Perception from an Epistemological Point of View Fred I. Dretske The Journal of Philosophy, Vol. 68, No. 19, Sixty-Eighth Annual Meeting of the American Philosophical Association Eastern Division. (Oct. 7, 1971), pp. 584-591. Stable URL: http://links.jstor.org/sici?sici=0022-362X%2819711007%2968%3A19%3C584%3APFAEPO%3E2.0.CO%3B2-5 The Journal of Philosophy is currently published by Journal of Philosophy, Inc..
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POINT OF VIEW *
OTHING much is to be gained by arguing about what, exactly, deserves the label 'The Causal Theory of Perception'. I shall therefore follow Professor Shimony's lead and talk about this theory as one which views man as a system that interacts dynamically with other systems and that, as a result of such interactions, is brought into various states-states which are (usually) a good index of the existence and character of these other systems. If one prefers to put this in a way that is not so heavily spiced with the terminology of classical physics, one could say (I hope) that according to this view a percipient is causally affected by his surroundings and that his resultant state is, generally speaking, a reliable index to the nature of these surroundings. When we approach perception from an evolutionary standpoint, this basic causal picture is articulated into a remarkably comprehensive account of man's perceptual resources. The basic causal picture gives us to understand that we are instruments, so to speak, capable of responding to and registering the goings-on around us. The evolutionary point of view supports this account by explaining why, for certain restricted purposes, we are such sensitive instruments and how we became that way. It helps us to understand the differences in, and the limitations of, the perceptual capabilities of different organisms. It tells us how our calibration, responsiveness, and threshold points can be modified over successive generations, and it does so in a way that makes intelligible the extraordinary compatibility of instrument and environment. T h e details are not always available, but the fundamental explanatory approach is scientifically sound and undeniably convincing. I don't know who is going to quarrel with this. I certainly am not. As Shimony observes, "the tacit premise that precise adaptation is the end-product of a long sequence of evolutionary modification is so well established in the case of anatomical features, for which the paleontological record is available, and it fits the evidence of comparative zoology so well, that it can hardly be questioned in the case of features of the perceptual apparatus" (577). It would be surprising, indeed, if the evolutionary point of view could not accommodate the facts about an organism's perceptual relationship
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* T o be presented in APA symposium on Evolution and the Causal Theory of Perception, December 28, 1971, commenting on Abner Shimony, "Perception from an Evolutionary Point of View," this JOURNAL, this issue, pp. 571-583; parenthetical page references are to this paper.
to his environment. One would certainly expect a theory that concerned itself with the origin and development of organisms, and did so in terms of the principles of natural selection, to have a great deal to say (potentially at least) about the organism's perceptual resources since these are adaptively important. We have the theory. The pattern is there. What remains is the difficult scientific task of putting all the pieces together. Shimony has sketched for us the way some of these pieces fit; in so doing he has neatly and convincingly fulfilled part of his expressed purpose-he has shown how evolutionary considerations strengthen the case for what he calls "the causal theory of perception." Shimony has another purpose, however-that of suggesting some points in the dialectic structure of epistemology at which the insights of an evolutionary point of view can be applied. It is here that I hesitate; for it seems to me that the evolutionary point of view has very little to offer epistemology. Despite the fact that they are concerned with some of the same phenomena, no one expects medical science to have anything very helpful to say about the traditional problem of evil. Neither, I submit, should one expect the scientific study of man's perceptual capabilities to have any special relevance to the epistemology of perception. Though they are concerned, in a sense, with the same phenomena, they are concerned with them for quite different purposes. The "continuing disassociation" that Shimony mentions (571), the neglect that epistemologists have shown for the evolutionary study of man is, I would argue, entirely understandable and largely inevitable. Darwin does not help us with Descartes. In today's world this will surely sound like a provincial and blinkered conception of what epistemology is all about. It might also sound anti-scientific. Let me, then, say something in its defense. The evolutionary study of man's perceptual powers does tell us something that sounds, on the face of it, vaguely relevant to epistemology. It tells us that, more often than not, or perhaps in the vast majority of cases, the normal members of a well-adapted species (such as you and I) are right in their perceptual judgments about their surroundings. I am not entirely certain it tells us this much, and some may want to qualify it further (by restricting the claim, for example, to those perceptual judgments which are concerned with the percipient's immediate practical needs), but let that pass. Is this fact, if it is a fact, of any epistemological significance? I think not. A high percentage of correct "answers," even when this percentage is amazingly high, does not imply any cognitive achieve-
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tllent on thc palt of the ~espondent.Train ;I i a l lo tdke 110thiilg but right-handed turns upon being placed in a maze. Place the food in such a way that a series of right-hand turns will (always) lead to it. Under such circumstances the rat will always reach the food; he will never go hungry. We now have a well-trained rat, but hardly a rodent with any special cognitive powers. T h e rat doesn't know where the food is; though he always finds it, we can easily suppose that he never knows where it is. I t will certainly be objected that the members of a well-adapted species are not like trained rats, trained to perform in a certain predetermined way that miraculously, or by some sympathetic manipulation of the environment, continues to yield "correct" responses. T h e world is not molded to our heart's desire; rather, we have been selected, or through successive generations molded, to have the sort of desires that this world can sustain. T h e important differences between our case and that of the rat described above is that we have developed so that our perceptual responses are partially determined by those elements in our surroundings about which our judgments are made. Unlike the rat, our twistings and turnings are (in part at least) a result of the location of the food in the maze. It is because the food is here, not there, that we arrive here, not there. T h e rat is like a broken thermometer, one that is stuck at 102". If used to take the temperature of a feverish person, it can give us the right answer, but this can hardly be called an "answer" or a "response" at all and, a fortiori, not a correct response. On the other hand, the evolutionary point of view teaches us that we are more like properly functioning thermometers, thermometers that read 102" because that is the temperature of our environment. Our amazingly accurate responses are explicable in terms of those features of our environment toward which these responses are directed, and this, or so it might be argued, is an epistemologically significant fact. Whether or not this is an epistemologically significant fact will depend, I suppose, on how liberal we want to make our epistemology, how liberal we want to be in classifying something as "cognitive" or "epistemic." As far as I can see, though, we do not yet have anything that remotely qualifies. Are we to say that an organism has displayed some cognitive achievement if it responds "correctly" (however this may be understood) to a situation, S, and S is causally responsible for the organism's response? Suppose Donald, generally quite ignorant about astronomical matters, observes the gradual disappearance of the sun on the western horizon and says that he
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can see that the earth is revolving from west to east. My realization that he is correct about the earth's rotation, and also that his judgment was prompted by the situation he purports to have observed, does not tempt me to say that he can observe (to be the case) what he says he has observed. Whether he knows, whether he is even reasonable in believing, that the earth is revolving from west to east, involves a number of subtle issues that go far beyond the facts we have already been given. It involves issues in epistemology. At this point some philosophers would want to talk about the right to be sure, about adequate evidence, about the best explanation, or about the conclusiveness of Donald's reasons. But however they choose to express it, each is trying to answer the question: What are the distinguishing characteristics of an epistemic achievement? The causal theory of perception, as we have been given it, does not even suggest an answer to this question-let alone take a position on the matter. Furthermore, it is epistemologically important to remember that the evolutionary view of man's perceptual capabilities does not give us a perfectly reliable correlation between what Shimony calls the "cognitive states" of the organism and the character of its surroundings. This is, at best, a statistical correlation. Shimony speaks of "unconscious statistical inference" (582) and describes the extraction of the signal from the noise as a matter of probability (579). This, of course, raises additional problems, problems for how this view can help us to understand man's ordinary cognitive achievements. For even if we grant (what no one would have granted one hundred years ago, and the skeptic would be loath to grant even now) that everyone knows that the causal theory of perception is true, even if we grant the validity of the evolutionary point of view, we still have the same problem of trying to understand how people can know what they commonly purport to know. For if you know that an amazingly high proportion of X's are Y, and know that this is an X, it is not at all obvious that you know it is Y. Quite the reverse. If this is all you know about the matter, it seems to me quite obvious that you do not know that it is Y. You have excellent reasons for thinking that it is Y and you would be quite reasonable in so believing, but you don't know. Hence, the epistemological problem of how a person can know that the distal stimulus is Y when he knows that the proximal stimulus is X remains, and it remains even if we concede a knowledge of the evolutionary theory of man and the causal basis of perception that it presupposes. Where, then, is the warrant for speaking, in terms of
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this view, of our cognitive states or of our ability to recognize distal stimuli-locutions which imply the possession of knowledge? It is tiresome to listen to skeptical quibbling when there are more exciting things to do. Nonetheless, skepticism has been the mainspring of epistemology for a long time, and it is still what keeps most debates ticking. I t may be worth mentioning, then, that the skeptic would (I suspect) be little impressed with the evolutionary view of man's perceptual powers. Doubtless he would regard it as he would instruction in the principles of television when his problem happened to be whether or not the fight he watched on television last week was fixed. Doubts about the integrity of the fight are not going to be allayed in this way. Even if he gracefully accepts the tutoring, he has the same problems. Indeed, he has more problems or, at least, greater scope for posing the same problem. For once he is acquainted with the actual machinery of transmission, new sources of possible error appear. Was there a fight taking place at all? Perhaps the whole affair was video-taped from some earlier period (he never thought of that possibility before). How can he be sure someone didn't "doctor" the tape to make the fight appear other than it was? If this sounds silly, it is because epistemology is silly, not because such considerations are irrelevant to epistemology. T o appreciate how the causal theory of perception merely provides the skeptic with greater scope for his fancies, one need only recall how malevolent demons, working in largely unexplained ways, have been partially displaced in the literature by brains properly festooned with electrodes. These science-fiction conjectures can be exploited by the skeptic, not i n spite of the causal theory of perception, but because of it. Getting straight about how our brain works, with or without these electrodes, is not going to answer the questions the skeptic is posing. Epistemological theories of perception may embody something like a causal theory of perception (understood in the way we have been discussing it). What makes these epistemological theories is not that they embody some claim about the causal processes at work in perception, but that they use such facts to say something about knowledge and how it can be acquired in perceptual situations. In the short time remaining I would like to sketch the progressive assimilation of a causal account into an epistemological view of perception. 1st Stage: For the sake of completeness (and contrast) we can think of the first stage as the causal account itself as embodied, say, in the evolutionary point of view. I have just argued that this is
not an epistemological theory. I agree with Shimony when he says that it is a scientific hypothesis, and that "its confirmation, like that of any well-established scientific hypothesis consists in its power to predict and explain the facts of our experience with greater accuracy, comprehensiveness, and simplicity than any rival hypothesis" (573). Of course, if we know that the hypothesis is true, or have good reasons for thinking it true, we can use it to make legitimate inferences about what (probably) is, was, or will be the case in our surroundings. But much the same could be said about any scientific theory.' 2nd Stage: One may take the view that part of what it means to say that someone sees (hears, feels, smells, etc.) something is that there is a certain causal relationship between the percipient and (some phase of the history of) the object allegedly seen (heard, . . .). This apparently is what Paul Grice thinks of as "The Causal Theory of Perception" in his influential article of the same title. He explicitly rejects the first stage as a philosophical theory, referring to it, instead, as a very general contingent proposition.* Depending on one's conception of the task of philosophy, one may br may not find this second stage of much philosophical importance. If one understands philosophy as (in part) the analysis of concepts, the getting clear about notions that figure, either directly or indirectly, in certain traditional philosophical problems, 1 I do not wish to deny the usefulness of the evolutionary point of view in explaining certain phenomenological and psychological features of perception. If I understand the point correctly, this is what occurs when one interprets Kant's a priori principles as evolutionary achievements that draw upon the experience of our pre-human ancestors. One might, for example, also try to provide a "theoretical explanation" for some of our normative principles, why and how we came to hold certain ethical beliefs. This, however, would not show that evolutionary considerations were especially relevant to moral theory. Similarly, Merleau-Ponty's insistence that "being-in-the-world" characterizes our perceptions strikes me as a phenomenological fact, not particularly philosophical in character at all. If (as Shimony seems to suggest) this "insight" about perception merely means that we focus upon objects rather than cues, then this "insight" turns out to be a rather homely fact that most people would find obvious and undeniable. zproceedings of the Aristotelian Society, supp. vol. xxxv (1961): 121-152; reprinted in Robert J. Swartz, ed., Perceiving, Sensing and Knowing (Garden City, New York: 1965), pp. 438-472. It is worth quoting Grice more fully to indicate the way he thinks his own theory of perception is related to the causal theory (as described in the first stage): "Such a belief [Ist stage] does not seem to be philosophical in character; its object has the appearance of being a very general contingent proposition; though it is worth remarking that if the version of the CTP [Causal Theory of Perception] with which I shall be primarily concerned is correct, it (or something like it) will turn out to be a necessary rather than a contingent truth" (121; Swartz, 438).
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then one could take it as a legitimate task for the philosopher to examine, and either accept or reject, this doctrine about the meaning of such perceptual verbs as 'see,' 'hear', and 'smell'. Strictly speaking, though, we are still a long way from epistemology. Since one can see (hear, feel, smell, etc.) an object while remaining completely ignorant of what it is that one is seeking (hearing, . .), it is not clear how this doctrine about the meaning of these perceptual verbs is supposed to contribute to our epistemological understanding. T o say that the locution 'S sees a cow' is a causal locution is on a par, epistemologically speaking, with saying that 'S killed a cow' is a causal locution. Neither doctrine tells us how, or even whether, the agent knows, or has any reason to believe, that what he has causally interacted with is a cow. T h e epistemological problems of perception really begin only after we suppose that we do see cows and clouds (or whatever)-the problem of how we can tell, how we know, that this is what we are seeing. 3rd Stage: One can go a step further and maintain that our knowledge of objects in perceptual situations is somehow dependent on our use of the causal relationship that exists between the object and ourselves during such encounters. It appears that in philosophy it is this view that has been commonly taken as T h e Causal Theory of Perception. Not only are we causally affected by our surroundings in perceptual situations (1st stage), not only is this fact part of what we mean in saying that we perceive something (2nd stage), but this fact can be (must be?) exploited in learning something about the content and character of these surroundings. I have already indicated why I think this view is in trouble, but this, surely, is what H. H. Price had in mind in his discussion of T h e Causal Theory of Perception.3 4 t h Stage: Finally, one can suppose that the causal relationship is not only useful (indispensable?) in acquiring knowledge about the things we see, hear, and touch, but that such a feature is built into the very meaning of those verbal constructions which entail that we possess such knowledge. Not only is 'seeing a cow' a causal locution (2nd stage), but the perceptual situations we describe by saying that we can see that it is a cow are also causal. By speaking in this way we imply that our knowledge that it is a cow has been acquired in virtue of, or by means of, the causal effects of the cow on us.4
.
3 "The Causal Theory," chapter IV of Perception (London: Methuen, 1954), reprinted in Swartz, op. cit.; see pp. 394-395. 4 Something close to this view is contained in Alvin Goldman's article ".A Causal Theory of Knowing," this JOURNAL, LXIV,12 (June 22, 1967): 357-372.
1 think the third and fourth stages just described could be (and have been) called epistemological theories of perception. The first is a scientific theoiy. Judging by what passes as philosophy these days, the second stage can perhaps be called a philosophical thesis. If one finds this classification overly rigid, leaving out much that one would like to put into epistemology, I can only invite clarification on what epistemology is supposed to be about. FRED I. DRETSKE
University of Wisconsin
ILLUSIONS IN MAN AND HIS INSTRUMENTS "
HE following discussion takes as a point of departure the first of Professor Shimony's list of features of human perception: There is a systematic selection by the sense organs of the information that they transmit to the brain (577/8). The three paragraphs below present the main ideas in summary. More extended treatments of each then follow in order. 1. From a biological-mathematical point of view one may regard the sense organs as "tuned filters," the characteristics of which have been determined, in part, by evolutionary pressures. But the tuning of these filters to transmit only certain types of information, while generally adaptive, inevitably gives rise to some uncertainties and ambiguities in perception-among these are some of the so-called illusions. 2. Man is probably unique among animals in that he is aware of at least some of the imperfections of his sense organs and limitations of his intellect and therefore takes steps to overcome them by means of various methods and instruments. But the numerous devices that are used to overcome these imperfections and limitations frequently have "illusions," too. 3. Man's sensory mechanisms and his instrumental aids to them are both subject to the same natural laws. Although one may be utilized to overcome certain specific limitations peculiar to the other, there are more general natural limitations on logical operations which neither can surmount. These natural limitations must be considered in any modern theory of knowledge.
* T o be presented in an APA symposium on Evolution and the Causal Theory of Perception, December 28, 1971, commenting on Abner Shimony, "Perception from an Evolutionary Point of View," this JOURNAL, this issue, pp. 571-583.
