Nowadays these fine old simplicities are lost: physicists assure us that there is no such thing as matter, and psychologists assure us that there is no such thing as mind. This is an unprecedented occurrence. Who ever heard of a cobbler saying that there was no such thing as boots, or a tailor maintaining that all men are really naked? Yet that would have been no odder than what physicists and certain psychologists have been doing. To begin with the latter, some of them attempt to reduce everything that seems to be mental activity to an activity of the body. There are, however, various difficulties in the way of reducing mental activity to physical activity. I do not think we can yet say with any assurance whether these difficulties are or are not insuperable. What we can say, on the basis of physics itself, is that what we have hitherto called our body is really an elaborate scientific construction not corresponding to any physical reality. The modern would-be materialist thus finds himself in a curious position, for, while he may with a certain degree of success reduce the activities of the mind to those of the body, he cannot explain away the fact that the body itself is merely a convenient concept invented by the mind. We find ourselves thus going round and round in a circle: mind is an emanation of body, and body is an invention of mind. Evidently this cannot be quite right, and we have to look for something that is neither mind nor body, out which both can spring.
Let us begin with the body. The plain man thinks that material objects must certainly exist, since they are evident to the senses. Whatever else may be doubted, it is certain that anything you can bump into must be real; this is the plain man's metaphysic. This is all very well, but the physicist comes along and shows that you never bump into anything: even when you run your hand along a stone wall, you do not really touch it. When you think you touch a thing, there are certain electrons and protons, forming part of your body, which are attracted and repelled by certain electrons and protons in the thing you think you are touching, but there is no actual contact. The electrons and protons in your body, becoming agitated by nearness to the other electrons and protons are disturbed, and transmit a disturbance along your nerves to the brain; the effect in the brain is what is necessary to your sensation of contact, and by suitable experiments this sensation can be made quite deceptive. The electrons and protons themselves, however, are only crude first approximations, a way of collecting into a bundle either trains of waves or the statistical probabilities of various different kinds of events. Thus matter has become altogether too ghostly to be used as an adequate stick with which to beat the mind. Matter in motion, which used to seem so unquestionable, turns out to be a concept quite inadequate for the needs of physics.
Nevertheless modern science gives no indication whatever of the existence of the soul or mind as an entity; indeed the reasons for disbelieving in it are very much of the same kind as the reasons for disbelieving in matter. Mind and matter were something like the lion and the unicorn fighting for the crown; the end of the battle is not the victory of one or the other, but the discovery that both are only heraldic inventions. The world consists of events, not of things that endure for a long time and have changing properties. Events can be collected into groups by their causal relations. If the causal relations are of one sort, the resulting group of events may be called a physical object, and if the causal relations are of another sort, the resulting group may be called a mind. Any event that occurs inside a man's head will belong to groups of both kinds; considered as belonging to a group of one kind, it is a constituent of his brain, and considered as belonging to a group of the other kind, it is a constituent of his mind.
Thus both mind and matter are merely convenient ways of organizing events. There can be no reason for supposing that either a piece of mind or a piece of matter is immortal. The sun is supposed to be losing matter at the rate of millions of tons a minute. The most essential characteristic of mind is memory, and there is no reason whatever to suppose that the memory associated with a given person survives that person's death. Indeed there is every reason to think the opposite, for memory is clearly connected with a certain kind of brain structure, and since this structure decays at death, there is every reason to suppose that memory also must cease. Although metaphysical materialism cannot be considered true, yet emotionally the world is pretty much the same as I would be if the materialists were in the right. I think the opponents of materialism have always been actuated by two main desires: the first to prove that the mind is immortal, and the second to prove that the ultimate power in the universe is mental rather than physical. In both these respects, I think the materialists were in the right. Our desires, it is true, have considerable power on the earth's surface; the greater part of the land on this planet has a quite different aspect from that which it would have if men had not utilized it to extract food and wealth. But our power is very strictly limited. We cannot at present do anything whatever to the sun or moon or even to the interior of the earth, and there is not the faintest reason to suppose that what happens in regions to which our power does not extend has any mental causes. That is to say, to put the matter in a nutshell, there is no reason to think that except on the earth's surface anything happens because somebody wishes it to happen. And since our power on the earth's surface is entirely dependent upon the sun, we could hardly realize any of our wishes if the sun grew could. It is of course rash to dogmatize as to what science may achieve in the future. We may learn to prolong human existence longer than now seems possible, but if there is any truth in modern physics, more particularly in the second law of thermodynamics, we cannot hope that the human race will continue for ever. Some people may find this conclusion gloomy, but if we are honest with ourselves, we shall have to admit that what is going to happen many millions of years hence has no very great emotional interest for us here and now. And science, while it diminishes our cosmic pretensions, enormously increases our terrestrial comfort. That is why, in spite of the horror of the theologians, science has on the whole been tolerated.