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


This description of perceptual consciousness differs sharply, of course, from the traditional Sense-datum Theory, which is based on a supposed distinction between two constituents of perceptual consciousness. (1) direct awareness of a sense-datum and (2) mediated "perception" of a physical object. There are, however, two versions, of the Sense-datum Theory itself which must be distinguished in order to understand precisely what is asserted and denied by the Percept Theory: I shall refer to these two versions as the "Discursive Inference Theory" and the "Sensory Core Theory".

(a) The Discursive Inference Theory

The Discursive Inference Theory is most easily illustrated by turning to some of the great epistemological works of the British empirical school. In the Essay concerning Human Understanding, for example, Locke seems to maintain that perception is a discursive process which begins with awareness of a sense-datum and ends with the "idea" of a physical object. According to this analysis the perception of a physical object always involves a sensation and a subsequent act of judgement; every perception, therefore, includes awareness of a sense-datum as a temporally distinct act or state of consciousness. When we look at an alabaster globe, for example, the idea thereby imprinted on our mind is that of a flat circle. But knowing from experience that the cause of this appearance is a convex body, "judgment frames to itself the perception of a convex figure".17 Locke admits that the transiting from sense-datum to judgement "in many cases by a settled habit . . . is performed so constantly and so quick that we take that for the perception of our sensation which is an idea formed by our judgment; so that the one, viz. that of sensation, serves only to excite the other and is scarce taken notice of itself".18 But he does not doubt that both the sensation and the idea of judgment always occur when we perceive a physical object and that they always occur one after the other.

Berkeley's analog as of perception in his New Theory of Vision is almost identical with Locke's. Perception is described as a process of discursive inference in which a sensation "suggests" a physical object to the observer. The mind no sooner perceives a sensation, Berkeley says, ". . . but it withal perceives the different idea of distance which was wont to be connected with that sensation". Thus, "having of a long time experienced certain ideas perceivable by touch . . . to have been connected with certain ideas of sight, I do, upon perceiving these ideas of sight, forthwith conclude what tangible ideas are like to follow".19 Berkeley recognises that there are times when "we find it difficult to discriminate between the immediate and mediate objects of sight. . . . They are, as it were, most closely twisted, blended, and incorporated together".20 But he does not seem to doubt that in every act of perception there are two successive events: the occurrence of a sense-datum and the occurrence of an idea which it suggests. Like Locke, in short, he maintains the Discursive Inference Theory, although frankly admitting that the successive components of perception may sometimes be hard to distinguish.

(b) The Sensory Core Theory

Almost all contemporary epistemologists who accept the Sense-datum Theory, however, have rejected the discursive inference version in favour of the Sensory Core Theory. Whereas Locke and Berkeley found it merely difficult to distinguish a temporally distinct state of direct awareness in every perception, most contemporary psychologists and epistemologists have found it quite impossible. In fact many of them have concluded that perceptual consciousness is never a discursive process involving a preliminary state of direct awareness. An observer might report, to be sure, that on a certain occasion he was aware of a mere noise and then subsequently judged it to be an air-raid warning; but his report would probably be more accurate if he said that he first heard (in the sense of "perceived") a siren or "some sort of whistle" and then subsequently refined his judgement. The fact that a series of perceptions may become increasingly refined or determinate, in short, does not constitute proof of the existence of separate states of direct awareness. "If the content of perception is first given and then, in a later moment interpreted", says Lewis, "we have no consciousness of such a first state of intuition unqualified by thought, though we do observe alteration and extension of interpretation of a given content as a psychological temporal process".21

The many philosophers who support the Sensory Core Theory, therefore, do so because they believe that direct awareness of a sense-datum is a constituent of perceptual consciousness even though perceptual consciousness is not a discursive process. They believe that perceptual consciousness is a twofold state consisting of (1) direct awareness of a sense-datum and (2) an element of interpretation (variously described as "belief", "acceptance", "expectation", "judgment", etc.) and they believe that these two parts exist simultaneously. In perceiving an apple, for example, the sense-datum -- perhaps a round, red patch -- is one part of what is before our minds; the element of interpretation which distinguishes the perception of an apple from the perception of a tomato, is the other. The distinctive feature of this theory, in short, is that it regards awareness of a sense-datum as literallv a part of perceptual consciousness, but not as a part temporally distinct.

I have called this theory of perception the "Sensory Core Theory" because it asserts that there is, in some more or less literal sense, a core of sense-data in every perception. Psychologists of the Titchenerian School are sometimes said to have believed quite literally that sense-data form a core or nucleus within every perception,22 but it is possible to accept the Sensory Core Theory, as I have defined it, without committing oneself to any such topographical analysis as Titchener's. Thus Price nowhere suggests that perceptual consciousness is strictly a nucleus of sensation surrounded by a fringe of images, but he does explicitly endorse the Sensory Core Theory. Perception involves no inference, he says, nor any discursive process whatsoever: "The two states of mind, the acquaintance with a sense datum and the perceptual consciousness [of the object] just arise together."23 Broad also accepts the Sensory Core Theory, for with certain important qualifications concerning the nature of perceptual belief, Broad is willing to say that "in a perceptual situation we are acquainted with an objective constituent which sensuously manifests certain qualities, and that this acquaintance gives rise to and is accompanied by a belief that the constituent is part of a larger spatio-temporal whole of a specific kind".24 Lewis has also endorsed the Sensory Core Theory by emphasing the fact that awareness of a sense-datum does not precede but accompanies the other constituent of perception. "Immediate awareness", he says, "is an element in knowledge rather than a state of mind occurring by itself or preceding conceptual interpretation"25 All these philosophers, and indeed the vast majority of contemporary epistemologists, believe that sense-data are distinguishable constituents of perception, and this, of course, is the view that is specifically rejected by James and other advocates of the Percept Theory.

It must be clearly understood that both the Percept Theory and the Sensory Core Theory are theories about the nature of ordinary perceptual states -- in which we are in some sense "conscious" of physical objects. Neither of these theories implies anything whatsoever concerning the existence of pure states of direct awareness -- states in which we are directly aware of sense-data but not conscious of physical objects in the manner characteristic of ordinary perception. Contemporary philosophers seem to disagree about the frequency and even the possibility of such non-perceptual sensory states, but their opinions on this subject seem to be independent of their conclusions concerning the validity of the Percept Theory and the Sensory Core Theory. Lewis calls such states "states of pure esthesis", and doubts whether there are any. James says that "pure sensations", which he defines as the objects of direct acquaintance, "can only be realised in the earliest days of life. They are all but impossible to adults with memories and stores of association acquired."26 Price believes that it is possible on rare occasions only, "in a moment of intense intellectual preoccupation", to "pass over into the state of pure sensing, where there is not even the vaguest and most inattentive acceptance of anything material at all".27 Other philosophers, and many psychologists, however, seem to believe that pure states of sense-datum awareness are more easily obtainable, and have even said that they must be obtained for certain psychological and epistemological purposes.28 Since the disagreements may be partly verbal, and since the issue is in any case not strictly relevant to an analysis of ordinary perceptual consciousness, I shall henceforth speak as though it were agreed that pure states of direct awareness are obtainable, but with the understanding, that "pure" may be interpreted to mean "approximately pure".

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15 William James, The Principles of Psychology, Vol. II, p. 80, Holt, New York, 1896. Italics mine except for "plus".

16 Ibid., Vol. II, p. 81.

17 John Locke, An Essay Concerning Human Understanding, Vol. I, pp. 185-186, Oxford, 1894.

18 Ibid., p. 186.

19 New Theory of Vision, in Works, Vol. I, p. 148.

20 Ibid., p. 151.

21 Mind and the World-Order, p. 66.

22 "A typical perception", Titchener said, "resolves to begin with unto a number of sensations . . . -- the part that we may conveniently call its core or nucleus". Around this nucleus, is the context which carries the meaning, "the fringe of related processes that gathers about the central group of sensations or images" (A Beginner's Psychology, pp. 114, 118, Macmillan, New York, 1922.)

23 Perception, p. 151. Italics mine.

24 C. D. Broad, The Mind and Its Place in Nature, p. 153, Harcourt Brace, New York, 1929. Italics mine.

25 Mind and the World-Order, p. 276.

26 The Principles of Psychology, Vol.II, p. 7.

27 Perception, p. 165.

28 This point is discussed more fully in Part II of this paper.

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