HOW WE KNOW THERE ARE OTHER MINDS

40. IS IT CERTAIN THAT WE KNOW IT?—I suppose there is no man in his sober senses who seriously believes that no other mind than his own exists. There is, to be sure, an imaginary being more or less discussed by those interested in philosophy, a creature called the Solipsist, who is credited with this doctrine. But men do not become solipsists, though they certainly say things now and then that other men think logically lead to some such unnatural view of things; and more rarely they say things that sound as if the speaker, in some moods, at least, might actually harbor such a view.

Thus the philosopher Fichte (1762-1814) talks in certain of his writings as though he believed himself to be the universe, and his words cause Jean Paul Richter, the inimitable, to break out in his characteristic way: "The very worst of it all is the lazy, aimless, aristocratic, insular life that a god must lead; he has no one to go with. If I am not to sit still for all time and eternity, if I let myself down as well as I can and make myself finite, that I may have something in the way of society, still I have, like petty princes, only my own creatures to echo my words. . . . Every being, even the highest Being, wishes something to love and to honor. But the Fichtean doctrine that I am my own body-maker leaves me with nothing whatever—with not so much as the beggar's dog or the prisoner's spider. . . . Truly I wish that there were men, and that I were one of them. . . . If there exists, as I very much fear, no one but myself, unlucky dog that I am, then there is no one at such a pass as I."

Just how much Fichte's words meant to the man who wrote them may be a matter for dispute. Certainly no one has shown a greater moral earnestness or a greater regard for his fellowmen than this philosopher, and we must not hastily accuse any one of being a solipsist. But that to certain men, and, indeed, to many men, there have come thoughts that have seemed to point in this direction—that not a few have had doubts as to their ability to prove the existence of other minds—this we must admit.

It appears somewhat easier for a man to have doubts upon this subject when he has fallen into the idealistic error of regarding the material world, which seems to be revealed to him, as nothing else than his "ideas" or "sensations" or "impressions." If we will draw the whole "telephone exchange" into the clerk, there seems little reason for not including all the subscribers as well. If other men's bodies are my sensations, may not other men's minds be my imaginings? But doubts may be felt also by those who are willing to admit a real external world. How do we know that our inference to the existence of other minds is a justifiable inference? Can there be such a thing as verification in this field?

For we must remember that no man is directly conscious of any mind except his own. Men cannot exhibit their minds to their neighbors as they exhibit their wigs. However close may seem to us to be our intercourse with those about us, do we ever attain to anything more than our ideas of the contents of their minds? We do not experience these contents; we picture them, we represent them by certain proxies. To be sure, we believe that the originals exist, but can we be quite sure of it? Can there be a proof of this right to make the leap from one consciousness to another? We seem to assume that we can make it, and then we make it again and again; but suppose, after all, that there were nothing there. Could we ever find out our error? And in a field where it is impossible to prove error, must it not be equally impossible to prove truth?

The doubt has seemed by no means a gratuitous one to certain very sensible practical men. "It is wholly impossible," writes Professor Huxley,[1] "absolutely to prove the presence or absence of consciousness in anything but one's own brain, though by analogy, we are justified in assuming its existence in other men." "The existence of my conception of you in my consciousness," says Clifford,[2] "carries with it a belief in the existence of you outside of my consciousness. . . . How this inference is justified, how consciousness can testify to the existence of anything outside of itself, I do not pretend to say: I need not untie a knot which the world has cut for me long ago. It may very well be that I myself am the only existence, but it is simply ridiculous to suppose that anybody else is. The position of absolute idealism may, therefore, be left out of count, although each individual may be unable to justify his dissent from it."

These are writers belonging to our own modern age, and they are men of science. Both of them deny that the existence of other minds is a thing that can be proved; but the one tells us that we are "justified in assuming" their existence, and the other informs us that, although "it may very well be" that no other mind exists, we may leave that possibility out of count.

Neither position seems a sensible one. Are we justified in assuming what cannot be proved? or is the argument "from analogy" really a proof of some sort? Is it right to close our eyes to what "may very well be," just because we choose to do so? The fact is that both of these writers had the conviction, shared by us all, that there are other minds, and that we know something about them; and yet neither of them could see that the conviction rested upon an unshakable foundation.

Now, I have no desire to awake in the mind of any one a doubt of the existence of other minds. But I think we must all admit that the man who recognizes that such minds are not directly perceived, and who harbors doubts as to the nature of the inference which leads to their assumption, may, perhaps, be able to say that he feels certain that there are other minds; but must we not at the same time admit that he is scarcely in a position to say: it is certain that there are other minds? The question will keep coming back again: May there not, after all, be a legitimate doubt on the subject?

To set this question at rest there seems to be only one way, and that is this: to ascertain the nature of the inference which is made, and to see clearly what can be meant by proof when one is concerned with such matters as these. If it turns out that we have proof, in the only sense of the word in which it is reasonable to ask for proof, our doubt falls away of itself.

41. THE ARGUMENT FOR OTHER MINDS.—I have said early in this volume (section 7) that the plain man perceives that other men act very much as he does, and that he attributes to them minds more or less like his own. He reasons from like to like—other bodies present phenomena which, in the case of his own body, he perceives to be indicative of mind, and he accepts them as indicative of mind there also. The psychologist makes constant use of this inference; indeed, he could not develop his science without it.

John Stuart Mill (1806-1873), whom it is always a pleasure to read because he is so clear and straightforward, presents this argument in the following form:[3]—

"By what evidence do I know, or by what considerations am I led to believe, that there exist other sentient creatures; that the walking and speaking figures which I see and hear, have sensations and thoughts, or, in other words, possess Minds? The most strenuous Intuitionist does not include this among the things that I know by direct intuition. I conclude it from certain things, which my experience of my own states of feeling proves to me to be marks of it. These marks are of two kinds, antecedent and subsequent; the previous conditions requisite for feeling, and the effects or consequences of it. I conclude that other human beings have feelings like me, because, first, they have bodies like me, which I know, in my own case, to be the antecedent condition of feelings; and because, secondly, they exhibit the acts, and other outward signs, which in my own case I know by experience to be caused by feelings. I am conscious in myself of a series of facts connected by a uniform sequence, of which the beginning is modifications of my body, the middle is feelings, the end is outward demeanor. In the case of other human beings I have the evidence of my senses for the first and last links of the series, but not for the intermediate link. I find, however, that the sequence between the first and last is as regular and constant in those other cases as it is in mine. In my own case I know that the first link produces the last through the intermediate link, and could not produce it without. Experience, therefore, obliges me to conclude that there must be an intermediate link; which must either be the same in others as in myself, or a different one. I must either believe them to be alive, or to be automatons; and by believing them to be alive, that is, by supposing the link to be of the same nature as in the case of which I have experience, and which is in all respects similar, I bring other human beings, as phenomena, under the same generalizations which I know by experience to be the true theory of my own existence. And in doing so I conform to the legitimate rules of experimental inquiry. The process is exactly parallel to that by which Newton proved that the force which keeps the planets in their orbits is identical with that by which an apple falls to the ground. It was not incumbent on Newton to prove the impossibility of its being any other force; he was thought to have made out his point when he had simply shown that no other force need be supposed. We know the existence of other beings by generalization from the knowledge of our own; the generalization merely postulates that what experience shows to be a mark of the existence of something within the sphere of our consciousness, may be concluded to be a mark of the same thing beyond that sphere."

Now, the plain man accepts the argument from analogy, here insisted upon, every day of his life. He is continually forming an opinion as to the contents of other minds on a basis of the bodily manifestations presented to his view. The process of inference is so natural and instinctive that we are tempted to say that it hardly deserves to be called an inference. Certainly the man is not conscious of distinct steps in the process; he perceives certain phenomena, and they are at once illuminated by their interpretation. He reads other men as we read a book—the signs on the paper are scarcely attended to, our whole thought is absorbed in that for which they stand. As I have said above, the psychologist accepts the argument, and founds his conclusions upon it.

Upon what ground can one urge that this inference to other minds is a doubtful one? It is made universally. We have seen that even those who have theoretic objections against it, do not hesitate to draw it, as a matter of fact. It appears unnatural in the extreme to reject it. What can induce men to regard it with suspicion?

I think the answer to this question is rather clearly suggested in the sentence already quoted from Professor Huxley: "It is wholly impossible absolutely to prove the presence or absence of consciousness in anything but one's own brain, though, by analogy, we are justified in assuming its existence in other men."

Here Professor Huxley admits that we have something like a proof, for he regards the inference as justified. But he does not think that we have absolute proof—the best that we can attain to appears to be a degree of probability falling short of the certainty which we should like to have.

Now, it should be remarked that the discredit cast upon the argument for other minds has its source in the fact that it does not satisfy a certain assumed standard. What is that standard? It is the standard of proof which we may look for and do look for where we are concerned to establish the existence of material things with the highest degree of certainty.

There are all sorts of indirect ways of proving the existence of material things. We may read about them in a newspaper, and regard them as highly doubtful; we may have the word of a man whom, on the whole, we regard as veracious; we may infer their existence, because we perceive that certain other things exist, and are to be accounted for. Under certain circumstances, however, we may have proof of a different kind: we may see and touch the things themselves. Material things are open to direct inspection. Such a direct inspection constitutes absolute proof, so far as material things are concerned.

But we have no right to set this up as our standard of absolute proof, when we are talking about other minds. In this field it is not proof at all. Anything that can be directly inspected is not another mind. We cannot cast a doubt upon the existence of colors by pointing to the fact that we cannot smell them. If they could be smelt, they would not be colors. We must in each case seek a proof of the appropriate kind.

What have we a right to regard as absolute proof of the existence of another mind? Only this: the analogy upon which we depend in making our inference must be a very close one. As we shall see in the next section, the analogy is sometimes very remote, and we draw the inference with much hesitation, or, perhaps, refuse to draw it at all. It is not, however, the kind of inference that makes the trouble; it is the lack of detailed information that may serve as a basis for inference. Our inference to other minds is unsatisfactory only in so far as we are ignorant of our own minds and bodies and of other bodies. Were our knowledge in these fields complete, we should know without fail the signs of mind, and should know whether an inference were or were not justified.

And justified here means proved—proved in the only sense in which we have a right to ask for proof. No single fact is known that can discredit such a proof. Our doubt is, then............