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