Chapter VI: Introduction: To Part III (1)

I

In the preceding lectures I have given reasons for thinking that in two great departments of human interest—Æsthetics and Ethics—the highest beliefs and emotions cannot claim to have any survival value. They must be treated as by-products of the evolutionary process; and are, therefore, on the naturalistic hypothesis, doubly accidental. They are accidental in the larger sense of being the product of the undesigned collocation and interplay of material entities—molecular atoms, sub-atoms, and ether—which preceded, and will presumably outlast, that fraction of time during which organic life will have appeared, developed, and perished. They are also accidental in the narrower sense of being only accidentally associated with that process of selective elimination, which, if Darwinism be true, has so happily imitated contrivance in the adaptation of organisms to their environment. They are the accidents of an accident.

I disagreed with this conclusion, but I did not attempt to refute it. I contented myself with pointing out that it was destructive of values; and that, the greater the values, the more destructive it became. The difficulty, indeed, on which I have so far insisted is not a logical one. We have not been concerned with premises and conclusions. Neither our æsthetic emotions nor our moral sentiments are the product of ratiocination; nor is it by ratiocination that they are likely to suffer essential wrong. If you would damage them beyond repair, yoke them to a theory of the universe which robs them of all general significance. Then, at the very moment when they aspire to transcendent authority, their own history will rise up in judgment against them, impugning their pretensions, and testifying to their imposture.

II

The inquiry on which I now propose to enter will follow a more or less parallel course, and will reach a more or less similar conclusion. Yet some characteristic differences it must necessarily exhibit. In the higher regions of æsthetics and ethics, emotions and beliefs are inextricably intertwined. They are what naturalists describe as “symbiotic.” Though essentially different, they are mutually dependent. If one be destroyed, the other withers away.

But Knowledge—the department of human interest to which I now turn—is differently placed. The values with which we shall be concerned are mainly rational; and intellectual curiosity is the only emotion with which they are associated. Yet here also two questions arise corresponding to those which we have already dealt with in a different connection: (1) what are the causes of our knowledge, or of that part of our knowledge which concerns the world of common sense and of science? (2) does the naturalistic account of these causes affect the rational value—in other words the validity—of their results?

We are, perhaps, more sensitive about the pedigree of our intellectual creed than we are about the pedigree of our tastes or our sentiments. We like to think that beliefs which claim to be rational are the product of a purely rational process; and though, where others are concerned, we complacently admit the intrusion of non-rational links in the causal chain, we have higher ambitions for ourselves.

Yet surely, on the naturalistic theory of the world, all such ambitions are vain. It is abundantly evident that, however important be the part which reason plays among the immediate antecedents of our beliefs, there are no beliefs which do not trace back their origin to causes which are wholly irrational. Proximately, these beliefs may take rank as logical conclusions. Ultimately, they are without exception rooted in matter and motion. The rational order is but a graft upon the causal order; and, if Naturalism be true, the causal order is blind.

III

Before I further develop this line of speculation it may help you to understand what I am driving at if I venture upon an autobiographical parenthesis. The point I have just endeavoured to make I have made before in these lectures, and I have made it elsewhere. It is one of a number of considerations which have led me to question the prevalent account of the theoretical ground-work of our accepted beliefs. Taken by itself, its tendency is sceptical; and, since it has been associated with arguments in favour of a spiritual view of the universe, I have been charged (and not always by unfriendly commentators) with the desire to force doubt into the service of orthodoxy by recommending mankind to believe what they wish, since all beliefs alike are destitute of proof. As we cannot extricate ourselves from the labyrinth of illusion, let us at least see to it that our illusions are agreeable.

This, however, is not what I have ever wanted to say, nor is it what I want to say now. If I have given just occasion for such a travesty of my opinions, it must have been an indirect consequence of my early, and no doubt emphatically expressed, contempt for the complacent dogmatism of the empirical philosophy, which in Great Britain reigned supreme through the third quarter of the nineteenth century. But was this contempt altogether unreasonable?

I went to Cambridge in the middle sixties with a very small equipment of either philosophy or science, but a very keen desire to discover _what_ I ought to think of the world, and _why_. For the history of speculation I cared not a jot. Dead systems seemed to me of no more interest than abandoned fashions. My business was with the ground-work of living beliefs; in particular, with the ground-work of that scientific knowledge whose recent developments had so profoundly moved mankind. And surely there was nothing perverse in asking modern philosophers to provide us with a theory of modern science!

I was referred to Mill; and the shock of disillusionment remains with me to the present hour. Mill possessed at that time an authority in the English Universities, and, for anything I know to the contrary, in the Scotch Universities also, comparable to that wielded forty years earlier by Hegel in Germany and in the Middle Ages by Aristotle. Precisely the kind of questions which I wished to put, his Logic was deemed qualified to answer. He was supposed to have done for scientific inference what Bacon tried to do, and failed. He had provided science with a philosophy.

I could have forgiven the claims then made for him by his admirers; I could have forgiven, though young and intolerant, what seemed to me the futility of his philosophic system, if he had ever displayed any serious misgiving as to the scope and validity of his empirical methods. If he had admitted, for example, that, when all had been done that could be done to systematise our ordinary modes of experimental inference, the underlying problem of knowledge still remained unsolved. But he seemed to hold, in common with the whole empirical school of which, in English-speaking countries, he was the head, that the fundamental difficulties of knowledge do not begin till the frontier is crossed which divides physics from metaphysics, the natural from the supernatural, the world of “phenomena” from the world of “noumena,” “positive” experiences from religious dreams. It may be urged that, if these be errors, they are errors shared by ninety-nine out of every hundred persons educated in the atmosphere of Western civilisation, whatever be their theological views: and I admit that it has sunk deep into our ordinary habits of thought. Apologetics are saturated with it, not less than agnosticism or infidelity. But, for my own part, I feel now, as I felt in the early days of which I am speaking, that the problem of knowledge cannot properly be sundered in this fashion. Its difficulties begin with the convictions of common sense, not with remote, or subtle, or otherworldly speculations; and if we could solve the problem in respect of the beliefs which, roughly speaking, everybody shares, we might see our way more clearly in respect of the beliefs on which many people are profoundly divided.

That Mill’s reasoning should have satisfied himself and his immediate disciples is strange. But that the wider public of thinking men, whom he so powerfully influenced, should on the strength of this flimsy philosophy adopt an attitude of dogmatic assurance both as to what can be known and what cannot, is surely stranger still. Thus, at least, I thought nearly half a century ago, and thus I think still.

Consider, for example, a typical form of the ordinary agnostic position: that presented by Leslie Stephen. The best work of this excellent writer was biographical and literary; but he was always deeply interested in speculation; and his own creed seems early to have taken its final shape under the philosophical influences of the British empiricists. He regarded the “appeal to experience” as the fundamental dogma of agnosticism, and by the “appeal to experience” he meant what Mill meant by it. He sincerely supposed that this gave you indisputable knowledge of “phenomena,” and that if you went beyond “phenomena” you were dreaming, or you were inventing.

This is a possible creed; and it is, in fact, the creed held implicitly, or explicitly, by many thousands of quite sensible people. But why should those who hold it suppose that it must always satisfy impartial inquirers? Why should they assume that those who reject it are sacrificing their reason to their prejudices or their fancies? It may represent the best we can do, but is it, after all, so obviously reasonable? On this subject the empirical agnostic has no doubts. He holds, with unshaken confidence, that nothing deserves to be believed but that which in the last resort is proved by “experience”; that the strength of our beliefs should be exactly proportioned to the evidence which “experience” can supply, and that every one knows or can discover exactly what this evidence amounts to. Leslie Stephen refers to a well-known aphorism of Locke, who declared that “there is one unerring mark by which a man may know whether he is a lover of truth in earnest, viz. the not entertaining any proposition with greater assurance than the proofs it is built on will warrant.” Upon which Leslie Stephen observes that the sentiment is a platitude, but, in view of the weakness of human nature, a useful platitude.

Is it a platitude? Did Locke act up to it? Did Hume act up to it, or any other of Leslie Stephen’s philosophic progenitors? Does anybody act up to it? Does anybody sincerely try to act up to it?

Read through the relevant chapters in Locke’s Essay, and observe his ineffectual struggles, self-imprisoned in the circle of his own sensations and ideas, to reach the external world in which he believed with a far “greater assurance” than was warranted by any proofs which _he_, at all events, was able to supply. Read Hume’s criticism of our grounds for believing in a real world without, or a real self within, and compare it with his admission that scepticism on these subjects is a practical impossibility.

But we need not go beyond the first chapter of “An Agnostic’s Apology” to find an illustration of my argument. Leslie Stephen there absolves himself from giving heed to the conclusions of philosophers, because there are none on which all philosophers are agreed, none on which there is even a clear preponderance of opinion. On the other hand, he is ready to agree with astronomers, because astronomers, “from Galileo to Adams and Leverrier,” substantially agree with each other. Agreement among experts is, in his opinion, a guarantee of truth, and disagreement a proof of error.

But then he forgets that these distressing differences among philosophers do not touch merely such entities as God and the soul, or the other subjects with which agnostics conceive man’s faculties are incapable of dealing. They are concerned (among other things) with the presuppositions on which our knowledge of “phenomena”—including, of course “astronomy from Galileo to Adams and Leverrier,” is entirely constructed. What, in these circumstances, is Locke’s “sincere lover of truth” to do? How is he to avoid “entertaining propositions with greater assurance than the proofs they are built on will warrant”? Where will he find a refuge from the “pure scepticism” which is, in Leslie Stephen’s opinion, the natural result of divided opinions? How is he to get on while he is making up his mind whether any theory of the world within his reach will satisfy unbiased reason?

The fact is that the adherents of this philosophic school apply, quite unconsciously, very different canons of intellectual probity to themselves and to their opponents. “Why,” asks Mr. Stephen, “should a lad who has just run the gauntlet of examination and escaped to a country parsonage be dogmatic?” If to be dogmatic is to hold opinions with a conviction in excess of any reason that can be assigned for them, there seems to be no escape for the poor fellow. The common lot of man is not going to be reversed for him. Though he abandon his parsonage and renounce his Church, though he scrupulously purify his creed from every taint of the “metempirical,” though he rigidly confine himself to themes which his critics declare to be within the range of his intellectual vision, fate will pursue him still. He may argue much or argue little; he may believe much or believe little; but, however much he argues and however little he believes, his beliefs will always transcend his arguments, and to faith, in his own despite, he must still appeal.

Those who accept Leslie Stephen’s philosophy suppose that for this young man, as for all others, a way of escape may be found by appealing to experience. But surely none are so sanguine as to suppose that, by appealing to experience, they are going to avoid what Mr. Stephen describes as “endless and hopeless controversies.” Alas, this is not so! The field of experience is no well-defined and protected region under whose clear skies useful knowledge flourishes unchallenged, while the mist-enshrouded territories of its metaphysical neighbours are devastated by unending disputations. On the contrary, it is the very battlefield of philosophy, the cockpit of metaphysics, strewn with abandoned arguments, where every strategic position has been taken and retaken, to which every school lays formal claim, which every contending system pretends to hold in effective occupation. Indeed, by a singular irony, the thinkers who, at this particular moment, talk most about experience are those metaphysicians of the Absolute in whose speculations Mr. Stephen saw no beginning of interest, except that of being (as he supposed) at once the refuge and the ruin of traditional religion. But these philosophers have no monopoly. All men nowadays speak well of experience. They begin to differ only when they attempt to say what experience is, to define its character, explain its credentials, and expound its message. But, unhappily, when this stage is reached their differences are endless.

IV

I am, of course, not concerned with Mr. Stephen except as a brilliant representative of a mode of thought to which I most vehemently object. I do not object to it merely because it is in my judgment insufficient and erroneous, still less because I dislike its conclusion. I object to it because it talks loudly of experience, yet never faces facts; and boasts its rationality, yet rarely reasons home. These are far graver crimes against the spirit of truth than any condemned in Locke’s pretentious aphorism, and they lead to far more serious consequences.

If you ask me what I have in mind when I say that agnostic empiricism never faces facts, I reply that it never really takes account of that natural history of knowledge, of that complex of causes, rational and non-rational, which have brought our accepted stock of beliefs into being. And if you ask me what I have in mind when I say that though it reasons, it rarely reasons home, I reply that, when it is resolved not to part with a conclusion, anything will serve it for an argument; only when it is incredulous does it know how to be critical.

This is not an error into which I propose to fall. But I hope that I shall not on that account be deemed indifferent to the claims of reason, or inclined to treat lightly our beliefs either about the material world or the immaterial. On the contrary, my object, and my only object, is to bring reason and belief into the closest harmony that at present seems practicable. And if you thereupon reply that such a statement is by itself enough to prove that I am no ardent lover of reason; if you tell me that it implies, if not permanent contentment, at least temporary acquiescence in a creed imperfectly rationalised, I altogether deny the charge. So far as I am concerned, there is no acquiescence. Let him that thinks otherwise show me a better way. Let him produce a body of beliefs which shall be at once living, logical, and sufficient;—not forgetting that it cannot be sufficient unless it includes within the circuit of its doctrines some account of itself regarded as a product of natural causes, nor logical unless it provides a rational explanation of the good fortune which has made causes which are not reasons, mixed, it may be, with causes which are not _good_ reasons, issue in what is, by hypothesis, a perfectly rational system. He who is fortunate enough to achieve all this may trample as he likes upon less successful inquirers. But I doubt whether, when this discoverer appears, he will be found to have reached his goal by the beaten road of empirical agnosticism. This, though it be fashionably frequented, is but a blind alley after all.

In the meanwhile we must, I fear, suffer under a system of beliefs which is far short of rational perfection. But we need not acquiesce, and we should not be contented. Whether this state of affairs will ever be cured by the sudden flash of some great philosophic discovery is another matter. My present aim, at all events, is far more modest. But they, at least, should make no complaint who hold that common-sense beliefs, and science which is a development of common-sense beliefs, are, if not true, at least on the way to truth. For this conviction I share. I profess it; I desire to act upon it. And surely I cannot act upon it better than by endeavouring, so far as I can, to place it in the setting which shall most effectually preserve its intellectual value. This, at all events, is the object to which the four lectures that immediately follow are designed to contribute.

LECTURE VI

PERCEPTION, COMMON SENSE, AND SCIENCE

I

Nothing would seem easier, at first sight, than to give a general description of the ordinary beliefs of ordinary people about our familiar world of things and persons. It is the world in which we live; it is for all men _a_ real world; it is for many men _the_ real world; it is the world of common sense, the world where the plain man feels at home, and where the practical man seeks refuge from the vain subtleties of metaphysics. Our stock of beliefs about it may perhaps be difficult to justify, but it seems strange that they should be difficult to describe; yet difficult, I think, they are.

Some statements about it may, however, be made with confidence. It is in space and time; i.e. the material things of which it is composed, including living bodies, are extended, have mutual position, and possess at least some measure of duration.

Things are not changed by a mere change of place, but a change of place relative to an observer always changes their appearance _for him_. Common sense is, therefore, compelled in this, as in countless other cases, to distinguish the appearance of a thing from its reality; and to hold, as an essential article of its working creed, that appearances may alter, leaving realities unchanged.

Common sense does not, however, draw the inference that our experiences of material things is other than direct and immediate. It has never held the opinion—or, if you will, the heresy—that what we perceive (at least by sight and touch) are states of our own mind, which somehow copy or represent external things. Neither has it ever held that the character or duration of external things in any way depends upon our observations of them. In perception there is no reaction by the perceiving mind on the object perceived. Things in their true reality are not affected by mere observation, still less are they constituted by it. When material objects are in question, common sense never supposes that _esse_ and _percipi_ are identical.

But then, what, according to common sense, _are_ things in their true reality? What are they “in themselves,” when no one is looking at them, or when only some of their aspects are under observation?

We can, at all events, say what (according to common sense) things are _not_. They are more than collections of aspects. If we could simultaneously perceive a “thing” at a thousand different distances, at a thousand different angles, under a thousand varieties of illumination, with its interior ideally exposed in a thousand different sections, common sense, if pressed, would, I suppose, still hold that these were no more than specimens of the endless variety of ways in which things may appear, without either changing their nature or fully revealing what that nature is. But though common sense might give this answer, it would certainly resent the question being put. It finds no difficulty in carrying on its work without starting these disturbing inquiries. It is content to say that, though a thing is doubtless always more than the sum of those aspects of it to which we happen to be attending, yet our knowledge _that_ it is and _what_ it is, however imperfect, is, for practical purposes, sufficiently clear and trustworthy, requiring the support neither of metaphysics nor psychology.—This, with all its difficulties, is, I believe, an account, true as far as it goes, of the world of things as common sense conceives it. This is the sort of world which science sets out to explain. Let me give an illustration.

We perceive some object—let us say the sun. We perceive it directly and not symbolically. What we see is not a mental image of the sun, nor a complex of sensations caused by the sun; but the sun itself. Moreover, this material external object retains its identity while it varies in appearance. It is red in the morning; it is white at midday; it is red once more in the evening; it may be obscured by clouds or hidden in eclipse; it vanishes and reappears once in every twenty-four hours; yet, amid all these changes and vanishings, its identity is unquestioned. Though we perceive it differently at different times, and though there are times when we do not perceive it at all, we know it to be the same; nor do we for a moment believe (with Heraclitus) that when it is lost to view it has, on that account, either altered its character or ceased to exist.

In the main, therefore, experience is, according to common sense, a very simple affair. We see something, or we feel something, or, like Dr. Johnson, we kick something, and “there’s an end on’t.” Experience is the source of all knowledge, and therefore of all explanation; but, in itself, it seems scarcely to require to be explained. Common sense is prepared to leave it where it finds it. No doubt the occurrence of optical or other illusions may disturb this mood of intellectual tranquillity. Common sense, when it has to consider the case of appearances, some of which are held, on extraneous grounds, to be real and others to be illusory, may feel that there are, after all, problems raised by perception—by the direct experience of things—which are not without their difficulties. But the case of illusions is exceptional, and rarely disturbs the even tenor of our daily round.

II

Now science, as it gladly acknowledges, is but an extension of common sense. It accepts, among other matters, the common-sense view of perception. Like common sense, it distinguishes the thing as it is from the thing as it appears. Like common sense, it regards the things which are experienced as being themselves unaffected by experience. But, unlike common sense, it devotes great attention to the way in which experience is produced by things. Its business is with the causal series. This, to be sure, is a subject which common sense does not wholly ignore. It would acknowledge that we perceive a lamp through the light which it sheds, and recognise a trumpet through the sound which it emits; but the nature of light or sound, and the manner in which they produce our experience of bright or sonorous objects, it hands over to science for further investigation.

And the task is cheerfully undertaken. Science also deems perception to be the source of all our knowledge of external nature. But it regards it as something more, and different. For perception is itself a part of nature, a natural process, the product of antecedent causes, the cause of subsequent effects. It requires, therefore, like other natural facts, to be observed and explained; and it is the business of science to explain it.

Thus we are brought face to face with the contrast on which so much of the argument of these lectures turns: the contrast between beliefs considered as members of a cognitive series, and beliefs considered as members of a causal series. In the cognitive series, beliefs of perception are at the root of our whole knowledge of natural laws. In the causal series, they are the effects of natural laws in actual operation. This is so important an example of this dual state that you must permit me to consider it in some detail.

We may examine what goes on between the perceiving person and the thing he perceives from either end; but it is by no means a matter of indifference with which end we begin. If we examine the relation of the perceiver to the perceived it does not seem convenient or accurate to describe that relation as a process. It is an experience, immediate and intuitive; not indeed infallible, but direct and self-sufficient. If I look at the sun, it is the sun I see, and not an image of the sun, nor a sensation which suggests the sun, or symbolises the sun. Still less do I see ethereal vibrations, or a retinal image, or a nervous reaction, or a cerebral disturbance. For, in the act of perceiving, no intermediate entities are themselves perceived.

But now if we, as it were, turn round, and, beginning at the other end, consider the relation of the perceived to the perceiver, no similar statements can be made. We find ourselves concerned, not with an act of intuition, but with a physical process, which is complicated, which occupies time, which involves many stages. We have left behind cognition; we are plunged in causation. Experience is no longer the immediate apprehension of fact; it is the transmission of a message conveyed from the object to the percipient by relays of material messengers. As to how the transmission is effected explanations vary with the growth of science. They have been entirely altered more than once since the modern era began, and with each alteration they become more complicated. They depend, not on one branch of science only, but on many. Newtonian astronomy, solar physics, the theory of radiation, the optical properties of the atmosphere, the physiology of vision, the psychology of perception, and I daresay many other branches of research, have to be drawn upon: and all this to tell us what it is we see, and how it is we come to see it.

III

Now there is no one who possesses the least smattering of philosophy who does not know that the views I have just endeavoured to describe are saturated with difficulties: difficulties connected with the nature of perception; difficulties connected with the nature of the object as perceived; difficulties connected with its unperceived physical basis; difficulties connected with the relation in which these three stand to each other. For common sense the material object consists of a certain number of qualities and aspects which are perceived, an inexhaustible number which might be perceived, but are not, and (perhaps) a vaguely conceived “somewhat” lying behind both. The medieval Aristotelian, if I rightly understand him (which very likely I do not), developed this “somewhat” into the notion of substance—an entity somewhat loosely connected with the qualities which it supported, and in no way explaining them. There was “substance” in a piece of gold, and “substance” in a piece of lead; but there was nothing unreasonable in the endeavour to associate the qualities of gold with the substance of lead, and thus for all practical purposes to turn lead into gold.

Modern science teaches a very different lesson. It has, perhaps, not wholly abandoned the notion of material substance, if this be defined as the unperceivable support of perceivable qualities; but it persistently strives to connect the characteristics of matter with its structure, and, among other characteristics, that of producing, or helping to produce, in us those immediate perceptions which we describe as our experience of matter itself.

An important stage in this endeavour was marked by the famous distinction between the primary and the secondary qualities of matter: the primary qualities being the attributes of external material things which were deemed to be independent of the observer (for example, impenetrability, density, weight, configuration); the secondary qualities being those which, apart from observers endowed with senses like our own, would either exist differently, or would not exist at all (for example, colour and taste). On this view the primary qualities were among the causes of the secondary qualities, and the secondary qualities were transferred from the thing perceived to the person perceiving.

I am not the least concerned to defend this theory. It has been much derided, and is certainly open to attack. But something like it seems to be an inevitable stage in the development of modern views of nature. The whole effort of physical science is to discover the material or non-psychical facts which shall, among other things, account for our psychical experiences. It is true that there are men of science, as well as philosophers, who regard all such constructions as purely arbitrary—mere labour-saving devices which have nothing to do with reality. But though I shall have something to say about these theories in my next course of lectures, for the present I need only observe that they do not represent ordinary scientific opinion, either as it is, or as it has ever been. Science thinks, rightly or wrongly, that she is concerned with a real world, which persists independently of our experience: she has never assented to the doctrine that the object of her patient investigations is no more than a well-contrived invention for enabling us to foretell, and perhaps to modify, the course of our personal feelings.

But then, if science is right, we are committed to a division between the contents of immediate experience and its causes, which showed itself dimly and tentatively in the distinction between the secondary and the primary qualities of matter, but has become deeper and more impassable with every advance in physics and physiology. It was possible to maintain (though, I admit, not very easy) that, while the secondary qualities of matter are due to the action of the primary qualities on our organs of perception, the primary qualities themselves are, nevertheless, the objects of direct experience. The fact, for example, that colour is no more than a sensation need not preclude us from perceiving the material qualities which, like shape, or motion, or mass, are the external and independent causes to which the sensation is due. I do not say that this view was ever explicitly entertained—nor does it signify. For, if we accept the teaching of science, it can, I suppose, be entertained no more. The physical causes of perception are inferred, but not perceived. The real material world has been driven by the growth of knowledge further and further into the realm of the unseen, and now lies completely hidden from direct experience behind the impenetrable screen of its own effects.

IV

For consider what the causal process of perception really is if we trace it from the observed to the observer—if we follow the main strands in the complex lines of communication through which the object seen reveals itself to the man who sees it.

I revert to my previous example—the sun. We need not consider those of its attributes which are notoriously arrived at by indirect methods—which are not perceived but inferred—its magnitude, for example, or its mass. Confining ourselves to what is directly perceived, its angular size, its shape (projected on a plane), its warmth, its brightness, its colour, its (relative) motion, its separation from the observer in space—how are these immediate experiences produced?

The answers have varied with the progress of science; nor, for my present purpose, does it greatly matter which answers we adopt. Let us take those which are commonly accepted at the present moment. They are not only the truest, but the fullest; and for that very reason they put the difficulty with which we are concerned in the highest relief. We begin our causal series with electrons, or, if you do not accept the electric theory of matter in any of its forms, then with atoms and molecules. We start with these, because the sun is a collection of them, and because it is their movements which set going the whole train of causes and effects by which the sun produces in us the perception of itself.

We may take, as the next stage, ethereal vibrations, of various lengths and various amplitudes, sent travelling into space by the moving particles. A fraction of these waves reaches our atmosphere, and of that fraction a fraction reaches our eyes, and of that fraction a further fraction falls within the narrow limits of length to which our eyes are sensitive. It is through these that we are able to _see_ the sun. Still another fraction, not necessarily identical in wave-lengths, affects the nerves which produce in us the sensation of warmth. It is through these that we are able to _feel_ the sun.

But, before we either see or feel, there is much still to be accomplished. The causal series is not nearly completed. Complicated neural processes, as yet only imperfectly understood; complicated cerebral processes—as yet understood still less—both involving physiological changes far more complicated than the electrical “accelerations” or electro-magnetic disturbances with which we have hitherto been dealing, bring us to the end of the material sequence of causes and effects, and lay the message from the object perceived on the threshold of the perceiving consciousness. So does a postman slip into your letter-box a message which has been first written, then carried by hand, then by a mail-cart, then by a train, then by hand again, till it reaches its destination, and nothing further is required except that what has been written should be read and understood.

Thus far the material process of transmission. The psychical process has still to come. Psychology is a science, not less than physiology or physics; and psychology has much to say on the subject of perception. It is true that scientific explorers whose point of departure is introspective; who concern themselves primarily with ideas, conceptions, sensations, and so forth, rarely succeed in fitting their conclusions without a break to those of their colleagues who begin with the “external” causes of perception. The two tunnels, driven from opposite sides of the mountain, do not always meet under its crest. Still, we cannot on that account ignore the teaching of psychology on the genesis of perceptual experience regarded, not as the ground of knowledge, but as a natural product.

I do not mean to attempt a summary of psychology from this point of view, any more than I have attempted a summary of physics or physiology. My argument is really independent, in this case as in the other, of particular systems. All I ask for is the admission that in perception there are conditions antecedently supplied by the perceiving consciousness which profoundly modify every perceptual experience—and that these conditions (unlike Kant’s forms) are natural growths, varying, like other natural growths, from individual to individual. This admission must, I think, be made by every empirical psychologist, to whatever school he happens to belong.

If this statement seems obscure in its general and abstract form, consider a particular application of it. Let us assume, with many psychologists, that Will, in the form of selective attention, lies at the root of our perceptual activities; that we may therefore be said, in a sense, voluntarily to create the objects we perceive; that experience of the present is largely qualified by memories of the past, and that the perceptual mould into which our sensations are run is largely a social product—born of the intercourse between human beings, and, in its turn, rendering that intercourse possible. Is it not clear that, on assumptions like these, consciousness, so far from passively receiving the messages conveyed to it through physical and physiological channels, actively modifies their character?

V

But why, it may be asked, should these considerations involve any difficulty? And, if there be a difficulty, what is its exact character?

In its most general form the difficulty is this. It is claimed by science that its conclusions are based upon experience. The experience spoken of is unquestionably the familiar perception of external things and their movements as understood by common sense; and, however much our powers of perception be increased by telescopes, microscopes, balances, thermometers, electroscopes, and so forth, this common-sense view suffers no alteration. The perceptions of a man of science are, in essence, the perceptions of ordinary men in their ordinary moments, beset with the same difficulties, accepted with the same assurance. Whatever be the proper way of describing scientific results, the experimental data on which they rest are sought and obtained in the spirit of “naïf realism.”

On this foundation science proceeds to build up a theory of nature by which the foundation itself is shattered. It saws off the branch on which it is supported. It kicks down the ladder by which it has climbed. It dissolves the thing perceived into a remote reality which is neither perceived nor perceivable. It turns the world of common sense into an illusion, and on this illusion it calmly rests its case.

But this is not the only logical embarrassment in which we are involved. When science has supplied us with a description of external things as they “really are,” and we proceed to ask how the physical reality reveals itself to us in experience, a new difficulty arises, or, if you like, the old difficulty with a new face. For science requires us to admit that experience, from this point of view, is equivalent to perception; and that perception is a remote psychological effect of a long train of causes, physical and physiological, originally set in motion by the external thing, but in no way resembling it. Look carefully at this process from the outside, and ask yourselves why there should be any such correspondence between the first of these causes and the last of these effects, as should enable us to know or infer the one from the other? Why should the long train of unperceivable intermediaries that connect the perceived with the perceiver be trusted to speak the truth?

I just now likened these intermediaries to relays of messengers. But messengers are expected to hand on their message in the form in which they have received it. The messengers change, but not the message. The metaphor, therefore, is far too complimentary to the train of physical causes which reveal the material thing to the perceiving consciousness. The neural changes which are in immediate causal contiguity with that psychical effect which we call “the experience of an external object” have no resemblance whatever either to the thing as it is perceived or to the thing as it really is. Nor have they any resemblance to the proximate cause which sets them going, namely, the ethereal vibrations; nor have these to the accelerated electrons which constitute the incandescent object which we “experience” as the sun. Nor has the sun, as experienced, the slightest resemblance to the sun as it really is.

Hume, in his “Dialogues on Natural Religion,” urges the absurdity of arguing from an effect like the universe to a cause like God, since the argument from a particular effect to a particular cause, or from a particular cause to a particular effect, is only legitimate when we have had some previous experience of that particular class of causal sequence; and nobody, it is plain, has had the opportunity of observing Creation. Whatever be the value of this argument in the case of God and the world, it seems to me conclusive in the case of matter and man. We cannot argue from purely psychical effects, like perceptions and sensations, to external causes, like physiological processes or ethereal vibrations, _unless_ we can experience both sets of facts in causal relation. And this, if we accept the conclusions of science, we can never do—partly because the intermediate members of the causal series are unperceivable; partly because, if they were perceivable, perception has been reduced by science to a purely psychical effect—which obviously cannot include its material cause. This last must for ever remain outside the closed circle of sensible experiences.

Here, of course, we find ourselves face to face with a familiar objection to those philosophies of perception which deny that we have any access to external reality, except through ideas which are its copy. But they are in a better case than science. They need not explicitly admit a discrepancy between their premises and their conclusions. They arrive at the subjectivity of perception by methods of introspection. They interrogate consciousness, and are convinced that every experience can be analysed into sensations and ideas, some of which, no doubt, suggest externality, but none of which are external. If, then, the worst comes to the worst, they can, and often do, lighten their philosophic ship by pitching the whole material universe overboard as a bit of superfluous cargo. But physical science cannot (at least in my opinion) do anything of the kind. Its whole business is with the material universe. Its premises are experiences of external things, not of internal sensation and ideas. And if it has associated its fortunes with a theory of perception which treats experience as a natural effect of the thing experienced; if it has thereby wandered within sight of the perilous problems which haunt the frontier where mind and matter meet, it has not done so in a spirit of reckless adventure, but in the legitimate pursuit of its own affairs.

This does not necessarily make things easier. We are not here concerned with questionings about the remoter provinces of knowledge—provinces unexplored except by specialists, negligible by ordinary men engaged on ordinary business. On the contrary, the difficulties to which I have called your attention threaten the unquestioned assumption of daily life, the presupposition of every scientific experiment, and the meaning of every scientific generalisation. They cannot be ignored.

On the other hand, threaten as they may, these difficulties can never modify our attitude either towards practical action or scientific theory. Beliefs which were inevitable before remain inevitable still. The supreme act of instinctive faith involved in the perception of external objects stands quite unshaken. Whatever we may think of Berkeley, we cannot give up Dr. Johnson. “Seeing,” says the proverb, “is believing”; and it speaks better than it knows.

VI

Can we, then, adopt a middle course, and, imitating the serene acquiescence of Hume, accept the position of sceptics in the study and believers in the market-place? This seems eminently unsatisfactory; and, since believers on this subject we must perforce remain, it behoves us to consider how, and on what terms, we can best qualify our scepticism.

Observe, then, that the particular difficulty which has been occupying our attention arises in the main from the assumption that our common-sense beliefs in the reality and character of material things have no other foundation than the fact that we so perceive them. From such premises it was impossible, it seemed, to infer that they exist otherwise than as they are perceived; and still more impossible to regard the immediate intuition by which we apprehend the object, and the long-drawn sequence of causes by which the object is revealed, as being the same process looked at from different ends.

But this difficulty is greatly mitigated if we hold that our belief in an independent world of material objects, however it may be caused, is neither a conclusion drawn from this or that particular experience nor from all our experiences put together, but an irresistible assumption. Grant the existence of external things, and it becomes possible and legitimate to attempt explanations of their appearance, to regard our perceptions of them as a psychical and physiological product of material realities which do not themselves appear and cannot be perceived. Refuse, on the other hand, to grant this assumption, and no inductive legerdemain will enable us to erect our scientific theories about an enduring world of material things upon the frail foundation of successive personal perceptions.

If this does not seem clear at first sight it is, I think, because we do not consider our experiences as a whole. A limited group of experiences—say Faraday’s experiments with electro-magnets—may guide us into new knowledge about the external world, including aspects of that world which are not open to sense perception. But then these experiences assume that this external world exists, they assume it to be independent of perception, they assume it to be a cause of perception. These assumptions once granted, experiment may be, and is, the source of fresh discoveries. But experiment based on these assumptions never can establish their truth; and if our theory of knowledge requires us to hold that “no proposition should be entertained with greater assurance than the proofs it is built on will warrant,” our fate is sealed, and we need never hope to extricate ourselves from the entanglements in which a too credulous empiricism has involved us. This means that one at least of the inevitable beliefs enumerated in the first lecture—the belief in an external world—is a postulate which science is compelled to use but is unable to demonstrate. How, then, are we to class it? It is not a law of thought in the accepted meaning of that expression. We are not rationally required to accept it by the very structure of our thinking faculties. Many people, indeed, theoretically reject it; none, so far as I know, regard it as self-evident. On the other hand, it is not an inference from experience; neither is it an analytic judgment in which the predicate is involved in the subject. Described in technical language, it would seem to be _a priori_ without being necessary, and synthetic without being empirical—qualities which, in combination, scarcely fit into any familiar philosophic classification.

According to the view which I desire to press in these lectures, this marks a philosophic omission. I regard the belief in an external world as one of a class whose importance has been ignored by philosophy, though all science depends on them. They refuse to be lost in the common herd of empirical beliefs; though they have no claim to be treated as axioms. We are inclined to accept them, but not rationally compelled. The inclination may be so strong as practically to exclude doubt; and it may diminish from this maximum to a faint feeling of probability. But, whatever be the strength of these beliefs, and whatever the nature of their claims, the importance of the part they play in the development and structure of our current creed cannot easily be exaggerated.

Before, however, I consider other specimens of this class, I must interpolate a long parenthesis upon probability. I have just described these fundamental beliefs as being “probable” in varying degrees. Gradations of probability are familiar to the mathematical theorist. Are we, then, here concerned with probability as conceived by the mathematician? It is evidently essential to settle this question before proceeding with the main argument; and I propose, therefore, to turn aside and devote the next lecture to its consideration.

LECTURE VII

PROBABILITY, CALCULABLE AND INTUITIVE

I

I wish I were a mathematician. There is in the history of the mathematical sciences, as in their substance, something that strangely stirs the imagination even of the most ignorant. Its younger sister, Logic, is as abstract, and its claims are yet wider. But it has never shaken itself free from a certain pretentious futility: it always seems to be telling us, in language quite unnecessarily technical, what we understood much better before it was explained. It never helps to discover, though it may guarantee discovery; it never persuades, though it may show that persuasion has been legitimate; it never aids the work of thought, it only acts as its auditor and accountant-general. I am not referring, of course, to what I see described in recent works as “modern scientific logic.” Of this I do not presume to speak. Still less am I referring to so-called Inductive Logic. Of this it is scarce worth while to speak.[9] I refer to their more famous predecessor, the formal logic of the schools.

But in what different tones must we speak of mathematics! Mill, if I remember rightly, said it was as full of mysteries as theology. But while the value of theology for knowledge is disputed, the value of mathematics for knowledge is indisputable. Its triumphs can be appreciated by the most foolish, they appeal to the most material. If they seem sometimes lost to ordinary view in the realms of abstract infinities, they do not disdain to serve us in the humbler fields of practice. They have helped mankind to all the greatest generalisations about the physical universe: and without them we should still be fumbling over simple problems of practical mechanics, entangled in a costly and ineffectual empiricism.

But while we thank the mathematician for his aid in conquering Nature, we envy him his powers of understanding her. Though he deals, it would seem, entirely with abstractions, they are abstractions which, at his persuasion, supply the key to the profoundest secrets of the physical universe. He holds the clues to mazes where the clearest intellect, unaided, would wander hopelessly astray. He belongs to a privileged caste.

I intend no serious qualification of this high praise when I add that, as regards the immediate subject of this lecture, I mean Probability, mathematicians do not seem to have given ignorant inquirers like myself all the aid which perhaps we have a right to ask. They have treated the subject as a branch of applied mathematics. They have supplied us with much excellent theory. They have exercised admirable skill in the solution of problems. But I own that, when we inquire into the rational basis of all this imposing superstructure, their explanations, from the lay point of view, leave much to be desired.

“Probability,” says an often-quoted phrase of Butler, “is the guide of life.” But the Bishop did not define the term; and he wrote before the theory of probability had attained to all its present dignities. Neither D’Alembert nor Laplace had discussed it. Quetelet had not applied it to sociology, nor Maxwell to physics. Jevons had not described it as the “noblest creation of the intellect.” It is doubtful whether Butler meant by it exactly what the mathematicians mean by it, and certain that he did not suspect any lurking ambiguity in the expression.

Nor, indeed, would the existence of such ambiguity be commonly admitted by any school of thought. The ordinary view is that the theory of probabilities is, as Laplace described it, “common sense reduced to calculation.” That there could be two kinds of probability, only one of which fitted this description, would be generally regarded as a heresy. But it is a heresy in which I myself believe; and which, with much diffidence, I now propose to defend.

II

The well-known paradox of the theory of probabilities is that, to all seeming, it can extract knowledge from ignorance and certainty from doubt. The point cannot be better put than by Poincaré in discussing the physical theory of gases, where the doctrine of probability finds an important application. Let me give you his view—partly in paraphrase, partly in translation. “For omniscience,” he says in substance, “chance would not exist. It is but the measure of our ignorance. When we describe an event as accidental we mean no more than that we do not fully comprehend the conditions by which it was brought about.