Philosophical Studies

The Status of Sense-Data

The term “sense-data” is ambiguous; and therefore I think I had better begin by trying to explain what the class of entities is whose status I propose to discuss.

There are several different classes of mental events, all of which, owing to their intrinsic resemblance to one another in certain respects, may, in a wide sense, be called “sensory experiences,” although only some among them would usually be called “sensations.” There are (1) those events, happening in our minds while we are awake, which consist in the experiencing of one of those entities, which are usually called “images,” in the narrowest sense of the term. Everybody distinguishes these events from sensations proper; and yet everybody admits that “images” intrinsically resemble the entities which are experienced in sensations proper in some very important respect. There are (2) the sensory experiences we have in dreams, some of which would certainly be said to be experiences of images, while others might be said to be sensations. There are (3) hallucinations, and certain classes of illusory sensory experiences. There are (4) those experiences, which used to be called the having of “after-images,” but which psychologists now say ought rather to be called “after-sensations.” And there are, finally, (5) that class of sensory experiences, which are immensely commoner than any of the above, and which may be called sensations proper, if we agree to use this term in such a way as to exclude experiences of my first four sorts.

Every event, of any one of these five classes, consists in the fact that an entity, of some kind or other, is experienced. The entity which is experienced may be of many different kinds; it may, for instance, be a patch of colour, or a sound, or a smell, or a taste, etc; or it may be an image of a patch of colour, an image of a sound, an image of a smell, an image of a taste, etc. But, whatever be its nature, the entity which is experienced must in all cases be distinguished from the fact or event which consists in its being experienced; since by saying that it is experienced we mean that it has a relation of a certain kind to something else. We can, therefore, speak not only of experiences of these five kinds, but also of the entities which are experienced in experiences of these kinds; and the entity which is experienced in such an experience is never identical with the experience which consists in its being experienced. But we can speak not only of the entities which are experienced in experiences of this kind, but also of the sort of entities which are experienced in experiences of this kind; and these two classes may again be different. For a patch of colour, even if it were not actually experienced, would be an entity of the same sort as some which are experienced in experiences of this kind: and there is no contradiction in supposing that there are patches of colour, which yet are not experienced; since by calling a thing a patch of colour we merely make a statement about its intrinsic quality, and in no way assert that it has to anything else any of the relations which may be meant by saying that it is experienced. In speaking, therefore, of the sort of entities which are experienced in experiences of the five kinds I have mentioned, we do not necessarily confine ourselves to those which actually are experienced in some such experience: we leave it an open question whether the two classes are identical or not. And the class of entities, whose status I wish to discuss, consists precisely of all those, whether experienced or not, which are of the same sort as those which are experienced in experiences of these five kinds.

I intend to call this class of entities the class of sensibles; so that the question I am to discuss can be expressed in the form: What is the status of sensibles? And it must be remembered that images and after-images are just as much “sensibles,” in my sense of the term, as the entities which are experienced in sensations proper; and so, too, are any patches of colour, or sounds, or smells, etc, (if such there be), which are not experienced at all.

In speaking of sensibles as the sort of entities which are experienced in sensory experiences I seem to imply that all the entities which are experienced in sensory experiences have some common characteristic other than that which consists in their being so experienced. And I cannot help thinking that this is the case, in spite of the fact that it is difficult to see what intrinsic character can be shared in common by entities so different from one another as are patches of colour, sounds, smells, tastes, etc. For, so far as I can see, some non-sensory experiences may be exactly similar to sensory ones in all intrinsic respects, except that what is experienced in them is different in kind from what is experienced in any sensory experience: the relation meant by saying that in them something is experienced may be exactly the same in kind, and so may the experient. And, if this be so, it seems to compel us to admit that the distinction between sensory and non-sensory experiences is derived from that between sensibles, and non-sensibles and not vice versâ. I am inclined, therefore, to think that all sensibles, in spite of the great differences between them, have some common intrinsic property, which we recognise, but which is unanalysable; and that, when we call an experience sensory, what we mean is not only that in it something is experienced in a particular way, but also that this something has this unanalysable property. If this be so, the ultimate definition of “sensibles” would be merely all entities which have this unanalysable property.

It seems to me that the term “sense-data” is often used, and may be correctly used, simply as a synonym for “sensibles”; and everybody, I think, would expect me, in discussing the status of sense-data, to discuss, among other things, the question whether there are any sensibles which are not “given.” It is true that the etymology of the term “sense-data” suggests that nothing should be called a sense-datum, but what is given; so that to talk of a non-given sense-datum would be a contradiction in terms. But, of course, etymology is no safe guide either as to the actual or the correct use of terms; and it seems to me that the term “sense-data” is often, and quite properly, used merely for the sort of entities that are given in sense, and not in any way limited to those which are actually given. But though I think I might thus have used “sense-data” quite correctly instead of “sensibles,” I think the latter term is perhaps more convenient; because though nobody ought to be misled by etymologies, so many people in fact are so. Moreover the term “sense-data” is sometimes limited in yet another way, viz, to the sort of sensibles which are experienced in sensations proper; so that in this sense “images” would not be “sense-data.” For both these reasons, I think it is perhaps better to drop the term “sense-data” altogether, and to speak only of “sensibles.”

My discussion of the status of sensibles will be divided into two parts. I shall first consider how, in certain respects, they are related to our minds; and then I shall consider how, in certain respects, they are related to physical objects.

(I)

(1) We can, I think, distinguish pretty clearly at least one kind of relation which sensibles, of all the kinds I have mentioned, do undoubtedly sometimes have to our minds.

I do now see certain blackish marks on a whitish ground, and I hear certain sounds which I attribute to the ticking of my clock. In both cases I have to certain sensibles—certain blackish marks, in the one case, and certain sounds, in the other—a kind of relation with which we are all perfectly familiar, and which may be expressed, in the one case, by saying that I actually see the marks, and in the other, by saying that I actually hear the sounds. It seems to me quite evident that the relation to the marks which I express by saying that I see them, is not different in kind from the relation to the sounds which I express by saying that I hear them. “Seeing” and “hearing,” when thus used as names for a relation which we may have to sensibles, are not names for different relations, but merely express the fact that, in the one case, the kind of sensible to which I have a certain kind of relation is a patch of colour, while, in the other case, the kind of sensible to which I have the same kind of relation is a sound. And similarly when I say that I feel warm or smell a smell these different verbs do not express the fact that I have a different kind of relation to the sensibles concerned, but only that I have the same kind of relation to a different kind of sensible. Even when I call up a visual image of a sensible I saw yesterday, or an auditory image of a sound I heard yesterday, I have to those images exactly the same kind of relation which I have to the patches of colour I now see and which I had yesterday to those I saw then.

But this kind of relation, which I sometimes have to sensibles of all sorts of different kinds, images as well as others, is evidently quite different in kind from another relation which I may also have to sensibles. After looking at this black mark, I may turn away my head or close my eyes, and then I no longer actually see the mark I saw just now. I may, indeed, have (I myself actually do have at this moment) a visual image of the mark before my mind; and to this image I do now have exactly the same kind of relation which I had just now to the mark itself. But the image is not identical with the mark of which it is an image; and to the mark itself it is quite certain that I have not now got the same kind of relation as I had just now, when I was actually seeing it. And yet I certainly may now have to that mark itself a kind of relation, which may be expressed by saying that I am thinking of it or remembering it. I can now make judgments about it itself—the very sensible which I did see just now and am no longer seeing: as, for instance, that I did then see it and that it was different from the image of it which I am now seeing. It is, therefore, quite certain that there is a most important difference between the relation I have to a sensible when I am actually seeing or hearing it, and any relation (for there may be several) which I may have to the same sensible when I am only thinking or or remembering it. And I want to express this difference by using a particular term for the former relation. I shall express this relation, which I certainly do have to a sensible when I actually see or hear it, and most certainly do not have to it, when I only think of or remember it, by saying that there is in my mind a direct apprehension of it. I have expressly chosen this term because, so far as I know, it has not been used hitherto as a technical term; whereas all the terms which have been so used, such as “presented,” “given,” “perceived,” seem to me to have been spoilt by ambiguity. People sometimes, no doubt, use these terms as names for the kind of relation I am concerned with. But you can never be sure, when an entity is said to be “given” or “presented” or “perceived,” that what is meant is simply and solely that it has to someone that relation which sensibles do undoubtedly have to me when I actually see or hear them, and which they do not have to me when I only think of or remember them.

I have used the rather awkward expression “There is in my mind a direct apprehension of this black mark,” because I want to insist that though, when I see the mark, the mark certainly has to something the fundamental relation which I wish to express by saying that it is directly apprehended, and though the event which consists in its being directly apprehended by that something is certainly a mental act of mine or which occurs in my mind, yet the something which directly apprehends it may quite possibly not be anything which deserves to be called “I” or “me.” It is quite possible, I think, that there is no entity whatever which deserves to be called “I” or “me” or “my mind”; and hence that nothing whatever is ever directly apprehended by me. Whether this is so or not, depends on the nature of that relation which certainly does hold between all those mental acts which are mine, and does not hold between any of mine and any of yours; and which holds again between all those mental acts which are yours, but does not hold between any of yours and any of mine. And I do not feel at all sure what the correct analysis of this relation is. It may be the case that the relation which unites all those acts of direct apprehension which are mine, and which is what we mean to say that they have to one another when we say they are all mine, really does consist in the fact that one and the same entity is what directly apprehends in each of them: in which case this entity could properly be called “me,” and it would be true to say that, when I see this black mark, I directly apprehend it. But it is also quite possible (and this seems to me to be the view which is commonest amongst psychologists) that the entity which directly apprehends, in those acts of direct apprehension which are mine, is numerically different in every different act; and that what I mean by calling all these different acts mine is either merely that they have some kind of relation to one another or that they all have a common relation to some other entity, external to them, which may or may not be something which deserves to be called “me.” On any such view, what I assert to be true of this black mark, when I say that it is seen by me, would not be simply that it is directly apprehended by me, but something more complex in which, besides direct apprehension, some other quite different relation was also involved. I should be asserting both (1) that the black mark is being directly apprehended by something, and (2) that this act of direct apprehension has to something else, external to it, a quite different relation, which is what makes it an act of mine. I do not know how to decide between these views, and that is why I wished to explain that the fundamental relation which I wish to call direct apprehension, is one which quite possibly never holds between me and any sensible. But, once this has been explained, I think no harm can result from using the expression “I directly apprehend A” as a synonym for “A direct apprehension of A occurs in my mind.” And in future I shall so speak, because it is much more convenient.

The only other point, which seems to me to need explanation, in order to make it quite clear what the relation I call “direct apprehension” is, concerns its relation to attention; and as to this I must confess I don’t feel clear. In every case where it is quite clear to me that I am directly apprehending a given entity, it seems also clear to me that I am, more or less, attending to it; and it seems to me possible that what I mean by “direct apprehension” may be simply identical with what is meant by “attention,” in one of the senses in which that word can be used. That it can, at most, only be identical with one of the relations meant by attention seems to me clear, because I certainly can be said to attend, in some sense or other, to entities, which I am not directly apprehending: I may, for instance, think, with attention, of a sensible, which I saw yesterday, and am certainly not seeing now. It is, therefore, clear that to say I am attending to a thing and yet am not directly apprehending it, is not a contradiction in terms: and this fact alone is sufficient to justify the use of the special term “direct apprehension.” But whether to say that I am directly apprehending a given thing and yet am not attending to it, in any degree at all, is or is not a contradiction in terms, I admit I don’t feel clear.

However that may be, one relation, in which sensibles of all sorts do sometimes stand to our minds, is the relation constituted by the fact that we directly apprehend them: or, to speak more accurately, by the fact that events which consist in their being directly apprehended are in our minds, in the sense in which to say that an event is in our minds means merely that it is a mental act of ours—that it has to our other mental acts that relation (whatever it may be) which we mean by saying that they are all mental acts of the same individual. And it is clear that to say of a sensible that it is directly apprehended by me, is to say of it something quite different from what I say of a mental act of mine, when I say that this mental act is in my mind: for nothing is more certain than that an act of direct apprehension or belief may be in my mind, without being itself directly apprehended by me. If, therefore, by saying that a sensible is in our minds or is ours, we mean merely that it is directly apprehended by us, we must recognise that we are here using the phrases “in our minds” or “ours” in quite a different sense from that in which we use them when we talk of our mental acts being “in our minds” or “ours.” And why I say this is because I think that these two relations are very apt to be confused. When, for instance, we say of a given entity that it is “experienced,” or when the Germans say that it is “erlebt,” it is sometimes meant, I think, merely that it is directly apprehended, but sometimes that it is in my mind, in the sense in which, when I entertain a belief, this act of belief is in my mind.

But (2) it seems to me to be commonly held that sensibles are often in our minds in some sense quite other than that of being directly apprehended by us or that of being thought of by us. This seems to me to be often what is meant when people say that they are “immediately experienced” or are “subjective modifications”; though, of course, both expressions are so ambiguous, that when people say that a given entity is immediately experienced or is a subjective modification, they may mean merely that it is directly apprehended. And since I think this view is held, I want to explain that I see no reason whatever for thinking that sensibles ever are experienced by us in any other sense than that of being directly apprehended by us. Two kinds of argument, I think, are sometimes used to show that they are.

(a) It is a familiar fact that, when, for instance, we are in a room with a ticking clock, we may seem suddenly to become aware of the ticks, whereas, so far as we can tell, we had previously not heard them at all. And it may be urged that in these cases, since the same kind of stimulus was acting on our ears all the time, we must have experienced the same kind of sensible sounds, although we did not directly apprehend them.

But I think most psychologists are now agreed that this argument is quite worthless. There seem to me to be two possible alternatives to the conclusion drawn. It may, I think, possibly be the case that we did directly apprehend the ticks all the time, but that we cannot afterwards remember that we did, because the degree of attention (if any) with which we heard them was so small, that in ordinary life we should say that we did not attend to them at all. But, what, I think, is much more likely is that, though the same stimulus was acting on our ears, it failed to produce any mental effect whatever, because our attention was otherwise engaged.

(b) It is said that sometimes when we suddenly become aware, say, of the eighth stroke of a striking clock, we can remember earlier strokes, although we seem to ourselves not to have directly apprehended them. I cannot say that I have ever noticed this experience in myself, but I have no doubt that it is possible. And people seem inclined to argue that, since we can remember the earlier strokes, we must have experienced them, though we did not directly apprehend them.

But here again, the argument does not seem to me at all conclusive. I should say, again, that it is possible that we did directly apprehend them, but only with a very slight degree of attention (if any). And, as an alternative, I should urge that there is no reason why we should not be able to remember a thing, which we never experienced at all.

I do not know what other arguments can be used to show that we sometimes experience sensibles in a sense quite other than that of directly apprehending them. But I do not know how to show that we do not; and since people whose judgment I respect, seem to hold that we do, I think it is worth while to say something as to what this sense of “experience” can be, in case it does occur.

I have said that sometimes when people say that a given entity is “experienced” they seem to mean that it belongs to some individual, in the sense in which my acts of belief belong to me. To say that sensibles were experienced by me in this sense would, therefore, be to say that they sometimes have to my acts of belief and acts of direct apprehension the same relation which these have to one another—the relation which constitutes them mine. But that sensibles ever have this kind of relation to my mental acts, is a thing which I cannot believe. Those who hold that they are ever experienced at all, in some sense other than that of being directly apprehended, always hold, I think, that, whenever they are directly apprehended by us, they also, at the same time, have to us this other relation as well. And it seems to me pretty clear that when I do directly apprehend a sensible, it does not have to me the same relation which my direct apprehension of it has.

If, therefore, sensibles are ever experienced by us at all, in any sense other than that of being directly apprehended by us, we must, I think, hold that they are so in an entirely new sense, quite different both from that in which to be experienced means to be directly apprehended, and from that in which to be experienced means to occur in some individual’s mind. And I can only say that I see no reason to think that they ever are experienced in any such sense. If they are, the fact that they are so is presumably open to the inspection of us all; but I cannot distinguish any such fact as occurring in myself, as I can distinguish the fact that they are directly apprehended. On the other hand, I see no way of showing that they are not experienced in some such sense; and perhaps somebody will be able to point it out to me. I do not wish to assume, therefore, that there is no such sense; and hence, though I am inclined to think that the only sense in which they are experienced is that of being directly apprehended, I shall, in what follows, use the phrase “experienced” to mean either directly apprehended or having to something this supposed different relation, if such a relation there be.

(3) We may now, therefore, raise the question: Do sensibles ever exist at times when they are not being experienced at all?

To this question it is usual to give a negative answer, and two different a priori reasons may be urged in favour of that answer.

The first is what should be meant by Berkeley’s dictum that the esse of sensibles is percipi. This should mean, whatever else it may mean, at least this: that to suppose a sensible to exist and yet not to be experienced in self-contradictory. And this at least seems to me to be clearly false. Anything which was a patch of colour would be a sensible; and to suppose that there are patches of colour which are not being experienced is clearly not self-contradictory, however false it may be.

It may, however, be urged (and this is the second argument) that, though to suppose a thing to be a sensible and yet not experienced is not self-contradictory, yet we can clearly see that nothing can have the one property without having the other. And I do not see my way to deny that we may be able to know, a priori that such a connection holds between two such properties. In the present case, however, I cannot see that it does hold, and therefore, so far as a priori reasons go, I conclude that there is no reason why sensibles should not exist at times when they are not experienced.

It may, however, be asked: Is there any reason to suppose that they ever do? And the reason, which weighs with me most, is one which applies, I think, to a certain class of sensibles only; a class which I will try to define by saying that it consists of those which would (under certain conditions which actually exist) be experienced in a sensation proper, if only a living body, having a certain constitution, existed under those conditions in a position in which no such body does actually exist. I think it is very probable that this definition does not define at all accurately the kind of sensibles I mean; but I think that what the definition aims at will become clearer when I proceed to give my reasons for supposing that sensibles, of a kind to be defined in some such way, do exist unexperienced. The reason is simply that, in Hume’s phrase, I have “a strong propensity to believe” that, e.g., the visual sensibles which I directly apprehend in looking at this paper, still exist unchanged when I merely alter the position of my body by turning away my head or closing my eyes, provided that the physical conditions outside my body remain unchanged. In such a case it is certainly true in some sense that I should see sensibles like what I saw the moment before, if only my head were still in the position it was at that moment or my eyes unclosed. But if, in such a case, there is reason to think that sensibles which I should see, if the position of my body were altered, exist in spite of the fact that I do not experience them, there is, I think, an equal reason to suppose it in other cases. We must, for instance, suppose that the sensibles which I should see now, if I were at the other end of the room, or if I were looking under the table, exist at this moment, though they are not being experienced. And similarly we must suppose that the sensibles which you would see, if you were in the position in which I am now, exist at this moment, in spite of the fact that they may be more or less different from those which I see, owing to the different constitution of our bodies. All this implies of course, that a vast number of sensibles exist at any moment, which are not being experienced at all. But still it implies this only with regard to sensibles of a strictly limited class, namely sensibles which would be experienced in a sensation proper, if a body, having a certain constitution, were in a position in which it is not, under the given physical conditions. It does not, for instance, imply that any images, of which it may be true that I should have them, under present physical conditions, if the position of my body were altered, exist now; nor does it imply that sensibles which would be experienced by me now in a sensation proper, if the physical conditions external to my body were different from what they are, exist now.

I feel, of course, that I have only succeeded in defining miserably vaguely the kind of sensibles I mean; and I do not know whether the fact that I have a strong propensity to believe that sensibles of a kind to be defined in some such way, do exist unexperienced, is any good reason for supposing that they actually do. The belief may, of course, be a mere prejudice. But I do not know of any certain test by which prejudices can be distinguished from reasonable beliefs. And I cannot help thinking that there may be a class of sensibles, capable of definition in some such way, which there really is reason to think exist unexperienced.

But, if I am not mistaken, there is an empirical argument which, though, even if it were sound, it would have no tendency whatever to show that no sensibles exist unexperienced, would, if it were sound, show that this very class of sensibles, to which alone my argument for unexperienced existence applies, certainly do not so exist. This, it seems to me, is the most weighty argument which can be used upon the subject; and I want, therefore, to give my reasons for thinking that it is fallacious.

The argument is one which asserts that there is abundant empirical evidence in favour of the view that the existence of the sensibles which we experience at any time, always depends upon the condition of our nervous system: so that, even where it also depends upon external physical conditions, we can safely say that sensibles, which we should have experienced, if only our nervous system had been in a different condition, certainly do not exist, when it is not in that condition. And the fallacy of this argument seems to me to lie in the fact that it does not distinguish between the existence of the sensibles which we experience and the fact that we experience them. What there is evidence for is that our experience of sensibles always depends upon the condition of our nervous system; that, according as the condition of the nervous system changes, different sensibles are experienced, even where other conditions are the same. But obviously the fact that our experience of a given sensible depends upon the condition of our nervous system does not directly show that the existence of the sensible experienced always also so depends. The fact that I am now experiencing this black mark is certainly a different fact from the fact that this black mark now exists. And hence the evidence which does tend to show that the former fact would not have existed if my nervous system had been in a different condition, has no tendency to show that the latter would not have done so either. I am sure that this distinction ought to be made; and hence, though I think there may be other reasons for thinking that the very existence of the sensibles, which we experience, and not merely the fact that we experience them does always depend upon the condition of our nervous systems, it seems to me certain that this particular argument constitutes no such reason.

And I think that those who suppose that it does are apt to be influenced by an assumption, for which also, so far as I can see, there is no reason. I have admitted that the only reason I can see for supposing that sensibles which we experience ever exist unexperienced, seems to lead to the conclusion that the sensibles which would be seen by a colour-blind man, if he occupied exactly the position which I, who am not colour-blind, now occupy, exist now, just as much as those which I now see. And it may be thought that this implies that the sensibles, which he would see, and which would certainly be very different from those which I see, are nevertheless at this moment in exactly the same place as those which I see. Now, for my part, I am not prepared to admit that it is impossible they should be in the same place. But the assumption against which I wish to protest, is the assumption that, if they exist at all, they must be in the same place. I can see no reason whatever for this assumption. And hence any difficulties there may be in the way of supposing that they could be in the same place at the same time as the sensibles which I see, do not at all apply to my hypothesis, which is only that they exist now, not that they exist in the same place in which mine do.

On this question, therefore, as to whether sensibles ever exist at times when they are not experienced, I have only to say (1) that I think there is certainly no good reason whatever for asserting that no sensibles do; and (2) that I think perhaps a certain amount of weight ought to be attached to our instinctive belief that certain kinds of sensibles do; and that here again any special arguments which may be brought forward to show that, whether some sensibles exist unexperienced or not, this kind certainly do not, are, so far as I can see, wholly inconclusive.

(II)

I now pass to the question how sensibles are related to physical objects. And here I want to say, to begin with, that I feel extremely puzzled about the whole subject. I find it extremely difficult to distinguish clearly from one another the different considerations which ought to be distinguished; and all I can do is to raise, more or less vaguely, certain questions as to how certain particular sensibles are related to certain particular physical objects, and to give the reasons which seem to me to have most weight for answering these questions in one way rather than another. I feel that all that I can say is very tentative.

To begin with, I do not know how “physical object” is to be defined, and I shall not try to define it. I shall, instead, consider certain propositions, which everybody will admit to be propositions about physical objects, and which I shall assume that I know to be true. And the question I shall raise is as to how these propositions are to be interpreted—in what sense they are true; in considering which, we shall at the same time consider how they are related to certain sensibles.

I am looking at two coins, one of which is a half-crown, the other a florin. Both are lying on the ground; and they are situated obliquely to my line of sight, so that the visual sensibles which I directly apprehend in looking at them are visibly elliptical, and not even approximately circular. Moreover, the half-crown is so much farther from me than the florin that its visual sensible is visibly smaller than that of the florin.

In these circumstances I am going to assume that I know the following propositions to be true; and no one, I think, will deny that we can know such propositions to be true, though, as we shall see, extremely different views may be taken as to what they mean. I know (a) that, in the ordinary sense of the word “see” I am really seeing two coins; an assertion which includes, if it is not identical with, the assertion that the visual experiences, which consist in my direct apprehension of those two elliptical patches of colour, are sensations proper, and are not either hallucinations nor mere experiences of “images”; (b) that the upper sides of the coins are really approximately circular, and not merely elliptical like the visual sensibles; (c) that the coins have another side, and an inside, though I don’t see it; (d) that the upper side of the half-crown is really larger than that of the florin, though its visual sensible is smaller than the visual sensible of the upper side of the florin: (e) that both coins continue to exist, even when I turn away my head or shut my eyes; but in saying this, I do not, of course, mean to say that there is absolutely no change in them; I daresay there must be some change, and I do not know how to define exactly what I do mean. But we can, I think, say at least this: viz., that propositions (h), (c), and (d) will still be true, although proposition (a) has ceased to be true.

Now all these propositions are, I think, typical propositions of the sort which we call propositions about physical objects; and the two coins themselves are physical objects, if anything is. My question is: In what sense are these propositions true?

And in considering this question, there are, I think, two principles which we can lay down as certain to begin with; though they do not carry us very far.

The one is (a) that the upper side of the coin, which I am said to see, is not simply identical with the visual sensible which I directly apprehend in seeing it. That this is so might be thought to follow absolutely from each of the two facts which I have called (b) and (d); but I am not quite sure that it does follow from either of these or from both together: for it seems to me just possible that the two sensibles in question, though not circular in my private space, may yet be circular in physical space; and similarly that though the sensible of the half-crown is smaller than that of the florin in my private space, it may be larger in physical space. But what I think it does follow from is the fact that another person may be seeing the upper side of the coin in exactly the same sense in which I am seeing it, and yet his sensible be certainly different from mine. From this it follows absolutely that the upper side of the coin cannot be identical with both sensibles, since they are not identical with one another. And though it does not follow absolutely that it may not be identical with one of the two, yet it does follow that we can get a case in which it is not identical with mine and I need only assume that the case I am taking is such a case.

From this it follows that we must distinguish that sense of the word “see” in which we can be said to “see” a physical object, from that sense of the word in which “see” means merely to directly apprehend a visual sensible. In a proposition of the form “I see A,” where A is a name or description of some physical object, though, if this proposition is to be true, there must be some visual sensible, B, which I am directly apprehending, yet the proposition “I see A” is certainly not always, and probably never, identical in meaning with the proposition “I directly apprehend B.” In asserting “I see A” we are asserting not only that we directly apprehend some sensible but also something else about this sensible—it may be only some proposition of the form, “and this sensible has certain other properties,” or it may be some proposition of the form “and I know this sensible to have certain other properties.” Indeed we have not only to distinguish that sense of the word “perceive” in which it is equivalent to “directly apprehend,” from one sense in which we can be said to perceive a physical object; we have also to distinguish at least two different senses in which we can be said to perceive physical objects, different both from one another and from “directly apprehend.” For it is obvious that though I should be said to be now seeing the half-crown, there is a narrower, and more proper, sense, in which I can only be said to see one side of it—not its lower side or its inside, and not therefore the whole half-crown.

The other principle, which we can lay down to start with is (β) that my knowledge of all the five propositions (a) to (e), is based, in the last resort, on experiences of mine consisting in the direct apprehension of sensibles and in the perception of relations between directly apprehended sensibles. It is based on these, in at least this sense, that I should never have known any of these propositions if I had never directly apprehended any sensibles nor perceived any relations between them.

What, in view of these two principles, can be the sense in which my five propositions are true?

(1) It seems to me possible that the only true interpretation which can be given to any of them is an interpretation of a kind which I can only indicate rather vaguely as follows: Namely, that all of them express only a kind of fact which we should naturally express by saying that, if certain conditions were fulfilled, I or some other person, should directly apprehend certain other sensibles. For instance the only true thing that can be meant by saying that I really see coins may be some such thing as that, if I were to move my body in certain ways, I should directly apprehend other sensibles, e.g. tactual ones, which I should not directly apprehend as a consequence of these movements, if these present visual experiences of mine were mere hallucinations or experiences of “images.” Again, the only true thing that can be meant by saying that the upper sides of the coins are really approximately circular may be some such thing as that, if I were looking straight at them, I should directly apprehend circular sensibles. And similarly, the only true interpretation of (c) may be some such fact as that, if I were to turn the coins over, or break them up, I should have certain sensations, of a sort I can imagine very well; of (d) that if I were at an equal distance from the half-crown and the florin, the sensible, I should then see corresponding to the half-crown would be bigger than that corresponding to the florin, whereas it is now smaller; of (e) that, if, when my eyes were closed, they had been open instead, I should have seen certain sensibles.

It is obvious, indeed, that if any interpretation on these lines is the only true interpretation of our five propositions, none of those which I have vaguely suggested comes anywhere near to expressing it in its ultimate form. They cannot do so for the simple reason that, in them, the conditions under which I should experience certain other sensibles are themselves expressed in terms of physical objects, and not in terms of sensibles and our experience of them. The conditions are expressed in such terms as “if I were to move my body,” “if I were to look straight at the coins,” “if I were to turn the coins over,” etc.; and all these are obviously propositions, which must themselves again be interpreted in terms of sensibles, if our original five propositions need to be so. It is obvious, therefore, that any ultimate interpretation of our five propositions, on these lines, would be immensely complicated; and I cannot come anywhere near to stating exactly what it would be. But it seems to me possible that some such interpretation could be found, and that it is the only true one.

The great recommendation of this view seems to me to be that it enables us to see, more clearly than any other view can, how our knowledge of physical propositions can be based on our experience of sensibles, in the way in which principle (β) asserts it to be. If, when I know that the coins are round, all that I know is some such thing as that if, after experiencing the sensibles I do now experience, I were to experience still others, I should finally experience a third set, we can understand, as clearly as we can understand how any knowledge can be obtained by induction at all, how such a knowledge could be based on our previous experience of sensibles, and how it could be verified by our subsequent experience.

On the other hand, apart from the difficulty of actually giving any interpretation on these lines, which will meet the requirements, the great objection to it seems to me to be this. It is obvious that, on this view, though we shall still be allowed to say that the coins existed before I saw them, are circular etc., all these expressions, if they are to be true, will have to be understood in a Pickwickian sense. When I know that the coins existed before I saw them, what I know will not be that anything whatever existed at that time, in the sense in which those elliptical patches of colour exist now. All that I know will be simply that, since the elliptical patches exist now, it is true, that, if certain unrealised conditions had been realised, I should have had certain sensations that I have not had; or, if certain conditions, which may or may not be realised in the future, were to be so, I should have certain experiences. Something like this will actually be the only true thing that can be meant by saying that the coins existed before I saw them. In other words, to say of a physical object that it existed at a given time will always consist merely in saying of some sensible, not that it existed at the time in question, but something quite different and immensely complicated. And thus, though, when I know that the coins exist, what I know will be merely some proposition about these sensibles which I am directly apprehending, yet this view will not contradict principle (a) by identifying the coins with the sensibles. For it will say that to assert a given thing of the coins is not equivalent to asserting the same thing of the sensibles, but only to asserting of them something quite different.

The fact that these assertions that the coins exist, are round, etc., will, on this view, only be true in this outrageously Pickwickian sense, seems to me to constitute the great objection to it. But it seems to me to be an objection only, so far as I can see, because I have a “strong propensity to believe” that, when I know that the coins existed before I saw them, what I know is that something existed at that time, in the very same sense in which those elliptical patches now exist. And, of course, this belief may be a mere prejudice. It may be that when I believe that I now have, in my body, blood and nerves and brain, what I believe is only true, if it does not assert, in the proper sense of the word “existence,” the present existence of anything whatever, other than sensibles which I directly apprehend, but only makes assertions as to the kind of experiences a doctor would have, if he dissected me. But I cannot feel at all sure that my belief, that, when I know of the present Existence of these things (as I think I do), I am knowing of the present existence (in the proper sense) of things other than any sensibles which I or any one else am now directly apprehending, is a mere prejudice. And therefore I think it is worth while to consider what, if it is not, these things, of whose existence I know, can be.

(2) It is certain that if, when I know that that half-crown existed before I saw it, I am knowing that something existed at that time in other than a Pickwickian sense, I only know this something by description; and it seems pretty clear that the description by which I know it is as the thing which has a certain connection with this sensible which I am now directly apprehending. But what connection? We cannot simply say, as many people have said, that by “that half-crown” I mean the thing which caused my experience of this sensible; because events which happen between the half-crown and my eyes, and events in my eyes, and optic nerves, and brains are just as much causes of my experiences as the half-crown itself. But it may perhaps be the case that the half-crown has some particular kind of causal relation to my experience, which these other events have not got—a kind which may be expressed, perhaps, by saying that it is its “source.” And hence, when I know that that half-crown is circular, I may perhaps be knowing that the source of this experience is circular.

But what sort of a thing can this “source” be?

One kind of view, which I think is very commonly held, is that it is something “spiritual” in its nature, or something whose nature is utterly unknown to us. And those who hold this view are apt to add, that it is not really “circular,” in any sense at all; nor is the “source” of my half-crown experience, in any sense at all, “bigger” than that of my florin experience. But if this addition were seriously meant, it would, of course, amount to saying that propositions (b) and (d) are not true, in any sense at all; and I do not think that those who make it, really mean to say this. I think that what they mean is only that the only sense in which those “sources” are circular, and one bigger than the other, is one in which to say this merely amounts to saying that the sensibles, which they would cause us to experience, under certain conditions, would be circular, and one bigger than the other. In other words, in order to give a true interpretation to the propositions that the coins are circular and one bigger than the other, they say that we must interpret them in the same kind of way in which view (1) interpreted them; and the only difference between their view and view (1), is that, whereas that said that you must give a Pickwickian interpretation both to the assertion that the coins exist, and to the assertion that they are circular, they say that you must not give it to the former assertion, and must to the latter.

To this view my objection is only that any reason there may be for saying that the “sources” exist in other than a Pickwickian sense, seems to me to be also a reason for saying that they are “circular” in a sense that is not Pickwickian. I have just as strong a propensity to believe that they are really circular, in a simple and natural sense, as that they exist in such a sense: and I know of no better reason for believing either.

(3) It may be suggested, next, that these “sources,” instead of being something spiritual in their nature or something of a nature utterly unknown, consist simply of sensibles, of a kind which I have previously tried to define; namely of all those sensibles, which anybody would, under the actual physical conditions, experience in sensations proper of which the half-crown and the florin were the source, if their bodies were in any of the positions relatively to those coins, in which they would get sensations from them at all. We saw before that it seems possible that all these sensibles do really exist at times when they are not experienced, and that some people, at all events, seem to have a strong propensity to believe that they do. And in favour of the view that some such huge collection of sensibles is the upper side of the half-crown, is the fact that we do seem to have a strong propensity to believe that any particular sensible, which we directly apprehend in looking at the upper side of the half-crown, and of our direct apprehension of which the upper side is the source, is in the place in which the upper side is. And that some sense might be given to the expression “in the same place as,” in which it could be true that sensibles of all sorts of different shapes and sizes, and of all sorts of different colours, were in the same place at the same time, seems to me to be possible. But the objection to this view seems to me to be the same as to the last; namely that if the upper side of the half-crown were identical with such a collection of sensibles, then the only sense in which it could be said to be “circular,” or bigger than that of the florin, would certainly be very Pickwickian, though not the same as on that view.

(4) If, for the reasons given, we reject both (1), (2), and (3) as interpretations of our five propositions, the only alternative I can think of that remains, is one which is roughly identical, so far as I can see, with Locke’s view. It is a view which asserts that the half-crown and the florin really did exist (in the natural sense) before I saw them; that they really are approximately circular (again in the natural sense); that, therefore, they are not composed of sensibles which I or others should directly apprehend under other conditions; and that therefore also neither these sensibles (even if such do now exist) nor those which I am now directly apprehending are in the place in which the coins are. It holds, therefore, that the coins do really resemble some sensibles, in respect of the “primary” qualities which these have; that they really are round, and one larger than the other, in much the same sense in which some sensibles are round and some larger than others. But it holds also that no sensibles which we ever do directly apprehend, or should directly apprehend, if at a given time we were in other positions, are parts of those coins; and that, therefore, there is no reason to suppose that any parts of the coins have any of the “secondary qualities”—colour, etc.—which any of these sensibles have.

On this view, it is plain, there is nothing to prevent us from holding that, as suggested in I (3), all sorts of unexperienced sensibles do exist. We are only prevented from holding that, if they do, those which have the same source all exist in the same place as their source. And the natural view to take as to the status of sensibles generally, relatively to physical objects, would be that none of them, whether experienced or not, were ever in the same place as any physical object. That none, therefore, exist “anywhere” in physical space; while, at the same time, we can also say, as argued in I (2), that none exist “in the mind,” except in the sense that some are directly apprehended by some minds. And the only thing that would need to be added, is that some, and some only, resemble the physical objects which are their source, in respect of their shape.

To this view I can see no objection except the serious one that it is difficult to answer the questions: How can I ever come to know that these sensibles have a “source” at all? And how do I know that these “sources” are circular? It would seem that, if I do know these things at all, I must know immediately, in the case of some sensibles, both that they have a source and what the shape of this source is. And to this it may be objected that this is a kind of thing which I certainly cannot know immediately. The argument in favour of an interpretation of type (i) seems to me to rest wholly on the assumption that there are only certain kinds of facts which I can know immediately; and hence that if I believe I know a fact, which is not of this kind, and which also I cannot have learnt immediately, my belief must be a mere prejudice. But I do not know how it can be shown that an assertion of the form: Facts of certain kinds are the only ones you can know immediately; is itself not a prejudice. I do not think, therefore, that the fact that, if this last view were true, we should have to admit that we know immediately facts of a kind which many people think we cannot know immediately, is a conclusive objection to it.