Part 8

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 of _his_ hand catching hold of his foot, which I have observed preceding my perception of _my_ hand 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 foot _is_ preceded by a similar feeling of pain, not in me but in 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 is _sufficient_ to justify a generalisation: and therefore I will allow that the degree of likeness _may_ be 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 as _necessary_, 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, _will_ justify the generalisation that my perception of any such movement, whether in my own body _or_ in 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, it _is_ probable that the feeling of pain exists, though I do not perceive it. But, if it _is_ probable that such a feeling of pain exists, such a feeling must stand _in the same relation_ to 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 of _my own._ They cannot possibly justify the belief in the existence of any such feeling _except_ one which stands to my perception in the same relation in which my feelings do stand to _my_ perceptions--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 feeling _of 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 pain _of my own_ preceding a perception _of 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 (_if_ justified in inferring any feeling at all), in inferring an unperceived feeling _of 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 connection between any of them and any feeling, perception, or thought in another person. The argument is perfectly general, since _all_ my 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 being _another persons_, I mean to say that it has _not_ got to any of mine. I can, therefore, merely from observation of _this_ class of data never obtain the slightest reason for belief in the existence of a feeling, perception, or thought which does _not_ stand in these relations to one of mine--which _is,_ 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, is _real_; that which I perceive when I perceive a movement of another's body is _real_ also. I can now observe not merely the relation between my _perception_ of a movement of my body and my own feelings, but also a relation between a _real_ movement 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 stand _in the same relation_ to 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 to _verify_ or _confirm_ the hypothesis that other persons exist. This hypothesis is one which "works." The assumption 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, _if_ the hypothesis were true; our perceptions behave _as if_ other 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 particular feelings: 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 with_ the 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 with_ the 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, _if_ another person had felt pain. In general terms, that is to say, I admit that the occurrence of B, _together with_ the 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 with_ the 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 exists _in this particular instance._ Or, on the other hand, it may be meant that, assuming A 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. _Either_ the one _or_ the 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 them _is_ just 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 me _reason_ to suppose that _if_ another person has certain perceptions or feelings _he_ will 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 perception _of my own_--to suppose that any perception of my own is the sort of thing which would occur _if_ another person had a particular feeling. What therefore, my opponent must affirm is that the observation of a perception of my own _without_ the 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 of the 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 which _these_ succeed one another generally lead to true predictions. Whether the observation of such beliefs _alone_ could give sufficient reason for it, is, I think, doubtful; but I 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, _unless_ some 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-contents _can_ (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 burning _does_ exist, _are_ true, 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 observe _other_ than 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-contents _do_ exist, my own observations cannot give me the slightest reason for believing that anybody else has ever 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 that _any_ particular 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 we _do_ know 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 and feelings, 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, _unless_ our own perceptions, thoughts and feelings are _not_ the 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 also _some_ of 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 kind _exist_ or are _real_ in 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, that _none_ of the colours which I perceive as occupying areas of certain shapes and sizes really exist 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 not _mean_ "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 none _do_ so: it _may_ be the case that whenever a thing exists, it is _also_ at the same time perceived, for anything that I have said or shall say to the contrary. I think, indeed, that, if such things as colours _do_ exist, 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, _if_ they exist when _I_ do 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, do _not_ exist, when they are not perceived and that other kinds of things--colours, for example, _do_ exist, 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 are _not_ "spiritual," do _sometimes_ exist, 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 may _appear_ to 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 both _really_ be 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 something _other_ than "being perceived as in a given place." For the argument itself admits that _both_ the heat _and_ the cold _are_ really _perceived_ as being in the same place, and that there is no difficulty in supposing that they are so; whereas It urges that there _is_ a difficulty in supposing that they both _really exist_ in it.