§ 1

In what I have so far said about the premises of common knowledge, I have, for the most part, confined my commentary to those which embody general principles. About the particular beliefs, which play at least as great a part in the structure of our creed, I have said little, and to these we must now turn our attention.

Their importance is not likely to be underrated by any school of thought, for they include the whole body of our experiences; and while some philosophers have held with passionate conviction that from our experiences, and from them alone, all knowledge is derived, no modern philosopher, howsoever low he may rate empiricism, doubts the value of the knowledge we obtain through the senses, the beliefs of ordinary observation, the perceptions of fact on which all the sciences are built.

Now there is no subject of speculative interest which less disturbs the “plain man”; nor is there any which, for over two centuries, has given more trouble to philosophers. Its theoretical importance is, of course, obvious enough. Physical science (so we all believe) is based mainly on experiences of the external world; experiences of the external world are gained through perception.1 Nothing, therefore, can be more needful for any “philosophy of the familiar ” than clear notions as to what perception directly tells us, and what is its value as a ground of belief.

One would have supposed that, to questions so simple and so fundamental, the wisdom of the world would by this time have discovered plain replies. But it has not been so. By most people the questions are never asked. The few who ask them differ about the answers. On one thing only do they seem to be agreed; namely, that the natural and unsophisticated opinions of mankind on the subject can hardly be accepted as they stand. Those who most approve them admit them to be “naïve”; and “naïve” in philosophy is by no means to be regarded as a term of praise.

As might perhaps have been anticipated, differences of opinion which, in the beginning, were concerned mainly with the immediate import of sense perception, have developed and ramified into controversies which embrace the profoundest problems of physics and metaphysics, the theory of knowledge, the nature of experience, the psychology of perception, the structure of reality.

From the point of view of these lectures the huge tangle of controversy thence resulting is something of a misfortune. The issues I desire to raise are doubtless important, but they are comparatively narrow; and in order to reach them I neither wish to drag my readers, nor to be dragged myself, into any survey of the long philosophic development from Descartes and Locke, through Berkeley Hume and Reid, Kant Fichte and Hegel, Mill and Spencer, the neo-Kantians and the neo-Hegelians, down to such modern representatives of opposing tendencies as Mr. Bradley, Signor Croce, the Pragmatists, the new Realists, and other distinguished leaders of contemporary speculation. If, therefore, my references to these great subjects seem meagre and inadequate (as from more than one point of view they certainly are) let the indulgent critic remember that I am not now dealing at large with the history of philosophy, the metaphysic of Nature, the epistemology and psychology of perception, but only with such fragments of these subjects as are relevant to what I wish to say about the “philosophy of the familiar.”

§ 2

Now the creed which we are endeavouring to rationalize is, in its most familiar form, crudely realistic. It proclaims the being of an external world, perceived, yet independent of perception, neither constituted by our thought nor qualified by2 our senses. Our experiences of it, howsoever limited, we conceive to be direct. We feel it, see it, hear it, smell it, taste it; and from the information thus immediately obtained, Science is supposed to draw with ever increasing accuracy and fulness the authentic outlines of physical reality.

Nothing could seemingly be simpler. Here, on the one side, lies the world of men and things ready to be observed. There, on the other, are intelligent persons ready to observe it. What operation leaves less room for explanation? What operation less requires it? Yet unless I am much mistaken the history of Philosophy shows what difficulties it has occasioned in the past; and few there are who will pretend that the present has provided us with an agreed solution.

The question which lies at the root of the whole problem is the character of the relation between the perceiver and the perceived. It is on this that agreement is most desirable; it is on this that it seems most remote. Philosophers have naturally enough approached the subject from the perceiver's side. I shall, however, adopt a different method, and begin with the things perceived. In so doing I shall assume their external and independent reality and the truth of the sciences which deal with them. This procedure would, of course, be quite indefensible were I (so to speak) speculating at large—endeavouring, in a mood of complete detachment, to establish undiscovered truths on indisputable premises. But it is legitimate enough for one who is searching for a philosophy of beliefs which are already accepted both by himself and by all those whom he is addressing.

Now when, in pursuance of this plan, I turn my attention to the physical pole of the perceiving process I am immediately struck by the fact that the passive role often assigned by common sense to Nature is one which, according to science, Nature never plays. We ought not, it seems, to talk of “ perceiver and perceived”; for in the true order of causal precedence the phrase should rather run “perceived and perceiver.” It is indeed commonly held that, by the exercise of selective attention and otherwise, the perceiver may, perhaps must, himself contribute to the character of his own experiences. Nor would it usually be denied that by the association of ideas and other psychical influences, the “evidence of the senses” may be largely qualified. But at bottom it is the active energies of the external world, including those of which the perceiver's own organism is the theatre, that mainly determine the character of the sense data which pass the threshold of his consciousness. In perception Nature reveals herself, and man can but strive to comprehend the revelation.

By what machinery is this revelation accomplished? How does the perceived communicate with the perceiver? The answer varies in different cases. But always there must be an organism adjusted to receive the message; always, when the object perceived is not itself in contact with the organism, there must be some ether physical agent connecting the two, and always the organism must be so associated with a mind that the physiological changes in the one are accompanied by significant experiences in the other.

All this is very familiar. Let me hasten to add that it is also very strange. Consider by way of illustration a concrete case; none the worse for having, I suppose, often done duty before. A remote and nameless star suddenly blazes into prominence. This, says Science, is due to the fact that centuries ago, and billions of miles away, a particular collection of electric charges began radiating into space with a new and catastrophic violence. As time went on an infinitesimal fraction of these radiations, which happened to be of the right frequency, happened also to reach a small planet where, and where only (so far as we know), there happened to be organic sensibilities rightly tuned for their reception. Thereupon there came into being a new effect, namely, the direct experience by man of this old and distant cataclysm, the news of which had during these many ages been wandering unnoticed through space in the shape of electromagnetic oscillations!

This, or something like this, is what happens when Nature reveals herself to man. It is a theme no doubt on which there are endless variations. The revealing light rays need not be emitted by the object; they may be reflected or diffracted by it. The object may be near or far. It may be heard or touched or smelt and not seen. But always (on this view) the experiences which are supposed to provide us with our knowledge of the external world are the “ end product ” of a complicated process which originates in the object perceived and finishes in the perceiving mind. This process always takes some time, and often takes much time. It may begin in a remote past, at the farthest star revealed by the most powerful telescope, or in a portion of matter which touches the perceiver's body. In every case the perception is an effect, in every case the “thing” perceived is one, but only one, of its causes. In no case is this “thing” identified with any element in the intermediate train of psycho-physical events by means of which it is ultimately revealed to the perceiver.

§ 3

I believe this theory (or some other essentially similar) to be inextricably bound up with any scientific view of the relation between man and his material surroundings. I have stated it in terms which, to the best of my knowledge, conform to the science of our day. But it could equally have been stated in conformity with the science of yesterday, of a hundred years ago, of two hundred. The changes in our scientific outlook since the days of Locke and Berkeley have been prodigious. But would not Newton, their contemporary, have said in substance very much what I have been trying to say? Would he not have allowed that, whatever else our perceptions may be, they are effects—the outcome of a complex process occupying time and traversing space, in which all the stages except the last are physical or physiological? Would he not have allowed that whatever else we may say about the object perceived, at least it is one among the causes of our perceiving it; and to that extent therefore may properly be described as self-revealing? For my present argument no more is required; and the fact that since Newton's day (for example) the corpuscular theory of light has been abandoned, and the electrical theory of matter discovered, though it may change the terms in which the discussion is conducted, does little or nothing to modify its essential import.3

Whatever may be said against this scientific version of realism, it escapes some difficulties which (as we shall see) other forms of realism sometimes find embarrassing. In particular, the discrepancies between what appears and what is are robbed of all their terrors. On the scientific theory of perception these discrepancies are not only natural and explicable, but inevitable—the obvious results of the conditions under which perceptual experiences are said to be produced. We can understand, for instance, why a wooded hill looks small and blue on the horizon, large and green when near. We can understand why two events, which in fact happen at the same moment, like the flash and the noise of an explosion, when perceived from afar seem divided by an interval of time which grows with the remoteness of the observer. We can understand why two events, which in fact happened centuries apart, appear in experience to be simultaneous. We can understand why a straight stick seems bent when half immersed in water; and why a bowl filled with liquid may, under fitting conditions, at the same moment feel warm to one hand and cold to the other. Errors of perception, the mere possibility of which involve some thinkers in a very nightmare of perplexity, thus become the most natural things imaginable much too natural, indeed, for the convenience of those who, like us, are concerned to find a satisfactory philosophy of familiar knowledge.

§ 4

This view of perception, which treats it as due to a train of causes, physical, physiological, and psychical, of which the object perceived is one, seems forced on us by scientific discovery. Clearly, therefore, it is not self-evident. Logically it involves elaborate inferences; historically it is, in its present form, the product of long research. Few conceptions are more remote from ordinary experience than those by which ordinary experience is scientifically explained. No man has ever seen, no man will ever see, such entities as atoms, electrons, electromagnetic oscillations, and the rest of the machinery by which physical nature affects the living organism. No man (as yet) can give any adequate account of the physiology of perception. No man can either perceive or imagine the mode in which physiological changes give birth to psychical experiences. Psychical experiences themselves are full of mystery and suggest endless problems. Whatever else therefore may be said about the process by which, in the order of causation, perceptions are produced, no one will suggest that our knowledge of it is due to immediate intuition.

On what, then, is this knowledge founded? The answer can only be that our knowledge of the perceptual process is itself founded on perceptions. Thus while science shows the way in which perceptions are produced, perceptions provide the grounds on which science is believed. We are therefore face to face (not for the first time or the last) with two contrasted but complementary processes—the one causal, the other cognitive; the one concerned to tell us “how,” the other concerned to tell us “why”; the one moving from conditions to consequences, the other moving from premises to conclusions; the one leading us through successive effects from electrons4 to experiences, the other leading us by the way of inference from experiences to electrons.

§ 5

Now as the first of these processes is undoubtedly the business of the sciences, so the second has been one of the chief preoccupations of philosophy. But from the point of view of our present argument no such separation is possible. The two must evidently be considered together. There can be no satisfactory “philosophy of the familiar” unless they can be made to harmonise, unless they can be fitted into one scheme—and this is an operation by no means so easy as we might at first be inclined to suppose.

So soon, indeed, as we attempt it we are brought face to face with a curious and somewhat perplexing paradox. For is it not plain that the premises of science agree but ill with its conclusions? Its premises are for the most part the immediate beliefs which embody the perceptual experiences which we obtain through the avenues of sense. These show us, so at least we commonly suppose, a world of objects infinitely varied in their character and distribution: large and small, hard and soft, warm and cold, coloured and dark, solid, liquid, gaseous. The beliefs embodying these experiences are the premises of science. What, then, are its conclusions? Its conclusions are that the real world of material objects is of quite other sort. It wholly consists (so it seems) of electrical sub-atoms, organized in minute, quasi-planetary systems, propagating disturbances of constant velocity through spaces unoccupied or occupied only by the ether. Relative position, relative motion, mass, and other familiar attributes of matter these entities no doubt possess. But to declare them endowed with qualities which are or could be immediately revealed in sense perception, would be untrue, almost meaningless.

The difficulty, it may be noted, makes itself felt long before we drive causal explanation back to electric charges and electromagnetic disturbances. Consider, by way of illustration, a much less remote example. The sky, as seen, is blue. This, according to common sense, is an immediate intuition of external fact. Science, however, in its search for truth, is not content with this simple statement; it must needs ask why the sky, as seen, is blue. The obvious answer—the one that satisfies all children and the vast majority of men—that the sky looks blue because it is blue, does not satisfy the physicist. He pursues his investigations, and comes to the conclusion that distributed through space in the neighbourhood of the earth are minute bodies which scatter the mid-day light of an unclouded sky in such fashion that, of the rays which excite the sensation of blue, an abnormal proportion reach the eyes of terrestrial observers. In other words, unseen particles, diverting imperceptible waves, in an imperceptible ether, produce in men of normal constitution the perception of a far-off, blue, dome-like expanse. This explains, or helps to explain, why the sky seems blue; but can we really treat it as equivalent to the common-sense statement that, judged by the immediate evidence of the senses, the sky is blue? I think not.

§ 6

That these two conceptions of physical reality—the one due to ordinary perception and the other to scientific inference—are entirely different, seems to me quite undeniable. That the second has its roots in the first is not likely to be disputed. But it will perhaps be asked whether these obvious truths possess any philosophical interest. What is there either puzzling or surprising in the fact that in the process by which scientific theories have been developed from unscientific observations the two should have widely diverged? Is not such divergence inevitable? May it not be at once the proof and the measure of progress? Why, then, should we complain?

This contention is plausible but unsound. Our troubles arise not from the fact that increasing knowledge has upset our instinctive beliefs, but from the fact that the new beliefs, though inconsistent with the old, sprang from them, coexist with them, and depend on them. Common sense in its scientific shape contradicts common sense in its unreflective shape, yet never ceases to lean upon it.

It may perhaps be urged that the supposed difficulty is due to an erroneous view of the relation between science and observation. After all (it will be said) the physicist who explains the colour of a summer sky sees it just like humbler men. He finds nothing strange in the discordance between reality as it is given in perception, and reality as it is conceived by science. He never regards himself as the victim of an optical delusion, nor dreams that he is faced with any problem in the theory of knowledge.

Nor indeed is he—provided he be permitted to assume that all perceptions are to be treated as effects, and all our knowledge of the material world as an inference from these effects to their independent causes. If this were a tenable theory there would be nothing calling for comment in the fact that the world, as it is perceived, has little likeness to the world as it exists, that the blue sky (for example) is in truth neither blue nor properly speaking (I suppose) a sky. There would be no contradiction to be solved, nor even a paradox to be smoothed away. For why, speaking generally, should effects resemble their causes? Why, in particular, should things or events in an external world, blindly acting through the complex machinery whose character I have tried to indicate, produce in the observer an intuitive apprehension of their true reality? Looked at a priori such a result would be surprising indeed. All that we have a right to expect from the causal point of view is, that the character of a perception should vary with the nature of its object, and with the varying conditions under which that object is presented to us.

But if from the causal point of view this be all that we have a right to expect, does it from the cognitive point of view give us all that we are bound to demand? Freely granting that, if we accept the scientific account of perception, things can hardly be as they seem, are we not at once forced to enquire by what right we argue from what they seem to what in fact they are? Can we lawfully travel from intuitions which are admittedly erroneous, to conclusions which we presume to be true? If we cannot, then what becomes of the empirical basis of science? If we can, then by what rational procedure is the feat accomplished?

• 1.

  But see the qualifications to this which are dealt with in Chapter VIII.

• 2.

  On this last point, however, I think ordinary common sense speaks somewhat hesitatingly.

• 3.

  As far as I understand the question, this statement would not require to be modified in consequence of recent developments of the theory of relativity.

• 4.

  I believe that according to recent practice “ electron ” is confined to negative electricity. But as (so far as I know) there is no single word for an electrical sub-atom I have left the word unchanged. No one will be misled.