Is a mind a structure of material units?
I think it is clear that the answer to this question is in the negative. Even if a mind consists of all the events in a brain, it does not consist of bundles of these events grouped as physics groups them, i.e. it does not lump together all the events that make up one piece of matter in the brain, and then all the events that make up another, and so on. Mnemic causation is what concerns us most in studying mind, but this seems to demand a recourse to physics, if we assume, as seems plausible, that mental mnemic causation is due to effects upon the brain. This question, however, is still an open one. If mnemic causation is ultimate, mind is emergent. If not, the question is more difficult. As we saw earlier, there certainly is knowledge in psychology which cannot ever form part of physics. But as this point is important, I shall repeat the argument in different terms.
The difference between physics and psychology is analogous to that between a postman’s knowledge of letters and the knowledge of a recipient of letters. The postman knows the movements of many letters, the recipient knows the contents of a few. We may regard the light and sound waves that go about the world as letters of which the physicist may know the destination; some few of them are addressed to human beings, and when read give psychological knowledge. Of course the analogy is not perfect, because the letters with which the physicist deals are continually changing during their journeys, as if they were written in fading ink, which, also, was not quite dry all the time, but occasionally got smudged with rain. However, the analogy may pass if not pressed.
It would be possible without altering the detail of previous discussions, except that of [Chapter XXV], to give a different turn to the argument, and make matter a structure composed of mental units. I am not quite sure that this is the wrong view. It arises not unnaturally from the argument as to data contained in [Chapter XXV]. We saw that all data are mental events in the narrowest and strictest sense, since they are percepts. Consequently all verification of causal laws consists in the occurrence of expected percepts. Consequently any inference beyond percepts (actual or possible) is incapable of being empirically tested. We shall therefore be prudent if we regard the non-mental events of physics as mere auxiliary concepts, not assumed to have any reality, but only introduced to simplify the laws of percepts. Thus matter will be a construction built out of percepts, and our metaphysic will be essentially that of Berkeley. If there are no non-mental events, causal laws will be very odd; for example, a hidden dictaphone may record a conversation although it did not exist at the time, since no one was perceiving it. But although this seems odd, it is not logically impossible. And it must be conceded that it enables us to interpret physics with a smaller amount of dubious inductive and analogical inference than is required if we admit non-mental events.
In spite of the logical merits of this view, I cannot bring myself to accept it, though I am not sure that my reasons for disliking it are any better than Dr. Johnson’s. I find myself constitutionally incapable of believing that the sun would not exist on a day when he was everywhere hidden by clouds, or that the meat in a pie springs into existence at the moment when the pie is opened. I know the logical answer to such objections, and qua logician I think the answer a good one. The logical argument, however, does not even tend to show that there are not non-mental events; it only tends to show that we have no right to feel sure of their existence. For my part, I find myself in fact believing in them in spite of all that can be said to persuade me that I ought to feel doubtful.
There is an argument, of a sort, against the view we are considering. I have been assuming that we admit the existence of other people and their perceptions, but question only the inference from perceptions to events of a different kind. Now there is no good reason why we should not carry our logical caution a step further. I cannot verify a theory by means of another man’s perceptions, but only by means of my own. Therefore the laws of physics can only be verified by me in so far as they lead to predictions of my percepts. If then, I refuse to admit non-mental events because they are not verifiable, I ought to refuse to admit mental events in every one except myself, on the same ground. Thus I am reduced to what is called “solipsism”, i.e. the theory that I alone exist. This is a view which is hard to refute, but still harder to believe. I once received a letter from a philosopher who professed to be a solipsist, but was surprised that there were no others! Yet this philosopher was by way of believing that no one else existed. This shows that solipsism is not really believed even by those who think they are convinced of its truth.
We may go a step further. The past can only be verified indirectly, by means of its effects in the future; therefore the type of logical caution we have been considering should lead us to abstain from asserting that the past really occurred: we ought to regard it as consisting of auxiliary concepts convenient in stating the laws applicable to the future. And since the future, though verifiable if and when it occurs, is as yet unverified, we ought to suspend judgment about the future also. If we are not willing to go so far as this, there seems no reason to draw the line at the precise point where it was drawn by Berkeley. On these grounds I feel no shame in admitting the existence of non-mental events such as the laws of physics lead us to infer. Nevertheless, it is important to realise that other views are tenable.
[CHAPTER XXVII]
MAN’S PLACE IN THE UNIVERSE
In this final chapter, I propose to recapitulate the main conclusions at which we have arrived, and then to say a few words on the subject of Man’s relation to the universe in so far as philosophy has anything to teach on this subject without extraneous help.
Popular metaphysics divides the known world into mind and matter, and a human being into soul and body. Some—the materialists—have said that matter alone is real and mind is an illusion. Many—the idealists in the technical sense, or mentalists, as Dr. Broad more appropriately calls them—have taken the opposite view, that mind alone is real and matter is an illusion. The view which I have suggested is that both mind and matter are structures composed of a more primitive stuff which is neither mental nor material. This view, called “neutral monism”, is suggested in Mach’s Analysis of Sensations, developed in William James’s Essays in Radical Empiricism, and advocated by John Dewey, as well as by Professor R. B. Parry and other American realists. The use of the word “neutral” in this way is due to Dr. H. M. Sheffer,[15] formerly of Harvard, who is one of the ablest logicians of our time.