brain, and the less sure are we of the solidity of the "bridge which Clifford has built for us. That his own ideas about this "bridge" were decidedly nebulous seems clear even from what is said in the above-mentioned extract. It appears worth while to point this out briefly now, though the whole matter will have to be discussed later more thoroughly. In the extract the dramatis persona to whom we seem to be introduced at the outset are: an external object, which we will call a square; a retinal image of that object, which is also square; a disturbance of the ganglion, which we have no reason to believe square; and a mental image, which is a square. Consciousness, i.e. the mental image, belongs to the disturbance of the ganglion, and, as this is something quite different from the external object, consciousness also is something quite different from the external object. --- In this scheme, there seems to be no doubt about the fact that the mental image is one thing and the external object another. There are even two things mentioned as between them in some sense of the word — the retinal image and the disturbance of the ganglion. No reason is apparent why this scheme should not serve, no matter what the particular character of the external object may be. That is to say, we have every reason to believe that an external brain will be related to the retinal image of the brain, to the corresponding disturbance of the ganglion, and to the mental image of the brain, just as an external square is to its retinal image, ganglionic disturbance, and mental image. In the latter part of the extract, however, we learn with surprise that if we place a man's brain in the midst of a hall and look at it, our perceptions will not be identical with each other, but they will all be identical with the brain in question (" that which I call your brain, the material fact, is merely my perception "). The brain seen is thus not an external thing at all, and cannot be placed in the above scheme at two removes from the perception or mental image. It is the mental image itself; and now the external thing is not a brain, but something very different —it is some one else's consciousness ("what I perceive as your brain is really in itself your consciousness, is You"). The correspondence or parallelism, then, seems to be not between mind and brain, but between the mind of one man and the mind of another. But if this be so, why are we told that the actual reality which underlies what we call matter is not the same thing as the mind, is not the same thing as our perception, but is made of the same stuff? Does this mean simply that when we have a perception which we call the brain of another man, we may assume that there corresponds to this, unperceived by us, certain other perceptions of various sorts that we may call the mind of the other man? But, even if we assume this to be true, does it not seem rather odd to say that certain perceptions in one mind are identical with certain more or less different perceptions in another — to say that "what I perceive as your brain is really in itself your consciousness"? It is this identity or quasi-identity of the two that furnishes Clifford with his "bridge." Can nothing better be said for this "bridge" than what is said in the preceding sentences? As matters stand, there may be parallelism, but there seems to be no identity whatever except perhaps an identity of kind, and the "bridge" simply disappears. Yet there are few who read Clifford's pages without being impressed by the fact that there is at least some plausibility in his theory. The source of this plausibility I shall investigate in the next chapter, where I shall subject the conception of parallelism to a preliminary criticism, leaving out of view some of the difficulties which have come to the surface just above, and which it is convenient to reserve for later discussion. CHAPTER XX WHAT IS PARALLELISM? In this chapter I shall assume that there is a world of material things, including human bodies, without inquiring very narrowly how we are to conceive this world, and in what sense it is external. Descartes' study of the human body led him to believe, as we have seen, that the nervous system is more directly the organ of mind than is anything else in the body, and that the brain is, so to speak, the very citadel of the place. The modern science of cerebral psychology has continued the investigation which he began, and has continued it along the same lines. Although we may begin by speaking somewhat vaguely of mind and body, we always end, when we wish to be exact, by speaking of mind and brain, or rather of this or that mental phenomenon and this or that part of the brain. Infinite labor has been expended in the effort to determine with accuracy and in all possible detail the correspondences between mental activity and cerebral activity, and this labor has not been wholly without result. The localization of cerebral functions is not an empty phrase to any one who has examined the results which have so far been obtained. The supposition that these results as a whole may, in the further progress of science, have to be abandoned, may be dismissed as unworthy of serious attention. They may undoubtedly be modified in detail, but we have every reason to believe that the method of research which has led to their formulation is a sound one, and that it will one day give us results far more complete and satisfactory. It is no more absurd to regard some particular 'manifestation of consciousness as related to the activity of some particular part of the brain, than it is to think of consciousness as related to the brain as a whole, instead of thinking of it as vaguely related to the whole body. And the same sort of evidence that inclines us to regard the brain as the special organ of conscious ness may incline us to particularize still more. How far we are justified in going is solely a question of evidence, and it is a rash man who will undertake to set an arbitrary limit to such investigations. That the progress of science has ousted the Cartesian soul from its place in the pineal gland will be a matter of smail regret to those who have given the subject adequate attention. That soul was not a soul at all; that is to say, it was not a consciousness, but was a material thing that could be located in this part of the brain or in that, like the veriest lump of matter. And any soul that the interactionist is inclined to put in its place must, since it is to take its place and become a cog in a material mechanism, be itself a material thing, and not a something of a different order. He who truly realizes this, loses his inclination to be an interactionist, and he casts about for some other way of conceiving the relation of mind and brain. He is pretty sure to become an adherent of the doctrine of parallelism, and to say with Professor Clifford and many others that physical phenomena and mental phenomena must not be conceived as patched together into one system, but must be conceived as belonging to different orders, must be relegated to separate series which never intersect one another. It is a fair question to ask: Just how much does a man mean by the word, when he speaks of physical phenomena and mental as being parallel? The word may, like most words, be abused, and its use may be an occasion of falling into more or less serious error. One cannot follow the arguments which have led to the adoption of the doctrine of parallelism without assuming, at least provisionally, the existence of an external world of things and of minds perceived to be distinct from them. A material object exists; I perceive it; the object makes an impression upon the retina of the eye; as a result of this a certain disturbance is set up somewhere in the brain; I have a mental image of the object. The object is one thing, the impression upon the retina another, the cerebral change still another, and the mental image something distinct from all of these. Investigation seems to show that the mental image is more intimately related to the cerebral disturbance than to any other motion of matter, and we say that the mental image and the cerebral disturbance are parallel. How much have we a right to mean by this? For one thing, we evidently mean that these two things are so related that the existence of the one may be taken as evidence of the existence of the other. Given the cerebral disturbance, the mental image is given; and given the mental image, the cerebral disturbance is given. The one may be taken as a sign or as a guarantee of the other. We evidently mean, moreover, that the mental image does not belong to the same series with the cerebral disturbance, and hence cannot interact with it. Neither can cause the other; neither can be the effect of the other. Any attempt to put them in such a relation partakes, as Clifford expresses it, of "the crude materialism of the savage"; and although this relationship may be cloaked by ambiguity of expression or by inconsistency of statement, it becomes unmistakable when we try to conceive quite clearly just what interaction implies. When this second point is borne well in mind, we realize that there are certain ways in which we must not think of the parallelism of the mental and the physical. We must not conceive of a man's mind as lying beside his brain in space, as we do conceive of parallel lines as lying beside each other. We must not think of it as fitted to his brain as a gilt halo is fitted to the head of a saint in a picture by Fra Angelico. The warning is by no means superfluous, for the error appears to be a very easy one to fall into. We are all apt to talk as though the relation of mind and brain were more or less analogous to this; and when, before our classes, we attempt to make clear certain psychological facts by the aid of diagrams upon a blackboard, we place brains and ideas side by side, as though they really occurred side by side in nature. The endeavor to point out to the student that this diagrammatic representation is faulty is met by the triumphant query: "When a man goes to Europe, may we not assume that he takes his mind with him?" And the man of science may deprecate dogmatism on the subject of mind and matter, and may declare himself to be without any hypothesis whatever, and yet we may find him, when he permits himself "to suggest a rough and crude analogy," writing as follows: "That the brain is the organ of consciousness is patent, but that consciousness is located in the brain is what no psychologist ought to assert; for just as the energy of an electric discharge, though apparently on the conductor, is not on the conductor |