I assume, then, that we observe, on the one hand, coloured patches of certain shapes and sizes, and their spatial relations to one another, together with all the other kinds of "contents," which we should usually be said to perceive "through the senses." And, on the other hand, we also sometimes observe our own perceptions of such "contents" and our thoughts. And these two kinds of "content" are different from one another: my perception of a red patch with gold letters on it, is not itself a red patch with gold letters on it; and hence, when I observe my perception of this patch, I observe something different from that which I observe when I merely perceive the patch. Either of these two kinds of "content"—either colours, moving or at rest, sounds, smells, and all the rest—or, on the other hand, my perceptions of these—either of these two kinds, or both, might conceivably, since both are observed, give grounds for a generalisation concerning what exists. But, as I have said, if observations are to give any ground for such a generalisation, it must be assumed that what Isobservedexistsor isreal.And since, as I have insisted, when I observe myperceptionof a red patch with gold letters on it, I observe something different from what I observed when I merely observed a red patch with gold letters on it, it follows that to assume the existence of my perception of this red and gold isnotthe same thing as to assume the existence of the red and gold itself.
But what, it may be asked, do I mean by this property of "existence" or "reality," which may, it would seem, belong to every content, which I observe, or may again belong to none, or which may belong to some and not to others? What is this property which may belong to my perception of a movement, and yet not belong to the movement perceived, or which may again belong to the movement perceived and not to my perception of it, or which may again belong to both or to neither?
It is necessary, I think, to ask this question at this point, because there are some philosophers who hold that, in the case of some kinds of "content," at all events, to say that they "exist" is to say that they are "perceived." Some hold that to say "A exists" is to say neither more nor less than "A is perceived"—that the two expressions are perfect synonyms; and others again would say that by "A exists or is real" we may meanmorethan that "A is perceived," but that we must at least mean this. Now, I have hitherto used the word "existence" pretty freely, and I think that, when I used it, I used it in its ordinary sense. I think it will generally have suggested to you precisely what I meant to convey, and I think that, in some cases at all events, it will not even have occurred to you to doubt whether you did understand what I meant by it. But, if these philosophers are right, then, if youhaveunderstood what I meant by it, I have all along been using it in a sense, which renders the end ofmy last paragraph perfect nonsense. If these philosophers are right, then, when I assert that whatisperceived may yetnotexist, I am really asserting that whatisperceived may yetnotbe perceived—I am contradicting myself. I am, of course, quite unaware that I am doing so. But these philosophers would sayeitheryou are contradicting yourself,oryou are not using the word "exists" in its ordinary sense. And either of these alternatives would be fatal to my purpose. If I am not using the word in its ordinary sense, then I shall not be understood by anyone; and, if I am contradicting myself, then what I say will not be worth understanding.
Now, with one class of these philosophers—the class to which, I think, Berkeley belongs—I think I can put myself right comparatively easily. The philosophers I mean are those who say that it is only in the case of one particular class of "contents" (the kind of "content" which Berkeley calls "ideas") that to say "the 'content' A exists" is to say "A is perceived," and who admit that in the case of other contents—myself and my perceptions and thoughts, for example—to say thattheseexist or are real, is to say of them something different from this. These philosophers admit, that is to say, that the word "exists" has two different senses: and that in only one of these senses is it synonymous with the words "is perceived." When (they hold) I say of such a content as a red patch with gold letters on it that it "exists" Idomean that it is perceived; but when I say of myperceptionof such a patch thatitexists, I donotmean that my perception is perceived but something different from this. Now, it would be nothing strange that one and the same word should be used in two different senses; many words are used in many different senses. But it would, I think, be something very strange indeed, if in the case ofa word which we constantly apply to all sorts of different objects, we should uniformly apply it to one large class of object in the one sense and the one sense only and the other large class in the other sense and the other sense only. Usually, in the case of such ambiguous words, it happens that, in different contexts, we apply it to one and the same object inbothsenses. We sometimes wish to say of a given object that it has the one property, and sometimes we wish to say of the same object that it has the other property; and hence we apply the same word to the same object, at one time in one sense, and at another in the other. I think, therefore, that, even if there were these two different senses of the word "existence," it would be very unlikely that we should not commonly, in some contexts, apply it in the sense, in which (as is alleged) it does apply to perceptions, to "contents" which are not perceptions. Indeed, I think, it is quite plain that we constantly do ask, with regard to what is not a perception, whetheritexists, in precisely the same sense, in which we ask, with regard to a perception, whetheritexists. We ask in precisely the same sense: Was the Roc a real bird, or merely an imaginary one? and, did Sindbad's perception of the Roc really exist, or is it a fiction that he perceived a Roc? I think, therefore, that the sense in which these philosophers admit that we do apply the word "existence" to perceptions, is one in which we also commonly apply it to "contents" other than perceptions. But, even if this is not the case, I can set myself right with them by a simple explanation. I need merely explain that the sense in which I am proposing to enquire whether a red patch exists, is precisely the sense in which they admit that my perception of a red patch does exist. And in this sense, it is plain that to suppose that a thing may exist, which is notperceived, or that it maynotexist, although it is perceived, is at least not self-contradictory.
But there may be other philosophers who will say that, in the case of a perception also, to say that it exists or is real is to say that it is perceived—either that alone or something more as well. And to these philosophers I would first point out that they are admitting that the proposition "This perception is real" is significant. There is some sense or other in which we may say: "Alexander's perception of an elephant was real or did exist, but Sindbad's perception of a Roc wasnotreal—never did exist": the latter proposition is, in some sense or other, not self-contradictory. And then I would ask of them: When they say, that to call a perception "real" is to assert that it is perceived, do they mean by this that to call it real is to assert that it isreallyperceived, or not? If they say "No," then they are asserting that to call a perception "real" is merely to say that it was perceived in the sense in which Sindbaddidperceive a Roc: they are asserting that to call it "real" is not to say, in any sense, that it wasreallyperceived: they are asserting that to call a perception "real" is to say that it was perceived, in some sense quite other than that in which we ordinarily use the word: for we certainly commonly mean, when we say "A was perceived," that a perception of A was "real": we should commonly say that Sindbad didnotperceive a Roc—meaning that no such perception ever did exist. I do not think they do mean this; and, in any case, if they do, I think it is plain that they are wrong. When we say that a perception is "real," we certainly do not mean merely that it is the object of another perception, which may itself be quite unreal—purely Imaginary. I assume, therefore, that when they say: To call a perception "real" is to say that it is perceived; they mean, what we should naturallyunderstand, namely, that: To call it "real" is to say that it isreallyperceived—to say that it is the object of another perception, which is alsorealin the same sense. And, if they mean this, then what they say is certainly untrue. Their definition of reality is circular. It cannot be the case that theonlysense in which a perception may be said to be real, is one in which to call it so is to assert that not it alone, but another perception is real also. It cannot be the case that the assertion "A is real" isidenticalwith the assertion "A and B are both real," where A and B are different, and "real" is used in the same sense as applied to both. If it is to be true that the assertion "A is real"ever, in any sense, includes the assertion "A isreallyperceived," there must be another sense of the word "real," in which to assert "A is real" is to assertlessthan "A isreallyperceived"—the sense, namely, in which we here assert that theperceptionof A is real.
We find, therefore, that the other class of philosophers were at least right in this: they were right in allowing that the sense in which we commonly say that our perceptions exist is one in which "exist" does not include, even as a part of its meaning, "is perceived." We find that there is a common sense of the word "existence," in which to say "A exists" must meanlessthan "A isreallyperceived": since, otherwise, the only possible definition of the word "existence" would be a circular definition. And I may point out that two other definitions, which have been sometimes suggested by philosophers as giving what we commonly mean by "reality" or "existence" are vitiated by the same fault—they also are circular. Some philosophers have sometimes suggested that when we call a thing "real," we mean that it is "systematically connected" in some way with other things. But,when we look into their meaning, we find that what they mean is (what, indeed, is alone plausible)—systematically connected with otherrealthings. And it may possibly be the case that we sometimes use the word "real" in this sense: but, at least, it must be certainly the case, that, if we do, wealsouse it in another and simpler sense—the sense in which it is employed in the proposed definition. And other philosophers have suggested that what we mean by "real" is—"connected in some way with a purpose—helping or hindering, or the object of a purpose." But if we look into their meaning, we find they mean—connected with arealpurpose. And hence, even if we do sometimes mean by "real," "connected with arealpurpose," it is plain we also sometimes mean by "real" something simpler than this—that namely, which is meant by "real" in the proposed definition.
It is certain, therefore, that we do commonly use the word "existence" in a sense, in which to say "A exists" isnotto say "A is perceived," or "A is systematically connected with other real things," or "A is purposive." There is a simpler sense than any of these—the sense in which we say that our own perceptions do exist, and that Sindbad's perceptions did not exist. But when I say this, I am by no means denying that what exists, in this simple sense, may not alwaysalsoexist in all the others; and that what exists in any of them may notalsoalways exist in this. It is quite possible that what exists is alwaysalsoperceived, and that what is perceived alwaysalsoexists. All that I am saying is that, even if this is so, this proposition is significant—is not merely a proposition about the meaning of a word. It is not self-contradictory to suppose that some things which exist are not perceived, and that some things which are perceived do not exist.
But, it may be asked: What is this common simple sense of the word "exists"? For my own part, it seems to me to be so simple that it cannot be expressed in other words, except those which are recognised as its synonyms. I think we are all perfectly familiar with its meaning: it is the meaning which you understood me to have throughout this paper, until I began this discussion. I think we can perceive at once what is meant by asserting that my perception of black marks on a white ground is "real," and that no such perception as Sindbad's of a Roc was ever "real": we are perfectly familiar with the property which the one perception is affirmed to possess, and the other to be without. And I think, as I have said, that this property is a simple one. But, whatever it is, this, which we ordinarily mean, is what I mean by "existence" or "reality." And this property, we have seen, is certainly neither identical with nor inclusive of that complex one which we mean by the words "is perceived."
I may now, then, at last approach the main question of my paper. Which among the "contents" which I observe will give me reason to suppose that my observation of some of them is generally preceded or accompanied or followed by the existence of certain particular perceptions, thoughts or feelings in another person? I have explained that the "contents" which I actually observe may be divided into two classes: on the one hand, those which, as we commonly say, we perceive "through the senses"; and, on the other hand, my perceptions of these last, my thoughts, and my feelings. I have explained that if any of these observed contents are to give reason for a generalisation about what exists,theymust exist. And I have explained that with regard to both classes of "contents" I am using the word "exist" in precisely the same sense—a sense,in which it is certainly not self-contradictory to suppose that whatisperceived, does not exist, and that what isnotperceived, does exist; and, in which, therefore, the assumption that a red patch with gold letters on it exists, is adifferentassumption from the assumption that myperceptionof a red patch with gold letters on it exists; and the assumption that myperceptionof a red patch with gold letters on it exists, is adifferentassumption from the assumption that a red patch with gold letters on it exists.
What, then, that we observe, can give us any reason for believing that anyone else has certain particular perceptions, thoughts or feelings? It has, I think, been very commonly assumed that the observation of my own perceptions, thoughts, and feelings, can, by itself, give me such a reason. And I propose, therefore, to examine this assumption. If, as I hope to show, it is false; it will then follow, that if our own observation gives us any reason whatever, for believing in the existence of other persons, we must assume the existence, not only of our own perceptions, thoughts and feelings, but also of some, at least, among that other class of data, which I may now, for the sake of brevity, call "sense-contents"; we must assume that some of them exist, in precisely the same sense in which we assume that our perceptions, thoughts, and feelings exist.
The theory which I propose to examine is, then, the following. My observation of my own thoughts, feelings, and perceptions may, it asserts, give me some reason to suppose that another person has thoughts, feelings, and perceptions similar to some of mine. Let us assume, accordingly, that my own thoughts, feelings, and perceptions do exist; but that none of the "sense-contents," which I also observe, do so. Where among my perceptions amI to look for any which might conceivably give me a reason for supposing the existence of other perceptions similar to my own? It is obvious where I must look. I have perceptions which I call perceptions of other people's bodies; and these are certainly similar in many respects to other perceptions of my own body. But I also observe that certain kinds of perceptions of my own body are preceded by certain other perceptions, thoughts, or feelings of mine. I may, for instance, observe that when I perceive my hand suddenly catch hold of my foot in a particular way, this perception was preceded by a particular kind of feeling of pain. I may, perhaps, observe this often enough to justify the generalisation that the perception of that particular motion of my body is generally preceded by that particular feeling of pain. And in this way I may perhaps have reason for quite a number of generalisations which assert that particular kinds of perceptions of my own body are generally preceded by other particular kinds of perceptions, thoughts, or feelings of my own.
But I may also, no doubt, have the perception, which I call the perception of another person's hand catching hold of his foot, in a manner similar to that in which I have perceived my own hand catch hold of my own foot. And my perception of another person's hand catching hold of his foot may undoubtedly be similar in many respects to my perception of my own hand catching hold of my own foot. But I shall not observe the same kind of feeling of pain preceding my perception ofhishand catching hold of his foot, which I have observed preceding my perception ofmyhand catching hold of my foot. Will my generalisation, then, give me any reason to suppose that nevertheless my perception of his hand catching hold of his footispreceded by a similar feeling of pain, not in me butin him? We undoubtedly do assume that when I perceive another person's body making movements similar to those which I have observed my own body making, this perception has generally been preceded by some feeling or perception of his similar to that which I have observed to precede my perception of similar movements in my own body. We do assume this; and it is precisely the kind of generalisation, which, I have insisted, must be admitted to be true. But my present question is: Will such observations as I have described give any reason for thinking any such generalisation true? I think it is plain that they will not give the slightest reason for thinking so. In the first place, all the perceptions which I call perceptions of another person's body differ very considerably from any of those which I call perceptions of my own. But I am willing to waive this objection. I am not offering any theory as to what degree of likeness issufficientto justify a generalisation: and therefore I will allow that the degree of likenessmaybe sufficient. But there remains an objection which is, I think, quite fatal to the proposed inference. This objection is that the inference in question plainly does not satisfy the third condition which I suggested above asnecessary, wherever any generalisation is to be justified by observation. I am willing to allow that my observations of the fact that my perception of a certain movement in my own body is preceded by a certain feeling of pain,willjustify the generalisation that my perception of any such movement, whether in my own bodyorin that of another person, is generally preceded by a similar feeling of pain. And I allow, therefore, that when I perceive a certain movement in another's body, itisprobable that the feeling of pain exists, though I do not perceive it. But, if itisprobable that such a feeling of painexists, such a feeling must standin the same relationto my perception of the movement in another person's body, in which a similar feeling of pain has been observed by me to stand to my perception of such a movement in my own body. That is to say the only kind of feeling of pain, which my observations do justify me in inferring, if (as I admit they may) they justify me in inferring any at all, is a feeling of pain ofmy own.They cannot possibly justify the belief in the existence of any such feelingexceptone which stands to my perception in the same relation in which my feelings do stand tomyperceptions—one, that is to say, which is my own. I have no more reason to believe that the feeling of pain which probably precedes my perception of a movement in another person's body can be the feelingof another person, than, in my former example, I had reason to suppose that the hen, whose existence probably preceded that of a given egg, could be a hen, which had never been near the egg in question. The two cases are exactly analogous. I observe a feeling of painof my ownpreceding a perceptionof my own.I observe the two, that is to say, as standing to one another, in those relations (whatever they may be) in which any perception of mine stands to any other thought, perception or feeling of mine, and which are, at all events, different from any relation in which a perception or feeling of another person can stand to one of mine. I never perceive the feeling and the perception as standing in any other relation. In any case, therefore, where I do observe something like the perception, but do not observe the feeling, I can only be justified (ifjustified in inferring any feeling at all), in inferring an unperceived feelingof my own.
For this reason I think that no observations of my own perceptions, feelings or thoughts can give me the slightest reason for supposing a connectionbetween any of them and any feeling, perception, or thought in another person. The argument is perfectly general, sinceallmy perceptions, feelings and thoughts do have to one another those relations in virtue of which I call them mine; and which, when I talk of a perception, feeling or thought as beinganother persons, I mean to say that it hasnotgot to any of mine. I can, therefore, merely from observation ofthisclass of data never obtain the slightest reason for belief in the existence of a feeling, perception, or thought which doesnotstand in these relations to one of mine—whichis,that is to say, the feeling, perception or thought, of another person. But how different is the case, if we adopt the hypothesis, which I wish to recommend—if we assume the existence of that other class of data which I have called "sense-contents!" On this hypothesis, that which I perceive, when I perceive a movement of my own body, isreal; that which I perceive when I perceive a movement of another's body isrealalso. I can now observe not merely the relation between myperceptionof a movement of my body and my own feelings, but also a relation between arealmovement of my body and my own feelings. And there is no reason why I should not be justified in inferring that another person's feelings standin the same relationto the real movements of his body, in which I observe my own feelings to stand to similar real movements of mine.
But there is another argument which may still be urged by those who hold that my own perceptions, thoughts, and feelings, by themselves, may be sufficient to justify a belief in the existence of other persons. It may be said: "Our observation of our own perceptions may be sufficient toverifyorconfirmthe hypothesis that other persons exist. This hypothesis is one which "works." Theassumption that other persons have particular thoughts, feelings and perceptions enables us to predict that they will have others and that our own perceptions will be modified accordingly: it enables us to predict future perceptions of our own; and we find that these predictions are constantly verified. We observe that we do have the perceptions, which the hypothesis leads us to expect we should have. In short, our perceptions occur just as they would do,ifthe hypothesis were true; our perceptions behaveas ifother persons had the perceptions, thoughts and feelings which we suppose them to have. Surely, then, they confirm the truth of the hypothesis—they give some reason to think it probably true?"
All this, which I have supposed an opponent to urge, I admit to be true. I admit that the fact that an hypothesis works may give some reason to suppose it true. I admit that my perceptions occur just as they would do, if other people had the perceptions which I suppose them to have. I admit that that assumption enables me to make predictions as to future perceptions of my own, and that I observe these predictions to come true. I admit all this. But I admit it only in a sense in which it in no way conflicts with the position which I am maintaining. The words, which I have put into the mouth of a supposed opponent, may, in fact, mean three different things, which it is worth while to distinguish. In two of those meanings, which I shall admit to be true and which are what make them seem plausible, they do not deny what I assert. Only in the third sense are they an objection to my position: and in that sense they are false.
One of the meanings which I admit to be true is as follows:—I have not only admitted but insisted that some of my perceptions are just such as would occur if another person had certain particularfeelings: I have insisted that I should not have just those perceptions which I do have, unless some other person had certain feelings and perceptions which I suppose him to have. And I admit further that the fact that I have one of the perceptions in question—for instance, that of another person's hand catching hold of his foot—this fact,together withthe true assumption that I should not have this perception, unless some other person felt pain, will justify the assertion that another person has felt pain. In this sense, I admit, the fact that I perceive what I do perceive will give me reason to suppose that another person has felt pain. And, on the other hand, I also admit that the fact that I have this perception,together withthe true assumption that when I have it another person has felt pain, may help to justify the assumption that the perception in question is one which I should not have had unless another person had felt pain—it helps to justify the generalisation that certain of my perceptions are just what would occur,ifanother person had felt pain. In general terms, that is to say, I admit that the occurrence of B,together withthe assumption that B is just the sort of thing which would occur if A existed, will justify the assertion that A exists in that particular instance. And I also admit that the occurrence of B,together withthe assumption that A exists in that particular instance, may help to justify the assumption that B is just the sort of thing which would exist, if A existed. In other words: When it is said that the observation of B's existence confirms or verifies the assumption that A exists, either of two things may be meant. It may be meant that, assuming B to be the sort of thing which would exist if A existed, the observation of B confirms the assumption that A existsin this particular instance.Or, on the other hand, it may be meant that, assumingA to exist in this particular instance, the observation of B may confirm the generalisation, that B is just the sort of thing which would exist, if A existed.Eitherthe oneorthe other of these two things is, I think, what is generally assumed, when it is assumed that what we do observe confirms or verifies the assumption that there exists some particular thing which we don't observe. And I am admitting that both these assumptions are true.
But neither of them conflicts in any way with the position I am maintaining. What I am maintaining is that no observation of my own perceptions,by itself,can confirm the generalisation that any one of themisjust what would occur if another person had a particular feeling. I admit this generalisation to be true; and I admit that my observation of my own perceptions and feelings may give mereasonto suppose thatifanother person has certain perceptions or feelingshewill also have certain others. What I deny is that they give me the slightest reason to suppose that the existence of any such feeling or perception in another has any connection with the existence of any perceptionof my own—to suppose that any perception of my own is the sort of thing which would occurifanother person had a particular feeling. What therefore, my opponent must affirm is that the observation of a perception of my ownwithoutthe assumption (which Reid makes) that in that particular instance any feeling or perception of another person, of any kind whatever, has preceded it, may give me reason to suppose that that perception of my own is of a kind which is generally preceded by a particular kind of feeling in another person. And this, I think, is plainly false.
But there is yet a third thing which may be meant, and which I am willing to admit may be true. It may be said: "I believe many generalisations ofthe following kind. I believe that when I have a perception A, some other person has generally had a feeling X; I believe that the existence of the feeling X is generally followed, in the same person, by that of the feeling Y; and I believe also that when another person has the feeling Y, I generally have the perception B. I believe all this." And it must, I think, be admitted that we do believe generalisations of this kind, and generalisations in which there are not merely two steps between A and B, but a great number of steps. "But then," it may be said, "my belief in this generalisation causes me, when I observe my perception A, to expect that I shall have the perception B; and such expectations, I observe, are constantly realised." And this also, I think, must be admitted to be true. "But, finally," it may be said, "beliefs which produce expectations which are constantly realised are generally true. And hence the fact that these beliefs of mine about the connection of feelings in other persons with perceptions of my own do lead to expectations which are realised, gives me reason to suppose that these generalisations are true and hence that other persons do have particular kinds of feelings." And I am willing to admit that this also is true. I am willing to admit that true predictions can, as a rule, only be produced by true beliefs. The generalisation that this is so, is, indeed, one which can only be justified by the observations of beliefs, which are, in some way, independently proved to be true; and hence, if it is to be justified, without assuming the existence of anything other than my own perceptions, thoughts, and feelings, it can only be justified by my observation that beliefs with regard to the manner in whichthesesucceed one another generally lead to true predictions. Whether the observation of such beliefsalonecould give sufficient reason for it, is, I think, doubtful; butI am willing to admit that it may be so. One thing, however, is, I think, quite plain: namely, that this generalisation "Beliefs which lead to true predictions are generally true" cannot be true,unlesssome other of the "contents" which I observe, beside my own perceptions, thoughts, and feelings, do exist. That is to say, in giving a reason for supposing the existence of other people, this generalisation also gives a reason for the very theory which I am advocating, namely, that some of those data which I have called "sense-contents" do exist. It does this, because it is quite certain that beliefs in generalisations about the existence of sense-contentscan(and do) constantly lead to true predictions. The belief that when I have observed a fire of a certain size in my grate, something similar to what I have observed will continue to exist for a certain time, can, and constantly does, lead to the true prediction that, when I come back to my room in half an hour's time, I shall observe a fire of a certain size still burning. We make predictions on such grounds, I think, every day and all day long. And hence unless such beliefs as that what I observe when I see a fire burningdoesexist,aretrue, we certainly have no reason to suppose that beliefs which lead to true predictions are generally true. And hence on this hypothesis also it remains true: that, unless some of the contents which I observeotherthan my own perceptions, thoughts, and feelings, do exist, I cannot have the slightest reason for supposing that the existence of certain perceptions of my own is generally connected with that of certain perceptions, thoughts, or feelings in any other person.
I conclude therefore that, unless some of the observed data which I have called sense-contentsdoexist, my own observations cannot give me the slightest reason for believing that anybody else hasever had any particular perception, thought, or feeling. And, having arrived so far towards an answer to my first question: How do we know that any other persons exist? I may now point out that precisely the same answer must be given to my second question: How do we know thatanyparticular kind of thing exists, other than ourselves, our perceptions, thoughts, and feelings, and what we directly perceive? There is a view concerning what exists, which deserves, I think, much more respect than it generally receives from philosophers nowadays. The view I mean is the view that material objects, such as they are conceived by physical science, do really exist. It is held by some persons (and Reid is among them) that wedoknow of the existence, not only of other persons, but also of the movements of matter in space. It is held that we do know, with considerable precision, what kinds of movements of matter generally precede my perception, when I have a particular perception. It is held, for instance, that when I perceive a red and blue book side by side on a shelf, at a certain distance from me, there have existed, between two material objects, which may be called books, and another kind of material object, which may be called my eyes, certain wave-like motions of a material medium; that there have existed two different sets of waves, of which the one is connected with my perception of red and the other with my perception of blue; and that the relative heights and breadths of the two different sets of waves, and the relative velocity of their movements are very exactly known. It is held that some men have a vast amount of very precise information about the existence of objects of this kind; and I think the view that this is so deserves a great deal of respect. But what I wish now to point out is that no one's observation of his own perceptions, thoughts andfeelings, can, by itself, give him the slightest reason for believing in the existence of any such material objects. All the arguments by which I have tried to show that this kind of observation alone can give me no reason to believe in the existence of any kind of perception or feeling in another person, apply, with at least equal force, to show that it can give me no reason to believe in the existence of any kind of material object. On the other hand, if we are to admit the principle that "Beliefs which lead to true predictions, are generally true," this principle will give us at least as much reason to believe in the existence of certain kinds of material objects as to believe in the existence of other persons; since one of the most remarkable facts about beliefs in the existence of such objects is that they do so often lead to true predictions. But it must be remembered that we can have no reason for believing this principle itself,unlessour own perceptions, thoughts and feelings arenotthe only kind of observed "content" which really does exist: we can have no reason for it, unless some such things as what I perceive, when I see a red and blue book side by side, do really exist.
It would seem, therefore, that if my own observations do give me any reason whatever for believing in the existence either of any perception in any other person or of any material object, it must be true that not only my own perceptions, thoughts and feelings, but alsosomeof the other kinds of things which I directly perceive—colours, sounds, smells, etc.—do really exist: it must be true that some objects of this kindexistor arerealin precisely the same simple sense in which my perceptions of them exist or are real. Is there then any reason to think that this is not true? Is there any reason to think, for instance, thatnoneof the colours which I perceive as occupying areas of certain shapes and sizes reallyexist in the areas which they appear to occupy? This is a question which I wished to discuss at length, because I think that it is one in which there are real difficulties. But I have given so much space to other questions, that I can only deal with it very briefly here.
Some philosophers are very fond of asserting that a colour cannot exist except when it is perceived; and it might possibly be thought that when I suggest that colours do really exist, I am suggesting that they do exist when they are not perceived. I wish, therefore, briefly to point out that the question whether anything does exist, when it is not perceived, is one which I have not argued and shall not attempt to argue in this paper. I have, indeed, tried to show that since "exists" does notmean"is perceived," it is, at least, conceivable that things should exist, when they are not perceived. But I have admitted that it is quite possible nonedoso: itmaybe the case that whenever a thing exists, it isalsoat the same time perceived, for anything that I have said or shall say to the contrary. I think, indeed, that, if such things as coloursdoexist, my observation of their behaviour will justify me in concluding that they also exist when I myself am, at least, not aware of perceiving them: but since I have not attempted to determine what kinds of observation are sufficient to justify a generalisation, I do not pretend to say whether this is so or not: and still less do I pretend to say whether,ifthey exist whenIdo not perceive them, we are justified in supposing that someone else must be perceiving them. The question whether anything exists, when it is not perceived, and, if so, what things, seems to me to be one which can only be settled by observation; and thus, I conceive, observation might justify us in concluding that certain kinds of things—pains, for example, donotexist, when they are notperceived and that other kinds of things—colours, for example,doexist, when they are not perceived. The only way, in which, so far as I am aware, the theory I am advocating does conflict with ordinary Idealistic conclusions, is that it does suggest that things, which arenot"spiritual," dosometimesexist, as really and as truly, as things which are.
The theory, therefore, that nothing exists, except when it is perceived, is no objection (even if it be true) to the supposition that colours do exist. What objections are there to this supposition? All serious objections to it are, I think, of one type. They all rest upon the assumption that, if a certain kind of thing exists at a certain time in a certain place, certain other kinds of things cannot exist at the same time in the same place. They are all, that is to say, of the same type as Berkeley's argument: that, though the same body of water mayappearto be simultaneously both hot and cold (if one of the hands we plunge into it is warm and the other cold), yet the heat and the cold cannot bothreallybe in the same body at the same time. And it is worth noticing that anyone who uses this argument must admit that he understands what is meant by "really existing in a given place," and that he means by it somethingotherthan "being perceived as in a given place." For the argument itself admits thatboththe heatandthe coldarereallyperceivedas being in the same place, and that there is no difficulty in supposing that they are so; whereas It urges that thereisa difficulty in supposing that they bothreally existin it.
Now there is one obvious defect in this type of argument, if designed to prove thatnosensible quality exists at any place where it is perceived as being—a defect, which Berkeley himself admits in his "Principles," though he omits to notice it where he repeats the argument in his "Hylas." Even ifwe assume that the heat and the cold cannotbothexist in the same place (and I admit that, in this case, the contrary assumption does seem repugnant to Common Sense), it does not follow thatneitherexists there. That is to say this type of argument, even if we grant its initial assumption, will only entitle us to conclude thatsomesensible qualities which we perceive as being in a certain place at a certain time, do not exist in that place at that time. And this conclusion, I am inclined to think, is true. In the case, for instance, of the so-called "images" which we perceive in a looking-glass, we may very readily admit that the colours and shapes which we perceive donotexist at the places where they appear to be—namely at various distances behind the glass. But yet, so far as I can see, we have no reason whatever for supposing that they do not,exceptthe assumption that our observations give us reason to believe thatothersensible qualitiesdoexist in those positions behind the glass; and the assumption thatwheretheseothersensible qualities do exist, those which we see in the glass donotexist. I should, therefore, admit thatsomesensible qualities which we perceive as being in certain places, donotexist in those places, while still retaining my belief that others do. Andperhapsthis explanation is the one which should also be adopted in the case of sensible qualities which appear to be at a great distance from us. When, for instance, (as we say), "we see the moon,"whatwe perceive (if the moon be full) is a round bright silver disc, of a small size, at a place very distant from us. Does that silver disc exist at that place? With what suppositions does the assumption that itdoesconflict? Only, so far as I can see, with the supposition that the place in question isreallyoccupied by a body such as science has taught us to suppose that the moonreallyis—a spherical body immensely larger thanobjects, in comparison with which the silver disc which we perceive is small;or elsewith the supposition that the place in question is really occupied by some part of our atmosphere, or some part of the medium which science supposes to exist between our atmosphere and the moon;or elsewith the supposition that the place in question is really occupied by what we might see, if the moon were nearer to us by many thousands of miles. Unless we suppose that some other objectisin the place, in which the silver disc appears to be, and that this object is of a kind which cannot occupy thesameplace which is occupied by a silver disc, we have no reason to suppose that the silver disc doesnotreally exist in the place where it appears to be. And, in this case, weperhapshave reason for both suppositions and should therefore conclude that the silver disc, which we perceive, does not exist in any real place.
Part, therefore, of these objections to our theory may, I think, be met by admitting thatsomeof the ... sensible qualities which we perceive do not exist at the places where they appear to exist, though ethers do. But there is, I think, another class of cases, in which we may be justified in denying that two things which (it is asserted) cannot occupy the same space, really cannot. I will take an instance which is, I think, typical. When we look at a drop of blood with the naked eye, we perceive a small red spot, uniformly red all over. But when (as we say) we look at thesameobject under a microscope of a certain power, I am informed that we see a much larger spot, of similar shape, indeed, butnotuniformly red—having, in fact, small red spots at different positions in a yellowish field. And if we were again to look at thesameobject through a microscope of much higher power still, we might perceive yet a third different arrangement ofcolours. Is there any fatal objection to supposing that allthreeappearances—the uniform red spot, the yellowish field with reddish spots in it, and the third, whatever that may be—do all really occupy the same real spatial area? I cannot see that there is. We are familiar with the idea that a given spatial area may contain parts which are invisible to us. And hence, I think it is quite conceivable that parts of a given area may bereallyoccupied by one colour, while the whole isreallyoccupied by another. And this, I think, is what we actuallydobelieve in many cases. At all events, we certainly believe that the area which appears to be occupied by one colour really isthe same areaas that which appears to be occupied by another. And, unless we assume that the area, in both cases, really is the same, we can certainly have no reason to deny that each colour does really occupy the area which it appears to occupy.
For these reasons I think that the difficulties in the way of supposing thatsomeof the sensible qualities which we perceive as being in certain places, really exist in the places in which we perceive them to be, are not insuperable. I have indeed not done justice to these difficulties; but then, neither have I done justice to what is to be said on the other side. At all events, I think it is plain that we have no reason to assert, in any case whatever, that a perceived colour doesnotreally exist in the place where it is perceived as being,unlesswe assume that that very same place really is occupied by something else—eitherby some different sensible qualitiesorby material objects such as physical science supposes to exist. But what reason can we give for such an assumption? I have tried to show that our own observations can give us none,unlesswe assume that some of the sensible qualities, which we observe as occupying certain places, do really exist in thoseplaces. And, if this is so, then we must admit that neither he who believes (with Reid) in the existence of other minds and of matter also, nor he who believes in the existence of other minds and denies that of matter, can have, in his own observations, the slightest reason either for his assertion or for his denial: we must admit that he can have no reason for either assertion or denial, except one which consists in the assumption of the existence or nonexistence of something which he doesnotobserve—something, therefore, of the very same kind as that for which he gives it as a reason. I am very unwilling to suppose that this is the case: I am very unwilling to suppose that he who believes that Sindbad the Sailor really saw what the "Arabian Nights" represent him as seeing, has just as good reason (so far as his own observation goes) for believing this as he who denies it has for denying it. Still this may be the case. Wemust, perhaps, be content to assume as certain that for which our observation gives no reason: to assume such propositions as that Sindbad didnotsee a Roc, and that youdohear my voice. But if it is said that these things are certain; then it also appears to me to be certain that the colours which I perceive do exist (someof them) where I perceive them. The more I look at objects round me, the more I am unable to resist the conviction that what I see does exist, as truly and as really, as my perception of it The conviction is overwhelming.
This being, then, the state of the case, I think I may at least plead that we have grounds for suspense of judgment as to whether what I see doesnotreally exist; grounds, too, for renewed enquiry, more careful than such enquiry has sometimes been in the past.