But now let us consider the cases in which we are not prepared to assert that the surface in question has changed perceptibly. The strange fact, from which the argument I mean is drawn, is that, in a very large number of such cases, it seems as if it were unmistakably true that the presented object, about which we are making our judgment when we talk of "This surface" at the later time, is perceptibly different, from that about which we are making it when we talk of the surface I saw just now. If, at the later time, I am at a sufficiently greater distance from the surface, the presented object which corresponds to it at the time seems to be perceptibly smaller, than the one which corresponded to it before. If I am looking at it from a sufficiently oblique angle, the later presented object often seems to be perceptibly different in shape—a perceptibly flatter ellipse, for instance. If I am looking at it, with blue spectacles on, when formerly I had none, the later presented object seems to be perceptibly different in colour from the earlier one. If I am perceiving it by touch alone, whereas formerly I was perceiving it by sight alone, the later presented object seems to be perceptibly different from the earlier, in respect of the fact that it is not coloured at all, whereas the earlier was, and that, on the other hand, it has certain tactual qualities, which the earlier had not got. All this seems to be as plain as it can be, and yet it makes absolutely no difference to the fact that of the surface in question we are not prepared to judge that it is perceptibly different from what it was. Sometimes, of course, where there seems to be no doubt that the later presented object is perceptibly different from the earlier, we may not notice that it is so. But even where we do notice the apparent difference, we do still continue to judge of the surface in question: This surface is not, so far as I can tell with certainty by perception, in any way different from what it was when I saw it or touched it just now; I am not prepared to assert that it has changed perceptibly. It seems, therefore, to be absolutely impossible that the surface seen at the later time should be identical with the object presented then, and the surface seen at the earlier identical with the object presented then, for the simple reason that, whereas with regard to the later seen surface I am not prepared to judge that it is in any way perceptibly different from that seen earlier, it seems that with regard to the later sense-datum I cannot fail to judge that it is perceptibly different from the earlier one: the fact that they are perceptibly different simply stares me in the face. It seems, in short, that when, in such a case, I judge: "This surface is not, so far as I can tell, perceptibly different from the one I saw just now," I cannot possibly be judging of the presented object "This is not, so far as I can tell, perceptibly different from that object which was presented to me just now," for the simple reason that I can tell, as certainly, almost, as I can tell anything, that it is perceptibly different.
That is the argument, as well as I can put it, for saying that this presented object, is not identical with this part of the surface of this inkstand; and that, therefore, when I judge "This is part of the surface of an inkstand," I am not judging of this presented object, which nevertheless is the ultimate subject of my judgment, that it is part of the surface of an inkstand. And this argument does seem to me to be a very powerful one.
But nevertheless it does not seem to me to be quite conclusive, because it rests on an assumption, which, though it seems to me to have great force, does not seem to me quite certain. The assumption I mean is the assumption that, in such cases as those I have spoken of, the later presented object really is perceptibly different from the earlier. This assumption has, if I am not mistaken, seemed to many philosophers to be quite unquestionable; they have never even thought of questioning it; and I own that it used to be so with me. And I am still not sure that I may not be talking sheer nonsense in suggesting that it can be questioned. But, if I am, I am no longer able to see that I am. What now seems to me to be possible is that the sense-datum which corresponds to a tree, which I am seeing, when I am a mile off, may not really be perceived to be smaller than the one, which corresponds to the same tree, when I see it from a distance of only a hundred yards, but that it is only perceived to seem smaller; that the sense-datum which corresponds to a penny, which I am seeing obliquely, is not really perceived to be different in shape from that which corresponded to the penny, when I was straight in front of it, but is only perceived to seem different—that all that is perceived is that the one seems elliptical and the other circular; that the sense-datum presented to me when I have the blue spectacles on is not perceived to be different in colour from the one presented to me when I have not, but only to seem so; and finally that the sense-datum presented when I touch this finger is not perceived to be different in any way from that presented to me when I see it, but only to seem so that I do not perceive the one to be coloured and the other not to be so, but only that the one seems coloured and the other not. If such a view is to be possible, we shall have, of course, to maintain that the kind of experience which I have expressed by saying one seems different from the other—"seems circular," "seems blue," "seems coloured," and so on—involves an ultimate, not further analysable, kind of psychological relation, not to be identified either with that involved in being "perceived" to be so and so, or with that involved in being "judged" to be so and so; since a presented object might, in this sense, seem to be elliptical, seem to be blue, etc., when it is neither perceived to be so, nor judged to be so. But there seems to me to be no reason why there should not be such an ultimate relation. The great objection to such a view seems to me to be the difficulty of believing that I don't actually perceive this sense-datum to be red, for instance, and that other to be elliptical; that I only perceive, in many cases, that it seems so. I cannot, however, now persuade myself that it is quite clear that I do perceive it to be so. And, if I don't, then it seems really possible that this presented object really is identical with this part of the surface of this inkstand; since, when I judge, as in the cases supposed, that the surface in question is not, so far as I can tell, perceptibly different from what it was, I might really be judging of the two sense-data that they also were not, so far as I can tell, perceptibly different, the only difference between the two that is perceptible, being that the one seems to be of a certain size, shape or colour, and the other to be of a different and incompatible size, shape or colour. Of course, in those cases, as in that of the balloon being blown up, where I "perceive" that the surface has changed, e.g. in size, it would have to be admitted that I do perceive of the two sense-data not merely that they seem different in size, but that they are so. But I think it would be possible to maintain that the sense in which, in these cases, I "perceive" them to be different, is a different one from that in which, both in these and in the others, I perceive them to seem so.
Possibly in making this suggestion that sense-data, in cases where most philosophers have assumed unhesitatingly that they are perceived to be different, are only really perceived to seem different, I am, as I said, talking sheer nonsense, though I cannot, at the moment, see that I am. And possibly, even if this suggestion itself is not nonsense, even if it is true, there may be other fatal objections to the view that this presented object really is identical with this part of the surface of this inkstand. But what seems to me certain is that, unless this suggestion is true, then this presented object is certainly not identical with this part of the surface of this inkstand. And since it is doubtful whether it is not nonsense, and still more doubtful whether it is true, it must, I think, be admitted to be highly doubtful whether the two are identical. But, if they are not identical, then what I am judging with regard to this presented object, when I judge "This is an inkstand," is certainly not that it is itself part of the surface of an inkstand; and hence, it is worth while to inquire further, what, if I am not judging this, I can be judging with regard to it.
And here, I think, the first natural suggestion to make is that just as, when I talk of "this inkstand," what I seem really to mean is "the inkstand of which this is part of the surface," so that the inkstand is only known to me by description as the inkstand of which this material surface is part of the surface, so again when I talk of "this material surface," what I really mean is "the material surface to which this (presented object) has a certain relation," so that this surface is, in its turn, only known to me by description as the surface which has a certain relation to this presented object. If that were so, then what I should be judging of this presented object, when I judge "This is part of the surface of an inkstand," would be not that it is itself such a part, but that the thing which stands to it in a certain relation is such a part: in short, what I should be judging with regard to it, would be "There's one thing and one only which stands to this in this relation, and the thing which does so is part of the surface of an inkstand."
But if we are to adopt the view that something of this sort is what we are judging, there occurs at once the pressing question: What on earth can the relation be with regard to which we are judging, that one and only one thing stands in it to this presented object? And this is a question to which, so far as I know, none of those philosophers, who both hold (as many do) that this presented object is not identical with this part of the surface of this inkstand, and also that there really is something of which it could be truly predicated that it is this part of the surface of this inkstand (that is to say, who reject all views of the Mill-Russell type), have given anything like a clear answer. It does not seem to have occurred to them that it requires an answer, chiefly, I think, because it has not occurred to them to ask what we can be judging when we make judgments of this sort. There are only two answers, that I can think of, which might be suggested with any plausibility.
Many philosophers, who take the view that the presented objects about which we make these judgments are sensations of ours, and some even who do not, are in the habit of talking of "the causes" of these objects as if we knew, in the case of each, that it had one and only one cause; and many of them seem to think that this part of the surface of this inkstand could be correctly described as the cause of this presented object. They suggest, therefore, the view that what I am judging in this case might be: "This presented object has one and only one cause, and that cause is part of the surface of an inkstand." It seems to me quite obvious that this view, at all events, is utterly untenable. I do not believe for a moment, nor does any one, and certainly therefore do not judge, that this presented object has only one cause: I believe that it has a whole series of different causes. I do, in fact, believe that this part of the surface of this inkstand is one among the causes of my perception of this presented object: that seems to me to be a very well established scientific proposition. And I am prepared to admit that there may be good reasons for thinking that it is one among the causes of this presented object itself, though I cannot myself see that there are any. But that it is the only cause of this presented object I certainly do not believe, nor, I think, does anybody, and hence my judgment certainly cannot be "The cause of this is part of the surface of an inkstand." It might no doubt, be possible to define some kind of causal relation, such that it might be plausibly held that it and it alone causes this presented object in that particular way. But any such definition would, so far as I can see, be necessarily very complicated. And, even when we have got it, it seems to me it would be highly improbable we could truly say that what we are judging in these cases is: "This presented object has one and only one cause, of this special kind." Still, I do not wish to deny that some such view may possibly be true.
The only other suggestion I can make is that there may be some ultimate, not further definable relation, which we might for instance, call the relation of "being a manifestation of," such that we might conceivably be judging: "There is one and only one thing of which this presented object is a manifestation, and that thing is part of the surface of an inkstand." And here again, it seems to me just possible that this may be a true account of what we are judging; only I cannot find the slightest sign that I am in fact aware of any such relation.
Possibly other suggestions could be made as to what the relation is, with regard to which it could be plausibly supposed that in all cases, where we make these judgments we are in fact judging of the presented object "There is one and only one thing which stands to this object in this relation." But it seems to me at least very doubtful whether there is any such relation at all; whether, therefore, our judgment really is of this form, and whether therefore, this part of the surface of this inkstand really is known to me by description as the thing which stands in a certain relation to this presented object. But if it isn't, and if, also, we cannot take the view that what I am judging is that this presented object itself is a part of the surface of an inkstand, there would seem to be no possible alternative but that we must take some view of what I have called the Mill-Russell type. Views of this type, if I understand them rightly, are distinguished from those which I have hitherto considered, by the fact that, according to them, there is nothing whatever in the Universe of which it could truly be predicated that it is this part of the surface of this inkstand, or indeed that it is a part of the surface of an inkstand, or an inkstand, at all. They hold, in short, that though there are plenty of material things in the Universe, there is nothing in it of which it could truly be asserted that it is a material thing: that, though, when I assert "This is an inkstand," my assertion is true, and is such that it follows from it that there is in the Universe at least one inkstand, and, therefore, at least one material thing, yet it does not follow from it that there is anything which is a material thing. When I judge "This is an inkstand," I am judging this presented object to possess a certain property, which is such that, if there are things, which possess that property, there are inkstands and material things, but which is such that nothing which possesses it is itself a material thing; so that in judging that there are material things, we are really always judging of some other property, which is not that of being a material thing, that there are things which possess it. It seems to me quite possible, of course, that some view of this type is the true one. Indeed, this paper may be regarded, if you like, as an argument in favour of the proposition that some such view must be true. Certainly one of my main objects in writing it was to put as plainly as I can some grave difficulties which seem to me to stand in the way of any other view; in the hope that some of those, who reject all views of the Mill-Russell type, may explain clearly which of the alternatives I have suggested they would adopt, or whether, perhaps, some other which has not occurred to me. It does not seem to me to be always sufficiently realised how difficult it is to find any answer to my question "What are we judging in these cases?" to which there are not very grave objections, unless we adopt an answer of the Mill-Russell type. That an answer of this type is the true one, I am not myself, in spite of these objections, by any means convinced. The truth is I am completely puzzled as to what the true answer can be. At the present moment, I am rather inclined to favour the view that what I am judging of this presented object is that it is itself a part of the surface of an inkstand—that, therefore, it really is identical with this part of the surface of this inkstand, in spite of the fact that this involves the view that, where, hitherto, I have always supposed myself to be perceiving of two presented objects that they really were different, I was, in fact, only perceiving that they seemed to be different. But, as I have said, it seems to me quite possible that this view is, as I have hitherto supposed, sheer nonsense; and, in any case, there are, no doubt, other serious objections to the view that this presented object is this part of the surface of this inkstand.