all.

List of tests.

The following is the list of tests as arranged by Binet in 1911, shortly before his untimely death:—

1. Age3:
   1. Points to nose, eyes, and mouth.
   2. Repeats two digits.
   3. Enumerates objects in a picture.
   4. Gives family name.
   5. Repeats a sentence of six syllables.
2. Age4:
   1. Gives his sex.
   2. Names key, knife, and penny.
   3. Repeats three digits.
   4. Compares two lines.
3. Age5:
   1. Compares two weights.
   2. Copies a square.
   3. Repeats a sentence of ten syllables.
   4. Counts four pennies.
   5. Unites the halves of a divided rectangle.
4. Age6:
   1. Distinguishes between morning and afternoon.
   2. Defines familiar words in terms of use.
   3. Copies a diamond.
   4. Counts thirteen pennies.
   5. Distinguishes pictures of ugly and pretty faces.
5. Age7:
   1. Shows right hand and left ear.
   2. Describes a picture.
   3. Executes three commissions, given simultaneously.
   4. Counts the value of six sous, three of which are double.
   5. Names four cardinal colors.
6. Age8:
   1. Compares two objects from memory.
   2. Counts from 20to0.
   3. Notes omissions from pictures.
   4. Gives day and date.
   5. Repeats five digits.
7. Age9:
   1. Gives change from twenty sous.
   2. Defines familiar words in terms superior to use.
   3. Recognizes all the pieces of money.
   4. Names the months of the year, in order.
   5. Answers easy “comprehension questions.”
8. Age10:
   1. Arranges five blocks in order of weight.
   2. Copies drawings from memory.
   3. Criticizes absurd statements.
   4. Answers difficult “comprehension questions.”
   5. Uses three given words in not more than two sentences.
9. Age12:
   1. Resists suggestion.
   2. Composes one sentence containing three given words.
   3. Names sixty words in three minutes.
   4. Defines certain abstract words.
   5. Discovers the sense of a disarranged sentence.
10. Age15:
    1. Repeats seven digits.
    2. Finds three rhymes for a given word.
    3. Repeats a sentence of twenty-six syllables.
    4. Interprets pictures.
    5. Interprets given facts.
11. Adult:
    1. Solves the paper-cutting test.
    2. Rearranges a triangle in imagination.
    3. Gives differences between pairs of abstract terms.
    4. Gives three differences between a president and a king.
    5. Gives the main thought of a selection which he has heard read.

It should be emphasized that merely to name the tests in this way gives little idea of their nature and meaning, and tells nothing about Binet’s method of conducting the 54experiments. In order to use the tests intelligently it is necessary to acquaint one’s self thoroughly with the purpose of each test, its correct procedure, and the psychological interpretation of different types of response.[10]

In fairness to Binet, it should also be borne in mind that the scale of tests was only a rough approximation to the ideal which the author had set himself to realize. Had his life been spared a few years longer, he would doubtless have carried the method much nearer perfection.

How the scale is used.

By means of the Binet tests we can judge the intelligence of a given individual by comparison with standards of intellectual performance for normal children of different ages. In order to make the comparison it is only necessary to begin the examination of the subject at a point in the scale where all the tests are passed successfully, and to continue up the scale until no more successes are possible. Then we compare our subject’s performances with the standard for normal children of the same age, and note the amount of acceleration or retardation.

Let us suppose the subject being tested is 9years of age. If he goes as far in the tests as normal 9-year-old children ordinarily go, we can say that the child has a “mental age” of 9years, which in this case is normal (our child being 9years of age). If he goes only as far as normal 8-year-old children ordinarily go, we say that his “mental age” is 8years. In like manner, a mentally defective child of 9years may have a “mental age” of only 4years, or a young genius of 9years may have a mental age of 12or13years.

Special characteristics of the Binet-Simon method.

Psychologists had experimented with intelligence tests for at least twenty years before the Binet scale made its appearance. The question naturally suggests itself why Binet should have been successful in a field where previous efforts had been for the most part futile. The answer to this question is found in three essential differences between Binet’s method and those formerly employed.

1. The use of age standards.

Binet was the first to utilize the idea of age standards, or norms, in the measurement of intelligence. It will be understood, of course, that Binet did not set out to invent tests of 10-year intelligence, 6-year intelligence, etc. Instead, as already explained, he began with a series of tests ranging from very easy to very difficult, and by trying these tests on children of different ages and noting the percentages of successes in the various years, he was able to locate them (approximately) in the years where they belonged.

This plan has the great advantage of giving us standards which are easily grasped. To say, for illustration, that a given subject has a grade of intelligence equal to that of the average child of 8years is a statement whose general import does not need to be explained. Previous investigators had worked with subjects the degree of whose intelligence was unknown, and with tests the difficulty of which was equally unknown. An immense amount of ingenuity was spent in devising tests which were used in such a way as to preclude any very meaningful interpretation of the responses.

The Binet method enables us to characterize the intelligence of a child in a far more definite way than had hitherto been possible. Current descriptive terms like “bright,” “moderately bright,” “dull,” “very dull,” “feeble-minded,” etc., have had no universally accepted meaning. A child who is designated by one person as “moderately bright” may be called “very bright” by another person. The degree of intelligence which one calls “moderate dullness,” another may call “extreme dullness,” etc. But every one knows what is meant by the term 8-year mentality, 4-year mentality, etc., even if he is not able to define these grades of intelligence in psychological terms; and by ascertaining experimentally what intellectual tasks children of different ages can perform, we are, of course, able to make our age standards as definite as we please.

Why should a device so simple have waited so long for a discoverer? We do not know. It is of a class with many other unaccountable mysteries in the development of scientific method. Apparently the idea of an age-grade method, as this is called, did not come to Binet himself until he had experimented with intelligence tests for some fifteen years. At least his first provisional scale, published in 1905, was not made up according to the age-grade plan. It consisted merely of 30tests, arranged roughly in order of difficulty. Although Binet nowhere gives any account of the steps by which this crude and ungraded scale was transformed into the relatively complete age-grade scale of 1908, we can infer that the original and ingenious idea of utilizing age norms was suggested by the data collected with the 1905 scale. However the discovery was made, it ranks, perhaps, from the practical point of view, as the most important in all the history of psychology.

2. The kind of mental functions brought into play.

In the second place, the Binet tests differ from most of the earlier attempts in that they are designed to test the higher and more complex mental processes, instead of the simpler and more elementary ones. Hence they set problems for the reasoning powers and ingenuity, provoke judgments about abstract matters, etc., instead of attempting to measure sensory discrimination, mere retentiveness, rapidity of reaction, and the like. Psychologists had generally considered the higher processes too complex to be measured directly, and accordingly sought to get at them indirectly by correlating supposed intelligence with simpler processes which could readily be measured, such as reaction time, rapidity of tapping, discrimination of tones and colors, etc. While they were disputing over their contradictory findings in this line of exploration, Binet went directly to the point and succeeded where they had failed.

It is now generally admitted by psychologists that higher intelligence is little concerned in such elementary processes as those mentioned above. Many of the animals have keen sensory discrimination. Feeble-minded children, unless of very low grade, do not differ very markedly from normal children in sensitivity of the skin, visual acuity, simple reaction time, type of imagery, etc. But in power of comprehension, abstraction, and ability to direct thought, in the nature of the associative processes, in amount of information possessed, and in spontaneity of attention, they differ enormously.

3. Binet would test “general intelligence.”

Finally, Binet’s success was largely due to his abandonment of the older “faculty psychology” which, far from being defunct, had really given direction to most of the earlier work with mental tests. Where others had attempted to measure memory attention, sense discrimination, etc., as separate faculties or functions, Binet undertook to ascertain the general level of intelligence. Others had thought the task easier of accomplishment by measuring each division or aspect of intelligence separately, and summating the results. Binet, too, began in this way, and it was only after years of experimentation by the usual methods that he finally broke away from them and undertook, so to speak, to triangulate the height of his tower without first getting the dimensions of the individual stones which made it up.

The assumption that it is easier to measure a part, or one aspect, of intelligence than all of it, is fallacious in that the parts are not separate parts and cannot be separated by any refinement of experiment. They are interwoven and intertwined. Each ramifies everywhere and appears in all other functions. The analogy of the stones of the tower does not really apply. Memory, for example, cannot be tested separately from attention, or sense-discrimination separately from the associative processes. After many vain attempts to disentangle the various intellective functions, Binet decided to test their combined functional capacity without any pretense of measuring the exact contribution of each to the total product. It is hardly too much to say that intelligence tests have been successful just to the extent to which they have been guided by this aim.

Memory, attention, imagination, etc., are terms of “structural psychology.” Binet’s psychology is dynamic. He conceives intelligence as the sum total of those thought processes which consist in mental adaptation. This adaptation is not explicable in terms of the old mental “faculties.” No one of these can explain a single thought process, for such process always involves the participation of many functions whose separate rÔles are impossible to distinguish accurately. Instead of measuring the intensity of various mental states (psycho-physics), it is more enlightening to measure their combined effect on adaptation. Using a biological comparison, Binet says the old “faculties” correspond to the separate tissues of an animal or plant, while his own “scheme of thought” corresponds to the functioning organ itself. For Binet, psychology is the science of behavior.

Binet’s conception of general intelligence.

In devising tests of intelligence it is, of course, necessary to be guided by some assumption, or assumptions, regarding the nature of intelligence. To adopt any other course is to depend for success upon happy chance.

However, it is impossible to arrive at a final definition of intelligence on the basis of a-priori considerations alone. To demand, as critics of the Binet method have sometimes done, that one who would measure intelligence should first present a complete definition of it, is quite unreasonable. As Stern points out, electrical currents were measured long before their nature was well understood. Similar illustrations could be drawn from the processes involved in chemistry physiology, and other sciences. In the case of intelligence it may be truthfully said that no adequate definition can possibly be framed which is not based primarily on the symptoms empirically brought to light by the test method. The best that can be done in advance of such data is to make tentative assumptions as to the probable nature of intelligence, and then to subject these assumptions to tests which will show their correctness or incorrectness. New hypotheses can then be framed for further trial, and thus gradually we shall be led to a conception of intelligence which will be meaningful and in harmony with all the ascertainable facts.

Such was the method of Binet. Only those unacquainted with Binet’s more than fifteen years of labor preceding the publication of his intelligence scale would think of accusing him of making no effort to analyze the mental processes which his tests bring into play. It is true that many of Binet’s earlier assumptions proved untenable, and in this event he was always ready, with exceptional candor and intellectual plasticity, to acknowledge his error and to plan a new line of attack.

Binet’s conception of intelligence emphasizes three characteristics of the thought process: (1) Its tendency to take and maintain a definite direction; (2) the capacity to make adaptations for the purpose of attaining a desired end; and (3) the power of auto-criticism.[11]

How these three aspects of intelligence enter into the performances with various tests of the scale is set forth from time to time in our directions for giving and interpreting the individual tests.[12] An illustration which may be given here is that of the “patience test,” or uniting the disarranged parts of a divided rectangle. As described by Binet, this operation has the following elements: “(1) to keep in mind the end to be attained, that is to say, the figure to be formed; (2) to try different combinations under the influence of this directing idea, which guides the efforts of the subject even though he may not be conscious of the fact; and (3) to judge the combination which has been made, to compare it with the model, and to decide whether it is the correct one.”

Much the same processes are called for in many other of the Binet tests, particularly those of arranging weights, rearranging dissected sentences, drawing a diamond or square from copy, finding a sentence containing three given words, counting backwards, etc.

However, an examination of the scale will show that the choice of tests was not guided entirely by any single formula as to the nature of intelligence. Binet’s approach was a many-sided one. The scale includes tests of time orientation, of three or four kinds of memory, of apperception, of language comprehension, of knowledge about common objects, of free association, of number mastery, of constructive imagination, and of ability to compare concepts, to see contradictions, to combine fragments into a unitary whole, to comprehend abstract terms, and to meet novel situations.

Other conceptions of intelligence.

It is interesting to compare Binet’s conception of intelligence with the definitions which have been offered by other psychologists. According to Ebbinghaus, for example, the essence of intelligence lies in comprehending together in a unitary, meaningful whole, impressions and associations which are more or less independent, heterogeneous, or even partly contradictory. “Intellectual ability consists in the elaboration of a whole into its worth and meaning by means of many-sided combination, correction, and completion of numerous kindred associations.... It is a combination activity.”

Meumann offers a twofold definition. From the psychological point of view, intelligence is the power of independent and creative elaboration of new products out of the material given by memory and the senses. From the practical point of view, it involves the ability to avoid errors, to surmount difficulties, and to adjust to environment.

Stern defines intelligence as “the general capacity of an individual consciously to adjust his thinking to new requirements: it is general adaptability to new problems and conditions of life.”

Spearman, Hart, and others of the English school define intelligence as a “common central factor” which participates in all sorts of special mental activities. This factor is explained in terms of a psycho-physiological hypothesis of “cortex energy,” “cerebral plasticity,” etc.

The above definitions are only to a slight extent contradictory or inharmonious. They differ mainly in point of view or in the location of the emphasis. Each expresses a part of the truth, and none all of it. It will be evident that the conception of Binet is broad enough to include the most important elements in each of the other definitions quoted.

Guiding principles in choice and arrangement of tests.

In choosing his tests Binet was guided by the conception of intelligence which we have set forth above. Tests were devised which would presumably bring into play the various mental processes thought to be concerned in intelligence, and then these tests were tried out on normal children of different ages. If the percentage of passes for a given test increased but little or not at all in going from younger to older children this test was discarded. On the other hand, if the proportion of passes increased rapidly with age, and if children of a given age, who on other grounds were known to be bright, passed more frequently than children of the same age who were known to be dull, then the test was judged a satisfactory test of intelligence. As we have shown elsewhere,[13] practically all of Binet’s tests fulfill these requirements reasonably well, a fact which bears eloquent testimony to the keen psychological insight of their author.

In arranging the tests into a system Binet’s guiding principle was to find an arrangement of the tests which would cause an average child of any given age to test “at age”; that is, the average 5-year-old must show a mental age of 5years, the average 8-year-old a mental age of 8years, etc. In order to secure this result Binet found that his data seemed to require the location of an individual test in that year where it was passed by about two thirds to three fourths of unselected children.

It was in the assembling of the tests that the most serious faults of the scale had their origin. Further investigation has shown that a great many of the tests were misplaced as much as one year, and several of them two years. On the whole, the scale as Binet left it was decidedly too easy in the lower ranges, and too difficult in the upper. As a result, the average child of 5years was caused to test at not far from 6years, the average child of 12years not far from 11. In the Stanford revision an effort has been made to correct this fault, along with certain other generally recognized imperfections.

Some avowed limitations of the Binet tests.

The Binet tests have often been criticized for their unfitness to perform certain services which in reality they were never meant to render. This is unfair. We cannot make a just evaluation of the scale without bearing in mind its avowed limitations.

For example, the scale does not pretend to measure the entire mentality of the subject, but only general intelligence. There is no pretense of testing the emotions or the will beyond the extent to which these naturally display themselves in the tests of intelligence. The scale was not designed as a tool for the analysis of those emotional or volitional aberrations which are concerned in such mental disorders as hysteria, insanity, etc. These conditions do not present a progressive reduction of intelligence to the infantile level, and in most of them other factors besides intelligence play an important rÔle. Moreover, even in the normal individual the fruitfulness of intelligence, the direction in which it shall be applied, and its methods of work are to a certain extent determined by the extraneous factors of emotion and volition.

It should, nevertheless, be pointed out that defects of intelligence, in a large majority of cases, also involve disturbances of the emotional and volitional functions. We do not expect to find perfectly normal emotions or will power of average strength coupled with marked intellectual deficiency, and as a matter of fact such a combination is rare indeed. In the course of an examination with the Binet tests, the experienced clinical psychologist is able to gain considerable insight into the subject’s emotional and volitional equipment, even though the method was designed primarily for another purpose.

A second misunderstanding can be avoided by remembering that the Binet scale does not pretend to bring to light the idiosyncrasies of special talent, but only to measure the general level of intelligence. It cannot be used for the discovery of exceptional ability in drawing, painting, music, mathematics, oratory, salesmanship, etc., because no effort is made to explore the processes underlying these abilities. It can, therefore, never serve as a detailed chart for the vocational guidance of children, telling us which will succeed in business, which in art, which in medicine, etc. It is not a new kind of phrenology. At the same time, as we have already pointed out, it is capable of bounding roughly the vocational territory in which an individual’s intelligence will probably permit success, nothing else preventing.[14]

In the third place, it must not be supposed that the scale can be used as a complete pedagogical guide. Although intelligence tests furnish data of the greatest significance for pedagogical procedure, they do not suggest the appropriate educational methods in detail. These will have to be worked out in a practical way for the various grades of intelligence, and at great cost of labor and patience.

Finally, in arriving at an estimate of a subject’s grade of intelligence and his susceptibility to training, it would be a mistake to ignore the data obtainable from other sources. No competent psychologist, however ardent a supporter of the Binet method he might be, would recommend such a policy. Those who accept the method as all-sufficient are as much in error as those who consider it as no more important than any one of a dozen other approaches. Standardized tests have already become and will remain by far the most reliable single method for grading intelligence, but the results they furnish will always need to be interpreted in the light of supplementary information regarding the subject’s personal history, including medical record, accidents, play habits, industrial efficiency, social and moral traits, school success, home environment, etc. Without question, however, the improved Binet tests will contribute more than all other data combined to the end of enabling us to forecast a child’s possibilities of future improvement, and this is the information which will aid most in the proper direction of his education.