An Introduction to Philosophy

by George Stuart Fullerton

CHAPTER X

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, gratuitous and can be dismissed. We may claim that we have verification of the existence of other minds. Such verification, however, must consist in showing that, in any given instance, the signs of mind really are present. It cannot consist in presenting minds for inspection as though they were material things.

One more matter remains to be touched upon in this section. It has doubtless been observed that Mill, in the extract given above, seems to place "feelings," in other words, mental phenomena, between one set of bodily motions and another. He makes them the middle link in a chain whose first and third links are material. The parallelist cannot treat mind in this way. He claims that to make mental phenomena effects or causes of bodily motions is to make them material.

Must, then, the parallelist abandon the argument for other minds? Not at all. The force of the argument lies in interpreting the phenomena presented by other bodies as one knows by experience the phenomena of one's own body must be interpreted. He who concludes that the relation between his own mind and his own body can best be described as a "parallelism," must judge that other men's minds are related to their bodies in the same way. He must treat his neighbor as he treats himself. The argument from analogy remains the same.

42. WHAT OTHER MINDS ARE THERE?—That other men have minds nobody really doubts, as we have seen above. They resemble us so closely, their actions are so analogous to our own, that, although we sometimes give ourselves a good deal of trouble to ascertain what sort of minds they have, we never think of asking ourselves whether they have minds.

Nor does it ever occur to the man who owns a dog, or who drives a horse, to ask himself whether the creature has a mind. He may complain that it has not much of a mind, or he may marvel at its intelligence—his attitude will depend upon the expectations which he has been led to form. But regard the animal as he would regard a bicycle or an automobile, he will not. The brute is not precisely like us, but its actions bear an unmistakable analogy to our own; pleasure and pain, hope and fear, desire and aversion, are so plainly to be read into them that we feel that a man must be "high gravel blind" not to see their significance.

Nevertheless, it has been possible for man, under the prepossession of a mistaken philosophical theory, to assume the whole brute creation to be without consciousness. When Descartes had learned something of the mechanism of the human body, and had placed the human soul—hospes comesque corporis—in the little pineal gland in the midst of the brain, the conception in his mind was not unlike that which we have when we picture to ourselves a locomotive engine with an engineer in its cab. The man gives intelligent direction; but, under some circumstances, the machine can do a good deal in the absence of the man; if it is started, it can run of itself, and to do this, it must go through a series of complicated motions.

Descartes knew that many of the actions performed by the human body are not the result of conscious choice, and that some of them are in direct contravention of the will's commands. The eye protects itself by dropping its lid, when the hand is brought suddenly before it; the foot jerks away from the heated object which it has accidentally touched. The body was seen to be a mechanism relatively independent of the mind, and one rather complete in itself. Joined with a soul, the circle of its functions was conceived to be widened; but even without the assistance of the soul, it was thought that it could keep itself busy, and could do many things that the unreflective might be inclined to attribute to the efficiency of the mind.

The bodies of the brutes Descartes regarded as mechanisms of the same general nature as the human body. He was unwilling to allow a soul to any creature below man, so nothing seemed left to him save to maintain that the brutes are machines without consciousness, and that their apparently purposive actions are to be classed with such human movements as the sudden closing of the eye when it is threatened with the hand. The melancholy results of this doctrine made themselves evident among his followers. Even the mild and pious Malebranche could be brutal to a dog which fawned upon him, under the mistaken notion that it did not really hurt a dog to kick it.

All this reasoning men have long ago set aside. For one thing, it has come to be recognized that there may be consciousness, perhaps rather dim, blind, and fugitive, but still consciousness, which does not get itself recognized as do our clearly conscious purposes and volitions. Many of the actions of man which Descartes was inclined to regard as unaccompanied by consciousness may not, in fact, be really unconscious. And, in the second place, it has come to be realized that we have no right to class all the actions of the brutes with those reflex actions in man which we are accustomed to regard as automatic.

The belief in animal automatism has passed away, it is to be hoped, never to return. That lower animals have minds we must believe. But what sort of minds have they?

It is hard enough to gain an accurate notion of what is going on in a human mind. Men resemble each other more or less closely, but no two are precisely alike, and no two have had exactly the same training. I may misunderstand even the man who lives in the same house with me and is nearly related to me. Does he really suffer and enjoy as acutely as he seems to? or must his words and actions be accepted with a discount? The greater the difference between us, the more danger that I shall misjudge him. It is to be expected that men should misunderstand women; that men and women should misunderstand children; that those who differ in social station, in education, in traditions and habits of life, should be in danger of reading each other as one reads a book in a tongue imperfectly mastered. When these differences are very great, the task is an extremely difficult one. What are the emotions, if he has any, of the Chinaman in the laundry near by? His face seems as difficult of interpretation as are the hieroglyphics that he has pasted up on his window.

When we come to the brutes, the case is distinctly worse. We think that we can attain to some notion of the minds to be attributed to such animals as the ape, the dog, the cat, the horse, and it is not nonsense to speak of an animal psychology. But who will undertake to tell us anything definite of the mind of a fly, a grasshopper, a snail, or a cuttlefish? That they have minds, or something like minds, we must believe; what their minds are like, a prudent man scarcely even attempts to say. In our distribution of minds may we stop short of even the very lowest animal organisms? It seems arbitrary to do so.

More than that; some thoughtful men have been led by the analogy between plant life and animal life to believe that something more or less remotely like the consciousness which we attribute to animals must be attributed also to plants. Upon this belief I shall not dwell, for here we are evidently at the limit of our knowledge, and are making the vaguest of guesses. No one pretends that we have even the beginnings of a plant psychology. At the same time, we must admit that organisms of all sorts do bear some analogy to each other, even if it be a remote one; and we must admit also that we cannot prove plants to be wholly devoid of a rudimentary consciousness of some sort.

As we begin with man and descend the scale of beings, we seem, in the upper part of the series, to be in no doubt that minds exist. Our only question is as to the precise contents of those minds. Further down we begin to ask ourselves whether anything like mind is revealed at all. That this should be so is to be expected. Our argument for other minds is the argument from analogy, and as we move down the scale our analogy grows more and more remote until it seems to fade out altogether. He who harbors doubts as to whether the plants enjoy some sort of psychic life, may well find those doubts intensified when he turns to study the crystal; and when he contemplates inorganic matter he should admit that the thread of his argument has become so attenuated that he cannot find it at all.

43. THE DOCTRINE OF MIND-STUFF.—Nevertheless, there have been those who have attributed something like consciousness even to inorganic matter. If the doctrine of evolution be true, argues Professor Clifford,[4] "we shall have along the line of the human pedigree a series of imperceptible steps connecting inorganic matter with ourselves. To the later members of that series we must undoubtedly ascribe consciousness, although it must, of course, have been simpler than our own. But where are we to stop? In the case of organisms of a certain complexity, consciousness is inferred. As we go back along the line, the complexity of the organism and of its nerve-action insensibly diminishes; and for the first part of our course we see reason to think that the complexity of consciousness insensibly diminishes also. But if we make a jump, say to the tunicate mollusks, we see no reason there to infer the existence of consciousness at all. Yet not only is it impossible to point out a place where any sudden break takes place, but it is contrary to all the natural training of our minds to suppose a breach of continuity so great."

We must not, says Clifford, admit any breach of continuity. We must assume that consciousness is a complex of elementary feelings, "or rather of those remoter elements which cannot even be felt, but of which the simplest feeling is built up." We must assume that such elementary facts go along with the action of every organism, however simple; but we must assume also that it is only when the organism has reached a certain complexity of nervous structure that the complex of psychic facts reaches the degree of complication that we call Consciousness.

So much for the assumption of something like mind in the mollusk, where Clifford cannot find direct evidence of mind. But the argument does not stop here: "As the line of ascent is unbroken, and must end at last in inorganic matter, we have no choice but to admit that every motion of matter is simultaneous with some . . . fact or event which might be part of a consciousness."

Of the universal distribution of the elementary constituents of mind Clifford writes as follows: "That element of which, as we have seen, even the simplest feeling is a complex, I shall call Mind-stuff. A moving molecule of inorganic matter does not possess mind or consciousness; but it possesses a small piece of mind-stuff. When molecules are so combined together as to form the film on the under side of a jellyfish, the elements of mind-stuff which go along with them are so combined as to form the faint beginnings of Sentience. When the molecules are so combined as to form the brain and nervous system of a vertebrate, the corresponding elements of mind-stuff are so combined as to form some kind of consciousness; that is to say, changes in the complex which take place at the same time get so linked together that the repetition of one implies the repetition of the other. When matter takes the complex form of a living human brain, the corresponding mind-stuff takes the form of a human consciousness, having intelligence and volition."

This is the famous mind-stuff doctrine. It is not a scientific doctrine, for it rests on wholly unproved assumptions. It is a play of the speculative fancy, and has its source in the author's strong desire to fit mental phenomena into some general evolutionary scheme. As he is a parallelist, and cannot make of physical phenomena and of mental one single series of causes and effects, he must attain his end by making the mental series complete and independent in itself. To do this, he is forced to make several very startling assumptions:—

(1) We have seen that there is evidence that there is consciousness somewhere—it is revealed by certain bodies. Clifford assumes consciousness, or rather its raw material, mind-stuff, to be everywhere. For this assumption we have not a whit of evidence.

(2) To make of the stuff thus attained a satisfactory evolutionary series, he is compelled to assume that mental phenomena are related to each other much as physical phenomena are related to each other. This notion he had from Spinoza, who held that, just as all that takes place in the physical world must be accounted for by a reference to physical causes, so all happenings in the world of ideas must be accounted for by a reference to mental causes, i.e. to ideas. For this assumption there is no more evidence than for the former.

(3) Finally, to bring the mental phenomena we are familiar with, sensations of color, sound, touch, taste, etc., into this evolutionary scheme, he is forced to assume that all such mental phenomena are made up of elements which do not belong to these classes at all, of something that "cannot even be felt." For this assumption there is as little evidence as there is for the other two.

The fact is that the mind-stuff doctrine is a castle in the air. It is too fanciful and arbitrary to take seriously. It is much better to come back to a more sober view of things, and to hold that there is evidence that other minds exist, but no evidence that every material thing is animated. If we cannot fit this into our evolutionary scheme, perhaps it is well to reexamine our evolutionary scheme, and to see whether some misconception may not attach to that.

[1] "Collected Essays," Vol. I, p. 219, New York, 1902.

[2] "On the Nature of Things-in-Themselves," in "Lectures and Essays," Vol. II.

[3] "Examination of Sir William Hamilton's Philosophy," Chapter XII.

[4] "On the Nature of Things-in-Themselves."