The Structure and Measurement of Intelligence

Hans Eysenck

• Publisher: Routledge
• Year: 2019
• Print ISBN: 9781138538900
• eBook ISBN: 9781351473132
• Topic: Psychology
• Subtopic: Cognitive Psychology & Cognition
• Index: Psychology

What is meant by the term "intelligence" and, once de- fined, how do we go about achieving a valid measurement of this faculty? This classic textbook, originally published in 1979, and now reissued with a new preface by Sybil Eysenck, incorporates a broad range of findings and reanalyzes much of the existing literature in this area. In The Structure and Measurement of Intelligence, Hans Eysenck draws on methods for determining the effect of genetics and environment on the development of intelligence and examines the validity of the term as defined in relation to internal as well as external criteria. He tests a number of hypotheses on intelligence against empirical research findings and considers various criticisms in detail. The significance of intelligence and its measurement in society are explored in depth. Eysenck greatly expands upon such questions as: Does IQ measure intelligence? How valid is the nature versus nurture argument? and, How might socioeconomic status influence one's intelligence? Designed primarily for students and scholars in psychology and education, this text will make thought-provoking reading for all concerned with the development and measurement of intelligence in the individual.

1 Intelligence: The Development of a Concept

A first-rate theory predicts; a second-rate theory forbids; and a third-rate theory explains after the event

A. I. Kitagorodskii

It has been well said that psychology has a long past, but a short history. People have puzzled over psychological problems for thousands of years, ever since the dawn of recorded history, yet the development of a science of psychology is scarcely a hundred years old. Plato and Arisotle already discussed the notion of "intelligence", but it is only in this century that attempts have been made successfully to measure this important variable. Many misunderstandings have attended this venture, and it will be one of the functions of this book to clarify the points on which these misunderstandings have arisen. However, before doing so it may be useful to trace quite quickly, and without too much detail, the early development of the concept with which this book is essentially concerned. Like most scientific concept, this one arose out of everyday observation. The concept of temperature arose from the different feeling caused in human beings by fire and sunlight, on the one hand, and ice and snow, on the other; in this way were the notions of "cold" and "hot" born, and became the subject matter of science. Similarly, the concept of intelligence arose from observations of people trying to solve problems, to learn difficult and demanding things like mathematics, languages, and history; some seemed to find no difficulty in all this, and succeeded brilliantly, while others were very slow, and often failed altogether. Some countries, like ancient China, used civil service examinations based on such acquired learning to select its governing elite; these examinations were probably early ancestors of our modern scholastic selection techniques.

Plato clearly distinguished between the three major aspects of the mind or soul, which he called intellect, emotion, and will; in a celebrated passage in the Phaedrus he gives a picturesque analogy in which he compares the intellect with a charioteer who holds the reins, while emotion and will are compared to the horses that draw the chariot. The former guides and directs, while the latter supply the motive power. Aristotle simplified this three-fold classification; he contrasts the cognitive or intellectual capacities with the "orectic" ones, grouping together emotion and will. Cicero made a lasting contribution by translating the Platonic and Aristotelian concept of cognitive or intellectual ability into "intelligentia"; thus was born the concept of intelligence.

Other notions which play an important part in our modern discussions were equally familiar to the Greeks. Thus Plato draws a clear distinction between nature and nurture; he clearly favours the genetic causes in accounting for individual differences in intellect and personality, as is shown in the famous fable of the different metals – perhaps the first clear-cut recognition in print of the importance of individual differences in history! As Plato puts it, "The God who created you has put different metals into your composition – gold into those who are fit to be rulers, silver into those who are to act as their executives, and a mixture of iron and brass into those whose task it will be to cultivate the soil or manufacture goods." He also recognized the fact of genetic regression (the tendency of very intelligent and very dull parents to have children who regress to the mean, i. e. who are less bright, or less dull, than their parents), as when he says: "Yet occasionally a golden parent may beget a silver child, or a silver parent a child of gold; indeed, any kind of parent may at times give birth to any kind of child." And he considered it the most important task of the Republic to allocate tasks and duties according to the innate abilities of the person concerned: "The rulers have therefore received this paramount command from the Gods – that first and foremost they shall scrutinize each child to see what metal has gone to his making, and then allocate or promote him accordingly." The penalty for failure is severe, "for an oracle has predicted that our state will be doomed to disaster as soon as its guardianship falls into the hands of men of baser metal." Modern meritocratic society has come close to fulfilling at least some of Plato's dreams, although of course it would be unwise to consider intelligence by itself the equivalent of his differentiation of the men of gold, or silver, and of iron or brass.

Aristotle made another lasting contribution when he contrasted the actual observed activity or behaviour with some hypothetical underlying capacity on which it depended; in this way we arrive at the notion of an ability. Intelligence is an ability which may or may not be shown in practice, and which has to be deduced from observed behaviour, using certain scientific rules of experimental procedure. How this can be done we shall see in later chapters; here let us merely note the importance of such latent structure concepts as abilities (in connection with cognitive task), traits (in connection with personality), or attitudes (in connection with social views and opinions).

Philosophers throughout the ages were more interested in intellectual matters than in orectic ones, and it is no surprise that in modern times it was a philosopher, Herbert Spencer, who put forward the theory of intelligence which is still widely held. All cognition, he held, involves both an analytic or discriminative and a synthetic or integrative process; its essential function is to enable the organism to adjust itself more effectively to a complex and everchanging environment. During the evolution of the animal kingdom, and during the growth of the individual child, the fundamental capacity of cognition "progressively differentiates into a hierarchy of more specialized abilities"; we shall encounter these specialized abilities (verbal, numerical, perceptual, etc.) again later on. Here let us merely note that it was Spencer who revived the term "intelligence" to designate the basic characteristic of all cognitive manifestation and differentiation. By his appeal to evolution, and his insistence on observational study of animal intelligence, Spencer added biological factors to the observational generalizations of the ancient Greeks.

A third line of approach was that of the physiologists, where the clinical work of Hughlings Jackson, the experimental investigations of Sherrington, and the microscopic studies of the brain carried out by Campbell, Brodman and others did much to confirm Spencer's theory of a "hierarchy of neural functions", with a basic type of activity developing by fairly definite stages into higher and more specialized forms. Thus in the adult human brain marked differences in the architecture of different areas and of different cell-layers are perceptible under the microscope, specializations which appear and develop progressively during the early months of infant life. The brain, so it was found, always acts as a whole; its activity, as Sherrington pointed out, is "patterned, not indifferently diffuse"; the patterning itself always "involves and implies integration." Lashley contributed, from his massive research activity, the concept of "mass action" of the brain, a mass action theoretically identified with intelligence by several writers.

It is on the basis of such antecedents in observation, biology and physiology that the early psychologists proceded to work out theories of intelligence, and attempts at measurement. They started with a fairly clear-cut, well worked out theory which saw intelligence as innate, all-round cognitive ability, based on the anatomical structure and physiological functioning of the cortex; an ability, moreover, which had important social consequences. In addition to this general ability the theory envisaged additional special verbal, numerical, perceptual and other abilities, differentiated from general mental ability through phylogenetic and ontogenetic development. Such a theory requires empirical support, of course; it cannot be assumed that the simple statement of a theory proves the theory to be correct. It may be false, in part or whole; it is also possible that there may be alternative theories which fit the facts better. It is with such issues as these that we shall be concerned in this book.

A few words may be said here about the nature of concepts. We must distinguish clearly between things and concepts. The table I am writing on, the chair I sit on, the room I am working in – these are all "things" which have existence in a sense that concepts like intelligence, gravitation, or temperature have not. Philosophers are likely to dispute even the existence of "things", or at least argue about the meaning of the term, "exist"; they are not likely to dispute that things and concepts are different in a very profound way. Plato of course regarded concepts ("ideas") as really existing, and things as pale copies only of the perfect ideas laid up in heaven; few modern philosophers would follow him in this. The distinction is important because it tells us immediately that there are questions which we cannot ask of concepts which we can quite meaningfully ask of things. We can ask: "Is this a desk?", or "Is there a desk in this room?", and expect a meaningful and truthful answer. All we need is a definition of the term, "desk"; given that we can answer factual questions about desks. But how can we define a concept? In the case of the desk we can appeal to sensible properties of a real object; it has a surface, four legs, drawers. But a concept has no such sensible properties; it is an abstraction! Concepts are invented, not discovered; this is true not only of intelligence, but of all scientific concepts. How then can we define a concept, and how can we answer such questions as: "How do you know that an IQ test really measures intelligence?".

The brief answer, upon which we shall elaborate later on, is that we cannot answer such a question because it is meaningless. It assumes that intelligence is a thing; if it were we could compare our IQ measurement with the real thing, and say whether it was or was not identical with it. There is no such thing as "intelligence" somewhere out there; we have invented the term to classify and coordinate a large number of facts, and the concept has no existence outside this large array of facts. We can therefore define our concept in terms of all the facts known about it; this is what science usually does. Or we can use what is called an "operational definition", i. e. we can define the concept in terms of the methods used to measure it, in this case IQ tests. This may seem arbitrary and circular, but it is what is often done in science; the notion of operational definition was first put forward by a physicist (Bridgman, 1927). Actually the two methods of defining concepts suggested here come to much the same thing; the operational definition is based on the most representative of all the various facts known about a particular topic or subject, and thus neatly summarizes all the known facts. The selection of a mercury thermometer to measure temperature is the more or less accidental choice from thousands of substances which expand with heat, and contract with cold, any of which could have been chosen. If we define temperature as that which is measured by this thermometer, then we simultaneously identify temperature with thousands of other, similar measurements which could have been made, as well as with a large number of other facts. (Actually different substances have different properties which make them more or less useful for the measurement of temperature; we shall come back to this point.) Similarly, a good IQ test summarizes many different facts about intelligence, and to define intelligence as that which IQ tests measure is not as nonsensical as it may appear at first sight – particularly when we remember that the adjective "good" in connection with an IQ test refers back to a large body of theory and experiment which alone enables us to say which are good and which are bad IQ tests (Eysenck, 1973.)

It is often disputed whether we can ever hope to measure something as elusive as intelligence. This is not a reasonable objection; all concepts are elusive and difficult to pin down. Mass, gravitation, temperature are no exceptions. Let us consider gravitation. We have been taught, and hence believe, that when a ball falls to the earth it is attracted by a physical force which pulls it down; if we are very sophisticated we might say that there is a mutual force of attraction between the ball and the earth which is proportional to their masses, and inversely proportional to the square of their distance apart. This force of attraction seems to us so tangible that we tend to reify it, i. e. regard it as a "thing" which exists in the same way as the ball and the earth. But this view is clearly mistaken.

Newton himself was of course well aware of the difficulties in which the notion of such a force, acting as a distance, involved him, and Leibnitz, in his famous letter to Clarke, gave explicit voice to the criticisms which later on Einstein would use as his stepping stones to an alternative theory. As is well known, Newton's theory in fact was found to be in error; it made wrong predictions about such observable events as the precession of the perihelion of the planet Mercury, and it failed to predict other events, such as the bending of light rays coming from distant stars, when they passed the sun. Einstein's theory explained the former, and predicted the latter, but there is no such attractive force as Newton postulated in his theory. Gravity in relativity theory is treated as a warping of space-time, rather as indicated in Fig. 1.1. This type of theory eliminates Newtonian "gravitation" from our armoury of concepts, although of course his mathematical equations still mirror the actual events (falling of apples; motion of planets) as well as ever. We now know that they are only valid in certain special cases, i. e. when the movements involved are rather slow as compared with the speed of light; they represent a special case of a wider, more complex law.

Fig. 1.1. Einstein's theory of attraction between objects in terms of a warping of spacetime

Can we accept Einstein's concepts as more "real" than Newton's? Here again the answer must be no. There is a third view, based on quantum theory; this would treat the interaction of bodies as analogous to the other fundamental forces in nature – the strong nuclear, the weak nuclear, and the electromagnetic force. The origin of these forces is now believed to be related to the exchange of elementary particles; thus a negatively charged electron would repel another electron by exchanging the fundamental quantum of electromagnetism, viz. the photon (as in Fig. 1.2). To account for interactio...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Dedication
• Contents
• Preface to the Transaction Edition
• Introduction
• 1 Intelligence: The Development of a Concept
• 2 General Intelligence and Special Aptitudes
• 3 The Measurement of IQ
• 4 Does IQ Measure Intelligence?
• 5 Nature and Nurture: Heredity
• 6 Nature and Nurture: Environment
• 7 Nature, Nurture and Socio-economic Status
• 8 Structure of Intellect Models: Guilford and Eysenck
• 9 Developmental Models: Piaget and Jensen
• 10 Intelligence and Society
• Epilogue
• Appendix A
• Appendix B
• Appendix C
• References
• Index