Knowledge and Belief (Problems of Philosophy)

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An encyclopedia of philosophy articles written by professional philosophers.

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 colour 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 , 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 a 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. 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. It might seem as though we were quite sure of being the same person to-day 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 colour, what is quite certain at once is not ' I am seeing a brown colour', but rather, 'a brown colour is being seen'. This of course involves something or somebody which or who sees the brown colour; but it does not of itself involve 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 colour 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-datum, 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 cloth laid on it, and so on, cannot be a mere collection of sense-data. If the cloth 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 cloth would be suspended in empty air, resting, by a miracle, 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 ten people are sitting round 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 above the private and particular sense-data which appear to various people.

The Knowledge Problem

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 light, 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 in 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 door banging, 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 the 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 my own can be a sense-datum to me. Thus the behaviour of the sense-data which represent 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 colour, 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 face—it is very difficult to suppose that what we hear is not the expression of a 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 by argument that we originally come 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-datum itself were instinctively believed to be the independent object, whereas argument shows that the object cannot be identical with the sense-datum. This discovery, however—which is not at all paradoxical in the case of taste 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 account 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 wholly 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 it is therefore worth while 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 forth, 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 are 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 acquiescence.

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 begun to doubt the adequacy of common sense, to justify the arduous and difficult labours that philosophical problems involve.

In the preceding chapter we agreed, 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 colour, 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 colour 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 rap 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 rap 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 sound. That which has the wave-motion is either aether or 'gross matter', but in either case is what the philosopher would call matter. The only properties which science assigns to it are position in 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 brain 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 colours 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 percipient. 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 connexion 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 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, as 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 ordnance 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 thus 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 colours or sounds or other sense-data. We can know all those things about physical space which a man born blind might know through other people about the space of sight; but the kind of things which a man born blind 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 perceptions 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.

The maturation of the Gettier problem

But the sense-datum which we call hearing the thunder does not take place until the disturbance of the air has travelled 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 colours 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 colours, and we might, by good luck, see an object as of the colour it really is. The colour 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' colour to be a sort of medium colour, 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 colour 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 light is reflected from the object in the direction of the eye. The intervening air alters colours unless it is perfectly clear, and any strong reflection will alter them completely.

Thus the colour 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 colour, whether the object from which the waves start has any colour or not. Thus it is quite gratuitous to suppose that physical objects have colours, 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. Idealists tell us that what appears as matter is really something mental; namely, either as Leibniz 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 favour of their theory. 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 as 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 catalogue has a correspondence with the things catalogued.

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 Berkeley. 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, in part 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 colour 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 ' esse ' is ' percipi '. 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 called 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 formerly in his mind, but afterwards ceased to be in his mind. And so when Berkeley 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, Berkeley was right in treating the sense-data which constitute 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 Berkeley 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 Berkeley 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 Berkeley'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 colour 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 colour 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 colour 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 colour is in the mind of the percipient. Berkeley's view, that obviously the colour 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 Berkeley. 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.

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 Berkeley'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. 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, Berkeley's argument is seen to be wrong in substance as well as in form, and his grounds for supposing that 'ideas'—i.

Hence his grounds in favour 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; whence 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 chimaera. 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. In this sense of the word we know that something is the case. This sort of knowledge may be described as knowledge of truths. This is the sense in which we know sense-data. Thus the statement which seemed like a truism becomes, when re-stated, the following: 'We can never truly judge that something with which we are not acquainted exists. I have not the honour 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 any one 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 a 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 some one else must be acquainted with the thing.

What happens, in cases where I have true judgement 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. In the preceding chapter we saw that there are two sorts of knowledge: knowledge of things, and knowledge of truths.

PHILOSOPHY - Epistemology: Analyzing Knowledge #2 (No-False-Lemma and No-Defeater Approaches)

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 the sense-data that make up the appearance of my table—its colour, shape, hardness, smoothness, etc. The particular shade of colour 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 colour, do not make me know the colour itself any better than I did before so far as concerns knowledge of the colour itself, as opposed to knowledge of truths about it, I know the colour perfectly and completely when I see it, and no further knowledge of it itself is even theoretically possible.

A synthetic overview of the theory of knowledge and epistemology.

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 acquaintance: 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 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 an 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 tolerably 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 what 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 past 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 subjects 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.

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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.

The "know" in the second case is knowing about things, and is called acquaintance. The statement is then rendered as "we cannot make judgements about anything with which we are not acquainted. When something is not known by direct experience, or, in Russell's terminology, by acquaintance, it is known by description. We know from the previous discussion of judgements and acquaintance, that there are two kinds of knowledge: knowledge of truths and knowledge of things. Knowledge of things is further partitioned into knowledge by acquaintance and knowledge by description.

Knowledge by acquaintance is the simplest kind of knowledge. It is without reference to any truths and accessed by direct experience. To given an example of knowledge by acquaintance Russell returns to the example of the table. The experience of the color of the table, is an experience of knowledge by acquaintance.

There is nothing that can be added to the experience of the "brownness" of the table. It is immediately accessible and complete. The table itself though, is not known to us by acquaintance. There are a set of sensations we associate with the table and we can, from these, create a description which only Russell's table will match.

Thus the table is known to us by description. Having categorized what can be known by acquaintance, Russell turns to knowledge by description. Anything that is referred to a "a so-and-so" is an ambiguous description. Things that are referred to as "the so-and-so" are a definite description.

Ambiguous descriptions are problematic and a definition of knowledge by description can be made without going into those problems. So Russell focuses on definite descriptions. A definite description is a set of properties that designate a particular object. Unless the object derives its existence from a logical analysis of the description, such as "the longest living man", some aspect of the description must be known to us by acquaintance. In fact, in the analysis of propositions made up of descriptions, each proposition which can be understood must consist entirely of constituents with which we are acquainted.

If there were not the case we could not make any judgment about the proposition. For the words in the proposition must have some meaning and that meaning derives from acquaintance. We are certain of knowledge we have by acquaintance, but such knowledge is private to us. Knowledge by description allows us to pass beyond the realm of private experience and gain knowledge of things we have not experienced. Given what we can know about things, Russell turns our attention to what we can infer. To do this he presents the judgement, "The sun will rise tomorrow.

What basis do we have to believe this is true? Our immediate answer is because it has always done so in the past, but this does not satisfy us with any certainty. Even if we appeal to science and the laws of motion our desire for certainty is not satisfied, for we should we believe that the laws of motion will continue to operate tomorrow as the have in the past?

The answer is that we do not know "for certain". As a kind of event A occurs together with a kind of event B and these two kinds of events never occur apart, each new occurrence increases the probability that these events will be related in the next occurrence. This probability approaches certainty, without limit. The following chapter elaborates on other kinds of knowledge that, like induction, is assumed true but can not be proven true. Russell next brings our attention to implication.

The simple argument if A is true then B is true. A is true, so B must be true is generally accepted, but there is nothing in our experience to prove that it is true. Yet, without proof, we are as certain of it as we are of our sensations. In addition to implication, there are other self-evident principles that allow us to reason about propositions. These are called the laws of thought though Russell finds the title misleading. The title is misleading because it is not that we must think this way, but that when we do think this way, we think correctly.

The Empiricists and Rationalists schools of philosophy each have different views as to how to we come to know these general principles. The Empiricists believe that general principles arise out of experience. The rationalists believe that the general principles are inate ideas. Russell declares that the rationalist are correct, in that experience can not prove these general principles are true, but that empiricists are correct in that our experience does suggest the principles.

It would be ridiculous to suggest that the principles are inate in the sense babies are born knowing them. Experience clearly plays a role in giving us an understanding of these prinicples. Since the term inate has this notion of being born into this knowledge, philosopers use the term a priori. Immanuel Kant made significant contributions to the understanding of a priori knowledge.

He showed that a priori knowledge can be synthetic , that is, new knowledge can be gained that is not implicit in the a priori proposition. Prior to Kant's work, it was general held that all a priori knowledge was analytic, that is any knowledge recognized from an a priori proposition was some how contained in the proposition and extracted by analysis.

David Hume, a slightly earlier contemporary of Kant's, had shown that cause could not be logically deduced from effect contrary to what the rationalist school, in which Kant had studied, believed. Hume went on to propose that no a prior knowledge is possible about cause and effect.

Kant countered this proposal by asserting that synthetic a priori knowledge is possible and indeed that all mathematics is synthetic a priori knowledge. No amount of analysis of 7 or of 5 will demonstrate the idea of This proposition and all mathematical propostions are synthetic. Having made and demonstrated this assertion, Russell explores Kant's answer to the question "How is mathematics possible?

To explain this surprising result, Kant begins by distinguishing "the thing in itself", what Russell has called the physical object, and our sense data. Our experience of an object is a combination of our sense data and our own judgements about the sense data. This combination of sense data and judgements Kant refered to as "phenomenon".

Since phenomena are a result of sense data and our own judgements and our judgements supply abstract concepts about the sense data, all our experience of the world is subject to reason, because nothing enters our experience which does not include the abstract judgements we supply. Russell points out that by attributing logic and arithmetic to the observer, the problem of how mathematics is possible is not answered.

This is because our own nature is changeable, where as logic and mathematics seems unchanging. A priori knowledge involves concepts which can not be placed in the physical world. To give and example of a concept not in the physical world, consider the sentence "I am in my room".

I am an entity in the physical world and so is my room, but "in" is not, at least not in the same way that "I" and "my room" are. The concept can not be attributed to the mind, either. For if an earwig is in my room, it is in my room whether I know it or not. In the chapter The World of Universals , Russell then explores what these concepts, being neither mental nor physical, are.

Plato gave an excellent account of universals in his "Theory of Ideas". When, for example, Plato seeks to define justice , he points out that we notice this or that just act, each of them has something in common and this commonality is justice. Russell clarifies that the idea here is not an idea in the sense that it is a thought, rather it is a pure form, the distillation of individual just acts. So though it is apprehended by minds, it is not a thought. To avoid confusion, Russell uses the term universal.

Universals are distinguished from particulars in that particulars are given by sensation.

We experience a white thing or a just act. There is a commonality of white things which gives us the universal white. Proper nouns and pronouns are particulars while other nouns, verbs, adverbs and prepositions are universals. It is remarkable that no sentence can be constructed without the use of at least one universal. Russell presents the following argument against the empiricists that deny the existence of universals. Suppose that there are no universals and that the idea of whiteness can only conceived of as a particular.

Then when we examine how we know that any given thing is white, we discover that it must have a relationship to some other white thing. This relationship is a universal. Universals have a unique sort of being in that while they are not sensations neither are they thoughts. Take, for example, the statement "Edinburgh is north of London".

The statement is true whether there is any one who thinks it. The statement's truth does not depend on any ones apprehension of it. Further, if a universal were a thought we would. Thus there are two realms of being, the realm of thoughts and sensations and the realm of universals. Our knowledge of universals relates these two realms. We have acquaintance with sensation that have a quality of color, texture and taste. When we experience something that is white and then some other sensation that also has that same color, it is easy to abstract out the universal "whiteness".

We also have acquaintance with relations between universals, and Russell demonstrates this through analysis of parts of a whole. Consider a page of paper. Some parts of the page are to the left of other parts, and some parts are above other parts. It is not difficult to see how we can abstract the concept of "to the left of" and "above" and "below" from acquaintance with our experiences. Similar arguments can be made for temporal relationships. Having established what universals are and how we come to know them, Russell asserts that all a priori knowledge deals exclusively with the relationship of universals.

He gives as an example of two and two are four, which he restates as "any collection formed of two twos is a collection of four". To see that this is a statement only about universals, we examine what words we must understand to understand the proposition. We can see that once we understand the words two , four and collection we will understand the proposition without any reference to any particular. The earlier question of how a priori knowledge can control or predict experience can now be seen to be a misapprehension.

Although statements that involve a priori knowledge can be applied to particulars, it is understood without reference to them and so there is no control or prediction involved, only the relationship of universals. Russell goes on to demonstrate the interesting fact that knowledge of universals can give us knowledge about things we can, by definition, never know by experience.

Concluding this explanation of how a priori knowledge is possible, there is a survey of the kinds of knowledge discussed in the book up to this point. There is knowledge of things and knowledge of truths. There is knowledge by acquaintance and knowledge by description. In the category of knowledge by acquaintance, we have knowledge of sense-data, universals and perhaps knowledge of ourselves.

In knowledge by description, we have some part whic is knowledge by acquaintance and some part which is knowledge of truths. Some knowledge of truths is known immediately. This kind of knowledge is called intuition. We commonly believe that we should have reasons for our beliefs and although we may not be ready with the reasons we believe something, we generally feel we can supply reasons for our beliefs. If we explore what those reasons might be, we quickly come to some general principle, such as induction.

As Russell presented in chapter six, such principles seem self evident and no reason can be given for believing them. In addition to general principles that are self evident, we also have intuitive knowledge about our sense-data, in that no evidence can be offered for our belief, yet we are certain that it is true. There are "truths of perceptions", which are what we believe are our sense perceptions.

There are also judgements of perception, such as "This red patch is round". Judgements of perception describe properties and relations of truths of perception. There is a third kind of intuitive knowledge, judgements of memory. Russell defines memory as an object immediately before the mind which is recognized as past. Judgements of memory are similar in self evidence to other kinds of intuitive knowledge, but differ from those related to truths of perception and general principles in that they may be mistaken.

From this observation we can see that self evidence has degrees of certainty. A general principle such as the law of the contradiction and a truth of perception have a near certain degree of self evidence. Memories of events that happened long ago, or which we did not attend to are much less certain. Russell presents three criteria for answering this question. A theory of truth must allow for beliefs to be false, as well as true.

It must assign truth or falsehood to be a property of the belief and the truth value must depend on things outside the belief. Russell then works through an example of false belief from Othello to establish the details for a theory of truth. A belief has object-terms, the things the belief is about and also object-relations, which describe how the object-terms are related to each other.

A belief is true is there is a complex unity of the object-terms and object-relations that correspond to a fact. This is a precise way of saying that a belief is true if it corresponds to a fact and false if it does not. To know which of our beliefs are true and which are false requires that we first understand the definition of "to know".

The simple definition that knowledge is true belief is insufficient. One may belief something that is true but believe it for reasons that are in error. Such a belief is a true belief but is not knowledge. To narrow the definition of knowledge to exclude this possibility Russell introduces the terms intuitive and derivative knowledge. So, Russell concludes, firmly held beliefs that are true beliefs that correspond to facts are knowledge. Firmly held beliefs that do not correspond to facts are error.

Beliefs which are neither knowledge or error are probable opinion. Coherence of beliefs give us more certainty about beliefs which held individually might seem doubtful. Many metaphysical writers attempt to show from a priori principles some grand design to explain the nature of the world.

In modern philosophy Hegel has been an influential example of this practice. Russell believes that such attempts are futile and that examining Hegel's system gives us some in sight as to why. Russell's interpretation of Hegel, which he believes is widely held, is that " everything short of the Whole is obviously fragmentary, and obviously incapable of existing without the complement supplied by the rest of the world. In the world of things each thing seems to imply something larger and as we seek to understand the larger thing we eventually arrive at the universe as a whole.

In the world of thought, the incompleteness appears as contradictions giving rise to the cycle of thesis anti-thesis and synthesis the famous Hegelian Dialectic. Following this dialectic to its conclusion leads to the "Absolute Idea" which describes reality. This reality is " one single harmonious system, not in space or time, not in any degree evil, wholly rational, and wholly spiritual. The flaw in Hegel's argument is equivocation with respect to the idea of the nature of things.

Hegel uses the nature of things both to mean all the truths of something and the thing itself. To explain Russell gives an example of a tooth ache. The sufferer knows the nature of the tooth ache in a way the dentist does not. The sufferer does not know many of the truths about the tooth ache that the dentist does. It does not follow that the sufferer does not know the nature of the tooth ache because he or she does not know all the truths about the tooth ache.

How do you know that what you know is true? That's epistemology

Russell criticizes Hegel and others who start off with a view to prove and then construct a system to prove it. These philosophers try to show that some perceived aspect of reality is actually contradictory. But as knowledge advances, we find again and again that the contradictions vanish and with them the a priori knowledge of the world proposed by the philosopher.

Kant is another example of a philosopher that reasons that some aspect of reality is self contradictory. His target was space-time. Because apparent space and time are infinitely large and infinitely small, the seem to present contradictions. Infinity was very problematic for mathematicians and philosophers until the late 19th century. Kant, writing in the 18th century, saw these apparent contradictions and proposed that our experience of space-time was subjective.

Knowledge and Belief (Problems of Philosophy) Knowledge and Belief (Problems of Philosophy)
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