Roderick Firth, Sense Data and the Percept Theory, 1949-50.

PART I
THE PHENOMENOLOGICAL BASIS OF THE PERCEPT THEORY

1. THE NATURE OF SENSE-DATA

(a) The Definition of "Sense Datum"

To understand the position of those who reject the Sense-datum Theory in favour of the Percept Theory, it is necessary to consider, at least briefly, the manner in which the term "sense- datum" is customarily defined. It must be recognised, first of all, that in order to define this term philosophers have always found it necessary to refer to a certain kind of perception or awareness. Sometimes, for example, sense-data are defined as the objects of direct perception or of immediate perception. Thus at the outset of Berkeley's Three Dialogues, Philonous defines what he calls "sensible things" as "those only which are immediately perceived by sense"2 Broad defines sensa as objects of which we are "directly aware" in a perceptual situation".3 Price defines sense-data as those things "directly present to consciousness" in perception.4 And Moore defines sense-data as the objects of "direct apprehension", citing as an example of such apprehension the having of an after-image.5 If, however, a philosopher wishes to speak without contradiction of unsensed sense-data, he may define sense-data as entities which could be directly or immediately observed. And if he wants to distinguish between a sense-datum and sense-field, he may define sense-data as the distinguishable parts of whatever could be observed in this manner. But in any case he makes some reference to a particular kind of observation or awareness, which he usually describes as "direct" or "immediate".

This does not mean, of course, that sense-data cannot be defined without using the word "observation" or the word "awareness"; in fact some philosophers are content to define sense-data as entities which are (or could be) sensed, or even as entities given to sense, and these definitions are merely verbal analyses of the term "sense-datum". The important point is simply that sense-data are defined not by an enumeration of their kinds but rather by reference to the manner in which we become conscious of them. We do not say that sense-data are patches of colour, rough things and smooth things, hot things and cold things, etc., for we could never be sure of exhausting the denotation of "sense- datum" in this way. Moreover, according to some theories, the surfaces of physical objects can likewise be described as "patches of colour", "rough", "smooth", etc., and the question whether or not some sense-data are surfaces of physical objects should not be prejudiced or confused by our definitions. Sense-data must be defined, therefore, by reference to the manner in which we become conscious of them: they are what we feel, sense, intuit, or immediately observe, or they are what is given to us, or what we are directly aware of, in perception. And once we understand the meaning of "sense-data" as so defined, we can presumably decide to some extent by empirical observation just what kinds of entities are properly called "sense-data".

(b) The Denotation of "Sense-Datum"

Nevertheless -- and here we come to a matter of the greatest importance in understanding and evaluating criticisms of the Sense-datum Theory -- philosophers have always found it impossible to explain the meaning of such terms as "direct awareness" and "immediate perception" without mentioning at least a few examples of the objects of such awareness or perception, namely, sense-data. This fact has been noticed and emphasised by Ayer and Moore. In The Foundations of Empirical Knowledge, Ayer points out that the terms "direct awareness" and "sense-datum" are correlative and that "since each of them is being used in a special, technical sense, it is not satisfactory merely to define one in terms of the other". "In order to show how one or the other of them is to be understood", therefore, it is necessary to use some other method of definition, "such as the method of giving examples".6 Moore makes the same point. That special sense of the word "see", he says, "which is the visual variety of what Berkeley called 'direct perception' . . . can only be explained by giving examples of cases where 'see' is used in that sense"7 It follows, therefore, that in order to understand what philosophers mean by the term "sense-datum", we must supplement our analysis of whatever explicit statements they may have made on the subject, by a careful examination of the examples which they have given.

Now such an examination of the examples which contemporary philosophers have given to illustrate the meaning of the words "sense-datum" and "direct awareness", will make it quite clear that all of them who are using these words in anything like the traditional way, are in agreement on two important points. They agree, in the first place, that the sense-data directly observable by any one sense are quite limited in their qualities. With respect to visual perception, for example, they agree with Berkeley that it is false to say that "we immediately perceive by sight anything beside light, and colours, and figures".8 Thus our sense-datum when we look at a dog, according to Russell, is "a canoid patch of colour".9 And when we look at a penny stamp, according to Broad, our sensum is "a red patch of approximately square shape''.10 And when we look at an apple, according to Lewis, what is given is a "round, ruddy . . . somewhat''.11 And when we look at a tomato, according to Price, our sense-datum is "a red patch of a round and somewhat bully shape".12 Thus it seems to be agreed by all these philosophers that when we gaze, for example, from a warm room at a distant, snow-capped mountain, our awareness of whiteness may properly be described as "direct", whereas our awareness of coldness may not. One of our sense-data is a white patch shaped like a mountain peak but our sensation of temperature, if we are aware of any at all, is one of warmth rather than coldness. In colloquial English, to be sure, we might say that the mountain "looks cold" or "appears cold", just as we might say that it "looks white" or "appears white", but such language is generally supposed to be unsatisfactory for theory of knowledge because it obscures the fact that the manner in which we are conscious of whiteness in such a case is very different from the manner in which we are conscious of coldness. The distinction in question is the very one that has traditionally been drawn by the use of such pairs of words as "impression" and "idea", "sensation" and "perception", "the given" and "the conceptual", "sense-datum" and "image", etc., and philosophers who use the term "direct awareness" in the traditional way must agree, therefore that the sense-data directly observable by any one sense are quite limited in their qualities.

In the second place, all philosophers who use the term "direct awareness" in the traditional way will agree on a still more important point, viz, that we are never directly aware of physical objects. It may seem, on first thought, that philosophers who accept the theory of perception called "direct realism", or some other more or less sophisticated variation of naive realism, are exceptions to this rule. Closer examination of their positions will probably show, however, that what these philosophers actually maintain is that some visual and tactual sense-data -- though not, of course, data of the other senses -- are literally the surfaces of physical objects. But these "surfaces" it should be noted, are not themselves physical objects: they are surfaces, and differ from physical objects in that they do not occupy a volume of space. And since these direct realists admit that it is only the surfaces of physical objects which we can perceive directly (i.e., that our sense-data are surfaces and not physical objects) we may conclude that their theory is not distinguished by any special propositions concerning the psychology of perception.

To emphasize the fact that physical objects are not accessible to direct observation, it has long been customary among philosophers and psychologists to reserve the verb "to perceive" for those cases in which the observation in question is not direct. According to this convention, which I shall adopt, the observing of physical objects is called "perceiving". Thus this second point of agreement among philosophers who use the correlative terms "sense-datum" and "direct awareness" in their traditional meanings, may be stated as follows: Physical objects are perceived but they are never the objects of direct awareness.

(c) Criticism of the Traditional Concept

Now in view of the necessity for defining the term "sense-datum" by the method of giving examples, it is clear that not only the truth but the very meaningfulness of the traditional Sense-datum Theory depends on the possibility of making the distinctions involved in these two points of agreement just formulated. Yet it is precisely these distinctions which have been denied by philosophers who accept the Percept Theory. They have sometimes developed their criticism in a rather haphazard manner, but I believe that their rejection of the Sense-datum Theory has always been based on objections to one or both of these two points of agreement.

The first objection consists in denying that there is any discoverable kind of observation or awareness which is present in every perception, and which takes as its objects only the kinds of things which have traditionally been offered as examples of sense-data. And this is not a trivial objection, for most advocates of the Percept Theory would go so far as to say that the experience of a man looking at a distant mountain from a warm room might comprise both whiteness and coldness, each in precisely the same manner, and neither in any other manner -- a statement which, as I have pointed out, has been either explicitly or implicitly denied by all philosophers who use the term "sense-datum" in its traditional meaning.

The second objection to the Sense-datum Theory is one which is not entailed by the first but which many psychologists and philosophers regard as an essential part of the Percept Theory. This objection consists in maintaining that in fact physical objects themselves are observed as directly as patches of colour, odours, tastes, and other so-called "sense-data". The direct and immediate experience of anyone who looks at the world about him, according to this interpretation of the Percept Theory, always consists of a number of full-bodied physical objects. And this, of course, is flatly to deny the distinction between perception and direct awareness which is essential to the Sense- datum Theory.

Now even the first of these two objections, if valid, is sufficient to necessitate a reformulation of most of the epistemological theories in the history of modern philosophy. Just how radical that reformulation would have to be, is a question which I shall discuss later. But the second objection to the Sense- datum Theory has implications which are even more serious, especially for those theories which maintain that physical objects are all, in some more or less literal sense, "composed of" sense-data (or of possible sense-data). Not only Berkeley and other subjectivists, but many more modern philosophers including Bergson, James, Russell, the new realists and many of the pragmatists and logical positivists, have supported the view that physical objects are knowable just because they are reducible to objects of direct awareness. But if sense-data are defined as the objects of direct awareness, and if, as some advocates of the Percept Theory have maintained, the objects of direct awareness may be physical objects, then physical objects are merely a subclass of sense-data. And the theory that physical objects are in some sense "composed of" sense-data is either false or tautological, of course, if it is understood that physical objects are themselves sense-data.

In recent years, moreover, the view that physical objects can be observed as directly as the entities which have traditionally been called "sense-data", has been used by a number of philosophers as a basis for criticizing one or more of these very epistemological positions. Wild, for example, has maintained in an article entitled "The Concept of the Given in Contemporary Philosophy", that what is actually given in perception is a "world of things". He quotes with approval a statement of Lewis that "it is indeed the thick experience of the world of things . . . which constitutes the datum for philosophical reflection", that "we do not see patches of colour, but trees and houses; we hear not indescribable sounds, but voices and violins". But then he goes on to criticize Lewis for abandoning this "classic view of the given" for the more restricted one of Berkeley and other modern empiricists. Modern empiricism, Wild asserts, "abandons the aim of classic philosophy to describe the thick experience of the world of things as it is given. Instead of this, it singles out a certain portion of the given as peculiarly accessible or given in some special sense". 13

Reichenbach, in his Experience and Prediction, has also declared that physical objects are immediately given in perception and has used this as an argument against positivistic theories of "reduction". Reichenbach's position, however, is much more extreme than Wild's. According to Wild, those things that are called "sense-data" by modern epistemologists are part of what is given; what he objects to is the view that "the immediately given alone is given". According to Reichenbach, however, such sense-data (what he calls "impressions") are not given at all. "What I observe", he says "are things, not impressions. I see tables, and houses, and thermometers, and trees, and men, and the sun, and many other things in the sphere of crude physical objects; but I have never seen my impressions of these things".14

Many statements of this kind have appeared in philosophical literature in recent years, and in most cases they appear to be based on the Percept Theory. The central thesis of this theory now seems to be accepted by most psychologists who are interested in the phenomenology of perception, although there are, as we shall see, differences of opinion concerning the implications of the theory. The central thesis was stated by William James in his Principles of Psychology as concisely, I believe, as it has ever been stated. A perception, he said, "is one state of mind or nothing"; if does not contain a sensation.

"We certainly ought not to say what is usually said by psychologists, and treat the perception as a sum of distinct psychic entities, the present sensation namely, plus a lot of images from the past, all 'integrated' together in a way impossible to describe. The perception is one state of mind or nothing."15

We may look at a physical object in such a way, James admitted, that what we apprehend approaches "sensational nudity"; thus by turning a painting upside down, or looking at it with a purely aesthetic attitude, "we lose much of its meaning, but, to compensate for the loss, we feel more freshly the value of the mere tints and shadings, and become aware of the lack of purely sensible harmony or balance that it may show".16 Nevertheless, the fact remains that sensations do not occur as constituents of perceptions, but at most only as complete and independent states of mind.

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Notes

2 Berkeley, Three Dialogues, in Works, Oxford, 1891, Vol. I, p. 381.

3 C. D. Broad, Scientific Thought, p. 239, Kegan Paul, London, 1923.

4 H. H. Price, Perception, p. 3, McBride, New York, 1933.

5 G. E. Moore, Philosophical Studies, p. 173 et seq., Harcourt Brace, New York, 1922, and "A Reply to My Critics", The Philosophy of G. E. Moore, p. 629, Northwestern U. Press, Chicago, 1942.

6 A. J. Ayer, The Foundations of Empirical Knowledge, p. 61, Macmillan, New York, 1940.

7 "A Reply to My Critics", in Philosophy of G. E. Moore, p. 628.

8 Principles, in Works, vol. I, p. 282.

9 Bertrand Russell, Inquiry into Meaning and Truth, p. 174, Norton, New York 1940. Quine has pointed out that Russell's word "canoid" means not "dog-shaped" but "basket-shaped". (Review of Russell's Inquiry into Meaning and Truth, p> 10 Scientific Thought, p. 119

11 C. I. Lewis, Mind and the World-Order, p. 119, Scribners, New York, 1929.

12 Perception, p. 3. We may overlook for the moment the disagreement among these philosophers concerning the number of spatial dimensions possessed by visual sense-data.

13 Ja.

13 John Wild, Philosophy and Phenomenological Research, pp. 70-71, September, 1940.

14 Hans Reichenbach, Experience and Prediction, p. 164, U. of Chicago Press, Chicago, 1938. It is interesting to observe that in The Unity of Science, Kegan Paul, London, 1934, pp. 45-48, Carnap himself had questioned what Reichenbach calls "the positivist dogma" that impressions are given. There is a view, Carnap said, that "material things are elements of the given", and although "it is not often held to-day, it is . . . more plausible than it appears and deserves more detailed investigation".

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