In spite of the elucidations of contemporary realists, a number of idealists continue to adduce in behalf of idealism certain facts having an obvious physical nature and explanation. The visible convergence of the railway tracks, for example, is cited as evidence that what is seen is a mental "content." Yet this convergence follows from the physical properties of light and a lens, and is physically demonstrated in a camera. Is the photograph, then, to be conceived as a psychical somewhat? That the time of the visibility of a light does not coincide with the time at which a distant body emitted the light is employed to support a similar idealistic conclusion, in spite of the fact that the exact difference in time may be deduced from a physical property of light—its rate. The dislocation in space of the light seen and the astronomical star is used as evidence of the mental nature of the former, though the exact angular difference is a matter of simple computation from purely physical data. The doubling of images of, say, the finger when the eyeball is pressed, is frequently proffered as a clincher. Yet it is a simple matter to take any body that reflects light, and by a suitable arrangement of lenses to produce not only two but many images, projected into space. If the fact that under definite physical conditions (misplacement of lenses), a finger yields two images proves the psychical character of the latter, then the fact that under certain conditions a sounding body yields one or more echoes is, by parity of reasoning, proof that the echo is made of mental stuff.[59]

If, once more, the differences in form and color of a table to different observers, occupying different physical positions, is proof that what each sees is a psychical, private, isolated somewhat, then the fact that one and the same physical body has different effects upon, or relations with, different physical media is proof of the mental nature of these effects. Take a lump of wax and subject it to the same heat, located at different positions; now the wax is solid, now liquid—it might even be gaseous. How "psychical" these phenomena! It almost seems as if the transformation of the physical into the mental in the cases cited exemplifies an interesting psychological phenomenon. In each case the beginning is with a real and physical existence. Taking "the real object," the astronomical star, on the basis of its physical reality, the idealist concludes to a psychical object, radically different! Taking the single object, the finger, from the premise of its real singleness, he concludes to a double mental content, which then takes the place of the original single thing! Taking one-and-the-same-object, the table, presenting its different surfaces and reflections of light to different real organisms, he eliminates the one-table-in-its-different-relations in behalf of a multiplicity of totally separate psychical tables! The logic reminds us of the story of the countryman who, after gazing at the giraffe, remarked, "There ain't no such animal." It almost seems, I repeat, as if this self-contradiction in the argument creates in some minds the impression that the object—not the argument—is undergoing the extraordinary reversal of form.

However this may be, the problem indicated in the foregoing cases is simply the good old problem of the many in one, or, less cryptically, the problem of the maintenance of a continuity of process throughout differences. I do not pretend that this situation, though the most familiar thing in life, is wholly without difficulties. But its difficulty is not one of epistemology, that is, of the relation of known to a knower; to take it as such, and then to use it as proof of the psychical nature of a final term, is also to prove that the trail the rocket stick leaves behind is psychical, or that the flower which comes in a continuity of process from a seed is mental.

II

Contemporary realists have so frequently and clearly expounded the physical explanation of such cases as have been cited that one is at a loss as to why idealists go on repeating the cases without even alluding to the realistic explanation. One is moved to wonder whether this neglect is just one of those circumstances which persistently dog philosophical discussions, or whether something in the realistic position gives ground (from at least an ad hominem point of view) for the neglect. There is a reason for adopting the latter alternative. Many realists, in offering the type of explanation adduced above, have treated the cases of seen light, doubled imagery, as perception in a way that ascribes to perception an inherent cognitive status. They have treated the perceptions as cases of knowledge, instead of as simply natural events having, in themselves (apart from a use that may be made of them), no more knowledge status or worth than, say, a shower or a fever. What I intend to show is that if "perceptions" are regarded as cases of knowledge, the gate is opened to the idealistic interpretation. The physical explanation holds of them as long as they are regarded simply as natural events—a doctrine I shall call naÏve realism; it does not hold of them considered as cases of knowledge—the view I call presentative realism.

The idealists attribute to the realists the doctrine that "the perceived object is the real object." Please note the wording; it assumes that there is the real object, something which stands in a contrasting relation with objects not real or else less real. Since it is easily demonstrable that there is a numerical duplicity between the astronomical star and its effect of visible light, between the single finger and the doubled images, the latter evidently, when the former is dubbed "the" real object, stands in disparaging contrast to its reality. If it is a case of knowledge, the knowledge refers to the star; and yet not the star, but something more or less unreal (that is, if the star be "the" real object), is known.

Consider how simply the matter stands in what I have called naÏve realism. The astronomical star is a real object, but not "the" real object; the visible light is another real object, found, when knowledge supervenes, to be an occurrence standing in a process continuous with the star. Since the seen light is an event within a continuous process, there is no point of view from which its "reality" contrasts with that of the star.

But suppose that the realist accepts the traditionary psychology according to which every event in the way of a perception is also a case of knowing something. Is the way out now so simple? In the case of the doubled fingers or the seen light, the thing known in perception contrasts with the physical source and cause of the knowledge. There is a numerical duplicity. Moreover the thing known by perception is by this hypothesis in relation to a knower, while the physical cause is not. Is not the most plausible account of the difference between the physical cause of the perceptive knowledge and what the latter presents precisely this latter difference—namely, presentation to a knower? If perception is a case of knowing, it must be a case of knowing the star; but since the "real" star is not known in the perception, the knowledge relation must somehow have changed the "object" into a "content." Thus when the realist conceives the perceptual occurrence as an intrinsic case of knowledge or of presentation to a mind or knower, he lets the nose of the idealist camel into the tent. He has then no great cause for surprise when the camel comes in—and devours the tent.

Perhaps it will seem as if in this last paragraph I had gone back on what I said earlier regarding the physical explanation of the difference between the visible light and the astronomical star. On the contrary, my point is that this explanation, though wholly adequate as long as we conceive the perception to be itself simply a natural event, is not at all available when we conceive it to be an attempt at knowing its cause. In the former case, we are dealing with a relation between natural events. In the latter case, we are dealing with the difference between an object as a cause of knowledge and an object as known, and hence in relation to mind. By the "method of difference" the sole explanation of the difference between the two objects is then the absence or presence of relation to a knower.

In the case of the seen light,[60] reference to the velocity of light is quite adequate to account for its time and space differences from the star. But viewed as a case of what is known (on the supposition that perception is knowing), reference to it only increases the contrast between the real object and the object known in perception. For, being just as much a part of the object that causes the perception as is the star itself, it (the velocity of light) ought logically to be part of what is known in the perception, while it is not. Since the velocity of light is a constituent element in the star, it should be known in the perception; since it is not so known, reference to it only increases the discrepancy between the object of the perception—the seen light—and the real, astronomical star. The same is true of any physical condition that might be referred to: The very things that, from the standpoint of perception as a natural event, are conditions that account for its happening are, from the standpoint of perception as a case of knowledge, part of the object which, if knowledge is to be valid, ought to be known, but is not.

In this fact we have, perhaps, the ground of the idealist's disregard of the oft-proffered physical explanation of the difference between the perceptual event and the (so-called) real object. And it is quite possible that some realists who read these lines will feel that in my last paragraphs I have been making a covert argument for idealism. Not so, I repeat; they are an argument for a truly naÏve realism. The presentative realist, in his appeal to "common-sense" and the "plain man," first sophisticates the umpire and then appeals. He stops a good way short of a genuine naÏvetÉ. The plain man, for a surety, does not regard noises heard, lights seen, etc., as mental existences; but neither does he regard them as things known. That they are just things is good enough for him. That they are in relation to mind, or in relation to mind as their "knower," no more occurs to him than that they are mental. By this I mean much more than that the formulae of epistemology are foreign to him; I mean that his attitude to these things as things involves their not being in relation to him as a mind or a knower. He is in the attitude of a liker or hater, a doer or an appreciator. When he takes the attitude of a knower he begins to inquire. Once depart from thorough naÏvetÉ, and substitute for it the psychological theory that perception is a cognitive presentation to a mind of a causal object, and the first step is taken on the road which ends in an idealistic system.

For simplicity's sake, I have written as if my main problem were to show how, in the face of a supposed difficulty, a strictly realistic theory of the perceptual event may be maintained. But my interest is primarily in the facts, and in the theory only because of the facts it formulates. The significance of the facts of the case may, perhaps, be indicated by a consideration which has thus far been ignored. In regarding a perception as a case of knowledge, the presentative realist does more than shove into it a relation to mind which then, naturally and inevitably, becomes the explanation of any differences that exist between its subject-matter and some causal object with which it contrasts. In many cases—very important cases, too, in the physical sciences—the contrasting "real object" becomes known by a logical process, by inference—as the contemporary position of the star is determined by calculations from data, not by perception. This, then, is the situation of the presentative realist: If perception is knowledge of its cause, it stands in unfavorable contrast with another indirect mode of knowledge; its object is less valid than the object of inference. I do not adduce these considerations as showing that the case is hopeless for the presentative realist;[61] I am willing to concede he can find a satisfactory way out. But the difficulty exists; and in existing it calls emphatic attention to a case which is certainly and indisputably a case of knowledge—namely, propositions arrived at through inference, judgments as logical assertions.

With relation to the unquestionable case of knowledge, the logical or inferential case, perceptions occupy a unique status, one which readily accounts for their being regarded as cases of knowledge, although in themselves they are natural events. (1) They are the sole ultimate data, the sole media, of inference to all natural objects and processes. While we do not, in any intelligible or verifiable sense, know them, we know all things that we do know with or by them. They furnish the only ultimate evidence of the existence and nature of the objects which we infer, and they are the sole ultimate checks and tests of the inferences. The visible light is a necessary part of the evidence on the basis of which we infer the existence, place, and structure of the astronomical star, and some other perception is the verifying check on the value of the inference. Because of this characteristic use of perceptions, the perceptions themselves acquire, by "second intention," a knowledge status. They become objects of minute, accurate, and experimental scrutiny. Since the body of propositions that forms natural science hangs upon them, for scientific purposes their nature as evidence, as signs, entirely overshadows their natural status, that of being simply natural events. The scientific man, as scientific, cares for perceptions not in themselves, but as they throw light upon the nature of some object reached by evidence. And since every such inference tries to terminate in a further perception (as its test of validity), the value of inferential knowing depends on perception. (2) Independently of science, daily life uses perceptions as signs of other perceptions. When a perception of a certain kind frequently recurs and is constantly used as evidence of some other impending perceptual event, the function of habit (a natural function, be it noted, not a psychical or epistemological function) often brings it about that the perception loses its original quality in acquiring a sign-value. Language is, of course, the typical case. Noises, in themselves mere natural events, through habitual use as signs of other natural events become integrated with what they mean. What they stand for is telescoped, as it were, into what they are. This happens also with other natural events, colors, tastes, etc. Thus, for practical purposes, many perceptual events are cases of knowledge; that is, they have been used as such so often that the habit of so using them is established or automatic.

In this brief reference to facts that are perfectly familiar, I have tried to suggest three points of crucial importance for a naÏve realism: first, that inferential or evidential knowledge (that involving logical relation) is in the field as an obvious and undisputed case of knowledge; second, that this function, although embodying the logical relation, is itself a natural and specifically detectable process among natural things—it is not a non-natural or epistemological relation; third, that the use, practical and scientific, of perceptual events in the evidential or inferential function is such as to make them become objects of inquiry and limits of knowledge, and to such a degree that this acquired characteristic quite overshadows, in many cases, their primary nature.

If we add to what has been said the fact that, like every natural function, the inferential function turns out better in some cases and worse in others, we get a naturalistic or naÏvely realistic conception of the "problem of knowledge": Control of the conditions of inference—the only type of knowledge detectable in direct existence—so as to guide it toward better conclusions.

IV

I do not flatter myself that I will receive much gratitude from realists for attempting to rescue them from that error of fact which exposes their doctrine to an idealistic interpretation. The superstition, growing up in a false physics and physiology and perpetuated by psychology, that sensations-perceptions are cases of knowledge, is too ingrained. But—crede experto—let them try the experiment of conceiving perceptions as pure natural events, not as cases of awareness or apprehension, and they will be surprised to see how little they miss—save the burden of carrying traditionary problems. Meantime, while philosophic argument, such as this, will do little to change the state of belief regarding perceptions, the development of biology and the refinement of physiology will, in due season, do the work.

In concluding my article, I ought to refer, in order to guard against misapprehension, to a reply that the presentative realist might make to my objection. He might say that while the seen light is a case of knowledge or presentative awareness, it is not a case of knowledge of the star, but simply of the seen light, just as it is. In this case the appeal to the physical explanations of the difference of the seen light from its objective source is quite legitimate. At first sight, such a position seems innocent and tenable. Even if innocent, it would, however, be ungrounded, since there is no evidence of the existence of a knower, and of its relation to the seen light. But further consideration will reveal that there is a most fundamental objection. If the notion of perception as a case of adequate knowledge of its own object-matter be accepted, the knowledge relation is absolutely ubiquitous; it is an all-inclusive net. The "ego-centric predicament" is inevitable. This result of making perception a case of knowing will now occupy us.