From Why I Am Not a Christian, 1957.
Before we can profitably discuss whether we shall continue to exist after death, it is well to be clear as to the sense in which a man is the same person as he was yesterday. Philosophers used to think that there were definite substances, the soul and the body, that each lasten on from day to day, that a soul, once created, continued to exist throughout all future time, whereas a body ceased temporarily from death till the resurrection of the body.
The part of this doctrine which concerns the present life is pretty certainly false. The matter of the body is continually changing by processes of nutriment and wastage. Even if it were not, atoms in physics are no longer supposed to have continuous existence; there is no sense in saying: this is the same atom as the one that existed a few minutes ago. The continuity of a human body is a matter of appearance and behavior, not of substance.
The same thing applies to the mind. We think and feel and act, but there is not, in addition to thoughts and feelings and actions, a bare entity, the mind or the soul, which does or suffers these occurrences. The mental continuity of a person is a continuity of habit and memory: there was yesterday one person whose feelings I can remember, and that person I regard as myself of yesterday; but, in fact, myself of yesterday was only certain mental occurrences which are now remembered and are regarded as part of the person who now recollects them. All that constitutes a person is a series of experiences connected by memory and by certain similarities of the sort we call habit.
If, therefore, we are to believe that a person survives death, we must believe that the memories and habits which constitute a person will continue to be exhibited in a new set of occurrences.
No one can prove that this will not happen. But it is easy to see that it is very unlikely. Our memories and habits are bound up with the structure of our brain. in much the same way in which a river is connected with the riverbed. The water in the river is always changing, but it keeps to the same course because previous rains have worn a channel. In like manner, previous events have worn a channel in the brain, and our thoughts flow along this channel. This is the cause of memory and mental habits. But the brain, as a structure, is dissolved at death, and memory therefore may be expected to be also dissolved. This is no more reason to think otherwise than to expect a river to persist in its old course after an earthquake has raised a mountain where a valley used to be.
All memory, and therefore (one may say) all minds, depend upon a property which is very noticeable in certain kinds of material structures but exists little if at all in other kinds. This is the property of forming habits as a result of frequent similar occurrences. For example: a bright light makes the pupils of the eyes contract; and if you repeatedly flash a-light in a man's eyes and beat a gong at the same time, the gong alone will, in the end, cause his pupils to contract. This is a fact about the brain and nervous system - that is to say, about a certain material structure. It will be found that exactly similar facts explain our response to language and our use of it, our memories and the emotions they arouse, our moral or immoral habits of behavior, and indeed everything that constitutes our mental personality, except the part determined by heredity. The part determined by heredity is handed on to our posterity but cannot, in the individual, survive the disintegration of the body. Thus both the hereditary and the acquired parts of a personality are, so far as our experience bound up with the characteristics of certain bodily structures. We all know that memory may be obliterated by an injury to the brain, that a virtuous person may be rendered vicious by encephalitis lethargica, and, that a clever child can be turned into an idiot by lack of iodine. In view of such familiar facts, it seems scarcely probable that the mind survives the total destruction of brain structure which occurs at death.
It is not rational arguments but emotions that cause belief in a future life.
The most important of these emotions is fear of death, which is instinctive and biologically useful. If we genuinely and wholeheartedly believed in the future life, we should cease completely to fear death. The effects would be curious and probably such as most of us would deplore. But our human and subhuman ancestors have fought and exterminated their enemies throughout many geological ages and have profited by courage; it is therefore an advantage to the victors in the struggle for life to be able, on occasion, to overcome the natural fear of death. Among animals and savages, instinctive pugnacity suffices for this purpose; but at a certain stage of development, as the Mohammedans first proved, belief in Paradise has considerable military value as reinforcing natural pugnacity. We should therefore admit that militarists are wise in encouraging the belief in immortality, always supposing that this belief does not become so profound as to produce indifference to the affairs of the world.
Another emotion which encourages the belief in survival is admiration of the excellence of man. As the Bishop of Birmingham says, "His mind is a far finer instrument than anything that had appeared earlier - he knows right and wrong. He can build Westminster Abbey. He can make an airplane. He can calculate the distance of the sun. . . . Shall, then, man at death perish utterly? Does that incomparable instrument, his mind, vanish when life ceases?"
The Bishop proceeds to argue that "the universe has been shaped and is governed by an intelligent purpose," and that it would have been unintelligent, having made man, to let him perish.
To this argument there are many answers. In the first, place, it has been found, in the scientific investigation of nature, that the intrusion of moral or aesthetic values has always been an obstacle to discovery. It used to be thought that the heavenly bodies must move in circles because the circle is the most perfect curve, that species must be immutable because God would only create what was perfect and what therefore stood in no need of improvement, that it was useless to combat epidemics except by repentance because they were sent as a punishment for sin, and so on. It has been found, however, that, so far as we can discover, nature is indifferent to our values and can only be understood by ignoring our notions of good and bad. The Universe may have a purpose, but nothing that we know suggests that, if so, this purpose has any similarity to ours.
Nor is there in this anything surprising. Dr. Barnes tells us that man "knows right and wrong." But, in fact, as anthropology shows, menís views of right and wrong have varied to such an extent that no single item has been permanent. We cannot say, therefore, that man knows right and wrong, but only that some men do. Which men? Nietzsche argued in favor of an ethic profoundly different from Christ's, and some powerful governments have accepted his teaching. If knowledge of right and wrong is to be an argument for immortality, we must first settle on whether to believe Christ or Nietzsche, and then argue that Christians are immortal, but Hitler and Mussolini are not, or vice versa. The decision will obviously be made on the battlefield, not in the study. Those who have the best poison gas will have the ethic of the future and will therefore be the immortal ones.
Our feelings and beliefs on the subject of good and evil are, like everything else about us, natural facts, developed in the struggle for existence and not having any divine or supernatural origin. In one of Aesop's fables, a lion is shown pictures of huntsmen catching lions and remarks that, if he had painted them, they would have shown lions catching huntsmen. Man, says Dr. Barnes, is a fine fellow because he can make airplanes. A little while ago there was a popular song about the cleverness of flies in walking upside down on the ceiling, with the chorus: "Could Lloyd George do it? Could Mr. Baldwin do it? Could Ramsay Mac do it? Why, NO." On this basis a very telling argument could be constructed by a theologically-minded fly, which no doubt the other flies would find most convincing.
Moreover, it is only when we think abstractly that we have such a high opinion of man. Of men in the concrete, most of us think the vast majority very bad. Civilized states spend more than half their revenue on killing each others citizens. Consider the long history of the activities inspired by moral fervor: human sacrifices, persecutions of heretics, witch-hunts, pogroms leading up to wholesale extermination by poison gases, which one at least of Dr. Barnes's episcopal colleagues must be supposed to favor, since he holds pacifism to be un-Christian. Are these abominations, and the ethical doctrines by which they are prompted, really evidence of an intelligent Creator? And can we really wish that the men who practiced them should live forever? The world in which we live can be understood as a result of muddle and accident; but if it is the outcome of deliberate purpose, the purpose must have been that of a fiend. For my part, I find accident a less painful and more plausible hypothesis.