CHAPTER 1 OF THE PROBLEMS OF PHILLOSOPHY In the following pages I have confined myself in the main to those problems of philosophy in regard to which I thought it possible to say something positive and constructive since merely negative criticism seemed out of place. For this reason, theory of knowledge occupies a larger space than metaphysics in the present volume and some topics much discussed by philosophers are treated very briefly, if at all. I have derived valuable assistance from unpublished writings of G. E. Moore and J. M. Keynes from the former as regards the relations of sense data to physical objects and from the latter as regards probability and induction. I have also profited greatly by the criticisms and suggestions of Professor Gilbert Murray. CHAPTER 1. APPEARANCE IN REALITY Is there any knowledge in the world which is so certain that no reasonable man could doubt it? This question, which at first sight might not seem difficult, is really one of the most difficult that can be asked. When we have realized the obstacles in the way of a straightforward and confident answer, we shall be well launched on the study of philosophy. For philosophy is merely the attempt to answer such ultimate questions, not carelessly and dogmatically as we do in ordinary life and even in the sciences, but critically, after exploring all that makes such questions puzzling and after realizing all the vagueness and confusion that underlie our ordinary ideas. In daily life, we assume as certain many things which, on a closer scrutiny, are found to be so full of apparent contradictions that only a great amount of thought enables us to know what it is that we really may believe. In the search for certainty, it is natural to begin with our present experiences, and in some sense, no doubt, knowledge is to be derived from them. But any statement as to what it is that our immediate experiences make us know is very likely to be wrong. It seems to me that I am now sitting in a chair, at a table of a certain shape, on which I see sheets of paper with writing or print. By turning my head, I see out of the window buildings and clouds in the sun. I believe that the sun is about 93 million miles from the earth, that it is a hot globe many times bigger than the earth, that owing to the earth's rotation, it rises every morning, and will continue to do so for an indefinite time in the future. I believe that, if any other normal person comes into my room, he will see the same chairs and tables and books and papers as I see, and that the table which I see is the same as the table which I feel pressing against my arm. All this seems to be so evident as to be hardly worth stating, except an answer to a man who doubts whether I know anything. Yet all this may be reasonably doubted, and all of it requires much careful discussion before we can be sure that we have stated it in a form that is wholly true. To make our difficulties plain, let us concentrate attention on the table. To the eye it is oblong, brown, and shiny. To the touch it is smooth, and cool, and hard. When I tap it, it gives out a wooden sound. Anyone else who sees and feels and hears the table will agree with this description, so that it might seem as if no difficulty would arise. But as soon as we try to be more precise, our troubles begin. Although I believe that the table is really of the same color all over, the parts that reflect the light look much brighter than the other parts, and some parts look white because of reflected light. I know that, if I move, the parts that reflect the light will be different, so that the apparent distribution of colors on the table will change. It follows that, if several people are looking at the same table at the same moment, no two of them will see exactly the same distribution of colors, because no two can see it from exactly the same point of view. And any change in the point of view makes some change in the way the light is reflected. For most practical purposes, these differences are unimportant, but to the painter they are all important. The painter has to unlearn the habit of thinking that things seem to have the color which common sense says they really have, and to learn the habit of seeing things as they appear. Here we have already the beginning of one of the distinctions that caused most trouble in philosophy, the distinction between appearance and reality, between what things seem to be and what they are. The painter wants to know what things seem to be, the practical man and the philosopher want to know what they are, but the philosophers wish to know this is stronger than the practical man's, and is more troubled by knowledge as to the difficulties of answering the question. To return to the table. It is evident from what we have found, that there is no color which preeminently appears to be the color of the table, or even of any one particular part of the table. It appears to be of different colors from different points of view, and there is no reason for regarding some of these as more really its color than others. And we know that even from a given point of view, the color will seem different by artificial light, or to a color blind man, or to a man wearing blue spectacles, while in the dark there will be no color at all, though to touch and hearing the table will be unchanged. This color is not something which is inherent in the table, but something depending upon the table and the spectator, and the way the light falls on the table. When in ordinary life we speak of the color of the table, we only mean the sort of color which it will seem to have to a normal spectator from an ordinary point of view under usual conditions of light. But the other colors which appear under other conditions have just as good a right to be considered real, and therefore to avoid favoritism we are compelled to deny that, in itself the table has any one particular color. The same thing applies to the texture. With the naked eye one can see the grain, but otherwise the table looks smooth and even. If we looked at it through a microscope we should see roughnesses and hills and valleys and all sorts of differences that are imperceptible to the naked eye. Which of these is the real table? We are naturally tempted to say that what we see through the microscope is more real, but that in turn would be changed by a still more powerful microscope. If then we cannot trust what we see with the naked eye, why should we trust what we see through a microscope? Thus, again, the confidence in our senses with which we began deserts us. The shape of the table is no better. We are all in the habit of judging as to the real shapes of things, and we do this so unreflectingly that we come to think we actually see the real shapes. But in fact, as we all have to learn if we try to draw, a given thing looks different in shape from every different point of view. If our table is really rectangular, it will look from almost all points of view, as if it had two acute angles and two obtuse angles. If opposite sides are parallel, it will look as if they converge to a point away from the spectator. If they are of equal length, they will look as if the nearest side were longer. All these things are not commonly noticed in looking at a table because experience has taught us to construct the real shape from the apparent shape. And the real shape is what interests us as practical men. But the real shape is not what we see. It is something inferred from what we see. And what we see is constantly changing in shape as we move about the room. So that, here again, the senses seem not to give us the truth about the table itself, but only about the appearance of the table. Similar difficulties arise when we consider the sense of touch. It is true that the table always gives us a sensation of hardness, and we feel that it resists pressure. But the sensation we obtain depends on how hard we press the table, and also upon what part of the body we press with. Thus the various sensations, due to various pressures or various parts of the body, cannot be supposed to reveal directly any definite property of the table, but at most to be signs of some property which perhaps causes all the sensations, but is not actually apparent in any of them. And the same applies still more obviously to the sounds which can be elicited by wrapping the table. Thus it becomes evident that the real table, if there is one, is not the same as what we immediately experience by sight or touch or hearing. The real table, if there is one, is not immediately known to us at all, but must be an inference from what is immediately known. Hence, two very difficult questions that once arise. Namely, one, is there a real table at all? Two, if so, what sort of object can it be? It will help us in considering these questions to have a few simple terms of which the meaning is definite and clear. Let us give the name of sense data to the things that are immediately known in sensation, such things as colors, sounds, smells, hardnesses, roughnesses, and so on. We shall give the name sensation to the experience of being immediately aware of these things. Thus, whenever we see a color, we have a sensation of the color, but the color itself is a sense datum, not a sensation. The color is that of which we are immediately aware, and the awareness itself is the sensation. It is plain that if we are to know anything about the table, it must be by means of the sense data, brown color, oblong shapes, smoothness, etc., which we associate with the table. But for the reasons which have been given, we cannot say that the table is the sense data, or even that the sense data are directly properties of the table. Thus a problem arises as to the relation of the sense data to the real table, supposing there is such a thing. The real table, if it exists, we will call a physical object. Thus we have to consider the relation of the sense data to physical objects. The collection of all physical objects is called matter. Thus our two questions may be restated as follows. One, is there any such thing as matter? Two, if so, what is its nature? The philosopher who first brought prominently forward the reasons for regarding the immediate objects of our senses as not existing independently of us was Bishop Berkeley, 1685-1753. His three dialogues between Hylas and Philonoas, in opposition to skeptics and atheists, undertake to prove that there is no such thing as matter at all, and that the world consists of nothing but minds and their ideas. Hylas has hitherto believed in matter, but he has no match for Philonoas, who mercilessly drives him into contradictions and paradoxes and makes his own denial of matter seem in the end as if it were almost common sense. The arguments employed are of very different value. Some are important in sound, others are confused or quibbling. But Berkeley retains the merit of having shown that the existence of matter is capable of being denied without absurdity, and that if there are any things that exist independently of us, they cannot be the immediate objects of our sensations. There are two different questions involved when we ask whether matter exists, and it is important to keep them clear. We commonly mean by matter, something which is opposed to mind, something which we think of as occupying space, and as radically incapable of any sort of thought or consciousness. It is chiefly in this sense that Berkeley denies matter. That is to say, he does not deny that the sense data which we commonly take as signs of the existence of the table are really signs of the existence of something independent of us, but he does deny that this something is non-mental, that it is neither mind nor ideas entertained by some mind. He admits that there must be something which continues to exist when we go out of the room or shut our eyes, and that what we call seeing the table does really give us reason for believing in something which persists even when we are not seeing it. But he thinks that this something cannot be radically different in nature from what we see, and cannot be independent of seeing altogether, though it must be independent of our seeing. He has thus led to regard the real table as an idea in the mind of God. Such an idea has the required permanence and independence of ourselves without being, as matter would otherwise be, something quite unknowable, in the sense that we can only infer it, and can never be directly and immediately aware of it. Other philosophers since Berkeley have also held that, although the table does not depend for its existence upon being seen by me, it does depend upon being seen, or otherwise apprehended in sensation, by some mind, not necessarily the mind of God, but more often the whole collective mind of the universe. This they hold, as Berkeley does, chiefly because they think there can be nothing real, or at any rate nothing known to be real, except minds and their thoughts and feelings. We might state the argument by which they support their view in some such way as this. Whatever can be thought of is an idea in the mind of the person thinking of it. Therefore, nothing can be thought of except ideas and minds. Therefore, anything else is inconceivable, and what is inconceivable cannot exist. Such an argument, in my opinion, is fallacious, and of course those who advance it do not put it so shortly or so crudely. But whether valid or not, the argument has been very widely advanced in one form or another, and very many philosophers, perhaps a majority, have held that there is nothing real except minds and their ideas. Such philosophers are called idealists. When they come to explaining matter, they either say, like Berkeley, that matter is really nothing but a collection of ideas, or they say, like Leibniz, 1646-1716, that what appears as matter is really a collection of more or less rudimentary minds. But these philosophers, though they deny matter as opposed to mind, nevertheless in another sense admit matter. It will be remembered that we ask two questions, namely, one, is there a real table at all? Two, if so, what sort of object can it be? Now both Berkeley and Leibniz admit that there is a real table, but Berkeley says it is certain ideas in the mind of God, and Leibniz says it is a colony of souls. Thus both of them answer our first question in the affirmative, and only diverge from the views of ordinary mortals in their answer to our second question. In fact, almost all philosophers seem to be agreed that there is a real table. They almost all agree that, however much our sense data, color, shapes, moodness, etc., may depend upon us, yet their occurrence is a sign of something existing independently of us, something differing perhaps completely from our sense data, and yet to be regarded as causing those sense data whenever we are in a suitable relation to the real table. Now obviously this point in which the philosophers are agreed, the view that there is a real table, whatever its nature may be, is vitally important, and it will be worthwhile to consider what reasons there are for accepting this view before we go on to the further question as to the nature of the real table. Our next chapter, therefore, will be concerned with the reasons for supposing that there is a real table at all. Before we go farther, it will be well to consider for a moment what it is that we have discovered so far. It has appeared that, if we take any common object or the sort that is supposed to be known by the senses, what the senses immediately tell us is not the truth about the object as it is apart from us, but only the truth about certain sense data, which so far as we can see, depend upon the relations between us and the object. Thus what we directly see and feel is merely appearance, which we believe to be a sign of some reality behind. But if the reality is not what appears, have we any means of knowing whether there is any reality at all? And if so, have we any means of finding out what it is like? Such questions are bewildering, and it is difficult to know that even the strangest hypotheses may not be true. Thus our familiar table, which is roused by the slightest thoughts in us hither too, has become a problem full of surprising possibilities. The one thing we know about it is that it is not what it seems.  Leibniz tells us it is a community of souls. Berkeley tells us it is an idea in the mind of God. Sober science, scarcely less wonderful, tells us that it is a vast collection of electric charges in violent motion. Among these surprising possibilities, doubt suggests that perhaps there is no table at all. Philosophy, if it could not answer so many questions as we could wish, has at least the power of asking questions which increase the interest of the world, and show the strangeness and wonder lying just below the surface, even in the commonest things of daily life. Chapter 2 of The Problems of Philosophy This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit LibriVox.org. The Problems of Philosophy by Bertrand Russell Chapter 2 The Existence of Matter In this chapter, we have to ask ourselves whether in any sense at all there is such a thing as matter. Is there a table which has a certain intrinsic nature and continues to exist when I am not looking? Or is the table merely a product of my imagination? A dream table in a very prolonged dream. This question is of the greatest importance. For if we cannot be sure of the independent existence of objects, we cannot be sure of the independent existence of other people's bodies. And therefore, still less of other people's minds, since we have no grounds for believing in their minds, except such as are derived from observing their bodies. Thus, if we cannot be sure of the independent existence of objects, we shall be left alone in a desert. It may be that the whole outer world is nothing but a dream, and that we alone exist. This is an uncomfortable possibility, but although it cannot be strictly proved to be false, there is not the slightest reason to suppose that it is true. In this chapter, we have to see why this is the case. Before we embark upon doubtful matters, let us try to find some more or less fixed point from which to start. Although we are doubting the physical existence of the table, we are not doubting the existence of the sense data which made us think there was a table. We are not doubting that while we look, a certain color and shape appear to us, and while we press, a certain sensation of hardness is experienced by us. All this, which is psychological, we are not calling in question. In fact, whatever else may be doubtful, some at least of our immediate experiences seem absolutely certain. Descartes 1596-1615, the founder of modern philosophy, invented a method which may still be used with profit, the method of systematic doubt. He determined that he would believe nothing which he did not see quite clearly and distinctly to be true. Whatever he could bring himself to doubt, he would doubt, until he saw reason for not doubting it. By applying this method, he gradually became convinced that the only existence of which he could be quite certain was his own. He imagined a deceitful demon who presented unreal things to his senses in the perpetual phantasmagoria. It might be very improbable that such a demon existed, but still it was possible, and therefore, doubt concerning things perceived by the senses was possible. But doubt concerning his own existence was not possible. For if he did not exist, no demon could deceive him. If he doubted, he must exist. If he had any experiences whatever, he must exist. Thus his own existence was an absolute certainty to him. I think, therefore I am, he said. Kogito ergo sum. And on the basis of this certainty, he said to word to build up again the world of knowledge which his doubt had laid in ruins. By inventing the method of doubt and by showing that subjective things are the most certain, Descartes performed a great service to philosophy. And one which makes him still useful to all students of the subject. But some care is needed in using Descartes argument. I think, therefore I am, says rather more than is strictly certain. It might seem as though we were quite sure of being the same person today as we were yesterday. And this is no doubt true in some sense. But the real self is as hard to arrive at as the real table. And does not seem to have that absolute convincing certainty that belongs to particular experiences. When I look at my table and see a certain brown color, what is quite certain at once is not I'm seeing a brown color, but rather a brown color is being seen. This of course involves something or somebody, which or who sees the brown color. But it does not of itself involves that more or less permanent person whom we call I. So far as immediate certainty goes, it might be that the something which sees the brown color is quite momentary and not the same as the something which has some different experience the next moment. Thus, it is our particular thoughts and feelings that have primitive certainty. And this applies to dreams and hallucinations as well as to normal perceptions. When we dream or see a ghost, we certainly do have the sensations we think we have. But for various reasons, it is held that no physical object corresponds to these sensations. Thus, the certainty of our knowledge of our own experiences does not have to be limited in any way to allow for exceptional cases. Here, therefore, we have for what it is worth a solid basis from which to begin our pursuit of knowledge. The problem we have to consider is this. Granted that we are certain of our own sense data, have we any reason for regarding them as signs of the existence of something else, which we can call the physical object. When we have enumerated all the sense data, which we should naturally regard as connected with the table, have we said all there is to say about the table? Or is there still something else, something not a sense data, something which persists when we go out of the room? Common sense unhesitatingly answers that there is. What can be bought and sold and pushed about and have a clock laid on it, and so on, cannot be a mere collection of sense data. If the clock completely hides the table, we shall derive no sense data from the table. And therefore, if the table were merely sense data, it would have ceased to exist, and the clock would be suspended in empty air, resting biomerical in the place where the table formerly was. This seems plainly absurd, but whoever wishes to become a philosopher must learn not to be frightened by absurdities. One great reason why it is felt that we must secure a physical object in addition to the sense data is that we want the same object for different people. When 10 people are sitting around a dinner table, it seems preposterous to maintain that they are not seeing the same tablecloth, the same knives and forks and spoons and glasses. But the sense data are private to each separate person. What is immediately present to the sight of one is not immediately present to the sight of another. They all see things from slightly different points of view, and therefore see them slightly differently. Thus, if there are to be public neutral objects, which can be in some sense known to many different people, there must be something over and about the private and particular sense data which appeared to various people. What reason then have we for believing that there are such public neutral objects? The first answer that naturally occurs to one is that although different people may see the table slightly differently, still they all see more or less similar things when they look at the table. And the variations in what they see follow the laws of perspective and reflection of life, so that it is easy to arrive at a permanent object underlying all the different people's sense data. I bought my table from the former occupant of my room. I could not buy his sense data, which died when he went away, but I could and did buy the confident expectation of more or less similar sense data. Thus, it is the fact that different people have similar sense data, and that one person in a given place at different times has similar sense data, which makes us suppose that over and above the sense data, there is a permanent public object which underlies or causes the sense data of various people at various times. Now and so far as the above considerations depend upon supposing that there are other people besides ourselves, they beg the very question at issue. Other people are represented to me by certain sense data, such as the sight of them or the sound of their voices. And if I had no reason to believe that there were physical objects independent of my sense data, I should have no reason to believe that other people exist except as part of my dream. Thus, when we are trying to show that there must be objects independent of our own sense data, we cannot appeal to the testimony of other people since this testimony itself consists of sense data and does not reveal other people's experiences unless our own sense data are signs of things existing independently of us. We must therefore, if possible, find in our own purely private experiences characteristics which show or tend to show that there are in the world things other than ourselves and our private experiences. In one sense, it must be admitted that we can never prove the existence of things other than ourselves and our experiences. No logical absurdity results from the hypothesis that the world consists of myself and my thoughts and feelings and sensations and that everything else is mere fancy. In dreams, a very complicated world may seem to be present and yet, on waking, we find it was a delusion. That is to say, we find that the sense data in the dream do not appear to have corresponded with such physical objects as we should naturally infer from our sense data. It is true that when the physical world is assumed, it is possible to find physical causes for the sense data in dreams. A doorbanging, for instance, may cause us to dream of a naval engagement. But although in this case, there is a physical cause for the sense data, there is not a physical object corresponding to the sense data in the way in which an actual naval battle would correspond. There is no logical impossibility in the supposition that the whole of life is a dream, in which we ourselves create all the objects that come before us. But although this is not logically impossible, there is no reason whatever to suppose that it is true. And it is, in fact, a less simple hypothesis, viewed as a means of accounting for the facts of our own life, than the common sense hypothesis that there really are objects independent of us, whose action on us causes our sensations. The way in which simplicity comes in from supposing that there really are physical objects is easily seen. If the cat appears at one moment in one part of the room and at another in another part, it is natural to suppose that it has moved from one to the other, passing over a series of intermediate positions. But if it is merely a set of sense data, it cannot have ever been in any place where I did not see it. Thus, we shall have to suppose that it did not exist at all while I was not looking, but suddenly sprang into being in a new place. If the cat exists, whether I see it or not, we can understand from our own experience how it gets hungry between one meal and the next. But if it does not exist when I am not seeing it, it seems odd that appetite should grow during non-existence as fast as during existence. And if the cat consists only of sense data, it cannot be hungry. Since no hunger, but by own, can be a sense datum to me. Thus, the behavior of the sense data which represents the cat to me, though it seems quite natural when regarded as an expression of hunger, becomes utterly inexplicable when regarded as mere movements and changes of patches of color which are as incapable of hunger as a triangle is of playing football. But the difficulty in the case of the cat is nothing compared to the difficulty in the case of human beings. When human beings speak, that is, when we hear certain noises which we associate with ideas and simultaneously see certain motions of lips and expressions of faith, it is very difficult to suppose that what we hear is not the expression of the thought as we know it would be if we emitted the same sounds. Of course, similar things happen in dreams where we are mistaken as to the existence of other people. But dreams are more or less suggested by what we call waking life and are capable of being more or less accounted for on scientific principles if we assume that there really is a physical world. Thus every principle of simplicity urges us to adopt the natural view that there really are objects other than ourselves and our sense data which have an existence not dependent upon our perceiving them. Of course, it is not my argument that we originally came by our belief in an independent external world. We find this belief ready in ourselves as soon as we begin to reflect. It is what may be called an instinctive belief. We should never have been led to question this belief but for the fact that at any rate in the case of sight it seems as if the sense data itself were instinctively believed to be the independent object. Whereas argument shows that the object cannot be identical with the sense data. This discovery, however, which is not at all paradoxical in the case of case and smell and sound and only slightly so in the case of touch leaves undiminished our instinctive belief that there are objects corresponding to our sense data. Since this belief does not lead to any difficulties but on the contrary tends to simplify and systematize our accounts of our experiences there seems no good reason for rejecting it. We may therefore admit though with a slight doubt derived from dreams that the external world does really exist and is not fully dependent for its existence upon our continuing to perceive it. The argument which has led us to this conclusion is doubtless, less strong than we could wish but it is typical of many philosophical arguments and is therefore worthwhile to consider briefly its general character and validity. All knowledge we find must be built up upon our instinctive beliefs and if these are rejected nothing is left but among our instinctive beliefs some are much stronger than others while many have by habit and association become entangled with other beliefs not really instinctive but falsely supposed to be part of what is believed instinctively. Philosophy should show us the hierarchy of our instinctive beliefs beginning with those we hold most strongly and presenting each as much isolated and as free from irrelevant additions as possible. It should take care to show that in the form in which they are finally set for our instinctive beliefs do not clash but form a harmonious system. There can never be any reason for rejecting one instinctive belief except that it clashes with others thus if they're found to harmonize the whole system becomes worthy of acceptance. It is of course possible that all or any of our beliefs may be mistaken and therefore all ought to be held with at least some slight element of doubt but we cannot have reason to reject a belief except on the ground of some other belief. Hence by organizing our instinctive beliefs and their consequences by considering which among them is most possible if necessary to modify or abandon we can arrive on the basis of accepting as our sole data what we instinctively believe at an orderly systematic organization of our knowledge in which though the possibility of error remains its likelihood is diminished by the interrelation of the parts and by the critical scrutiny which has preceded acquisitions. This function at least philosophy can perform. Most philosophers rightly or wrongly believe that philosophy can do much more than this that it can give us knowledge not otherwise attainable concerning the universe as a whole and concerning the nature of ultimate reality. Whether this be the case or not the more modest function we have spoken of can certainly be performed by philosophy and certainly suffices for those who have once began to doubt the adequacy of common sense to justify the artist and difficult laborers as philosophical problems involve. End of chapter 2 Chapter 3 of The Problems of Philosophy This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer please visit LibriVox.org The Problems of Philosophy by Bertrand Russell Chapter 3 The Nature of Matter In the preceding chapter we agree though without being able to find demonstrative reasons that it is rational to believe that our sense data for example those which we regard as associated with my table are really signs of the existence of something independent of us and our perceptions. That is to say over and above the sensations of color, hardness, noise and so on which make up the appearance of the table to me I assume that there is something else of which these things are appearances. The color ceases to exist if I shut my eyes. The sensation of hardness ceases to exist if I remove my arm from contact with the table. The sound ceases to exist if I cease to wrap the table with my knuckles. But I do not believe that when all these things cease the table ceases. On the contrary I believe that it is because the table exists continuously that all these sense data will reappear when I open my eyes replace my arm and begin again to wrap with my knuckles. The question we have to consider in this chapter is what is the nature of this real table which persists independently of my perception of it. To this question physical science gives an answer somewhat incomplete it is true and in part still very hypothetical but yet deserving of respect so far as it goes. Physical science more or less unconsciously has drifted into the view that all natural phenomena ought to be reduced to motions. Light and heat and sound are all due to wave motions which travel from the body emitting them to the person who sees light or feels heat or hears some. That which has the wave motion is either ether or gross matter but in either case is what the philosopher would call matter. The only properties which science assigns to it are position and space and the power of motion according to the laws of motion. Science does not deny that it may have other properties but if so such other properties are not useful to the man of science and in no way assist him in explaining the phenomena. It is sometimes said that light is a form of wave motion but this is misleading for the light which we immediately see which we know directly by means of our senses is not a form of wave motion but something quite different something which we all know if we are not blind though we cannot describe it so as to convey our knowledge to a man who is blind. A wave motion on the contrary could quite well be described to a blind man since he can acquire a knowledge of space by the sense of touch and he can experience a wave motion by a sea voyage almost as well as we can but this which a blind man can understand is not what we mean by light we mean by light just that which a blind man can never understand and which we can never describe to him now this something which all of us who are not blind know is not according to science really to be found in the outer world it is something caused by the action of certain waves upon the eyes and nerves and brains of the person who sees the light when it is said that light is waves what is really meant is that waves are the physical cause of our sensations of light but light itself the thing which seeing people experience and blind people do not is not supposed by science to form any part of the world that is independent of us and our senses and very similar remarks would apply to other kinds of sensations it is not only colors and sounds and so on that are absent from the scientific world of matter but also space as we get it through sight or touch it is essential to science that its matter should be in a space but the space in which it is cannot be exactly the space we see or feel to begin with space as we see it is not the same as space as we get it by the sense of touch it is only by experience in infancy that we learn how to touch things we see or how to get a sight of things which we feel touching us but the space of science is neutral as between touch and sight thus it cannot be either the space of touch or the space of sight again different people see the same object as of different shapes according to their point of view a circular coin for example though we should always judge it to be circular will look oval unless we are straight in front of it when we judge that it is circular we are judging that it has a real shape which is not its apparent shape but belongs to it intrinsically apart from its appearance but this real shape which is what concerns science must be in a real space not the same as anybody's apparent space the real space is public the apparent space is private to the recipient in different people's private spaces the same object seems to have different shapes thus the real space in which it has its real shape must be different from the private spaces the space of science therefore though connected with the spaces we see and feel is not identical with them and the manner of its connection requires investigation we agreed provisionally that physical objects cannot be quite like our sense data but may be regarded as causing our sensations these physical objects are in the space of science which we may call physical space it is important to notice that if our sensations are to be caused by physical objects there must be a physical space containing these objects and our sense organs and nerves and brain we get a sensation of touch from an object when we are in contact with it that is to say when some part of our body occupies a place in the physical space quite close to the space occupied by the object we see an object roughly speaking when no opaque body is between the object and our eyes in physical space similarly we only hear or smell or taste an object when we are sufficiently near to it or when it touches the tongue or has some suitable position in physical space relatively to our body we cannot begin to state what different sensations we shall derive from a given object under different circumstances unless we regard the object and our body as both in one physical space for it is mainly the relative positions of the object and our body that determine what sensations we shall derive from the object now our sense data are situated in our private spaces either the space of sight or the space of touch or such vaguer spaces as other senses may give us if a science and common sense assume there is one public all embracing physical space in which physical objects are the relative positions of physical objects in physical space must more or less correspond to the relative positions of sense data in our private spaces there is no difficulty in supposing this to be the case if we see on a road one house nearer to us than another our other senses will bear out the view that it is nearer for example it will be reached sooner if we walk along the road other people will agree that the house which looks nearer to us is nearer the ordinance map will take the same view and thus everything points to a spatial relation between the houses corresponding to the relation between the sense data which we see when we look at the houses thus we may assume that there is a physical space in which physical objects have spatial relations corresponding to those which the corresponding sense data have in our private spaces it is this physical space which is dealt with in geometry and assumed in physics and astronomy assuming that there is physical space and that it does correspond to private spaces what can we know about it we can know only what is required in order to secure the correspondence that is to say we can know nothing of what it is like in itself but we can know the sort of arrangement of physical objects which results from their spatial relations we can know for example that the earth and moon and sun are in one straight line during an eclipse though we cannot know what a physical straight line is in itself as we know the look of a straight line in our visual space thus we come to know much more about the relations of distances in physical space than about the distances themselves we may know that one distance is greater than another or that it is along the same straight line as the other but we cannot have that immediate acquaintance with physical distances that we have with distances in our private spaces or with colors or sounds or other sense data we can know all these things about physical space which a man bombed line might know through other people about the space of sight but the kind of things which a man bombed line could never know about the space of sight we also cannot know about physical space we can know the properties of the relations required to preserve the correspondence with sense data but we cannot know the nature of the terms between which the relations hold with regard to time our feeling of duration or of the lapse of time is notoriously an unsafe guide as to the time that has elapsed by the clock times when we are bored or suffering pain pass slowly times when we are agreeably occupied pass quickly and times when we are sleeping pass almost as if they did not exist thus in so far as time is constituted by duration there is the same necessity for distinguishing a public and a private time as there was in the case of space but in so far as time consists in an order of before and after there is no need to make such a distinction the time order which events seem to have is so far as we can see the same as the time order which they do have at any rate no reason can be given for supposing that the two orders are not the same the same is usually true of space if a regiment of men are marching along a road the shape of the regiment will look different from different points of view but the men will appear arranged in the same order from all points of view hence we regard the order as true also in physical space whereas the shape is only supposed to correspond to the physical space so far as is required for the preservation of the order in saying that the time order which events seem to have is the same as the time order which they really have it is necessary to guard against a possible misunderstanding it must not be supposed that the various states of different physical objects have the same time order as the sense data which constitute the perception of those objects considered as physical objects the thunder and lightning are simultaneous that is to say the lightning is simultaneous with the disturbance of the air in the place where the disturbance begins namely where the lightning is but the sense stadium which we call hearing the thunder does not take place until the disturbance of the air has traveled as far as to where we are similarly it takes about eight minutes for the sun's light to reach us thus when we see the sun we are seeing the sun of eight minutes ago so far as our sense data afford evidence as to the physical sun they afford evidence as to the physical sun of eight minutes ago if the physical sun had ceased to exist within the last eight minutes that would make no difference to the sense data which we call seeing the sun this affords a fresh illustration of the necessity of distinguishing between sense data and physical objects what we have found as regards space is much the same as what we find in relation to the correspondence of the sense data with their physical counterparts if one object looks blue and another red we may reasonably presume that there is some corresponding difference between the physical objects if two objects both look blue we may presume a corresponding similarity but we cannot hope to be acquainted directly with the quality in the physical object which makes it look blue or red science tells us that this quality is a certain sort of wave motion and this sounds familiar because we think of wave motions in the space we see but the wave motions must really be in physical space with which we have no direct acquaintance thus the real wave motions have not that familiarity which we might have supposed them to have and what holds for colors is closely similar to what holds for other sense data thus we find that although the relations of physical objects have all sorts of knowable properties derived from their correspondence with the relations of sense data the physical objects themselves remain unknown in their intrinsic nature so far at least as can be discovered by means of the senses the question remains whether there is any other method of discovering the intrinsic nature of physical objects the most natural though not ultimately the most defensible hypothesis to adopt in the first instance at any rate as regards visual sense data would be that though physical objects cannot for the reasons we have been considering be exactly like sense data yet they may be more or less like according to this view physical objects will for example really have colors and we might by good luck see an object as of the color it really is the color which an object seems to have at any given moment will in general be very similar though not quite the same from many different points of view we might thus suppose the real color to be a sort of medium color intermediate between the various shades which appear from the different points of view such a theory is perhaps not capable of being definitely refuted but it can be shown to be groundless to begin with it is plain that the color we see depends only upon the nature of the light waves that strike the eye and is therefore modified by the medium intervening between us and the object as well as by the manner in which the light is reflective from the object in the direction of the eye the intervening air alters colors unless it is perfectly clear and any strong reflection will alter them completely thus the color we see is a result of the ray as it reaches the eye and not simply a property of the object from which the ray comes hence also provided certain waves reach the eye we shall see a certain color whether the object from which the wave start has any color or not thus it is quite gratuitous to suppose that physical objects have colors and therefore there is no justification for making such a supposition exactly similar arguments will apply to other sense data it remains to ask whether there are any general philosophical arguments enabling us to say that if matter is real it must be of such and such a nature as explained above very many philosophers perhaps most have held that whatever is real must be in some sense mental or at any rate that whatever we can know anything about must be in some sense mental such philosophers are called idealists idealists tell us that what appears as matter is really something mental namely either as lightness held more or less rudimentary minds or as Berkeley contended ideas in the minds which as we should commonly say perceive the matter thus idealists deny the existence of matter as something intrinsically different from mind though they do not deny that our sense data are signs of something which exists independently of our private sensations in the following chapter we shall consider briefly the reasons in my opinion fallacious which idealists advance in favor of their theory End of Chapter 3 Chapter 4 of the Problems of Philosophy This is a LibriVox recording All LibriVox recordings are in the public domain For more information or to volunteer please visit LibriVox.org Recording by Rich Meyers The Problems of Philosophy by Bertrand Russell Chapter 4 Idealism The word idealism is used by different philosophers in somewhat different senses We shall understand by it the doctrine that whatever exists or at any rate whatever can be known to exist must be in some sense mental This doctrine which is very widely held among philosophers has several forms and is advocated on several different grounds The doctrine is so widely held and so interesting in itself that even the briefest survey of philosophy must give some account of it Those who are unaccustomed to philosophical speculation may be inclined to dismiss such a doctrine as obviously absurd There is no doubt that common sense regards tables and chairs and the sun and moon and material objects generally as something radically different from minds and the contents of minds and is having an existence which might continue if minds ceased We think of matter as having existed long before there were any minds and it is hard to think of it as a mere product of mental activity But whether true or false idealism is not to be dismissed as obviously absurd We have seen that even if physical objects do have an independent existence they must differ very widely from sense data and can only have a correspondence with sense data in the same sort of way in which a catalog has a correspondence with the things cataloged Hence common sense leaves us completely in the dark as to the true intrinsic nature of physical objects and if there were good reason to regard them as mental we could not legitimately reject this opinion merely because it strikes us as strange The truth about physical objects must be strange It may be unattainable but if any philosopher believes that he has attained it the fact that what he offers as the truth is strange ought not to be made a ground of objection to his opinion The grounds on which idealism is advocated are generally grounds derived from the theory of knowledge that is to say from a discussion of the conditions which things must satisfy in order that we may be able to know them The first serious attempt to establish idealism on such grounds was that of Bishop Barkley He proved first by arguments which were largely valid that our sense data cannot be supposed to have an existence independent of us but must be impart at least in the mind in the sense that their existence would not continue if there were no seeing or hearing or touching or smelling or tasting So far, his contention was almost certainly valid even if some of his arguments were not so but he went on to argue that sense data were the only things of whose existence our perceptions could assure us and that to be known is to be in a mind and therefore to be mental Hence, he concluded that nothing can ever be known except what is in some mind and that whatever is known without being in my mind must be in some other mind In order to understand his argument it is necessary to understand his use of the word idea He gives the name idea to anything which is immediately known as, for example, sense data are known Thus, a particular color which we see is an idea So is a voice which we hear and so on But the term is not wholly confined to sense data There will also be things remembered or imagined for with such things also we have immediate acquaintance at the moment of remembering or imagining All such immediate data he calls ideas He then proceeds to consider common objects such as a tree, for instance He shows that all we know immediately when we perceive the tree consists of ideas in his sense of the word And he argues that there is not the slightest ground for supposing that there is anything real about the tree except what is perceived Its being, he says, consists in being perceived In the Latin of the schoolmen its essay is per kipi He fully admits that the tree must continue to exist even when we shut our eyes or when no human being is near it But this continued existence, he says, is due to the fact that God continues to perceive it The real tree, which corresponds to what we call the physical object, consists of ideas in the mind of God Ideas more or less like those we have when we see the tree but differing in the fact that they are permanent in God's mind so long as the tree continues to exist All our perceptions according to him consist in a partial participation in God's perceptions and it is because of this participation that different people see more or less the same tree Thus, apart from minds and their ideas there is nothing in the world nor is it possible that anything else should ever be known since whatever is known is necessarily an idea There are in this argument a good many fallacies which have been important in the history of philosophy and which it will be as well to bring to light In the first place, there is a confusion engendered by the use of the word idea We think of an idea as essentially something in somebody's mind and thus when we are told that a tree consists entirely of ideas it is natural to suppose that, if so, the tree must be entirely in minds But the notion of being in the mind is ambiguous We speak of bearing a person in mind not meaning that the person is in our minds but that a thought of him is in our minds When a man says that some business he had to arrange went clean out of his mind he does not mean to imply that the business itself was ever in his mind but only that a thought of the business was formally in his mind but afterwards ceased to be in his mind And so, when Barkley says that the tree must be in our minds if we can know it all that he really has a right to say is that a thought of the tree must be in our minds To argue that the tree itself must be in our minds is like arguing that a person whom we bear in mind is himself in our minds This confusion may seem too gross to have been really committed by any competent philosopher but various attendant circumstances rendered it possible In order to see how it was possible we must go more deeply into the question as to the nature of ideas Before taking up the general question of the nature of ideas we must disentangle two entirely separate questions which arise concerning sense data and physical objects We saw that for various reasons of detail Barkley was right in treating the sense data which constitutes our perception of the tree as more or less subjective in the sense that they depend upon us as much as upon the tree and would not exist if the tree were not being perceived But this is an entirely different point from the one by which Barkley seeks to prove that whatever can be immediately known must be in a mind For this purpose, arguments of detail as to the dependence of sense data upon us are useless It is necessary to prove generally that by being known things are shown to be mental This is what Barkley believes himself to have done It is this question and not our previous question as to the difference between sense data and the physical object that must now concern us Taking the word idea in Barkley's sense there are two quite distinct things to be considered whenever an idea is before the mind There is on the one hand the thing of which we are aware say the color of my table and on the other hand the actual awareness itself the mental act of apprehending the thing The mental act is undoubtedly mental But is there any reason to suppose that the thing apprehended is in any sense mental? Our previous arguments concerning the color did not prove it to be mental They only proved that its existence depends upon the relation of our sense organs to the physical object in our case the table That is to say they proved that a certain color will exist in a certain light if a normal eye is placed at a certain point relatively to the table They did not prove that the color is in the mind of the recipient Barkley's view that obviously the color must be in the mind seems to depend for its plausibility upon confusing the thing apprehended with the act of apprehension Either of these might be called an idea probably either would have been called an idea by Barkley The act is undoubtedly in the mind hence when we are thinking of the act we readily assent to the view that ideas must be in the mind Then forgetting that this was only true when ideas were taken as acts of apprehension we transfer the proposition that ideas are in the mind to ideas in the other sense i.e. to the things apprehended by our acts of apprehension Thus by an unconscious equivocation we arrive at the conclusion that whatever we can apprehend must be in our minds This seems to be the true analysis of Barkley's argument and the ultimate fallacy upon which it rests This question of the distinction between act and object in our apprehending of things is vitally important since our whole power of acquiring knowledge is bound up with it The faculty of being acquainted with things other than itself is the main characteristic of a mind acquaintance with objects essentially consists in a relation between the mind and something other than the mind It is this that constitutes the mind's power of knowing things If we say that the things known must be in the mind we are either unduly limiting the mind's power of knowing or we are uttering a mere tautology We are uttering a mere tautology if we mean by in the mind the same as by before the mind i.e. if we mean merely being apprehended by the mind But if we mean this we shall have to admit that what in this sense is in the mind may nevertheless be not mental Thus when we realize the nature of knowledge Barkley's argument is seen to be wrong in substance as well as in form and his grounds for supposing that ideas i.e. the objects apprehended must be mental are found to have no validity whatever Hence his grounds in favor of idealism may be dismissed It remains to see whether there are any other grounds It is often said, as though it were a self-evident truism that we cannot know that anything exists which we do not know It is inferred that whatever can in any way be relevant to our experience must be at least capable of being known by us Once it follows that, if matter were essentially something with which we could not become acquainted matter would be something which we could not know to exist and which could have for us no importance whatever It is generally also implied for reasons which remain obscure that what can have no importance for us cannot be real and that therefore matter if it is not composed of minds or of mental ideas is impossible and a mere chimera To go into this argument fully at our present stage would be impossible since it raises points requiring a considerable preliminary discussion But certain reasons for rejecting the argument may be noticed at once To begin at the end there is no reason why what cannot have any practical importance for us should not be real It is true that if theoretical importance is included everything real is of some importance to us since as persons desirous of knowing the truth about the universe we have some interest in everything that the universe contains But if this sort of interest is included it is not the case that matter has no importance for us provided it exists even if we cannot know that it exists We can obviously suspect that it may exist and wonder whether it does Hence it is connected with our desire for knowledge and has the importance of either satisfying or thwarting this desire Again, it is by no means a truism and is in fact false that we cannot know that anything exists which we do not know The word know is here used in two different senses One in its first use it is applicable to the sort of knowledge which is opposed to error the sense in which what we know is true the sense which applies to our beliefs and convictions i.e. to what are called judgments In this sense of the word we know that something is the case this sort of knowledge may be described as knowledge of truths Two, in the second use of the word know above the word applies to our knowledge of things which we may call acquaintance This is the sense in which we know sense data the distinction involved is roughly that between Sabois and Conatra in French or between Wiesen and Kennen in German Thus the statement which seemed like a truism becomes when restated the following We can never truly judge that something with which we are not acquainted exists This is by no means a truism but on the contrary a palpable falsehood I have not the honor to be acquainted with the emperor of China but I truly judge that he exists It may be said of course that I judge this because of other people's acquaintance with him This however would be an irrelevant retort since if the principle were true I could not know that anyone else is acquainted with him But further there is no reason why I should not know of the existence of something with which nobody is acquainted This point is important and demands elucidation If I am acquainted with the thing which exists my acquaintance gives me the knowledge that it exists But it is not true that conversely whenever I can know that a thing of a certain sort exists I or someone else must be acquainted with the thing What happens in cases where I have true judgment without acquaintance is that the thing is known to me by description and that in virtue of some general principle the existence of a thing answering to this description can be inferred from the existence of something with which I am acquainted In order to understand this point fully it will be well first to deal with the difference between knowledge by acquaintance and knowledge by description and then to consider what knowledge of general principles if any has the same kind of certainty as our knowledge of the existence of our own experiences These subjects will be dealt with in the following chapters End of chapter four Chapter five of the Problems of Philosophy This is a LibriVox recording All LibriVox recordings are in the public domain For more information or to volunteer please visit LibriVox.org The Problems of Philosophy By Bertrand Russell Chapter five Knowledge by acquaintance and knowledge by description In the preceding chapter we saw that there are two sorts of knowledge knowledge of things and knowledge of truths In this chapter we shall be concerned exclusively with knowledge of things of which in turn we shall have to distinguish two kinds Knowledge of things when it is of the kind we call knowledge by acquaintance is essentially simpler than any knowledge of truths and logically independent of knowledge of truths though it would be rash to assume that human beings ever in fact have acquaintance with things without at the same time knowing some truth about them Knowledge of things by description on the contrary always involves as we shall find in the course of the present chapter some knowledge of truths as its source and ground but first of all we must make clear what we mean by acquaintance and what we mean by description we shall say that we have acquaintance with anything of which we are directly aware without the intermediary of any process of inference or any knowledge of truths thus in the presence of my table I am acquainted with a sense data that make up the appearance of my table its color shape hardness smoothness etc all these are things of which I am immediately conscious when I am seeing and touching my table the particular shade of color that I am seeing may have many things said about it I may say that it is brown that it is rather dark and so on but such statements though they make me know truths about the color do not make me know the color itself any better than I did before so far as concerns knowledge of the color itself as opposed to knowledge of truths about it I know the color perfectly and completely when I see it and no further knowledge of it itself is even theoretically possible thus the sense data which make up the appearance of my table are things with which I have acquaintance things immediately known to me just as they are my knowledge of the table as a physical object on the contrary is not direct knowledge such as it is it is obtained through acquaintance with the sense data that make up the appearance of the table we have seen that it is possible without absurdity to doubt whether there is a table at all whereas it is not possible to doubt the sense data my knowledge of the table is of the kind which we shall call knowledge by description the table is the physical object which causes such and such sense data this describes the table by means of the sense data in order to know anything at all about the table we must know truths connecting it with things with which we have acquaintances we must know that such and such sense data are caused by a physical object there is no state of mind in which we are directly aware of the table all our knowledge of the table is really knowledge of truths and the actual thing which is the table is not strictly speaking known to us at all we know a description and we know that there is just one object to which this description applies though the object itself is not directly known to us in such a case we say that our knowledge of the object is knowledge by description all our knowledge both knowledge of things and knowledge of truths rests upon acquaintance as its foundation it is therefore important to consider what kinds of things there are with which we have acquaintance sense data as we have already seen are among the things with which we are acquainted in fact they supply the most obvious and striking example of knowledge by acquaintance but if they were the sole example our knowledge would be very much more restricted than it is we should only know what it is now present to our senses we could not know anything about the past not even that there was a past nor could we know any truths about our sense data for all knowledge of truths as we shall show demands acquaintance with things which are of and essentially different character from sense data the things which are sometimes called abstract ideas but which we shall call universals we have therefore to consider acquaintance with other things besides sense data if we are to obtain any tolerable adequate analysis of our knowledge the first extension beyond sense data to be considered is acquaintance by memory it is obvious that we often remember that we have seen or heard or had otherwise present to our senses and that in such cases we are still immediately aware of what we remember in spite of the fact that it appears as past and not as present this immediate knowledge by memory is the source of all our knowledge concerning the past without it there could be no knowledge of the past by inference since we should never know that there was anything passed to be inferred the next extension to be considered is acquaintance by introspection we are not only aware of things but we are often aware of being aware of them when i see the sun i am often aware of my seeing the sun thus my seeing the sun is an object with which i have acquaintance when i desire food i may be aware of my desire for food thus my desiring food is an object with which i am acquainted similarly we may be aware of our feeling pleasure or pain and generally of the events which happen in our minds this kind of acquaintance which may be called self-consciousness is the source of all our knowledge of mental things it is obvious that it is only what goes on in our own minds that can be thus known immediately what goes on in the minds of others is known to us through our perception of their bodies that is through the sense data in us which are associated with their bodies but for our acquaintance with the contents of our own minds we should be unable to imagine the minds of others and therefore we could never arrive at the knowledge that they have minds it seems natural to suppose that self-consciousness is one of the things that distinguish men from animals animals we may suppose though they have acquaintance with sense data never become aware of this acquaintance i do not mean that they doubt whether they exist but that they have never become conscious of the fact that they have sensations and feelings nor therefore of the fact that they the subject of their sensations and feelings exist we have spoken of acquaintance with the contents of our minds as self-consciousness but it is not of course consciousness of our self it is consciousness of particular thoughts and feelings the question whether we are also acquainted with our bare selves as opposed to particular thoughts and feelings is a very difficult one upon which it would be rash to speak positively when we try to look into ourselves we always seem to come upon some particular thought or feeling and not upon the i which has the thought or feeling nevertheless there are some reasons for thinking that we are acquainted with the i though the acquaintance is hard to disentangle from other things to make clear what sort of reason there is let us consider for a moment what our acquaintance with particular thoughts really involves when i am acquainted with my seeing the sun it seems plain that i am acquainted with two different things in relation to each other on the one hand there is the sense datum which represents the sun to me on the other hand there is that which sees this sense datum all acquaintance such as my acquaintance with a sense datum which represents the sun seems obviously a relation between the person acquainted and the object with which the person is acquainted when a case of acquaintance is one with which i can be acquainted as i am acquainted with my acquaintance with a sense datum representing the sun it is plain that the person acquainted is myself thus when i am acquainted with my seeing the sun, the whole fact with which I am acquainted is, self acquainted with sense datum. Further, we know the truth, I am acquainted with this sense datum. It is hard to see how we could know this truth or even understand what is meant by it, unless we are acquainted with something which we call, I. It does not seem necessary to suppose that we are acquainted with a more or less permanent person, the same today as yesterday, but it does seem as though we must be acquainted with that thing, whatever its nature, which sees the sun and has acquaintance with a sense data. Thus, in some sense, it would seem we must be acquainted with ourselves as opposed to our particular experiences. But the question is difficult, and complicated arguments can be adduced on either side. Hence, although acquaintance with ourselves seems probably to occur, it is not wise to assert that it undoubtedly does occur. We may therefore sum up as follows what has been said concerning acquaintance with things that exist. We have acquaintance in sensation with the data of the outer senses, and in introspection with the data of what may be called the inner sense, thoughts, feelings, desires, etc. We have acquaintance in memory with things which have been data either of the outer senses or of the inner sense. Whether it is probable, though not certain, that we have acquaintance with self as that which is aware of things or has desires towards things. In addition to our acquaintance with particular existing things, we also have acquaintance with what we shall call universals, that is to say, general ideas such as whiteness, diversity, brotherhood, and so on. Every complete sentence must contain at least one word which stands for a universal, since all verbs have a meaning which is universal. We shall return to universals later on in Chapter 9. For the present it is only necessary to guard against the supposition that whatever we can be acquainted with must be something particular and existent. Awareness of universals is called conceiving, and a universal of which we are aware is called a concept. It will not be seen that among the objects with which we are acquainted are not included physical objects as opposed to sense data nor other people's minds. These things are known to us by what I call knowledge by description which we must now consider. By a description I mean any phrase of the form a so-and-so or the so-and-so. A phrase of the form a so-and-so I shall call an ambiguous description. A phrase of the form the so-and-so in the singular I shall call a definite description. Thus a man is an ambiguous description and the man with the iron mask is a definite description. There are various problems connected with ambiguous descriptions, but I pass them by since they do not directly concern the matter we are discussing, which is the nature of our knowledge concerning objects in cases where we know that there is an object answering to a definite description, though we are not acquainted with any such object. This is a matter which is concerned exclusively with definite descriptions. I shall therefore in the sequel speak simply of descriptions when I mean definite descriptions. Thus a description will mean any phrase of the form the so-and-so in the singular. We shall say that an object is known by description when we know that it is the so-and-so, i.e. when we know that there is one object and no more having a certain property, and it will generally be implied that we do not have knowledge of the same object by acquaintance. We know that the man with the iron mask existed and many propositions are known about him, but we do not know who he was. We know that the candidate who gets the most votes will be elected, and in this case we are very likely also acquainted, in the only sense in which one can be acquainted with someone else, with the man who is in fact the candidate who will get most votes, but we do not know which of the candidates he is, i.e. we do not know any proposition of the form A is the candidate who will get most votes, where A is one of the candidates by name. We shall say that we have merely descriptive knowledge of the so-and-so, when, although we know that the so-and-so exists, and although we may possibly be acquainted with the object which is, in fact, the so-and-so, yet we do not know any proposition A is a so-and-so, where A is something with which we are acquainted. When we say the so-and-so exists, we mean that there is just one object which is the so-and-so. The proposition A is the so-and-so, means that A has the property so-and-so and nothing else has. Mr. A is the Unionist candidate for this constituency, means Mr. A is a Unionist candidate for this constituency and no one else is. The Unionist candidate for this constituency exists, means someone is a Unionist candidate for this constituency and no one else is. Thus, when we are acquainted with an object which is the so-and-so, we know that the so-and-so exists, but we may know that the so-and-so exists when we are not acquainted with any object which we know to be the so-and-so, and even when we are not acquainted with any object which, in fact, is the so-and-so. Common words, even proper names, are usually, really, descriptions. That is to say, the thought in the mind of a person using a proper name correctly can generally only be expressed explicitly if we replace the proper name by a description. Moreover, the description required to express the thought will vary for different people or for the same person at different times. The only thing constant, so long as the name is rightly used, is the object to which the name applies. But so long as this remains constant, the particular description involved usually makes no difference to the truth or falsehood of the proposition in which the name appears. Let us take some illustrations. Suppose some statement made about Bismarck. Assuming that there is such a thing as direct acquaintance with oneself, Bismarck himself might have used his name directly to designate the particular person with whom he was acquainted. In this case, if he made a judgment about himself, he himself might be a constituent of the judgment. Here the proper name has the direct use which it always wishes to have as simply standing for a certain object and not for a description of the object. But if a person who knew Bismarck made a judgment about him, the case is different. What this person was acquainted with were certain sense data which he connected, rightly we will suppose, with Bismarck's body. His body as a physical object and still more his mind were only known as the body and the mind connected with these sense data. That is, they were known by description. It is, of course, very much a matter of chance which characteristics of a man's appearance will come into a friend's mind when he thinks of him. Thus, the description actually in the friend's mind is accidental. The essential point is that he knows that the various descriptions all apply to the same entity in spite of not being acquainted with the entity in question. When we, who did not know Bismarck, make a judgment about him, the description in our minds will probably be some more or less vague mass of historical knowledge, far more in most cases than is required to identify him. But, for the sake of illustration, let us assume that we think of him as the first Chancellor of the German Empire. Here, all the words are abstract except German. The word German will, again, have different meanings for different people. To some, it will recall travels in Germany, to some the look of Germany on the map, and so on. But if we are to obtain a description which we know to be applicable, we shall be compelled at some point to bring in a reference to a particular with which we are acquainted. Such reference is involved in any mention of past, present, and future, as opposed to definite dates, or of here and there, or of what others have told us. Thus, it would seem that, in some way or other, a description known to be applicable to a particular must involve some reference to a particular with which we are acquainted if our knowledge about the thing described is not to be merely what follows logically from the description. For example, the most long lived of men is a description involving only universals, which must apply to some men, but we can make no judgments concerning this men which involve knowledge about him beyond what the description gives. If, however, we say, the first Chancellor of the German Empire was an astute diplomatist, we can only be assured of the truth of our judgment in virtue of something with which we are acquainted, usually a testimony heard or read. Apart from the information we convey to others, apart from the fact about the actual Bismarck which gives importance to our judgment, the thought we really have contains the one or more particulars involved, and otherwise consists wholly of concepts. All names of places, London, England, Europe, the Earth, the Solar System, similarly involve, when used, descriptions which start from someone or more particulars with which we are acquainted. I suspect that even the universe as considered by metaphysics involves such a connection with particulars. In logic, on the contrary, where we are concerned not merely with what does exist but with whatever might or could exist or be, no reference to actual particulars is involved. It would seem that when we make a statement about something only known by description we often intend to make our statement, not in the form involving the description, but about the usual thing described. That is to say, when we say anything about Bismarck we should like, if we could, to make the judgment which Bismarck alone can make, namely the judgment of which he himself is a constituent. In this we are necessarily defeated since the actual Bismarck is unknown to us, but we know that there is an object, B, called Bismarck, and that B was an astute diplomatist. We can thus describe the proposition we should like to affirm, namely, B was an astute diplomatist, where B is the object which was Bismarck. If we are describing Bismarck as the first Chancellor of the German Empire, the proposition we should like to affirm may be described as the proposition asserting concerning the actual object which was the first Chancellor of the German Empire, that this object was an astute diplomatist. What enables us to communicate in spite of the varying descriptions we employ is that we know there is a true proposition concerning the actual Bismarck, and that however we may vary the description, so long as the description is correct, the proposition described is still the same. This proposition which is described and is known to be true is what interests us, but we are not acquainted with the proposition itself, and do not know it, though we know it is true. It will be seen that there are various stages in the removal from acquaintance with particulars. There is Bismarck to people who knew him, Bismarck to those who only know of him through history, the man with the iron mask, the longest lived of men. These are progressively further removed from acquaintance with particulars. The first comes as near to acquaintance as is possible in regard to another person. In the second, we shall still be said to know who Bismarck was. In the third, we do not know who was the man with the iron mask, though we can know many propositions about him which are not logically deducible from the fact that he wore an iron mask. In the fourth, finally, we know nothing beyond what is logically deducible from the definition of the man. There is a similar hierarchy in the region of universals. Many universals, like many particulars, are only known to us by description. But here, as in the case of particulars, knowledge concerning what is known by description is ultimately reducible to knowledge concerning what is known by acquaintance. The fundamental principle in the analysis of propositions containing descriptions is this. Every proposition which we can understand must be composed wholly of constituents with which we are acquainted. We shall not, at this stage, attempt to answer all the objections which may be urged against this fundamental principle. For the present, we shall merely point out that, in some way or other, it must be possible to meet these objections, for it is scarcely conceivable that we can make a judgment or entertain a supposition without knowing what it is that we are judging or supposing about. We must attach some meaning to the words we use if we are to speak significantly and not utter mere noise, and the meaning we attach to our words must be something with which we are acquainted. Thus, when, for example, we make a statement about Julius Caesar, it is plain that Julius Caesar himself is not before our minds since we are not acquainted with him. We have, in mind, some description of Julius Caesar, the man who was assassinated on the Ides of March, the founder of the Roman Empire, or perhaps merely the man whose name was Julius Caesar. In this last description, Julius Caesar is a noise or shape with which we are acquainted. Thus our statement does not mean quite what it seems to mean, but means something involving instead of Julius Caesar, some description of him which is composed wholly of particulars and universals with which we are acquainted. The chief importance of knowledge by description is that it enables us to pass beyond the limits of our private experience. In spite of the fact that we can only know truths which are wholly composed of terms, which we have experienced in acquaintance, we can yet have knowledge by description of things which we have never experienced. In view of the very narrow range of our immediate experience, this result is vital, and until it is understood, much of our knowledge must remain mysterious, and therefore doubtful. End of chapter 5 Knowledge by acquaintance and knowledge by description. Chapter 6 of the Problems of Philosophy. This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer, please visit librivox.org. Recording by Jim Eastman. The Problems of Philosophy by Bertrand Russell Chapter 6 on Induction. In almost all our previous discussions, we have been concerned in the attempt to get clear as to our data in the way of knowledge of existence. What things are there in the universe whose existence is known to us owing to our being acquainted with them. So far our answer has been that we are acquainted with our sense data and probably with ourselves. These we know to exist. And past sense data, which I remembered, are known to have existed in the past. This knowledge supplies our data. But if we are to be able to draw inferences from these data, if we are to know of the existence of matter of other people, of the past before our individual memory begins, or of the future, we must know general principles of some kind by means of which inferences can be drawn. It must be known to us that the existence of some one sort of thing A is a sign of the existence of some other sort of thing B. Either at the same time as A, or at some earlier or later time, as for example, thunder is a sign of the earlier existence of lightning. If this were not known to us, we could never extend our knowledge beyond the sphere of our private experience. And this sphere, as we have seen, is exceedingly limited. The question we have now to consider is whether such an extension is possible, and if so, how it is affected. Let us take as an illustration a matter about which none of us, in fact, feel the slightest doubt. We are all convinced that the sun will rise tomorrow. Why? Is this belief a mere blind outcome of past experience, or can it be justified as a reasonable belief? It is not easy to find a test by which to judge whether a belief of this kind is reasonable or not, but we can at least ascertain what sort of general beliefs would suffice, if true, to justify the judgment that the sun will rise tomorrow, and the many other similar judgments upon which our actions are based. It is obvious that if we are asked why we believe that the sun will rise tomorrow, we shall naturally answer because it always has risen every day. We have a firm belief that will rise in the future because it has risen in the past. If we are challenged as to why we believe that it will continue to rise as here to fore, we may appeal to the laws of motion. The earth, we shall say, is a freely rotating body, and such bodies do not cease to rotate unless something interferes from outside. And there is nothing outside to interfere with the earth between now and tomorrow. Of course it might be doubted whether we are quite certain that there is nothing outside to interfere, but this is not the interesting doubt. The interesting doubt is as to whether the laws of motion will remain in operation until tomorrow. If this doubt is raised, we find ourselves in the same position as when the doubt about the sun rise was first raised. The only reason for believing the laws of motion will remain in operation is that they have operated hitherto, so far as our knowledge of the past enables us to judge. It is true that we have a greater body of evidence from the past in favor of the laws of motion than we have in favor of the sun rise, because the sunrise is merely a particular case of fulfillment of the laws of motion, and there are countless other particular cases. But the real question is, do any number of cases of a law being fulfilled in the past afford evidence that it will be fulfilled in the future? If not, it becomes plain that we have no ground whatever for expecting the sun to rise tomorrow, or for expecting the bread we shall eat at our next meal not to poison us, or for any of the other scarcely conscious expectations that control our daily lives. It is to be observed that all such expectations are only probable. Thus, we have not to seek for a proof that they must be fulfilled, but only for some reason in favor of the view that they are likely to be fulfilled. Now, in dealing with this question we must, to begin with, make an important distinction without which we should soon become involved in hopeless confusions. Experience has shown us that hitherto, the frequent repetition of some uniform succession or coexistence has been a cause of our expecting the same succession or coexistence on the next occasion. Food that has a certain appearance generally has a certain taste and it is a severe shock to our expectations when the familiar appearance is found to be associated with an unusual taste. Things which we see become associated by habit with certain tactile sensations which we expect if we touch them. One of the horrors of a ghost in many ghost stories is that it fails to give us any sensations of touch. Uneducated people who go abroad for the first time are so surprised as to be incredulous when they find their native language is not understood and this kind of association is not confined to men. In animals also it is very strong. A horse which has been often driven along a certain road resists the attempt to drive him in a different direction. Domestic animals expect food when they see the person who usually feeds them. We know that all these rather crude expectations of uniformity are liable to be misleading. The man who has fed the chicken every day throughout its life at last rings its neck instead showing that more refined views as to the uniformity of nature would have been useful to the chicken. But in spite of the misleadingness of such expectations they nevertheless exist. The mere fact that something has happened a certain number of times causes animals and men to expect that it will happen again. Thus our instincts certainly cause us to believe that the sun will rise tomorrow but we may be in no better opposition than the chicken which unexpectedly has its neck rung. We have therefore to distinguish the fact that past uniformities cause expectations as to the future. From the question whether there is any reasonable ground for giving weight to such expectations after the question of the validity has been raised. The problem we have to discuss is whether there is any reason for believing in what is called the uniformity of nature. The belief in the uniformity of nature is the belief that everything that has happened or will happen is an instance of some general law to which there are no exceptions. The crude expectations which we have been considering are all subject to exceptions and therefore liable to disappoint those who entertain them. But science habitually assumes at least as a working hypothesis that general rules which have exceptions can be replaced by general rules which have no exceptions. Unsupported bodies in air fall is a general rule to which balloons and aeroplanes are exceptions. But the laws of motion and the law of gravitation which account for the fact that most bodies fall also account for the fact that balloons and aeroplanes can rise. Thus the laws of motion and the law of gravitation are not subject to these exceptions. The belief that the sun will rise tomorrow might be falsified if the earth came suddenly into contact with a large body which destroyed its rotation. But the laws of motion and the law of gravitation would not be infringed by such an event. The business of science is to find uniformities such as the laws of motion and the law of gravitation to which so far as our experience extends there are no exceptions. In this search science has been remarkably successful and it may be conceded that such uniformities have held hitherto. This brings us back to the question have we any reason assuming that they have always held in the past to suppose that they will hold in the future. It has been argued that we have reason to know that the future will resemble the past because what was the future has constantly become the past and has always been found to resemble the past so that we really have experience of the future namely of the times which were formerly future which we may call past futures. But such an argument really begs the very question at issue. We have experience of past futures but not of future futures and the question is will future futures resemble past futures? This question is not to be answered by an argument which starts from past futures alone. We have therefore still to see for some principle which shall enable us to know that the future will follow the same laws as the past. The reference to the future in this question is not essential. The same question arises when we apply the laws that work in our experience to past things in which we have no experience as for example in geology or in theories as to the origin of the solar system. The question we really have to ask is when two things have been found to be often associated and no instance is known of the one occurring without the other does the occurrence of one of the two in a fresh instance give any good ground for expecting the other? On our answer to this question must depend the validity of the whole of our expectations as to the future the whole of the results obtained by induction and in fact practically all the beliefs upon which our daily life is based. It must be conceded to begin with that the fact that two things have been found often together and never apart does not by itself suffice to prove demonstratively that they will be found together in the next case we examine. The most we can hope is that the oftener things are found together the more probable it becomes that they will be found together another time and that if they have been found together often enough the probability will amount almost to certainty. It can never quite reach certainty because we know that in spite of frequent repetitions there sometimes is a failure at the last as in the case of the chicken whose neck is wrong. Thus probability is all we ought to seek. It might be urged as against the view we are advocating that we know all natural phenomena to be subject to the reign of law and that sometimes on the basis of observation we can see that only one law can possibly fit the facts of the case. Now to this view there are two answers. The first is that even if some law which has no exceptions applies to our case we can never in practice be sure that we have discovered that law and not one to which there are exceptions. The second is that the reign of law would seem to be itself only probable and that our belief that it will hold in the future or in unexamined cases in the past is itself based upon the very principle we are examining. The principle we are examining may be called the principle of induction and its two parts may be stated as follows. A. When a thing of a certain sort A has been found to be associated with a thing of a certain other sort B and has never been found dissociated from a thing of the sort B the greater the number of cases in which A and B have been associated the greater is the probability that they will be associated in a fresh case in which one of them is known to be present. B. Under the same circumstances a sufficient number of cases of association will make the probability of a fresh association nearly a certainty and will make it approach certainty without limit. As just stated the principle applies only to the verification of our expectation in a single fresh instance but we want also to know that there is a probability in favor of the general law that things of the sort A are always associated with things of the sort B provided a sufficient number of cases of association are known and no cases of failure of association are known. The probability of the general law is obviously less than the probability of the particular case since if the general law is true the particular case must also be true whereas the particular case may be true without the general law being true. Nevertheless the probability of the general law is increased by repetitions just as the probability of the particular cases. We may therefore repeat the two parts of our principle as regards to the general law thus. A. The greater the number of cases in which a thing of the sort A has been found associated with a thing of the sort B the more probable it is if no cases of failure of association are known that A is always associated with B. B. Under the same circumstances a sufficient number of cases of the association of A with B will make it nearly certain that A is always associated with B and will make this general law approach certainty without limit. It should be noted that probability is always relative to certain data. In our case the data are merely the known cases of coexistence of A and B. There may be other data which might be taken into account which would gravely alter the probability. For example a man who had seen a great many white swans might argue by our principle that on the data it was probable that all swans were white and this might be a perfectly sound argument. The argument is not disproved by the fact that some swans are black because a thing may very well happen in spite of the fact that some data render it improbable. In the case of the swans a man might know the color is a very variable characteristic in many species of animals and that therefore an induction as to color is peculiarly liable to error but this knowledge would be a fresh datum by no means proving that the probability relatively to our previous data had been wrongly estimated. The fact therefore that things often fail to fulfill our expectations is no evidence that our expectations will not probably be fulfilled in a given case or a given class of cases thus our inductive principle is at any rate not capable of being disproved by an appeal to experience. The inductive principle however is equally incapable of being proved by an appeal to experience. Experience might conceivably confirm the inductive principle as regards the cases that have been already examined but as regards unexamined cases it is the inductive principle alone that can justify any inference from what has been examined to what has not been examined. All arguments which on the basis of experience argue as to the future or the unexperienced parts of the past or present assume the inductive principle hence we can never use experience to prove the inductive principle without begging the question. Thus we must either accept the inductive principle on the ground of its intrinsic evidence or forego all justification of our expectations about the future. If the principle is unsound we have no reason to expect the sun to rise tomorrow to expect bread to be more nourishing than a stone or to expect that if we throw ourselves off the roof we shall fall. When we see what looks like our best friend approaching us we shall have no reason to suppose that his body is not inhabited by the mind of our worst enemy or of some total stranger. All our conduct is based upon associations which have worked in the past and which we therefore regard as likely to work in the future and this likelihood is dependent for its validity upon the inductive principle. The general principles of science such as the belief in the reign of law and the belief that every event must have a cause are as completely dependent upon the inductive principle as are the beliefs of daily life. All such general principles are believed because mankind have found innumerable instances of their truth and no instances of their falsehood. But this affords no evidence for their truth in the future unless the inductive principle is assumed. Thus, all knowledge which on a basis of experience tells us something about what is not experienced is based upon a belief which experience can neither confirm nor confute yet which at least in its more concrete applications appears to be as firmly rooted in us as many of the facts of experience. The existence and justification of such beliefs for the inductive principle as we shall see is not the only example raises some of the most difficult and most debated problems of philosophy. We will in the next chapter consider briefly what may be said to account for such knowledge and what is its scope and its degree of certainty. End of chapter 6 Chapter 7 of The Problems of Philosophy This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer go to LibriVox.org The Problems of Philosophy by Bertrand Russell Chapter 7 On Our Knowledge of General Principles We saw in the preceding chapter that the principle of induction while necessary to the validity of all arguments based on experience is itself not capable of being proved by experience and yet is unhesitatingly believed by everyone at least in all its concrete applications. In these characteristics the principle of induction does not stand alone. There are a number of other principles which cannot be proved or disproved by experience but are used in arguments which start from what is experienced. Some of these principles have even greater evidence than the principle of induction and the knowledge of them has the same degree of certainty as the knowledge of the existence of sense data. They constitute the means of drawing inferences from what is given in sensation and if what we infer is to be true it is just as necessary that our principles of inference should be true as it is that our data should be true. The principles of inference are apt to be overlooked because of their very obviousness. The assumption involved is assented to without our realizing that it is an assumption but it is very important to realize the use of principles in inference if a correct theory of knowledge is to be obtained for our knowledge of them raises interesting and difficult questions. In all our knowledge of general principles what actually happens is that first of all we realize some particular application of the principle and then we realize that the particularity is irrelevant and that there is a generality which may equally truly be affirmed. This is of course familiar in such matters as teaching arithmetic. Two and two or four is first learned in the case of some particular pair of couples and then in some other particular case and so on until at last it becomes possible to see that it is true of any pair of couples. The same thing happens with logical principles. Supposed to men are discussing what day of the month it is. One of them says at least you will admit that if yesterday was the 15th today must be the 16th. Yes says the other I admit that. And you know the first continues that yesterday was the 15th because you dined with Jones and your diary will tell you that was on the 15th. Yes says the second therefore today is the 16th. Now such an argument is not hard to follow and if it is granted that its premises are true in fact no one will deny that the conclusion must also be true. But it depends for its truth upon an instance of a general logical principle. The logical principle is as follows. Suppose it known that if this is true then that is true. When it is the case that if this is true that is true we shall say that this implies that and that that follows from this. Thus our principle states that if this implies that and this is true then that is true. In other words anything implied by a true proposition is true or whatever follows from a true proposition is true. This principle is really involved at least concrete instances of it are involved in all demonstrations. Whenever one thing which we believe is used to prove something else which we consequently believe this principle is relevant. If anyone asks why should I accept the results of valid arguments based on true premises we can only answer by appealing to our principle. In fact the truth of the principle is impossible to doubt and its obviousness is so great that at first sight it seems almost trivial. Such principles however are not trivial to the philosopher for they show that we may have indubitable knowledge which is in no way derived from objects of sense. The above principle is merely one of a certain number of self-evident logical principles. Some at least of these principles must be granted before any argument of proof becomes possible. When some of them have been granted others can be proved though these others so long as they are simple are just as obvious as the principles taking for granted. For no very good reason three of these principles have been singled out by tradition under the name of laws of thought. They are as follows. One, the law of identity. Whatever is is. Two, the law of contradiction. Nothing can both be and not be. Three, the law of excluded middle. Everything must either be or not be. These three laws are samples of self-evident logical principles but are not really more fundamental or more self-evident than various other similar principles. For instance, the one we consider just now which states that what follows from a true premise is true. The name laws of thought is also misleading for what is important is not the fact that we think in accordance with these laws but the fact that things behave in accordance with them. In other words, the fact that when we think in accordance with them we think truly. But this is a large question to which we must return at a later stage. In addition to the logical principles which enable us to prove from a given premise that something is certainly true, there are other logical principles which enable us to prove from a given premise that there is a greater or less probability that something is true. An example of such principles, perhaps the most important example is the inductive principle which we considered in the preceding chapter. One of the great historic controversies in philosophy is the controversy between the two schools called respectively empiricists and rationalists. The empiricists who are best represented by the British philosophers Locke, Berkeley and Hume maintained that all our knowledge is derived from experience. The rationalists who are represented by the continental philosophers of the 17th century especially Descartes and Leithnitz maintained that in addition to what we know by experience there are certain innate ideas and innate principles which we know independently of experience. It has now become possible to decide with some confidence as to the truth or falsehood of these opposing schools. It must be admitted for the reasons already stated that logical principles are known to us and cannot be themselves proved by experience since all proof presupposes them. In this therefore which was the most important point of the controversy the rationalists were in the right. On the other hand even that part of our knowledge which is logically independent of experience in the sense that experience cannot prove it is yet elicited and caused by experience. It is on occasion of particular experiences that we become aware of the general laws which their connections exemplify. It would certainly be absurd to suppose that there are innate principles in the sense that babies are born with the knowledge of everything which men know and which cannot be deduced from what is experienced. For this reason the word innate would not now be employed to describe our knowledge of logical principles. The phrase a priori is less objectionable and is more usual in modern writers. Thus while admitting that all knowledge is elicited and caused by experience we shall nevertheless hold that some knowledge is a priori in the sense that the experience which makes us think of it does not suffice to prove it but merely so directs our attention that we see its truth without requiring any proof from experience. There is another point of great importance in which the empiricists were in the right as against the rationalists. Nothing can be known to exist except by the help of experience. That is to say if we wish to prove that something of which we have no direct experience exists we must have among our premises the existence of one or more things of which we have direct experience. Our belief that the emperor of China exists for example rest upon testimony and testimony consists in the last analysis of sense data seen or heard in reading or being spoken to. Rationalists believe that from general consideration as to what must be they could deduce the existence of this or that in the actual world. In this belief they seem to have been mistaken. All the knowledge that we can acquire a priori concerning existence seems to be hypothetical. It tells us that if one thing exists another must exist or more generally that if one proposition is true another must be true. This is exemplified by the principles we have already dealt with such as if this is true and this implies that then that is true or if this and that have been repeatedly found connected they will probably be connected in the next instance in which one of them is found. Thus the scope and power of a priori principles is strictly limited. All knowledge that something exists alone. When anything is proved to exist without being known immediately both experience and a priori principles must be required in the proof. Knowledge is called empirical when it rests wholly or partly upon experience. Thus all knowledge which asserts existence is empirical and the only a priori knowledge concerning existence is hypothetical giving connections among things that exist or may exist but not giving actual existence. A priori knowledge is not all of the logical kind we have been hitherto considering. Perhaps the most important example of non-logical a priori knowledge is knowledge as to ethical value. I am not speaking of judgments as to what is useful or as to what is virtuous for such judgments do require empirical premises. I am speaking of judgments as to the intrinsic desirability of things. If something is useful it must be useful because it secures some hint. The end must if we have gone far enough be valuable on its own account and not merely because it is useful for some further end. Thus all judgments as to what is useful depend upon judgments as to what has value on its own account. We judge for example that happiness is more desirable than misery, knowledge, than ignorance, goodwill, than hatred, and so on. Such judgments must in part at least be immediate and a priori. Like our previous a priori judgments they may be elicited by experience and indeed they must be for it seems not possible to judge whether anything is intrinsically valuable unless we have experienced something of the same kind. But it is fairly obvious that they cannot be proved by experience for the fact that a thing exists or does not exist cannot prove either that it is good that it should exist or that it is bad. The pursuit of this subject belongs to ethics where the impossibility of deducing what ought to be from what is has to be established. In the present connection it is only important to realize that knowledge as to what is intrinsically of value is a priori in the same sense in which logic is a priori namely in the sense that the truth of such knowledge can be neither proved nor disproved by experience. All pure mathematics is a priori like logic. This was strenuously denied by the empirical philosophers who maintained that experience was as much the source of our knowledge of arithmetic as of our knowledge of geography. They maintained that by the repeated experience of seeing two things and two other things and finding that all together they made four things we were led by induction to the conclusion that two things and two other things would always make four things all together. If however this were the source of our knowledge that two and two are four we should proceed differently in persuading ourselves of its truth from the way in which we do actually proceed. In fact a certain number of instances are needed to make us think of too abstractly rather than of two coins or two books or two people or two of any other specified kind. But as soon as we are able to divest our thoughts of irrelevant particularity we become able to see the general principle that two and two are four. Any one instance is seen to be typical and the examination of other instances becomes unnecessary. The same thing is exemplified in geometry. If we want to prove some property of all triangles we draw some one triangle and reason about it but we can avoid making use of any property which it does not share with all other triangles and thus from our particular case we obtain a general result. We do not in fact feel our certainty that two and two are four increased by fresh instances because as soon as we have seen the truth of this proposition our certainty becomes so great as to be incapable of growing greater. Moreover we feel some quality of necessity about the proposition two and two are four which is absent from even the best attested empirical generalizations. Such generalizations always remain mere facts. We feel that there might be a world in which they were false though in the actual world they happen to be true. In any possible world on the contrary we feel that two and two would be four. This is not a mere fact but a necessity to which everything actual and possible must conform. The case may be made clearer by considering a genuinely empirical generalization such as all men are mortal. It is plain that we believe this proposition in the first place because there is no known instance of men living beyond a certain age and in the second place because there seem to be physiological grounds for thinking that an organism such as a man's body must soon or later wear out. Neglecting the second ground and considering merely our experience of men's mortality it is plain that we should not be content with one quite clearly understood instance of a man dying. Whereas in the case of two and two or four one instance does suffice when carefully considered to persuade us that the same must happen in any other instance. Also we can be forced to admit on reflection that there may be some doubt however slight as to whether all men are mortal. This may be made plain by the attempt to imagine two different worlds in one of which there are men who are not mortal while in the other two and two make five. When Swift invites us to consider the race of strode bugs who never die we are able to acquiesce an imagination but a world where two and two make five seems quite on a different level we feel that such a world if there were one would upset the whole fabric of our knowledge and reduce us to utter doubt. The fact is that in simple mathematical judgments such as two and two or four and also in many judgments of logic we can know the general proposition without inferring it from instances although some instances usually necessary to make clear to us what the general proposition means. This is why there is real utility in the process of deduction which goes from the general to the general or from the general to the particular as well as in the process of induction which goes from the particular to the particular or from the particular to the general. It is an old debate among philosophers whether deduction ever gives new knowledge. We can now see that in certain cases at least it does do so. If we already know that two and two always make four and we know that brown and Jones are two and so are Robinson and Smith we can deduce that brown and Jones and Robinson and Smith are four. This is new knowledge not contained in our premises because the general proposition two and two or four never told us there were such people as brown and Jones and Robinson and Smith and the particular premises do not tell us that there were four of them whereas the particular proposition deduced does tell us both these things. But the newness of knowledge is much less certain if we take the stock instance of deduction that is always given in books on logic namely all men are mortal Socrates is a man therefore Socrates is mortal. In this case what we really know beyond reasonable doubt is that certain men ABC were mortal since in fact they have died. If Socrates is one of these men it is foolish to go the round about way through all men are mortal to arrive at the conclusion that probably Socrates is mortal. If Socrates is not one of the men on whom our induction is based we shall still do better to argue straight from our ABC to Socrates than to go around by the general proposition all men are mortal. For the probability that Socrates is mortal is greater on our data than the probability that all men are mortal. This is obvious because if all men are mortal so is Socrates but if Socrates is mortal it does not follow that all men are mortal. Hence we shall reach the conclusion that Socrates is mortal with a greater approach to certainty if we make our argument purely inductive then if we go by way of all men are mortal and then use deduction. This illustrates the difference between general propositions known a priori such as two and two are four and empirical generalizations such as all men are mortal. In regard to the former deduction is the right mode of argument whereas in regard to the latter induction is always theoretically preferable and warrants a greater confidence in the truth of our conclusion because all empirical generalizations are more uncertain than the instances of them. We have now seen that there are propositions known a priori and that among them are the propositions of logic and pure mathematics as well as the fundamental propositions of ethics the question which must next occupy us is this how is it possible that there should be such knowledge and more particularly how can there be knowledge of general propositions in cases where we have not examined all the instances and indeed never can examine them all because their number is infinite these questions which were first brought prominently forward by the German philosopher Kant 1724 to 1804 are very difficult and historically very important. End of chapter 7 Chapter 8 of The Problems of Philosophy This is a LibriVox recording. All LibriVox recordings are in the public domain. For more information or to volunteer please visit LibriVox.org Recording by ML Cohen www.mojomu411.com Cleveland, Ohio August 2007 The Problems of Philosophy by Bertrand Russell Chapter 8 How a Priory Knowledge is Possible Immanuel Kant is generally regarded as the greatest of the modern philosophers Though he lived through the Seven Years War and the French Revolution he never interrupted his teaching of philosophy at Königsberg in East Prussia. His most distinctive contribution was the invention of what he called the critical philosophy which assuming as a datum that there is knowledge of various kinds inquired how such knowledge comes to be possible and deduced from the answer to this inquiry many metaphysical results as to the nature of the world. Whether these results were valid may well be doubted but Kant undubitably deserves credit for two things. First for having perceived that we have a Priory Knowledge which is not purely analytic that is such that the opposite would be self-contradictory and secondly for having made evident the philosophical importance of the theory of knowledge. Before the time of Kant it was generally held that whatever knowledge was a Priory must be analytic but this word means will be best illustrated by examples. If I say a bald man is a man a plain figure is a figure a bad poet is a poet I make a purely analytical judgment the subject spoken about is given as having at least two properties of which one is singled out to be asserted of it. Such propositions as the above are trivial and would never be enunciated in real life except by an order preparing the way for a piece of sophistry. They are called analytic because the predicate is obtained by merely analyzing the subject. Before the time of Kant it was thought that all judgments of which we could be certain a Priory were of this kind that in all of them there was a predicate which was only part of the subject of which it was asserted. If this were so we should be involved in a definite contradiction if we attempted to deny anything that could be known a Priory. A bald man is not bald would assert and deny baldness of the same man and would therefore contradict itself. Thus according to the philosophers before Kant the law of contradiction which asserts that nothing can at the same time have and not have a certain property suffice to establish the truth of all a Priory knowledge. Hume 1711 to 1776 who preceded Kant accepting the usual view as to what make knowledge a Priory discovered that in many cases which had previously been supposed analytic and notably in the case of cause and effect the connection was really synthetic. Before Hume rationales at least had supposed that the effect could be logically deduced from the cause if only we have sufficient knowledge. Hume argued correctly as we now be generally admitted that this could not be done hence he inferred the far more doubtful proposition that nothing could be known a Priory about the connection of cause and effect. Kant who had been educated in a rationalist tradition was much perturbed by Hume's skepticism and endeavored to find an answer to it. He perceived that not only the connection of cause and effect but all the propositions of arithmetic and geometry are synthetic that is not analytic and all these propositions no analysis of the subject will reveal the predicate. His stock instance was the proposition 7 plus 5 equals 12. He pointed out quite truly that 7 and 5 have to be put together to give 12. The idea of 12 was not contained in them nor even in the idea of adding them together. Thus he would lead to the conclusion that all pure mathematics though a Priory is synthetic and this conclusion raised a new problem of which he endeavored to find the solution. The question which Kant put at the beginning of his philosophy namely how is pure mathematics possible is an interesting and difficult one to which every philosophy which is not purely skeptical must find some answer. The answer of the pure empiricist that our mathematical knowledge is derived by induction from particular instances we have already seen to be inadequate for two reasons. First, that the validity of the inductive principle itself cannot be proved by induction. Secondly, that the general propositions of mathematics such as 2 and 2 always makes 4 can obviously be known with certainty by consideration of a single instance and gain nothing by enumeration of other cases in which they have been found to be true. Thus our knowledge of the general propositions of mathematics and the same applies to logic must be accounted for otherwise than our merely probable knowledge of empirical generalization such as all men are mortal. The problem arises through the fact that such knowledge is general whereas all experience is particular. It seems strange that we should apparently be able to know some truths in advance about particular things of which we have as yet no experience. But it cannot easily be doubted that logic and arithmetic will apply to such things. We do not know who will be the inhabitants of London a hundred years hence but we know that any two of them and any other two of them will make four of them. This apparent power of anticipating facts about things of which we have no experience is certainly surprising. Consolution of the problem though not valid in my opinion is interesting. It is however very difficult and is differently understood by different philosophers. We can therefore only give the nearest outline of it and even that will be thought misleading by many exponents of cons system. What Kant maintained was that in all our experience there are two elements to be distinguished the one due to the object that is to what we have called the physical object the other due to our own nature. We saw in discussing matter and sense data that the physical object is different from the associated sense data and that the sense data are to be regarded as resulting from an interaction between the physical object and ourselves. So far we are in agreement with Kant. But what is distinctive of Kant is the way in which he apportions the shares of ourselves and the physical objects respectively. He considers that the crude material given in sensation the color, hardness, etc is due to the object and that what we supply is the arrangement in space and time and all the relations between sense data which result from comparison or from considering one as the cause of the other or in any other way. His chief reason in favor of this view is that we seem to have a priori knowledge as to space and time and causality and comparison but not as to the actual crude material of sensation. We can be sure, he says, that anything we shall ever experience must show the characteristics affirmed of it in our a priori knowledge because these characteristics are due to our own nature and therefore nothing can ever come into our experience without acquiring these characteristics. The physical object which he calls the quote thing in itself and quote he regards as essentially unknowable. What can be known is the object as we have it in experience which he calls quote phenomenon. Kant's thing in itself is identical in definition with the physical object namely, it is the cause of sensations. In the properties deduced from the definition it is not identical since Kant held in spite of some inconsistencies regards cause that we can know that none of the categories are applicable to the quote thing in itself. The phenomenon being a joint product of us and the thing in itself is sure to have those characteristics which are due to us and is therefore sure to conform to our a priori knowledge. Hence this knowledge though true of all actual impossible experience must not be supposed to apply outside experience. Thus in spite of the existence of a priori knowledge we cannot know anything about the thing in itself or about what is not an actual or possible object of experience. In this way he tried to reconcile and harmonize the contentions of the rationalists with the arguments of the empiricists. Apart from the minor grounds on which Kant's philosophy may be criticized there is one main objection which seems fatal to any attempt to deal with the problem of a priori knowledge by his method. The thing to be accounted for is our certainty that the facts must always conform to logic and arithmetic. To say that logic and arithmetic are contributed by us does not account for this. How our nature is as much a fact of the existing world as anything and there can be no certainty that it will remain constant. It might happen if Kant is right that tomorrow our nature would so change as to make two and two become five. This possibility seems never to have occurred to him yet it is one which utterly destroys the certainty and universality which he is anxious to vindicate for arithmetical propositions. It is true that this possibility formally is inconsistent with the Kantian view that time itself is a form imposed by the subject upon phenomena so that our real self is not in time and has no tomorrow. But he will still have to sup