Chapter VII: Part 7

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.