The Sensory Order: An Inquiry into the Foundations of Theoretical Psychology

The Sensory Order: An Inquiry into the Foundations of Theoretical Psychology

by F. A. Hayek

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The Sensory Order, first published in 1952, sets forth F. A. Hayek's classic theory of mind in which he describes the mental mechanism that classifies perceptions that cannot be accounted for by physical laws. Hayek's substantial contribution to theoretical psychology has been addressed in the work of Thomas Szasz, Gerald Edelman, and Joaquin Fuster.


The Sensory Order, first published in 1952, sets forth F. A. Hayek's classic theory of mind in which he describes the mental mechanism that classifies perceptions that cannot be accounted for by physical laws. Hayek's substantial contribution to theoretical psychology has been addressed in the work of Thomas Szasz, Gerald Edelman, and Joaquin Fuster.

"A most encouraging example of a sustained attempt to bring together information, inference, and hypothesis in the several fields of biology, psychology, and philosophy."—Quarterly Review of Biology

F. A. Hayek (1899-1992), recipient of the Medal of Freedom in 1991 and co-winner of the Nobel Memorial Prize in Economics in 1974, taught at the University of London, the University of Chicago, and the University of Freiburg.

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A most encouraging example of a sustained attempt to bring together information, inference, and hypothesis in the several fields of biology, psychology, and philosophy.

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The Sensory Order

An Inquiry into the Foundations of Theoretical Psychology

By F. A. Hayek

The University of Chicago Press

Copyright © 1952 The University of Chicago Press
All rights reserved.
ISBN: 978-0-226-32130-1




1.1. The nature of the subject of this study makes its first task the most important and the most difficult: clearly to state the problem to which it will attempt an answer. We shall have moved a considerable distance towards the solution of our problem when we have made its meaning precise and have shown what kind of statement could be regarded as a solution.

1.2. The traditional heading under which our problem has been discussed in the past is that of the 'relation' between mind and body, or between mental and physical events. It can also be described by the questions of 'What is mind?' or 'What is the place of mind in the realm of nature?' But while these expressions indicate a general field of inquiry, they do not really make it clear what it is that we want to know. Before we can successfully ask how two kinds of events are related to each other (or connected with each other), we must have a clear conception of the distinct attributes by which they can be distinguished. The difficulty of any fruitful discussion of the mind-body problem consists largely in deciding what part of our knowledge can properly be described as knowledge of mental events as distinguished from our knowledge of physical events.

1.3. We shall attempt to avoid at first at least some of the difficulties of this general problem by concentrating on a more definite and specific question. We shall inquire how the physiological impulses proceeding in the different parts of the central nervous system can become in such a manner differentiated from each other in their functional significance that their effects will differ from each other in the same way in which we know the effects of the different sensory qualities to differ from each other. We shall have established a 'correspondence' between particular physiological events and particular mental events if we succeed in showing that there can exist a system of relations between these physiological events and other physiological events which is identical with the system of relations existing between the corresponding mental events and other mental events.

1.4. We select here for examination the problem of the determination of the order of sensory qualities because it seems to raise in the clearest form the peculiar problem posed by all kinds of mental events. It will be contended that an answer to the question of what determines the order of sensory qualities constitutes an answer to all questions which can be meaningfully asked about the 'nature' or 'origin' of these qualities; and further, that the same general principle which can be used to account for the differentiation of the different sensory qualities serves also as an explanation of the peculiar attributes of such other mental events as images, emotions, and abstract concepts.

1.5. For the purposes of this discussion we shall employ the term sensory 'qualities' to refer to all the different attributes or dimensions with regard to which we differentiate in our responses to different stimuli. We shall thus use this term in a wide sense in which it includes not only quality in the sense in which it is contrasted with intensity, extensity, clearness, etc., but in a sense in which it includes all these other attributes of a sensation. We shall speak of sensory qualities and the sensory order to distinguish these from the affective qualities and the other mental 'values' which make up the more comprehensive order of 'mental qualities'.


1.6. A precise statement of the problem raised by the existence of sensory qualities must start from the fact that the progress of the physical sciences has all but eliminated these qualities from our scientific picture of the external world. In order to be able to give a satisfactory account of the regularities existing in the physical world the physical sciences have been forced to define the objects of which this world exists increasingly in terms of the observed relations between these objects, and at the same time more and more to disregard the way in which these objects appear to us.

1.7. There exist now, in fact, at least two different orders in which we arrange or classify the objects of the world around us: one is the order of our sense experiences in which events are classified according to their sensory properties such as colours, sounds, odours, feeling of touch, etc.; the other is an order which includes both these same and other events but which treats them as similar or different according as, in conjunction with other events, they produce similar or different other external events.

1.8. Although the older branches of physics, particularly optics and acoustics, started from the study of sensory qualities, they are now no longer directly concerned with the perceptible properties of the events with which they are dealing. Nothing is more characteristic of this than the fact that we find it now necessary to speak of 'visible light' and 'audible sound' when we want to refer to the objects of sense perception. To the physicist 'light' and 'sound' now are defined in terms of wave motions, and in addition to those physical events, which, as is true of certain ranges of 'light' and 'sound' waves, cause definite sense experiences, he deals with imperceptible events like electricity, magnetism, etc., which do not directly produce specific sensory qualities.

1.9. Between the elements of these two orders there exists no simple one-to-one correspondence in the sense that several objects or events which in the one order belong to the same kind or class will also belong to the same kind or class in the other order. They constitute different orders precisely because events which to our senses may appear to be of the same kind may have to be treated as different in the physical order, while events which physically may be of the same or at least a similar kind may appear as altogether different to our senses.

1.10. These two orders have been variously described by different authors as the subjective, sensory, sensible, perceptual, familiar, behavioural or phenomenal world on the one hand, and and as the objective, scientific, 'geographical', physical, or sometimes 'constructional' on the other. In what follows we shall regularly employ the pair of terms 'phenomenal' and 'physical' to describe the order of events perceived in terms of sensory qualities and the order of events defined exclusively in terms of their relations respectively, although we shall occasionally employ the term 'sensory' as equivalent to phenomenal, especially (as in the title of this book) in the phrase 'sensory order'. We shall later (Chapters V and VIII) also describe these two orders as the 'macrocosm' and the 'microcosm' respectively. Their relation is the central problem of this book.

1.11. It is important not to identify the distinction between the phenomenal and the physical order with the distinction between either of these and what in ordinary language is described as the 'real' world. The contrast with which we are concerned is not between 'appearance' and 'reality' but between the differences of events in their effects upon each other and the differences in their effects on us. It is indeed doubtful whether on the plane on which we must examine these problems the term 'real' still has any clear meaning. For the purposes of our discussion, at any rate, we shall not be interested in what a thing 'is' or 'really is' (whatever that may mean), but solely in how a particular object or event differs from other objects or events belonging to the same order or universe of discourse. It seems that a question like 'what is x?' has meaning only within a given order, and that within this limit it must always refer to the relation of one particular event to other events belonging to the same order. We shall see that the mental and the physical world are in this sense two different orders in which the same elements can be arranged; though ultimately we shall recognize the mental order as part of the physical order, a part, however, whose precise position in that larger order we shall never be able to determine.

1.12. Historically the concept of the 'real' has been formed in contradistinction to mere 'illusions' based on sense deceptions or on other experiences of purely mental origin. There is, however, no fundamental difference between such corrections of one sense experience by others, as we employ, e.g., to discover an optical illusion, and the procedure employed by the physical sciences when they ascertain that two objects which may to all our senses appear to be alike do not behave in the same way in relation to others. To accept this latter test as the criterion of 'reality' would force us to regard the various constructs of physics as more 'real' than the things we can touch and see, or even to reserve the term 'reality' to something which by definition we can never fully know. Such a use of the term 'real' would clearly pervert its original meaning and the conclusion to be drawn from this is probably that it should be altogether avoided in scientific discussion.

1.13. The relation between the physical and the phenomenal order raises two distinct but related problems. The first of these problems presents the task of the physical sciences while the second creates the central problem of theoretical psychology. The task of the physical sciences is to replace that classification of events which our senses perform but which proves inadequate to describe the regularities in these events, by a classification which will put us in a better position to do so. The task of theoretical psychology is the converse one of explaining why these events, which on the basis of their relations to each other can be arranged in a certain (physical) order, manifest a different order in their effect on our senses.

1.14. The problems of the physical sciences arise thus from the fact that objects which appear alike to us do not always prove to behave in the same way towards other objects; or that objects which phenomenally resemble each other need not be physically similar to each other, and that sometimes objects which appear to us to be altogether different may prove to be physically very similar.

1.15. It is this fact which has made it necessary, in order to build up a science capable of predicting events, to replace the classification of objects or events which our senses effect by a new classification which corresponds more perfectly to the manner in which those objects or events resemble or differ from each other in the effects which they have upon each other. But this progressive substitution of a purely relational for a qualitative or sensory order of events provides the answer to only one part of the problem which is raised by the existence of the two orders. Even if we had fully answered this problem we should still not know why the different physical objects appear to us as they do.

1.16. It is because the physical sciences have shown that the objects of the external world do not regularly differ in their effects upon each other in the same way in which they differ in their effects upon our senses that the question why they appear to us as they do becomes a legitimate problem and indeed the central problem of theoretical psychology. In so far as the similarities or differences of the phenomena as perceived by us do not correspond with the similarities or differences which the perceived events manifest in their relations to each other, we are not entitled to assume that the world appears to us as it does because it is like that; the question why it appears to us as it does becomes a genuine problem.

1.17. It is, perhaps, still true that psychologists in general have not yet become fully aware of the fact that, as a result of the development of the physical sciences, the explanation of the qualitative order of the phenomenal world has become the exclusive task of psychology. What psychology has to explain is not something known solely through that special technique known as 'introspection', but something which we experience whenever we learn anything about the external world and through which indeed we know about the external world; and which yet has no place in our scientific picture of the external world and is in no way explained by the sciences dealing with the external world: qualities. Whenever we study qualitative differences between experiences we are studying mental and not physical events, and much that we believe to know about the external world is, in fact, knowledge about ourselves.

1.18. It is thus the existence of an order of sensory qualities and not a reproduction of qualities existing outside the perceiving mind which is the basic problem raised by all mental events. Psychology must concern itself, in other words, with those aspects of what we naïvely regard as the external world which find no place in the account of that world which the physical sciences give us.

1.19. This reformulation of the central problem of psychology has thus been made necessary by the fact that the physical sciences, even in their ideal perfect development, give us only a partial explanation of the world as we know it through our senses and must always leave an unexplained residue. After we have learnt to distinguish events in the external world according to the different effects they have upon each other, and irrespective of whether they appear to us as alike or different, the question of what makes them appear alike or different to us still remains to be solved. The empirical establishment of correspondences between certain phenomenal and certain physical constellations of events is no sufficient answer to this question. We want to know the kind of process by which a given physical situation is transformed into a certain phenomenal picture.

1.20. Since the peculiar order of events which we have called the phenomenal order manifests itself only in the responses of certain kinds of organisms to these events, and not in the relation of those events to each other, it is natural to search for an explanation of this order in some feature of the structure of these organisms. We shall eventually find it in the fact that these organisms are able within themselves to reproduce (or 'build models of') some of the relations which exist between the events in their environment.

1.21. The fact that the problem of psychology is the converse of the problem of the physical sciences means that while for the latter the facts of the phenomenal world are the data and the order of the physical world the quaesitum, psychology must take the physical world as represented by modern physics as given and try to reconstruct the process by which the organism classifies the physical events in the manner which is familiar to us as the order of sensory qualities. In other words: psychology must start from stimuli defined in physical terms and proceed to show why and how the senses classify similar physical stimuli sometimes as alike and sometimes as different, and why different physical stimuli will sometimes appear as similar and sometimes as different.


1.22. Before we proceed farther it is necessary to define more precisely some of the terms we shall have constantly to employ. This applies especially to the terms 'stimulus' and 'nervous impulse' and more particularly to the sense in which we shall speak of particular 'kinds' of stimuli or of the same and of different nervous impulses. It will be convenient also to consider already at this stage the meaning and significance of the famous principle of the 'specific energy of nerves.'

1.23. The term stimulus will be used throughout this discussion to describe an event external to the nervous system which causes (through or without the mediation of special receptor organs) processes in some nerve fibres which by these fibres are conducted from the point at which the stimulus acts to some other point of the nervous system. It appears that at least some receptor organs are sensitive not to the continuous action of any one given stimulus but only to changes in that stimulus. Whatever it is that is produced in the nerve fibre and propagated through it we shall call the impulse.

1.24. The physical event acting as a stimulus is described as such only with regard to its action on the receptors. This leads sometimes to a rather confusing distinction between the stimulus and its 'source', sometimes described as the stimulus object. What will here be described as stimulus will always be the proximal stimulus, i.e., the last known physical event in the chain which leads to the production of the impulse. In some instances (particularly in the case of odours) this proximal physical stimulus, however, is not certainly known, and we must be satisfied with reference to some more remote event which has then to be regarded as the source of an unknown proximal stimulus.


Excerpted from The Sensory Order by F. A. Hayek. Copyright © 1952 The University of Chicago Press. Excerpted by permission of The University of Chicago Press.
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Meet the Author

F. A. Hayek (1899–1992), recipient of the Presidential Medal of Freedom in 1991 and co-winner of the Nobel Memorial Prize in Economics in 1974, was a pioneer in monetary theory and a leading proponent of classical liberalism in the twentieth century. He taught at the University of London, the University of Chicago, and the University of Freiburg.

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