G. E. MOORE, Litt.D. (continued 4)

It is plain, then, that by "making a belief true," we mean something quite different from what Professor James means by "making" that belief. Conditions which have a hand in making a given true belief, may (it appears) have no hand at all in making it true; and conditions which have a hand in making it true may have no hand at all in making it. Certainly this is how we use the words. We should never say that we had made a belief true, merely because we had made the belief. But now, which of these two things does Professor James mean? Does he mean merely the accepted commonplace that we make our true beliefs, in the sense that almost all of them depend for their existence on what has been previously in some human mind? Or does he mean also that we make them true—that their truth also depends on what has been previously in some human mind?

I cannot help thinking that he has the latter, and not only the former in his mind. But, then, what does this involve? If his instances of "truth-making" are to be anything to the purpose, it should mean that, whenever I have a hand in causing one of my own beliefs, I always have to that extent a hand in making it true. That, therefore, I have a hand in actually making the sun rise, the wind blow, and the rain fall, whenever I cause my beliefs in these things. Nay, more, it should mean that, whenever I "make" a true belief about the past, I must have had a hand in making this true. And if so, then certainly I must have had a hand in causing the French Revolution, in causing my father's birth, in making Professor James write this book. Certainly he implies that some man or other must have helped in causing almost every event, in which any man ever truly believed. That it was we who made the planets revolve round the sun, who made the Alps rise, and the floor of the Pacific sink—all these things, and others like them, seem to be involved. And it is these consequences which seem to me to justify a doubt whether, in fact "our truths are to an unascertainable extent man-made." That some of our truths are man-made—indeed, a great many—I fully admit. We certainly do make some of our beliefs true. The Secretary probably had a belief that I should write this paper, and I have made his belief true by writing it. Men certainly have the power to alter the world to a certain extent; and, so far as they do this, they certainly "make true" any beliefs, which are beliefs in the occurrence of these alterations. But I can see no reason for supposing that they "make true" nearly all those of their beliefs which are true. And certainly the only reason which Professor James seems to give for believing this—namely, that the existence of almost all their beliefs depends on them—seems to be no reason for it at all. For unquestionably a man does not "make true" nearly every belief whose existence depends on him; and if so, the question which of their beliefs and how many, men do "make true" must be settled by quite other considerations.

In conclusion, I wish to sum up what seems to me to be the most important points about this "pragmatist theory of truth," as Professor James represents it. It seems to me that, in what he says about it, he has in his mind some things which are true and others which are false; and I wish to tabulate separately the principal ones which I take to be true, and the principal ones which I take to be false. The true ones seem to me to be these:—

That most of our true beliefs are useful to us; and that most of the beliefs that are useful to us are true.

That the world really does change in some respects; that facts exist at one time, which didn't and won't exist at others; and that hence the world may be better at some future time than it is now or has been in the past.

That the very same words may be true at one time and false at another—that they may express a truth at one time and a falsehood at another.

That the existence of most, if not all, of our beliefs, true as well as false, does depend upon previous events in our mental history; that we should never have had the particular beliefs we do have, had not our previous mental history been such as it was.

That the truth, and not merely the existence, of some of our beliefs, does depend upon us. That we really do make some alterations in the world, and that hence we do help to "make true" all those of our beliefs which are beliefs in the existence of these alterations.

To all of these propositions I have no objection to offer. And they seem to me to be generally admitted commonplaces. A certain class of philosophers do, indeed, imply the denial of every one of them—namely, those philosophers who deny the reality of time. And I think that part of Professor James' object is to protest against the views of these philosophers. All of these propositions do constitute a protest against such views; and so far they might be all that Professor James meant to assert. But I do not think that anyone, fairly reading through what he says, could get the impression that these things, and nothing more, were what he had in his mind. What gives colour and interest to what he says, seems to be obviously something quite different. And, if we try to find out what exactly the chief things are which give his discussion its colour and interest, it seems to me we may distinguish that what he has in his mind, wrapped up in more or less ambiguous language, are the following propositions, to all of which I have tried to urge what seem to me the most obvious objections:—

That utility is a property which distinguishes true beliefs from those which are not true; that, therefore, all true beliefs are useful, and all beliefs, which are useful, are true—by "utility" being sometimes meant "utility on at least one occasion," sometimes "utility in the long run," sometimes "utility for some length of time."

That all beliefs which are useful for some length of time are true.

That utility is the only property which all true beliefs have in common: that, therefore, if it were useful to me to believe in Professor James' existence, this belief would be true, even if he didn't exist; and that, if it were not useful to me to believe this, the belief would be false, even if he did.

That the beliefs, which we express by words, and not merely the words themselves, may be true at one time and not true at another; and that this is a general rule, though perhaps there may be some exceptions.

That whenever the existence of a belief depends to some extent on us, then also the truth of that belief depends to some extent on us; in the sense in which this implies, that, when the existence of my belief that a shower will fall depends upon me, then, if this belief is true, I must have had a hand in making the shower fall: that, therefore, men must have had a hand in making to exist almost every fact which they ever believe to exist.

HUME'S PHILOSOPHY

In both of his two books on the Human Understanding, Hume had, I think, one main general object. He tells us that it was his object to discover "the extent and force of human understanding," to give us "an exact analysis of its powers and capacity." And we may, I think, express what he meant by this in the following way. He plainly held (as we all do) that some men sometimes entertain opinions which they cannot know to be true. And he wished to point out what characteristics are possessed by those of our opinions which we can know to be true, with a view of persuading us that any opinion which does not possess any of these characteristics is of a kind which we cannot know to be so. He thus tries to lay down certain rules to the effect that the only propositions which we can, any of us, know to be true are of certain definite kinds. It is in this sense, I think, that he tries to define the limits of human understanding.

With this object he, first of all, divides all the propositions, which we can even so much as conceive, into two classes. They are all, he says, either propositions about "relations of ideas" or else about "matters of fact." By propositions about "relations of ideas" he means such propositions as that twice two are four, or that black differs from white; and it is, I think, easy enough to see, though by no means easy to define, what kind of propositions it is that he means to include in this division. They are, he says, the only kind of propositions with regard to which we can have "intuitive" or "demonstrative" certainty. But the vast majority of the propositions in which we believe and which interest us most, belong to the other division: they are propositions about "matters of fact." And these again he divides into two classes. So far as his words go, this latter division is between "matters of fact, beyond the present testimony of our senses, or the records of our memory," on the one hand, and matters of fact for which we have the evidence of our memory or senses, on the other. But it is, I think, quite plain that these words do not represent quite accurately the division which he really means to make. He plainly intends to reckon along with facts for which we have the evidence of our senses all facts for which we have the evidence of direct observation—such facts, for instance, as those which I observe when I observe that I am angry or afraid, and which cannot be strictly said to be apprehended by my senses. The division, then, which he really intends to make is (to put it quite strictly) into the two classes—(1) propositions which assert some matter of fact which I am (in the strictest sense) observing at the moment, or which I have so observed in the past and now remember; and (2) propositions which assert any matter of fact which I am not now observing and never have observed, or, if I have, have quite forgotten.

We have, then, the three classes—(1) propositions which assert "relations of ideas"; (2) propositions which assert "matters of fact" for which we have the evidence of direct observation or personal memory; (3) propositions which assert "matters of fact" for which we have not this evidence. And as regards propositions of the first two classes, Hume does not seem to doubt our capacity for knowledge. He does not doubt that we can know some (though, of course, not all) propositions about "relations of ideas" to be true; he never doubts, for instance, that we can know that twice two are four. And he generally assumes also that each of us can know the truth of all propositions which merely assert some matter of fact which we ourselves are, in the strictest sense, directly observing, or which we have so observed and now remember. He does, indeed, in one place, suggest a doubt whether our memory is ever to be implicitly trusted, but he generally assumes that it always can. It is with regard to propositions of the third class that he is chiefly anxious to determine which of them (if any) we can know to be true and which not. In what cases can any man know any matter of fact which he himself has not directly observed? It is Hume's views on this question which form, I think, the main interest of his philosophy.

He proposes, first of all, by way of answer to it, a rule, which may, I think, be expressed as follows: No man, he says, can ever know any matter of fact, which he has not himself observed, unless he can know that it is connected by "the relation of cause and effect," with some fact which he has observed. And no man can ever know that any two facts are connected by this relation, except by the help of his own past experience. In other words, if I am to know any fact, A, which I have not myself observed, my past experience must give me some foundation for the belief that A is causally connected with some fact, B, which I have observed. And the only kind of past experience which can give me any foundation for such a belief is, Hume seems to say, as follows: I must, he says, have found facts like A "constantly conjoined" in the past with facts like B. This is what he says; but we must not, I think, press his words too strictly. I may, for instance, know that A is probably a fact, even where the conjunction of facts like it with facts like B has not been quite constant. Or instead of observing facts like A conjoined with facts like B, I may have observed a whole series of conjunctions—for instance, between A and C, C and D, D and E, and E and B; and such a series, however long, will do quite as well to establish a causal connection between A and B, as if I had directly observed conjunctions between A and B themselves. Such modifications as this, Hume would, I think, certainly allow. But, allowing for them, his principle is, I think, quite clear. I can, he holds, never know any fact whatever, which I have not myself observed, unless I have observed similar facts in the past and have observed that they were "conjoined" (directly or indirectly) with facts similar to some fact which I do now observe or remember. In this sense, he holds, all our knowledge of facts, beyond the reach of our own observation, is founded on experience.

This is Hume's primary principle. But what consequences does he think will follow from it, as to the kind of facts, beyond our own observation, which we can know? We may, I think, distinguish three entirely different views as to its consequences, which he suggests in different parts of his work.

In the first place, where he is specially engaged in explaining this primary principle, he certainly seems to suppose that all propositions of the kind, which we assume most universally in everyday life, may be founded on experience in the sense required. He supposes that we have this foundation in experience for such beliefs as that "a stone will fall, or fire burn"; that Julius Caesar was murdered; that the sun will rise to-morrow; that all men are mortal He speaks as if experience did not merely render such beliefs probable, but actually proved them to be true. The "arguments from experience" in their favour are, he says, such as "leave no room for doubt or opposition." The only kinds of belief, which he definitely mentions as not founded on experience, are "popular superstitions" on the one hand, and certain religious and philosophical beliefs, on the other. He seems to suppose that a few (a very few) religious beliefs may, perhaps, be founded on experience. But as regards most of the specific doctrines of Christianity, for example, he seems to be clear that they are not so founded. The belief in miracles is not founded on experience; nor is the philosophical belief that every event is caused by the direct volition of the Deity. In short, it would seem, that in this doctrine that our knowledge of unobserved facts is confined to such as are "founded on experience," he means to draw the line very much where it is drawn by the familiar doctrine which is called "Agnosticism." We can know such facts as are asserted in books on "history, geography or astronomy," or on "politics, physics and chemistry," because such assertions may be "founded on experience"; but we cannot know the greater part of the facts asserted in books "of divinity or school metaphysics," because such assertions have no foundation in experience.

This, I think, was clearly one of Hume's views. He meant to fix the limits of our knowledge at a point which would exclude most religious propositions and a great many philosophical ones, as incapable of being known; but which would include all the other kinds of propositions, which are most universally accepted by common-sense, as capable of being known. And he thought that, so far as matters of fact beyond the reach of our personal observation are concerned, this point coincided with that at which the possibility of "foundation on experience" ceases.

But, if we turn to another part of his work, we find a very different view suggested. In a quite distinct section of both his books, he investigates the beliefs which we entertain concerning the existence of "external objects." And he distinguishes two different kinds of belief which may be held on this subject. "Almost all mankind, and philosophers themselves, for the greatest part of their lives," believe, he says, that "the very things they feel and see" are external objects, in the sense that they continue to exist, even when we cease to feel or see them. Philosophers, on the other hand, have been led to reject this opinion and to suppose (when they reflect) that what we actually perceive by the senses never exists except when we perceive it, but that there are other external objects, which do exist independently of us, and which cause us to perceive what we do perceive. Hume investigates both of these opinions, at great length in the Treatise, and much more briefly in the Enquiry, and comes to the conclusion, in both books, that neither of them can be "founded on experience," in the sense he has defined. As regards the first of them, the vulgar opinion, he does seem to admit in the Treatise that it is, in a sense, founded on experience; but not, he insists, in the sense defined. And he seems also to think that, apart from this fact, there are conclusive reasons for holding that the opinion cannot be true. And as regards the philosophical opinion, he says that any belief in external objects, which we never perceive but which cause our perceptions, cannot possibly be founded on experience, for the simple reason that if it were, we should need to have directly observed some of these objects and their "conjunction" with what we do perceive, which ex hypothesi, we cannot have done, since we never do directly observe any external object.

Hume, therefore, concludes, in this part of his work, that we cannot know of the existence of any "external object" whatever. And though in all that he says upon this subject, he is plainly thinking only of material objects, the principles by which he tries to prove that we cannot know these must, I think, prove equally well that we cannot know any "external object" whatever—not even the existence of any other human mind. His argument is: We cannot directly observe any object whatever, except such as exist only when we observe them; we cannot, therefore, observe any "constant conjunctions" except between objects of this kind: and hence we can have no foundation in experience for any proposition which asserts the existence of any other kind of object, and cannot, therefore, know any such proposition to be true. And this argument must plainly apply to all the feelings, thoughts and perceptions of other men just as much as to material objects. I can never know that any perception of mine, or anything which I do observe, must have been caused by any other man, because I can never directly observe a "constant conjunction" between any other man's thoughts or feelings or intentions and anything which I directly observe: I cannot, therefore, know that any other man ever had any thoughts or feelings—or, in short, that any man beside myself ever existed. The view, therefore, which Hume suggests in this part of his work, flatly contradicts the view which he at first seemed to hold. He now says we cannot know that a stone will fall, that fire will burn, or the sun will rise to-morrow. All that I can possibly know, according to his present principles, is that I shall see a stone fall, shall feel the fire burn, shall see the sun rise to-morrow. I cannot even know that any other men will see these things; for I cannot know that any other men exist. For the same reason, I cannot know that Julius Caesar was murdered, or that all men are mortal. For these are propositions asserting "external" facts—facts which don't exist only at the moment when I observe them; and, according to his present doctrine, I cannot possibly know any such proposition to be true. No man, in short, can know any proposition about "matters of fact" to be true, except such as merely assert something about his own states of mind, past, present or future—about these or about what he himself has directly observed, is observing, or will observe.

Here, therefore, we have a very different view suggested, as to the limits of human knowledge. And even this is not all. There is yet a third view, inconsistent with both of these, which Hume suggests in some parts of his work.

So far as we have yet seen, he has not in any way contradicted his original supposition that we can know some matters of fact, which we have never ourselves observed. In the second theory, which I have just stated, he does not call in question the view that I can know all such matters of fact as I know to be causally connected with facts which I have observed, nor the view that I can know some facts to be thus causally connected. All that he has done is to question whether I can know any external fact to be causally connected with anything which I observe; he would still allow that I may be able to know that future states of my own, or past states, which I have forgotten, are causally connected with those which I now observe or remember; and that I may know therefore, in some cases, what I shall experience in the future, or have experienced in the past but have now forgotten. But in some parts of his work he does seem to question whether any man can know even as much as this: he seems to question whether we can ever know any fact whatever to be causally connected with any other fact. For, after laying it down, as we saw above, that we cannot know any fact, A, to be causally connected with another, B, unless we have experienced in the past a constant conjunction between facts like A and facts like B, he goes on to ask what foundation we have for the conclusion that A and B are causally connected, even when we have in the past experienced a constant conjunction between them. He points out that from the fact that A has been constantly conjoined with B in the past, it does not follow that it ever will be so again. It does not follow, therefore, that the two really are causally connected in the sense that, when the one occurs, the other always will occur also. And he concludes, for this and other reasons, that no argument can assure us that, because they have been constantly conjoined in the past, therefore they really are causally connected. What, then, he asks, is the foundation for such an inference? Custom, he concludes, is the only foundation. It is nothing but custom which induces us to believe that, because two facts have been constantly conjoined on many occasions, therefore they will be so on all occasions. We have, therefore, no better foundation than custom for any conclusion whatever as to facts which we have not observed. And can we be said really to know any fact, for which we have no better foundation than this? Hume himself, it must be observed, never says that we can't. But he has been constantly interpreted as if the conclusion that we can't really know any one fact to be causally connected with any other, did follow from this doctrine of his. And there is, I think, certainly much excuse for this interpretation in the tone in which he speaks. He does seem to suggest that a belief which is merely founded on custom, can scarcely be one which we know to be true. And, indeed, he owns himself that, when he considers that this is our only foundation for any such belief, he is sometimes tempted to doubt whether we do know any fact whatever, except those which we directly observe. He does, therefore, at least suggest the view that every man's knowledge is entirely confined to those facts, which he is directly observing at the moment, or which he has observed in the past, and now remembers.

We see, then, that Hume suggests, at least, three entirely different views as to the consequences of his original doctrine. His original doctrine was that, as regards matters of fact beyond the reach of our own actual observation, the knowledge of each of us is strictly limited to those for which we have a basis in our own experience. And his first view as to the consequences of this doctrine was that it does show us to be incapable of knowing a good many religious and philosophical propositions, which many men have claimed that they knew; but that it by no means denies our capacity of knowing the vast majority of facts beyond our own observation, which we all commonly suppose that we know. His second view, on the other hand, is that it cuts off at once all possibility of our knowing the vast majority of these facts; since he implies that we cannot have any basis in experience for asserting any external fact whatever—any fact, that is, except facts relating to our own actual past and future observations. And his third view is more sceptical still, since it suggests that we cannot really know any fact whatever, beyond the reach of our present observation or memory, even where we have a basis in experience for such a fact: it suggests that experience cannot ever let us know that any two things are causally connected, and therefore that it cannot give us knowledge of any fact based on this relation.

What are we to think of these three views, and of the original doctrine from which Hume seems to infer them?

As regards the last two views, it may perhaps be thought that they are too absurd to deserve any serious consideration. It is, in fact, absurd to suggest that I do not know any external facts whatever; that I do not know, for instance, even that there are any men beside myself. And Hume himself, it might seem, does not seriously expect or wish us to accept these views. He points out, with regard to all such excessively sceptical opinions that we cannot continue to believe them for long together—that, at least, we cannot, for long together, avoid believing things flatly inconsistent with them. The philosopher may believe, when he is philosophising, that no man knows of the existence of any other man or of any material object; but at other times he will inevitably believe, as we all do, that he does know of the existence of this man and of that, and even of this and that material object. There can, therefore, be no question of making all our beliefs consistent with such views as this of never believing anything that is inconsistent with them. And it may, therefore, seem useless to discuss them. But in fact, it by no means follows that, because we are not able to adhere consistently to a given view, therefore that view is false; nor does it follow that we may not sincerely believe it, whenever we are philosophising, even though the moment we cease to philosophise, or even before, we may be forced to contradict it. And philosophers do, in fact, sincerely believe such things as this—things which flatly contradict the vast majority of the things which they believe at other times. Even Hume, I think, does sincerely wish to persuade us that we cannot know of the existence of external material objects—that this is a philosophic truth, which we ought, if we can, so long as we are philosophising, to believe. Many people, I think, are certainly tempted, in their philosophic moments, to believe such things; and, since this is so, it is, I think, worth while to consider seriously what arguments can be brought against such views. It is worth while to consider whether they are views which we ought to hold as philosophical opinions, even if it be quite certain that we shall never be able to make the views which we entertain at other times consistent with them. And it is the more worth while, because the question how we can prove or disprove such extreme views as these, has a bearing on the question how we can, in any case whatever, prove or disprove that we do really know, what we suppose ourselves to know.

What arguments, then, are there for or against the extreme view that no man can know any external fact whatever; and the still more extreme view that no man can know any matter of fact whatever, except those which he is directly observing at the moment, or has observed in the past and now remembers?

It may be pointed out, in the first place, that, if these views are true, then at least no man can possibly know them to be so. What these views assert is that I cannot know any external fact whatever. It follows, therefore, that I cannot know that there are any other men, beside myself, and that they are like me in this respect. Any philosopher who asserts positively that other men, equally with himself, are incapable of knowing any external facts, is, in that very assertion, contradicting himself, since he implies that he does know a great many facts about the knowledge of other men. No one, therefore, can be entitled to assert positively that human knowledge is limited in this way, since, in asserting it positively, he is implying that his own knowledge is not so limited. It cannot be proper, even in our philosophic moments, to take up such an attitude as this.

No one, therefore, can know positively that men in general, are incapable of knowing external facts. But still, although we cannot know it, it remains possible that the view should be a true one. Nay, more, it remains possible that a man should know that he himself is incapable of knowing any external facts, and that, if there are any other men whose faculties are only similar to his own, they also must be incapable of knowing any. The argument just used obviously does not apply against such a position as this. It only applies against the position that men in general positively are incapable of knowing external facts: it does not apply against the position that the philosopher himself is incapable of knowing any, or against the position that there are possibly other men in the same case, and that, if their faculties are similar to the philosopher's, they certainly would be in it. I do not contradict myself by maintaining positively that I know no external facts, though I do contradict myself if I maintain that I am only one among other men, and that no man knows any external facts. So far, then, as Hume merely maintains that he is incapable of knowing any external facts, and that there may be other men like him in this respect, the argument just used is not valid against his position. Can any conclusive arguments be found against it?

It seems to me that such a position must, in a certain sense, be quite incapable of disproof. So much must be granted to any sceptic who feels inclined to hold it. Any valid argument which can be brought against it must be of the nature of a petitio principii: it must beg the question at issue. How is the sceptic to prove to himself that he does know any external facts? He can only do it by bringing forward some instance of an external fact, which he does know; and, in assuming that he does know this one, he is, of course, begging the question. It is therefore quite impossible for any one to prove, in one strict sense of the term, that he does know any external facts. I can only prove that I do, by assuming that in some particular instance, I actually do know one. That is to say, the so-called proof must assume the very thing which it pretends to prove. The only proof that we do know external facts lies in the simple fact that we do know them. And the sceptic can, with perfect internal consistency, deny that he does know any. But it can, I think, be shown that he has no reason for denying it. And in particular it may, I think, be easily seen that the arguments which Hume uses in favour of this position have no conclusive force.

To begin with, his arguments, in both cases, depend upon the two original assumptions, (1) that we cannot know any fact, which we have not observed, unless we know it to be causally connected with some fact which we have observed, and (2) that we have no reason for assuming any causal connection, except where we have experienced some instances of conjunction between the two facts connected. And both of these assumptions may, of course, be denied. It is just as easy to deny them, as to deny that I do know any external facts. And, if these two assumptions did really lead to the conclusion that I cannot know any, it would, I think, be proper to deny them: we might fairly regard the fact that they led to this absurd conclusion as disproving them. But, in fact, I think it may be easily seen that they do not lead to it.

Let us consider, first of all, Hume's most sceptical argument (the argument which he merely suggests). This argument suggests that, since our only reason for supposing two facts to be causally connected is that we have found them constantly conjoined in the past, and since it does not follow from the fact that they have been conjoined ever so many times, that they always will be so, therefore we cannot know that they always will be so, and hence cannot know that they are causally connected. But obviously the conclusion does not follow. We must, I think, grant the premiss that, from the fact that two things have been conjoined, no matter how often, it does not strictly follow that they always are conjoined. But it by no means follows from this that we may not know that, as a matter of fact, when two things are conjoined sufficiently often, they are also always conjoined. We may quite well know many things which do not logically follow from anything else which we know. And so, in this case, we may know that two things are causally connected, although this does not logically follow from our past experience, nor yet from anything else that we know. And, as for the contention that our belief in causal connections is merely based on custom, we may, indeed, admit that custom would not be a sufficient reason for concluding the belief to be true. But the mere fact (if it be a fact) that the belief is only caused by custom, is also no sufficient reason for concluding that we can not know it to be true. Custom may produce beliefs, which we do know to be true, even though it be admitted that it does not necessarily produce them.

And as for Hume's argument to prove that we can never know any external object to be causally connected with anything which we actually observe, it is, I think, obviously fallacious. In order to prove this, he has, as he recognises, to disprove both of two theories. He has, first of all, to disprove what he calls the vulgar theory—the theory that we can know the very things which we see or feel to be external objects; that is to say, can know that these very things exist at times when we do not observe them. And even here, I think, his arguments are obviously inconclusive. But we need not stay to consider them, because, in order to prove that we cannot know any external objects, he has also to disprove what he calls the philosophic theory—the theory that we can know things which we do observe, to be caused by external objects which we never observe. If, therefore, his attempt to disprove this theory fails, his proof that we cannot know any external objects also fails; and I think it is easy to see that his disproof does fail. It amounts merely to this: That we cannot, ex hypothesi, ever observe these supposed external objects, and therefore cannot observe them to be constantly conjoined with any objects which we do observe. But what follows from this? His own theory about the knowledge of causal connection is not that in order to know A to be the cause of B, we must have observed A itself to be conjoined with B; but only that we must have observed objects like A to be constantly conjoined with objects like B. And what is to prevent an external object from being like some object which we have formerly observed? Suppose I have frequently observed a fact like A to be conjoined with a fact like B: and suppose I now observe B, on an occasion when I do not observe anything like A. There is no reason, on Hume's principles, why I should not conclude that A does exist on this occasion, even though I do not observe it; and that it is, therefore, an external object. It will, of course, differ from any object which I have ever observed, in respect of the simple fact that it is not observed by me, whereas they were. There is, therefore, this one respect in which it must be unlike anything which I have ever observed. But Hume has never said anything to show that unlikeness in this single respect is sufficient to invalidate the inference. It may quite well be like objects which I have observed in all other respects; and this degree of likeness may, according to his principles, be quite sufficient to justify us in concluding its existence. In short, when Hume argues that we cannot possibly learn by experience of the existence of any external objects, he is, I think, plainly committing the fallacy of supposing that, because we cannot, ex hypothesis have ever observed any object which actually is "external," therefore we can never have observed any object like an external one. But plainly we may have observed objects like them in all respects except the single one that these have been observed whereas the others have not. And even a less degree of likeness than this would, according to his principles, be quite sufficient to justify an inference of causal connection.

Hume does not, therefore, bring forward any arguments at all sufficient to prove either that he cannot know any one object to be causally connected with any other or that he cannot know any external fact. And, indeed, I think it is plain that no conclusive argument could possibly be advanced in favour of these positions. It would always be at least as easy to deny the argument as to deny that we do know external facts. We may, therefore, each one of us, safely conclude that we do know external facts; and, if we do, then there is no reason why we should not also know that other men do the same. There is no reason why we should not, in this respect, make our philosophical opinions agree with what we necessarily believe at other times. There is no reason why I should not confidently assert that I do really know some external facts, although I cannot prove the assertion except by simply assuming that I do. I am, in fact, as certain of this as of anything; and as reasonably certain of it. But just as I am certain that I do know some external facts, so I am also certain that there are others which I do not know. And the question remains: Does the line between the two fall, where Hume says it falls? Is it true that the only external facts I know are facts for which I have a basis in my own experience? And that I cannot know any facts whatever, beyond the reach of my own observation and memory, except those for which I have such a basis?

This, it seems to me, is the most serious question which Hume raises. And it should be observed that his own attitude towards it is very different from his attitude towards the sceptical views which we have just been considering. These sceptical views he did not expect or wish us to accept, except in philosophic moments. He declares that we cannot, in ordinary life, avoid believing things which are inconsistent with them; and, in so declaring, he, of course, implies incidentally that they are false: since he implies that he himself has a great deal of knowledge as to what we can and cannot believe in ordinary life. But, as regards the view that our knowledge of matters of fact beyond our own observation is entirely confined to such as are founded on experience, he never suggests that it is impossible that all our beliefs should be consistent with this view, and he does seem to think it eminently desirable that they should be. He declares that any assertion with regard to such matters, which is not founded on experience, can be nothing but "sophistry and illusion"; and that all books which are composed of such assertions should be "committed to the flames." He seems, therefore, to think that here we really have a test by which we may determine what we should or should not believe, on all occasions: any view on such matters, for which we have no foundation in experience, is a view which we cannot know to be even probably true, and which we should never accept, if we can help it. Is there any justification for this strong view?

It is, of course, abstractly possible that we do really know, without the help of experience, some matters of fact, which we never have observed. Just as we know matters of fact, which we have observed, without the need of any further evidence, and just as we know, for instance, that 2+2=4, without the need of any proof, it is possible that we may know, directly and immediately, without the need of any basis in experience, some facts which we never have observed. This is certainly possible, in the same sense in which it is possible that I do not really know any external facts: no conclusive disproof can be brought against either position. We must make assumptions as to what facts we do know and do not know, before we can proceed to discuss whether or not all of the former are based on experience; and none of these assumptions can, in the last resort, be conclusively proved. We may offer one of them in proof of another; but it will always be possible to dispute the one which we offer in proof. But there are, in fact, certain kinds of things which we universally assume that we do know or do not know, just as we assume that we do know some external facts; and if among all the things which we know as certainly as this, there should turn out to be none for which we have no basis in experience, Hume's view would I think, be as fully proved as it is capable of being. The question is: Can it be proved in this sense? Among all the facts beyond our own observation, which we know most certainly, are there any which are certainly not based upon experience? For my part, I confess, I cannot feel certain what is the right answer to this question: I cannot tell whether Hume was right or wrong. But if he was wrong—if there are any matters of fact, beyond our own observation, which we know for certain, and which yet we know directly and immediately, without any basis in experience, we are, I think, faced with an eminently interesting problem. For it is, I think, as certain as anything can be that there are some kinds of facts with regard to which Hume was right—that there are some kinds of facts which we cannot know without the evidence of experience. I could not know, for instance, without some such evidence, such a fact as that Julius Caesar was murdered. For such a fact I must, in the first instance, have the evidence of other persons; and if I am to know that their evidence is trustworthy, I must have some ground in experience for supposing it to be so. There are, therefore, some kinds of facts which we cannot know without the evidence of experience and observation. And if it is to be maintained that there are others, which we can know without any such evidence, it ought to be pointed out exactly what kind of facts these are, and in what respects they differ from those which we cannot know without the help of experience. Hume gives us a very clear division of the kinds of propositions which we can know to be true. There are, first of all, some propositions which assert "relations of ideas "; there are, secondly, propositions which assert "matters of fact" which we ourselves are actually observing, or have observed and now remember; and there are, thirdly, propositions which assert "matters of fact" which we have never actually observed, but for believing in which we have some foundation in our past observations. And it is, I think, certain that some propositions, which we know as certainly as we know anything, do belong to each of these three classes. I know, for instance, that twice two are four; I know by direct observation that I am now seeing these words, that I am writing, and by memory that this afternoon I saw St. Paul's; and I know also that Julius Caesar was murdered, and I have some foundation in experience for this belief, though I did not myself witness the murder. Do any of those propositions, which we know as certainly as we know these and their like, not belong to either of these three classes? Must we add a fourth class consisting of propositions which resemble the two last, in respect of the fact that they do assert "matters of fact," but which differ from them, in that we know them neither by direct observation nor by memory, nor yet as a result of previous observations? There may, perhaps, be such a fourth class; but, if there is, it is, I think, eminently desirable that it should be pointed out exactly what propositions they are which we do know in this way; and this, so far as I know, has never yet been done, at all clearly, by any philosopher.

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.