The Nature of Intelligence

Chapter 12. A Definition of Intelligence

L.L. Thurstone

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1. Intelligence as incompleteness of expected behaviour
2. Consummatory behaviour
3. Animal intelligence
4. A child's intelligence
5. Adult intelligence


We started our discussion of intelligent and non-intelligent behaviour with the assumption that conduct originates in the organism itself and that it is only secondarily determined by the environment. `'With this assumption we place the stimulus in the rôle of a modifier of intended conduct, or as the medium through which self-expression takes place. We look for causal factors beyond the stimulus— in the organism itself— and it is in the impulses of the inner self that we must find the datum for psychology. We find that this point of view is implied or stated by most of the writers in the field of abnormal psychology, and that it is not the point of view represented by most of the scientific psychologists. We have described various aspects of this fundamental process of self-expression, one aspect of which constitutes what we

(157) know as intelligence. It is now our purpose to summarize these observations about the reflex circuit into a definition of intelligence which shall be consistent with the point of view that we have outlined. Such definitions we have already given as parts of the discussion of related topics, but we shall summarize them here with special regard to what we know as different degrees or levels of intelligence. We assume, first of all, that there is a continuum between

the impulses that constitute the inner self, the conscious life that is present to introspection, and the behaviour for which consciousness is the natural preparation. These three phases of the psychological act terminate in what we know as the overt act or overt behaviour. We postulate a functional identity of the three phases of the psychological act, in that consciousness is assumed to be made of the same stuff that behaviour is made of. Consciousness is incomplete behaviour. Mental states constitute conduct which is in the process of being formed. The sequence from the impulses that constitute the inner self to the behaviour by which satisfactions are to be attained is primarily one of delimitation. In the early phase of the circuit, the impulse is relatively vague, unlocalized, diffuse, universal. At the terminal or overt phase it is relatively definite, localized, specific, and particular.

The psychological differentiae for the several levels of the psychological act relate to the degree of definition of the impulse. Those states of mind in which the impulse is as yet. only loosely specified are known as universals They are the higher thought processes. Those states of mind in which the expected experience is relatively well specified

(158) are known as perception or as the simpler ideational processes. The higher thought processes differ from the simpler ideational processes mainly in the degree of definition of the expected adjustment.

It should be evident that if the act is made focal when it is as yet only a universal, there is ample opportunity to specify the details over a wide range of behaviour. If, on the other hand, the act is made focal when it is almost completely specified, there is considerable restriction in the range of behaviour through which it may be finally expressed. This greater latitude of choice over a wide range of possible types of adjustment constitutes the biological advantage of the higher thought processes. We have discussed this characteristic of the reflex circuit also with regard to overt and mental trial and error. The higher thought processes have been described as a trial-and-error process that is carried out with loosely organized and tentative alternatives, whereas the perceptual and overt forms of trial and error are carried out with alternatives that are already closely specified. They leave little latitude for further choice.

The focal point in the reflex circuit we have defined as that stage in the expression of an impulse at which the impulse becomes conscious. The impulse may become focal when it is almost ready to precipitate into overt action, or it may become focal while it is still only a vague, loosely organized desire. In the latter case the impulse contains relatively few attributes when it becomes focal, whereas in tree former case it is already specified as to most of its details. That part of the reflex circuit which temporally precedes the focus of consciousness is called the preconscious.

( 159) The part of the reflex circuit which succeeds the focus of consciousness is subject to introspective description. It is characteristic of the preconscious phase of the circuit that it is not subject to observation and inhibitive control.

The intelligence of any particular psychological act is a function of the incomplete stage of the act at which it is the subject of trial-and-error choice. Intelligence, considered as a mental trait, is the capacity to make impulses focal at their early, unfinished stage of formation. Intelligence is therefore the capacity for abstraction, which is an inhibitory process. In the intelligent moment the impulse is inhibited while it is still only partially specified, while it is still only loosely organized. It is then known as a universal or a concept. The trial-and-error choice and elimination, in intelligent conduct, is carried out with alternatives that are so incomplete and so loosely organized that they point only toward types of behaviour without specifying the behaviour in detail.


In the lowest form of conduct that w e can imagine with regard to its intelligence, we have every impulse of the organism expressed in purely random forms without consciousness. It is purely reflex. In such behaviour every impulse expresses itself without inhibition or anticipation of the experience. Such random behaviour is continued until the

(160) satisfactions of the organism are attained. The life of such organisms is limited entirely to contact experience of the consummatory sort. Consciousness implies anticipation of experience and that is impossible in a life that is limited to consummatory and random contact experience.


The first sign of intelligence appears when the consummatory contact experience is associated with sense-experience. After a few repetitions of such association the sense-experience alone comes to represent the completion of the experience. The sense-impression comes to mean the expected consummation in contact form. The trial-and-error elimination of failures is then removed from the realm of completely enacted contact experience to the realm in which these contact experiences are merely indicated by their corresponding sensory cues. The impulses that are checked in terms of the expected experience, with which the sensory cues of the moment have been associated, are said to be conscious. Consciousness is, functionally considered, just this expectation of a completed experience in terms of the indices of the moment. It implies a shift of the trial-and-error life of the actor from overt experience to the incomplete experience which is the sensory cue. This has been shown to be essentially a process of conditioning in the behaviouristic sense. Animal intelligence is limited in the degree of incompleteness of expected experience at which its trial-and-error life may be carried out. It is limited in its capacity for abstraction to that degree of it which is marked by the use of sensory cues as indices of

(161) expected experience. Its trial-and-error choice of behaviour is therefore limited to the immediate present.


If we continue the progress marked by the shift of the trial-and-error point from among overt particulars to the stage at which these particulars are anticipated in terms of the sensory cues, we come to the stage of development of mind at which the actor can make focal his impulses for trial-and-error choice in the absence of the stimulus. That is ideation. It is directly continuous with the intelligence that is limited to the immediate present. This further progress simply means that the impulse is made focal at a still less defined stage when it has still fewer attributes, being stripped even of those attributes which are implied by the sensory cue.

The intelligence of the child is greatly in advance of that of the animal in that it is able to anticipate experience which is not perceptually present. The child is capable of ideational trial and error even though the process is for a time limited to the situations in which perceptual experience is imaginally represented rather than universals of higher order. The child's imagination is limited to the situations in which its bodily relations are imaginally specified. It remains for the intelligence level of the adult to be able to imagine expected experience so incompletely specified that one's bodily relations are not imaginally represented.



In the normal adult intelligence we have the capacity to represent expected experience in terms of cues that point toward types of experience and in which the bodily relations of the actor are not even specified. This is conceptual thinking. The types of experience are represented in conceptual thinking by symbols that are less detailed than the perceptual cues. The visual and auditory images that serve as indices of meaning in the adult mind are in reality incomplete acts which are being accepted or rejected in terms of the purposes of the moment. The meaning of a concept is the potential particularization of the imaginal cue into expected experience.

We have seen that the differentiation of the exploring function of the receptors is the beginning of the development of intelligence. The biological function of intelligence is to protect the organism from bodily risk and to satisfy its wants with the least possible chance of recording failure on the environment. This is accomplished by deflecting an impulse which is headed toward failure before the failure is realized. It is made possible by the fact that, psychologically, a part of an experience serves the purpose of guiding the whole of the experience. The percept represents the experience that would be met if the percept were ignored. The deflection of an impulse toward or away irons an experience is determined by that small part of the experience which constitutes the sensory cue or its ideational equivalent. If a certain course of action is declared to be a bad policy

(163) and thereby rejected, the future failure is eliminated when the impulse is only conceptual and before the details of the impending failure have been realized.

In a biological sense the higher thought processes serve the same purpose for the organism as the simplest anatomical differentiation of the exploring function. The two are exactly the same in kind. They differ only in the degree of incompleteness of the experiences that are being chosen and eliminated.

It is of some interest to speculate about the nature of the continued development of intelligence. Further development of intelligence might give facility in selecting effective behaviour with impulses that are close to their source, while they are in what we know as the preconscious or subconscious. To think would then be to use terms that are less and less cognitive but more and more loaded with affectivity. It might possibly come about that the highest possible form of intelligence is one in which the alternatives are essentially nothing but affective states. Some characteristics of genius would not be inconsistent with such a view.


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