Essays in Experimental Logic

by John Dewey

This position thus freely resumed here needs to be adequately guarded on all sides. It implies that the question of the existence or presence of the subject-matter of even a complex sense perception may be treated as a question of physics. It also implies that the existence of a sense perception may be treated as a problem of physics. But the position is not that all the problems of sense perception are thereby exhausted. There is still, on the contrary, the problem of the cognitive status of sense perception. So far from denying this fact, I mean rather to emphasize it in holding that this knowledge aspect is not to be identified—as it has been in both realistic and idealistic epistemologies—with the simple occurrence of presented subject-matter and with the occurrence of a perceptive act. It is often stated, for example, that primitive sense objects when they are stripped of all inferential material cannot possibly be false—but with the implication that they, therefore, must be true. Well, I meant to go this statement one better—to state that they are neither true nor false—that is, that the distinction of true-or-false is as irrelevant and inapplicable as to any other existence, as it is, say, to being more than five feet high or having a low blood pressure. This position when taken leaves over the question of sense perception as knowledge, as capable of truth or falsity. It is this question, then, which I intend to discuss in this paper.

I

My first point is that some sense perceptions at least (as matter of fact the great bulk of them), are without any doubt forms of practical judgment—or, more accurately, are terms in practical judgments as propositions of what to do. When in walking down a street I see a sign on the lamp-post at the corner, I assuredly see a sign. Now in ordinary context (I do not say always or necessarily) this is a sign of what to do—to continue walking or to turn. The other term of the proposition may not be stated or it may be; it is probably more often tacit. Of course, I have taken the case of the sign purposely. But the case may be extended. The lamp-post as perceived is to a lamp-lighter a sign of something else than a turn, but still a sign of something to be done. To another man, it may be a sign of a possible support. I am anxious not to force the scope of cases of this class beyond what would be accepted by an unbiased person, but I wish to point out that certain features of the perceived object, as a cognitive term, which do not seem at first sight to fall within this conception of the object, as, an intellectual sign of what to do, turn out upon analysis to be covered by it. It may be said, for example, that our supposed pedestrian perceives much besides that which serves as evidence of the thing to be done. He perceives the lamp-post, for example, and possibly the carbons of the arc. And these assuredly do not enter into the indication of what to do or how to do it.

The reply is threefold. In the first place, it is easy—and usual—to read back into the sense perception more than was actually in it. It is easy to recall the familiar features of the lamp-post; it is practically impossible—or at least very unusual—to recall what was actually perceived. So we read the former into the latter. The tendency is for actual perception to limit itself to the minimum which will serve as sign. But, in the second place, since it is never wholly so limited, since there is always a surplusage of perceived object, the fact stated in the objection is admitted. But it is precisely this surplusage which has not cognitive status. It does not serve as a sign, but neither is it known, or a term in knowledge. A child, walking by his father's side, with no aim and hence no reason for securing indications of what to do, will probably see more in his idle curiosity than his parent. He will have more presented material. But this does not mean that he is making more propositions, but only that he is getting more material for possible propositions. It means, in short, that he is in an aesthetic attitude of realization rather than in a cognitive attitude. But even the most economical observer has some aesthetic, non-cognitive surplusage.[92] In the third place, surplusage is necessary for the operation of the signifying function. Independently of the fact that surplusage may be required to render the sign specific, action is free (its variation is under control) in the degree in which alternatives are present. The pedestrian has probably the two alternatives in mind: to go straight on or to turn. The perceived object might indicate to him another alternative—to stop and inquire of a passer-by. And, as is obvious in a more complicated case, it is the extent of the perceived object which both multiplies alternative ways of acting and gives the grounds for selecting among them. A physician, for example, deliberately avoids such hard-and-fast alternatives as have been postulated in our instance. He does not observe simply to get an indication of whether the man is well or ill; but in order to determine what to do he extends his explorations over a wide field. Much of his perceived object field is immaterial to what he finally does; that is, does not serve as sign. But it is all relevant to judging what he is to do. Sense perception as a term in practical judgment must include more than the element which finally serves as sign. If it did not, there would be no perception, but only a direct stimulus to action.[93]

The conclusion that such perceptions as we have been considering are terms in an inference is to be carefully discriminated from the loose statement that sense perceptions are unconscious inferences. There is a great difference between saying that the perception of a shape affords an indication for an inference and saying that the perception of shape is itself an inference. That definite shapes would not be perceived, were it not for neural changes brought about in prior inferences, is a possibility; it may be, for aught I know, an ascertained fact. Such telescoping of a perceived object with the object inferred from it may be a constant function; but in any case the telescoping is not a matter of a present inference going on unconsciously, but is the result of an organic modification which has occurred in consequence of prior inferences. In similar fashion, to say that to see a table is to get an indication of something to write on is in no way to say that the perception of a table is an inference from sensory data. To say that certain earlier perceived objects not having as perceived the character of a table have now "fused" with the results of inferences drawn from them is not to say that the perception of the table is now an inference. Suppose we say that the first perception was of colored patches; that we inferred from this the possibility of reaching and touching, and that on performing these acts we secured certain qualities of hardness, smoothness, etc., and that these are now all fused with the color-patches. At most this only signifies that certain previously inferred qualities have now become consolidated with qualities from which they were formerly inferred. And such fusion or consolidation is precisely not inference. As matter of fact, such "fusion" of qualities, given and formerly inferred, is but a matter of speaking. What has really happened is that brain processes which formerly happened successively now happen simultaneously. What we are dealing with is not a fact of cognition, but a fact of the organic conditions of the occurrence of an act of perception.

Let us apply the results to the question of sense "illusions." The bent reed in the water comes naturally to mind. Purely physical considerations account for the refraction of the light which produces an optical image of a bent stick. This has nothing to do with knowledge or with sense perception—with seeing. It is simply and wholly a matter of the properties of light and a lens. Such refractions are constantly produced without our noting them. In the past, however, light refracted and unrefracted has been a constant stimulus to responsive actions. It is a matter of the native constitution of the organism that light stimulates the eyes to follow and the arms to reach and the hands to clutch and handle. As a consequence, certain arrangements of reflected and refracted light have become a sign to perform certain specific acts of handling and touching. As a rule, stimuli and reactions occur in an approximately homogeneous medium—the air. The system of signs or indexes of action set up has been based upon this fact and accommodated to it. A habit or bias in favor of a certain kind of inference has been set up. We infer from a bent ray of light that the hand, in touching the reflecting object, will, at a certain point, have to change its direction. This habit is carried over to a medium in which the conclusion does not hold. Instead of saying that light is bent—which it is—we infer that the stick is bent: we infer that the hand could not protract a straight course in handling the object. But an expert fisherman never makes such an error in spearing fish. Reacting in media of different refractive capacities, he bases his signs and inferences upon the conditions and results of his media. I see no difference between these cases and that of a man who can read his own tongue. He sees the word "pain" and infers it means a certain physical discomfort. As matter of fact, the thing perceived exists in an unfamiliar medium and signifies bread. To the one accustomed to the French language the right inference occurs.[94] There is neither error nor truth in the optical image: It just exists physically. But we take it for something else, we behave to it as if it were something else. We mis-take it.

II

So far as I can see, the pronounced tendency to regard the perceived object as itself the object of a peculiar kind of knowledge instead of as a term in knowledge of the practical kind has two causes. One is the confirmed habit of neglecting the wide scope and import of practical judgments. This leads to overlooking the responsive act as the other term indicated by the perception, and to taking the perceived object as the whole of the situation just by itself. The other cause is the fact that because perceived objects are constantly employed as evidence of what is to be done—or how to do something—they themselves become the objects of prolonged and careful scrutiny. We pass naturally and inevitably from recognition to observation. Inference will usually take care of itself if the datum is properly determined. At the present day, a skilled physician will have little difficulty in inferring typhoid instead of malaria from certain symptoms provided he can make certain observations—that is, secure certain data from which to infer. The labor of intelligence is thus transferred from inference to the determination of data, the data being determined, however, in the interests of inference and as parts of an inference.

At this point, a significant complication enters in. The ordinary assumption in the discussion of the relation of perceived objects to knowledge is that "the" object—the real object—of knowledge in perception is the thing which caused the qualities which are given. It is assumed, that is, that the other term of a proposition in which a sense datum is one term must be the thing which produced it. Since this producing object does not for the most part appear in ordinary sense perception, we have on our hands perception as an epistemological problem—the relation of an appearance to some reality which it, somehow, conceals rather than indicates. Hence also the difficulties of "reconciling" scientific knowledge in physics where these causes are the terms of the propositions with "empirical" or sense perception knowledge where they do not even appear. Here is where the primary advantage of recognizing that ordinary sense perceptions are forms of practical judgment comes in. In practical judgments, the other term is as open and aboveboard as is the sensory quality: it is the thing to be done, the response to be selected. To borrow an illustration of Professor Woodbridge's: A certain sound indicates to the mother that her baby needs attention. If she turns out to be in error, it is not because sound ought to mean so many vibrations of the air, and as matter of fact doesn't even suggest air vibrations, but because there is wrong inference as to the act to be performed.

I imagine that if error never occurred in inferences of this practical sort the human race would have gone on quite contented with them. However that may be, errors do occur and the endeavor to control inference as to consequences (so as to reduce their likelihood of error) leads to propositions where the knowledge-object of the perceived thing is not something to be done, but the cause which produced it. The mother finds her baby peacefully sleeping and says the baby didn't make the noise. She investigates and decides a swinging door made it. Instead of inferring a consequence, she infers a cause. If she had identified the noise in the first place, she would have concluded that the hinges needed oiling.