Part 4

Now I think you may have noticed that when you make a statement to another person, and he answers "How do you know that that is so?" he very often means to suggest that you do _not_ know it. And yet, though he means to suggest that you do not _know_ it, he may not for a moment wish to suggest that you do not _believe_ it, nor even that you have not that degree or kind of conviction, which goes beyond mere belief, and which may be taken to be essential to anything which can properly be called knowledge. He does not mean to suggest for a moment that you are saying something which you do not believe to be true, or even that you are not thoroughly convinced of its truth. What he does mean to suggest is that what you asserted was not _true_, even though you may not only have believed it but felt sure that it was true. He suggests that you don't _know_ it, in the sense that what you believe or feel sure of is not true.

Now I point this out, not because I myself mean to suggest that we don't know the existence of other persons, but merely in order to show that the word "know" is sometimes used in a sense in which it is not merely equivalent to "believe" or "feel sure of." When the question "How do you _know_ that?" is asked, the questioner does not merely mean to ask "how do you come to believe that, or to be convinced of it?" He sometimes, and I think generally, means to ask a question with regard to the _truth_, and not with regard to the _existence_ of your belief. And similarly when I ask the question "How do we know that other people exist?" I do _not_ mean to ask "How do we come to believe in or be convinced of their existence?" I do not intend to discuss this question _at all._ I shall not ask what _suggests_ to us our belief in the existence of other persons or of an external world; I shall not ask whether we arrive at it by inference or by "instinct" or in any other manner, which ever has been or may be suggested: I shall discuss no question of any kind whatever with regard to its origin, or cause, or the way in which it arises. These psychological questions are _not_ what I propose to discuss. When I ask the question "How do we know that other people exist?" I do _not_ mean:

"How does our belief in their existence arise?"

But if I do not mean this what do I mean P I have said that I mean to ask a question with regard to the _truth_ of that belief; and the particular question which I mean to ask might be expressed in the words: _What reason have_ we for our belief in the existence of other persons? But these are words which themselves need some explanation, and I will try to give it.

In the first place, then, when I talk of "a reason," I mean _only_ a good reason and _not_ a bad one. A bad reason is, no doubt, a reason, in one sense of the word; but I mean to use the word "reason" exclusively in the sense in which it is equivalent to "good reason." But what, then, is meant by a good reason for a belief? I think I can express sufficiently accurately what I mean by it in this connection, as follows:--A good reason for a belief is a proposition which is true, and which would not be true unless the belief were also true. We should, I think, commonly say that when a man knows such a proposition, he has a good reason for his belief; and, when he knows no such proposition, we should say that he has no reason for it. When he knows such a proposition, we should say he knows something which is a reason for thinking his belief to be true--something from which it _could_ be validly inferred. And if, in answer to the question "How do you know so and so?" he were to state such a proposition, we should, I think, feel that he had answered the question which we meant to ask. Suppose, for instance, in answer to the question "How do you know that?" he were to say "I saw it in the _Times."_ Then, if we believed that he had seen it in the _Times_, and also believed that it would not have been in the _Times_, unless it had been true, we should admit that he had answered our question. We should no longer doubt that he did _know_ what he asserted, we should no longer doubt that his belief was true. But if, on the other hand, we believed that he had not seen it in the _Times_--if, for instance, we had reason to believe that what he saw was not the statement which he made, but some other statement which he mistook for it; or if we believed that the kind of statement in question was one with regard to which there was no presumption that, being in the _Times_, it would be true: in _either_ of these cases we should, I think, feel that he had _not_ answered our question. We should still doubt whether what he had said was true. We should still doubt whether he _knew_ what he asserted; and since a man cannot tell you how he _knows_ a thing unless he does know that thing, we should think that, though he might have told us truly how he _came to believe it,_ he had certainly not told us how he _knew_ it. But though we should thus hold that he had _not_ told us _how he knew_ what he had asserted, and that he had given us no reason for believing it to be true; we must yet admit that he had given us a reason in a sense--a _bad_ reason, a reason which was no reason because it had no tendency to show that what he believed was true; and we might also be perfectly convinced that he had given us _the reason_ why he believed it--the proposition by believing which he was induced also to believe his original assertion.

I mean, then, by my question, "How do we know that other people exist?" what, I believe, is ordinarily meant, namely, "What reason have we for believing that they exist?" and by this again I mean, what I also believe is ordinarily meant, namely, "What proposition do we believe, which is both true itself and is also such that it would not be true, unless other people existed?" And I hope it is plain that this question, thus explained, is quite a different question from the psychological question, which I said I did _not_ mean to ask--from the question, "How does our belief in the existence of other people arise?" My illustration, I hope, has made this plain. For I have pointed out that we may quite well hold that a man has told us how a belief of his arises, and even what was the reason which made him adopt that belief, and yet may have failed to give us any _good reason_ for his belief--any proposition which is both true itself, and also such that the truth of his belief follows from it. And, indeed, it is plain that if any one ever believes what is false, he is believing something for which there _is_ no good reason, in the sense which I have explained, and for which, therefore, he cannot possibly have a good reason; and yet it plainly does not follow that his belief did not arise in anyway whatever, nor even that he had no reason for it--no bad reason. It is plain that false beliefs do arise in some way or other--they have origins and causes: and many people who hold them _have_ bad reasons for holding them--their belief does arise (by inference or otherwise) from their belief in some other proposition, which is not itself true, or else is not a _good_ reason for holding that, which they infer from it, or which, in some other way, it induces them to believe. I submit, therefore, that the question, "What good reason have we for believing in the existence of other people?" is different from the question, "How does that belief arise?" But when I say this, I must not be misunderstood; I must not be understood to affirm that the answer to both questions _may_ not, in a sense, be the same. I fully admit that the very same fact, which suggests to us the belief in the existence of other people, _may_ also be a good reason for believing that they do exist. All that I maintain is that the question whether it is a good reason for that belief is a different question from the question whether it suggests that belief: if we assert that a certain fact _both_ suggests our belief in the existence of other persons and is _also_ a good reason for holding that belief, we are asserting two different things and not one only. And hence, when I assert, as I shall assert, that we _have_ a good reason for our belief in the existence of other persons, I must not be understood also to assert either that we infer the existence of other persons from this good reason, or that our belief in that good reason suggests our belief in the existence of other persons in any other way. It is plain, I think, that a man may believe two true propositions, of which the one would not be true, unless the other were true too, without, in any sense whatever, having arrived at his belief in the one _from_ his belief in the other; and it is plain, at all events, that the question whether his belief in the one _did_ arise from his belief in the other, is a different question from the question whether the truth of the one belief follows from the truth of the other.

I hope, then, that I have made it a little clearer what I mean by the question: "What reason have we for believing in the existence of other people?" and that what I mean by it is at all events different from what is meant by the question: "How does our belief in the existence of other people arise?"

But I am sorry to say that I have not yet reached the end of my explanations as to what my meaning is. I am afraid that the subject may seem very tedious. I can assure you that I have found it excessively tedious to try to make my meaning clear to myself. I have constantly found that I was confusing one question with another, and that, where I had thought I had a good reason for some assertion, I had in reality no good reason. But I may perhaps remind you that this question, "How do we know so and so?" "What reason have we for believing it?" is one of which philosophy is full; and one to which the most various answers have been given. Philosophy largely consists in giving reasons; and the question what are good reasons for a particular conclusion and what are bad, is one upon which philosophers have disagreed as much as on any other question. For one and the same conclusion different philosophers have given not only different, but incompatible, reasons; and conversely different philosophers have maintained that one and the same fact is a reason for incompatible conclusions. We are apt, I think, sometimes to pay too little attention to this fact. When we have taken, perhaps, no little pains to assure ourselves that our own reasoning is correct, and especially when we know that a great many other philosophers agree with us, we are apt to assume that the arguments of those philosophers, who have come to a contradictory conclusion, are scarcely worthy of serious consideration. And yet, I think, there is scarcely a single reasoned conclusion in philosophy, as to which we shall not find that some other philosopher, who has, so far as we know, bestowed equal pains on his reasoning, and with equal ability, has reached a conclusion incompatible with ours. We may be satisfied that we are right, and we may, in fact, be so; but it is certain that _both_ cannot be right: either our opponent or we must have mistaken bad reasons for good. And this being so, however satisfied we may be that it is not we who have done so, I think we should at least draw the conclusion that it is by no means easy to avoid mistaking bad reasons for good; and that no process, however laborious, which is in the least likely to help us in avoiding this should be evaded. But it is at least possible that one source of error lies in mistaking one kind of reason for another--in supposing that, because there is, in one sense, a reason for a given conclusion, there is also a reason in another, or that because there is, in one sense, no reason for a given conclusion, there is, therefore, no reason at all. I believe myself that this _is_ a very frequent source of error: but it is at least a possible one. And where, as disagreements show, there certainly is error on one side or the other, and reason, too, to suppose that the error is not easy to detect, I think we should spare no pains in investigating any source, from which it is even possible that the error may arise. For these reasons I think I am perhaps doing right in trying to explain as clearly as possible not only what reasons we have for believing in an external world, but also in what sense I take them to be reasons.

I proceed, then with my explanation. And there is one thing, which, I think my illustration has shown that I do _not_ mean. I have defined a reason for a belief as a true proposition, which would not be true unless the belief itself--what is believed--were also true; and I have used, as synonymous with this form of words, the expressions: A reason for a belief is a true proposition from which the truth of the belief _follows_ from which it _could_ be _validly inferred._ Now these expressions might suggest the idea that I mean to restrict the word "reason," to what, in the strictest sense, might be called a _logical_ reason--to propositions from which the belief in question _follows,_ according to the rules of inference accepted by Formal Logic. But I am _not_ using the words "follow," "validly inferred," in this narrow sense; I do _not_ mean to restrict the words "reason for a belief" to propositions from which the laws of Formal Logic state that the belief could be deduced. The illustration which I gave is inconsistent with this restricted meaning. I said that the fact that a statement appeared in the _Times_ might be a good reason for believing that that statement was true. And I am using the word "reason" in the wide and popular sense, in which it really might be. If, for instance, the _Times_ stated that the King was dead, we should think that was a good reason for believing that the King was dead; we should think that the _Times_ would not have made such a statement as that unless the King really were dead. We should, indeed, not think that the statement in the _Times_ rendered it absolutely _certain_ that the King was dead. But it _is_ extremely unlikely that the _Times_ would make a statement of this kind unless it were true; and, in that sense, the fact of the statement appearing in the _Times_ would render it _highly probable_--much more likely than not--that the King was dead. And I wish it to be understood that I am using the words "reason for a belief" in this extremely wide sense. When I look for a good reason for our belief in the existence of other people, I shall not reject any proposition merely on the ground that it only renders their existence probable--only shows it to be more likely than not that they exist. Provided that the proposition in question does render it _positively probable_ that they exist, then, if it also conforms to the conditions which I am about to mention, I shall call it a "good reason."

But it is not every proposition which renders it probable that other people exist, which I shall consider to be a good answer to my question. I have just explained that my meaning is wide in one direction--in admitting _some_ propositions which render a belief merely probable; but I have now to explain that it is restricted in two other directions. I do mean to exclude certain propositions which do render that belief probable. When I ask: What reason have _we_ for believing in the existence of other people? a certain ambiguity is introduced by the use of the plural "we." If each of several different persons has a reason for believing that he himself exists, then it is not merely probable, but certain, according to the rules of Formal Logic, that, in a sense, _they_ "have a reason for believing" that several people exist; each has a reason for believing that he himself exists; and, therefore, all of them, taken together, have reasons for supposing that several persons exist. If, therefore, I were asking the question: What reason have _we_ for believing in the existence of other persons? in this sense, it would follow that if each of us has a reason for believing in his own existence, these reasons, taken together, would be a reason for believing in the existence of all of us. But I am not asking the question in this sense: it is plain that this is not its natural sense. What I do mean to ask is: Does _each single one_ of us know any proposition, which is a reason for believing that _others_ exist? I am using "we," that is to say, in the sense of "each of us." But again I do mean _each_ of us: I am not merely asking whether some _one_ man knows a proposition which is a reason for believing that other men exist. It would be possible that some one man, or some few men, should know such a proposition, and yet the rest know no such proposition. But I am not asking whether this is the case. I am asking whether among propositions of the kind which (as we commonly suppose) all or almost all men know, there is any which is a reason for supposing that other men exist. And in asking this question I am not begging the question by supposing that all men do exist. My question might, I think, be put quite accurately as follows. There are certain kinds of belief which, as we commonly suppose, all or almost all men share. I describe this kind of belief as "our" beliefs, simply as an easy way of pointing out which kind of belief I mean, but without assuming that all men do share them. And I then ask: Supposing a single man to have beliefs of this kind, which among them would be a good reason for supposing that other men existed having like beliefs?

This, then, is the first restriction which I put upon the meaning of my question. And it is, I think, a restriction which, in their natural meaning, the words suggest. When we ask: What reason have we for believing that other people exist? we naturally understand that question to be equivalent to: What reason has _each_ of us for that belief? And this question again is naturally equivalent to the question: Which among the propositions that a single man believes, but which are of the kind which (rightly or wrongly) we assume all men to believe, are such that they would not be true unless some other person than that man existed? But there is another restriction which, I think, the words of my question also naturally suggest. If we were to ask anyone the question: How do you know that you did see that statement in the _Times_? and he were to answer "Because I did see it in the _Times_ and in the _Standard_ too," we should not think that he had given us a _reason_ for the belief that he saw it in the _Times._ We should not think his answer a _reason_, because it asserts the very thing for which we require a reason. And similarly when I ask: How do we know that any thing or person exists, other than ourselves and what we directly perceive? What reason have we for believing this? I must naturally be understood to mean: What proposition, _other_ than one which itself asserts or presupposes the existence of something beyond ourselves and our own perceptions, is a reason for supposing that such a thing exists? And this restriction obviously excludes an immense number of propositions of a kind which all of us do believe. We all of us believe an immense number of different propositions about the existence of things which we do not directly perceive, and many of these propositions are, in my sense, good reasons for believing in the existence of still other things. The belief in the existence of a statement in the _Times,_ when we have not seen that statement, may, as I implied, be a good reason for believing that someone is dead. But no such proposition can be a good answer to my question, because it asserts the very kind of thing for which I require a reason: it asserts the existence of something other than myself and what I directly perceive. When I am asking: What reason have I for believing in the existence of anything but myself, my own perceptions, and what I do directly perceive? you would naturally understand me to mean: What reason, _other than_ the existence of such a thing, have I for this belief?

Each of us, then, we commonly assume, believes some true propositions, which do not themselves assert the existence of anything other than himself, his own perceptions, or what he directly perceives. Each of us, for instance, believes that he himself has and has had certain particular perceptions: and these propositions are propositions of the kind I mean--propositions which do not themselves assert the existence of anything _other than_ himself, his own perceptions, and what he directly perceives: they are, I think, by no means the only propositions of this kind, which most of us believe: but they _are_ propositions of this kind. But, as I say, I am not assuming that each of us--each of several different people--does believe propositions of this kind. All that I assume is that at least one man does believe some such propositions. And then I ask: Which among those true propositions, which one man believes, are such that they would probably not be true, unless some other man existed and had certain particular perceptions? Which among them are such that it _follows_ (in the wide sense, which I have explained) from their truth, that it is more likely than not that some other man has perceptions? This is the meaning of my question, so far as I have hitherto explained it: and I hope this meaning is quite clear. It is in this sense that I am asking: What reason have we for believing that other people exist? How do we know that they exist? This, indeed, is not _all_ that I mean by that question: there is one other point--the most important one--which remains to be explained. But this is _part_ of what I mean to ask; and before I go on to explain what else I mean, I wish first to stop and enquire what is the answer to this part of my question. What is the answer to the question: Which among the true propositions, of a kind which (as we commonly assume) each of us believes, and which do not themselves assert the existence of anything other than that person himself, his own perceptions, or what he directly perceives, are such that they would probably not be true unless some other person existed, who had perceptions in some respects similar to his own?