perception or belief. We assume, for instance, that when we hear or read certain words, somebody besides ourselves has thought the thoughts, which constitute the meaning of those words; and it is plain, I think, that we have no reason for this assumption except one which is also a reason for the assumption that when certain words are heard or read, somebody generally has had certain thoughts. And my enquiry, therefore, at least includes the enquiry: What reasons have we for such generalisations as these? for generalisations which assert a connection between the existence of a certain kind of perception in one man, and that of a certain kind of perception or belief in another man?
And to this question, I think, but one answer can be given. If we have any reason for such generalisations at all, some reason must be given, in one way or another, by observation—by observation, understood in the wide sense in which it includes "experiment." No philosopher, I think, has ever failed to assume that observation does give a reason for some generalisations—for some propositions which assert that when one kind of thing exists, another generally exists or has existed in a certain relation to it. Even those who, like Hume, imply that observation cannot give a reason for anything, yet constantly appeal to observation in support of generalisations of their own. And even those who hold that observation can give no reason for any generalisation about the relation of one man's perceptions to another's, yet hold that it can give a reason for generalisations about the relation of some to others among a man's own perceptions. It is, indeed, by no means agreed how observation can give a reason for any generalisation. Nobody knows what reason we have, if we have any, for supposing that it can. But that it can, everyone, I think, assumes. I think, therefore, most philosophers will agree, that if we can find any reason at all for generalisations of the kind in which I am interested, a reason for some of them at all events must be found in observation. And what I propose to ask is: What reason can be found in observation for even a single proposition of the kind I have described? for a proposition which asserts that when one man has one kind of perception, another man generally has or has had another.
But, when it is said that observation gives us a reason for generalisations, two things may be meant neither of which I mean. In the first place, we popularly use "observation" in a sense in which we can be said to observe the perceptions, feelings and thoughts of other people: in which, therefore, we can be said to observe the very things with regard to which I am asking what reason we have for believing in their existence. But it is universally[1] agreed that there is a sense in which no man can observe the perceptions, feelings or thoughts of any other man. And it is to this strict sense that I propose to confine the word. I shall use it in a sense, in which we can certainly be said to observe nothing but ourselves, our own perceptions, thoughts and feelings, and what we directly perceive. And in the second place, it may be said that observations made by another person may give me a reason for believing some generalisation. And it is certainly the case that for many of the generalisations in which we all believe, if we have a reason in observation at all, it is not in our own observation that we have it: part of our reason, at all events, lies in things which other people have observed but which we ourselves have not observed. But in asking this particular question, I am not asking for reasons of this sort. The very question that I am asking is: What reason has any one of us for supposing that any other person whatever has ever made any observations? And just as, in the first meaning which I gave to this question, it meant: What thing, that any single man observes is such that it would probably not have existed, unless some other man had made a particular observation? So now I am asking: Which among the things, which one single man observes, are such that they would probably not have existed, unless it were true that some of them generally stood in certain relations to observations of some other person? I am asking: Which among my own observations give me a reason for supposing that some of them are of a kind which are generally preceded or accompanied by observations of other people? Which, for instance, among my own observations give a good reason for the generalisation that when I hear certain words, somebody else has generally had certain particular thoughts, or that whenever anyone hears certain words, somebody else has generally had the thoughts which constitute what we call the meaning of those words? I am asking: Which among the vast series of observations, which any one individual makes during his lifetime, give a good reason for any generalisation whatever of this kind—a generalisation which asserts that some of them are generally preceded by certain thoughts, perceptions or feelings in other persons? I quite admit that there are some generalisations of this kind for which the observations of some particular men will not give a reason. All that I ask is: Is there even one generalisation of this kind, for which the kind of observations, which (as we commonly assume) each man, or nearly every man does make, do give a reason? Among observations of the kind which (as we commonly assume) are common to you and to me, do yours, by themselves, give any reason for even one such generalisation? And do mine, by themselves, give any reason for even one such generalisation? And if they do, which, among these observations, is it which do so?
My question is, then: What reason do my own observations give me, for supposing that any perception whatever, which I have, would probably not occur, unless some other person had a certain kind of perception? What reason do my own observations give me for supposing, for instance, that I should not be perceiving what I do now perceive, unless someone were hearing the sound of my voice? What reason do your own observations give you for supposing that you would not be perceiving just what you are perceiving, unless I were perceiving more or less black marks on a more or less white ground? The question does, I think, appear to be a reasonable one; and most philosophers, I think, have assumed that there is an answer to it. Yet it may be said that there is no answer to it: that my own observations give me no reason whatever for any single proposition of this kind. There are certain philosophers (even apart from thorough sceptics, with whom, as I have said, I am not now arguing) who have denied that they do. There are certain philosophers who hold that nothing which any single one of us observes or can observe, gives the slightest reason for supposing that any of his own perceptions are generally connected with certain perceptions in other people. There are philosophers who hold that the only generalisations for which our own observations do give any warrant are generalisations concerning the manner in which our own perceptions, thoughts and feelings do and probably will succeed one another; and who conclude that, this being so, we have no reason whatever for believing in the existence of any other people. And these philosophers are, I think, right in drawing this conclusion from this premiss. It does not, indeed, follow from their premiss that we have not a reason in the sense which I first explained, and in which, I insisted, it must be admitted that we have a reason. It does not follow that some of our perceptions are not such as would probably not exist, unless some other person had certain perceptions. But, as I have urged, when we say that we have a reason for asserting the existence of something not perceived, we commonly mean something more than this. We mean not only that, since what we perceive does exist, the unperceived thing probably exists too; we mean also that we have some reason for asserting this connection between the perceived and the unperceived. And holding, as we do, that no reason can be given for asserting such a connection, except observation, we should say that, if observation gives no reason for asserting it, we have no reason for asserting it; and having no reason for asserting this connection between the perceived and the unperceived, we should say that we have none either for asserting the even probable existence of the unperceived. This, I think, is what we commonly mean by saying that we have no reason to believe in the existence of a particular thing which we do not perceive. And hence, I think, those philosophers who hold that our own observations give us no reason whatever for any generalisation whatever concerning the connection of any of them with those of other people, are quite right in concluding that we have no reason to assert that any other person ever did have any particular thought or perception whatever. I think that the words of this conclusion, understood in their natural meaning, express precisely what the premiss asserts. We need not, indeed, conclude, as many of these philosophers are inclined to do, that, because we have no reason for believing in the existence of other people, it is therefore highly doubtful whether they do exist. The philosophers who advocate this opinion commonly refute themselves by assigning the existence of other people as part of their reason for believing that it is very doubtful whether any other people exist. That for which we have no reason may, nevertheless,