Some Shorter Statements of the AFR

Below are some of C. S. Lewis’s shorter statements of the argument from reason. His longer defenses of this argument can be found in his book Miracles: A Preliminary Study, primarily chapter 3, as well as the essays “Bulverism” and “Meditation in a Toolshed” in God in the Dock, and “De Futilitate” in Christian Reflections. A more recent book defending it is C. S. Lewis’s Dangerous Idea: In Defense of the Argument from Reason by Victor Reppert. I will only include quotes where he uses the argument in terms of reason; he uses similar arguments to defend the veracity of ethics (such as in part one of Mere Christianity) and aesthetics (as in part one of The Abolition of Man). I won’t include page numbers, as most of his books are available in multiple editions, and thus multiple paginations. I’ll precede each quote by the book it’s found in, and if it’s a particular essay in the book, the essay’s title will come after the quote.

All My Road Before Me: The Diary of C. S. Lewis, 1922-1927:
In his [Bertrand Russell’s] “Worship of a Free Man” I found a very clear and noble statement of what I myself believed a few years ago. But he does not face the real difficulty -- that our ideals are after all a natural product, facts with a relation to all other facts, and cannot survive the condemnation of the fact as a whole. The Promethean attitude would be tenable only if we were really members of some other whole outside the real whole: wh[ich] we’re not.
(Saturday, 5 January, 1924; before he was a Christian)

The Pilgrim’s Regress (fiction):
In the warmth of the afternoon they went on again, and it came into John’s mind to ask the lady the meaning of her second riddle.
         ‘It has two meanings,’ said she, ‘and in the first the bridge signifies Reasoning. The Spirit of the Age wishes to allow argument and not to allow argument.’
         ‘How is that?’
         ‘You heard what they said. If anyone argues with them they say that he is rationalizing his own desires, and therefore need not be answered. But if anyone listens to them they will then argue themselves to show that their own doctrines are true.’
         ‘I see. And what is the cure for this?’
         ‘You must ask them whether any reasoning is valid or not. If they say no, then their own doctrines, being reached by reasoning, fall to the ground. If they say yes, then they will have to examine your arguments and refute them on their merits: for if some reasoning is valid, for all they know, your bit of reasoning may be one of the valid bits.’

God in the Dock: Essays on Theology and Ethics (Update: alternately titled Undeceptions):
Mechanism, like all materialist systems, breaks down at the problem of knowledge. If thought is the undesigned and irrelevant product of cerebral motions, what reason have we to trust it?
(“Evil and God”)

The belief in such a supernatural reality itself can neither be proved nor disproved by experience. The arguments for its existence are metaphysical, and to me conclusive. They turn on the fact that even to think and act in the natural world we have to assume something beyond it and even assume that we partly belong to that something. In order to think we must claim for our own reasoning a validity which is not credible if our own thought is merely a function of our brain, and our brains a by-product of irrational physical processes. In order to act, above the level of mere impulse, we must claim a similar validity for our judgments of good and evil. In both cases we get the same disquieting result. The concept of nature itself is one we have reached only tacitly by claiming a sort of super-natural status for ourselves.
(“Miracles”)

If the solar system was brought about by an accidental collision, then the appearance of organic life on this planet was also an accident, and the whole evolution of Man was an accident too. If so, then all our present thoughts are mere accidents -- the accidental by-product of the movement of atoms. And this holds for the thoughts of the materialists and astronomers as well as for anyone else’s. But if their thoughts -- i.e., of Materialism and Astronomy -- are merely accidental by-products, why should we believe them to be true? I see no reason for believing that one accident should be able to give me a correct account of all the other accidents. It’s like expecting that the accidental shape taken by the splash when you upset a milk-jug should give you a correct account of how the jug was made and why it was upset.
(“Answers to Questions on Christianity”)

In so far as natural science can give a satisfactory account of man as a purely biological entity, it excludes the soul and therefore excludes immortality. That, no doubt, is why the scientists who are most, or most nearly, concerned with man himself are the most anti-religious.
         Now most assuredly if naturalism is right then it is at this point, at the study of man himself, that it wins its final victory and overthrows all our hopes: not only our hope of immortality, but our hope of finding significance in our lives here and now. On the other hand, if naturalism is wrong, it will be here that it will reveal its fatal philosophical defect, and that is what I think it does.
         On the fully naturalistic view all events are determined by laws. Our logical behaviour, in other words our thoughts, and our ethical behaviour, including our ideals as well as our acts of will, are governed by biochemical laws; these, in turn, by physical laws which are themselves actuarial statements about the lawless movements of matter. These units never intended to produce the regular universe we see: the law of averages (successor to Lucretius’s exiguum clinamen) has produced it out of the collision of these random variations in movement. The physical universe never intended to produce organisms. The relevant chemicals on earth, and the sun’s heat, thus juxtaposed, gave rise to this disquieting disease of matter: organization. Natural selection, operating on the minute differences between one organism and another, blundered into that sort of phosphorescence or mirage which we call consciousness -- and that, in some cortexes beneath some skulls, at certain moments, still in obedience to physical laws, but to physical laws now filtered through laws of a more complicated kind, takes the form we call thought. Such, for instance, is the origin of this paper: such was the origin of Professor Price’s paper. What we should speak of as his ‘thoughts’ were merely the last link of a causal chain in which all the previous links were irrational. He spoke as he did because the matter of his brain was behaving in a certain way: and the whole history of the universe up to that moment had forced it to behave in that way. What we called his thought was essentially a phenomenon of the same sort as his other secretions -- the form which the vast irrational process of nature was bound to take at a particular point of space and time.
         Of course it did not feel like that to him or to us while was going on. He appeared to himself to be studying the nature of things, to be in some way aware of realities, even supersensuous realities, outside his own head. But if strict naturalism is right, he was deluded: he was merely enjoying the conscious reflection of irrationally determined events in his own head. It appeared to him that his thoughts (as he called them) could have to outer realities that wholly immaterial relation which we call truth or falsehood: though, in fact, being but the shadow of cerebral events, it is not easy to see that they could have any relation to the outer world except causal relations. And when Professor Price defended scientists, speaking of their devotion to truth and their constant following of the best light they knew, it seemed to him that he was choosing an attitude in obedience to an ideal. He did not feel that he was merely suffering a reaction determined by ultimately amoral and irrational sources, and no more capable of rightness or wrongness than a hiccup or a sneeze.
         It would have been impossible for Professor Price to have written, or us to have read, his paper with the slightest interest if he and we had consciously held the position of strict naturalism throughout. But we can go further. It would be impossible to accept naturalism itself if we really and consistently believed naturalism. For naturalism is a system of thought. But for naturalism all thoughts are mere events with irrational causes. It is, to me at any rate, impossible to regard the thoughts which make up naturalism in that way and, at the same time, to regard them as a real insight into external reality. Bradley distinguished idea-event from idea-making, but naturalism seems to me committed to regarding ideas simply as events. For meaning is a relation of a wholly new kind, as remote, as mysterious, as opaque to empirical study, as soul itself.
         Perhaps this may be even more simply put in another way. Every particular thought (whether it is a judgment of fact or a judgment of value) is always and by all men discounted the moment they believe that it can be explained, without remainder, as the result of irrational causes. Whenever you know what the other man is saying is wholly due to his complexes or to a bit of bone pressing on his brain, you cease to attach any importance to it. But if naturalism were true then all thoughts whatever would be wholly the result of irrational causes. Therefore, all thoughts would be equally worthless. Therefore, naturalism is worthless. If it is true, then we can know no truths. It cuts its own throat.
         I remember once being shown a certain kind of knot which was such that if you added one extra complication to make assurance doubly sure you suddenly found that the whole thing had come undone in your hands and you had only a bit of string. It is like that with naturalism. It goes on claiming territory after territory: first the inorganic, then the lower organisms, then man’s body, then his emotions. But when it takes the final step and we attempt a naturalistic account of thought itself, suddenly the whole thing unravels. The last fatal step has invalidated all the preceding ones: for they were all reasonings and reason itself has been discredited. We must, therefore, either give up thinking altogether or else begin over again from the ground floor.
         There is no reason, at this point, to bring in either Christianity or spiritualism. We do not need them to refute naturalism. It refutes itself. Whatever else we may come to believe about the universe, at least we cannot believe naturalism. The validity of rational thought, accepted in an utterly non-naturalistic, transcendental (if you will), supernatural sense, is the necessary presupposition of all other theorizing. There is simply no sense in beginning with a view of the universe and trying to fit the claims of thought in at a later stage. By thinking at all we have claimed that our thoughts are more than mere natural events. All other propositions must be fitted in as best they can round that primary claim.
(“Religion without Dogma?”)

The Weight of Glory and Other Addresses:
Thus, to digress for a moment, it seems to me very likely that the real relation between mind and body is one of Transposition. We are certain that, in this life at any rate, thought is intimately connected with the brain. The theory that thought therefore is merely a movement in the brain is, in my opinion, nonsense, for if so, that theory itself would be merely a movement, an event among atoms, which may have speed and direction, but of which it would be meaningless to use the words “true” or “false.” We are driven then to some kind of correspondence. But if we assume a one-for-one correspondence, this means that we have to attribute an almost unbelievable complexity and variety of events to the brain. But I submit that a one-for-one relation is probably quite unnecessary. All our examples suggest that the brain can respond -- in a sense, adequately and exquisitely correspond -- to the seemingly infinite variety of consciousness without providing one single physical modification for each single modification of consciousness.
(“Transposition”)

The picture so often painted of Christians huddling together on an ever narrower strip of beach while the incoming tide of “Science” mounts higher and higher corresponds to nothing in my own experience. That grand myth which I asked you to admire a few minutes ago is not for me a hostile novelty breaking in on my traditional beliefs. On the contrary, that cosmology is what I started from. Deepening distrust and final abandonment of it long preceded my conversion to Christianity. Long before I believed Theology to be true I had already decided that the popular scientific picture at any rate was false. One absolutely central inconsistency ruins it; it is the one we touched on a fortnight ago. The whole picture professes to depend on inferences from observed facts. Unless inference is valid, the whole picture disappears. Unless we can be sure that reality in the remotest nebula or the remotest part obeys the thought laws of the human scientist here and now in his laboratory -- in other words, unless Reason is an absolute -- all is in ruins. Yet those who ask me to believe this world picture also ask me to believe that Reason is simply the unforeseen and unintended by-product of mindless matter at one stage of its endless and aimless becoming. Here is flat contradiction. They ask me at the same moment to accept a conclusion and to discredit the only testimony on which that conclusion can be based. The difficulty is to me a fatal one; and the fact that when you put it to many scientists, far from having an answer, they seem not even to understand what the difficulty is, assures me that I have not found a mare’s nest but detected a radical disease in their whole mode of thought from the very beginning. The man who has once understood the situation is compelled henceforth to regard the scientific cosmology as being, in principle, a myth; though no doubt a great many true particulars have been worked into it.
...
         I was taught at school, when I had done a sum, to “prove my answer.” The proof or verification of my Christian answer to the cosmic sum is this. When I accept Theology I may find difficulties, at this point or that, in harmonising it with some particular truths which are imbedded in the mythical cosmology derived from science. But I can get in, or allow for, science as a whole. Granted that Reason is prior to matter and that the light of that primal Reason illuminates finite minds, I can understand how men should come, by observation and inference, to know a lot about the universe they live in. If, on the other hand, I swallow the scientific cosmology as a whole, then not only can I not fit in Christianity, but I cannot even fit in science. If minds are wholly dependent on brains, and brains on biochemistry, and biochemistry (in the long run) on the meaningless flux of the atoms, I cannot understand how the thought of those minds should have any more significance than the sound of the wind in the trees. And this is to me the final test. This is how I distinguish dreaming and waking. When I am awake I can, in some degree, account for and study my dream. The dragon that pursued me last night can be fitted into my waking world. I know that there are such things as dreams; I know that I had eaten an indigestible dinner; I know that a man of my reading might be expected to dream of dragons. But while in the nightmare I could not have fitted in my waking experience. The waking world is judged more real because it can thus contain the dreaming world; the dreaming world is judged less real because it cannot contain the waking one. For the same reason I am certain that in passing from the scientific points of view to the theological, I have passed from dream to waking. Christian theology can fit in science, art, morality, and the sub-Christian religions. The scientific point of view cannot fit in any of these things, not even science itself. I believe in Christianity as I believe that the Sun has risen, not only because I see it, but because by it I see everything else.
(“Is Theology Poetry?”)

Christian Reflections:
After studying his environment man has begun to study himself. Up to that point, he had assumed his own reason and through it seen all other things. Now, his own reason has become the object: it is as if we took out our eyes to look at them. Thus studied, his own reason appears to him as the epiphenomenon which accompanies chemical or electrical events in a cortex which is itself the by-product of a blind evolutionary process. His own logic, hitherto the king whom events in all possible worlds must obey, becomes merely subjective. There is no reason for supposing that it yields truth.
         As long as this dethronement refers only to the theoretical reason, it cannot be wholehearted. The scientist has to assume the validity of his own logic (in the stout old fashion of Plato or Spinoza) even in order to prove that it is merely subjective, and therefore he can only flirt with subjectivism. It is true that this flirtation sometimes goes pretty far. There are modern scientists, I am told, who have dropped the words truth and reality out of their vocabulary and who hold that the end of their work is not to know what is there but simply to get practical results. This is, no doubt, a bad symptom. But, in the main, subjectivism is such an uncomfortable yokefellow for research that the danger, in this quarter, is continually counteracted.
(“The Poison of Subjectivism”)

I grew up believing in this Myth and I felt -- I still feel -- its almost perfect grandeur. Let no one say we are an unimaginative age: neither the Greeks nor the Norsemen ever invented a better story. Even to the present day, in certain moods, I could almost find it in my heart to wish that it was not mythical, but true. And yet, how could it be?
         What makes it impossible that it should be true is not so much the lack of evidence for this or that scene in the drama or the fatal self-contradiction which runs right through it. The Myth cannot even get going without accepting a good deal from the real sciences. And the real sciences cannot be accepted for a moment unless rational inferences are valid: for every science claims to be a series of inferences from observed facts. It is only by such inferences that you can reach your nebulae and protoplasm and dinosaurs and sub-men and cave-men at all. Unless you start by believing that reality in the remotest space and the remotest time rigidly obeys the laws of logic, you can have no ground for believing in any astronomy, any biology, any paleontology, any archaeology. To reach the positions held by the real scientists -- which are then taken over by the Myth -- you must -- in fact, treat reason as an absolute. But at the same time the Myth asks me to believe that reason is simply the unforeseen and unintended by-product of a mindless process at one stage of its endless and aimless becoming. The content of the Myth thus knocks from under me the only ground on which I could possibly believe the Myth to be true. If my own mind is a product of the irrational -- if what seem my clearest reasonings are only the way in which a creature conditioned as I am is bound to feel -- how shall I trust my mind when it tells me about Evolution? They say in effect, ‘I will prove that what you call a proof is only the result of mental habits which result from heredity which results from bio-chemistry which results from physics.’ But this is the same as saying: ‘I will prove that proofs are irrational’: more succinctly, ‘I will prove that there are no proofs’: The fact that some people of scientific education cannot by any effort be taught to see the difficulty, confirms one’s suspicion that we here touch a radical disease in their whole style of thought. But the man who does see it, is compelled to reject as mythical the cosmology in which most of us were brought up. That it has embedded in it many true particulars I do not doubt: but in its entirety, it simply will not do. Whatever the real universe may turn out to be like, it can’t be like that.
(“The Funeral of a Great Myth”)

Present Concerns:
...let us begin by supposing that Nature is all that exists. Let us suppose that nothing ever has existed or ever will exist except this meaningless play of atoms in space and time: that by a series of hundredth chances it has (regrettably) produced things like ourselves -- conscious beings who now know that their own consciousness is an accidental result of the whole meaningless process and is therefore itself meaningless, though to us (alas!) it feels significant.
         In this situation there are, I think, three things one might do:
         (1) You might commit suicide. Nature which has (blindly, accidentally) given me for my torment this consciousness which demands meaning and value in a universe that offers neither, has luckily also given me the means of getting rid of it. I return the unwelcome gift. I will be fooled no longer.
         (2) You might decide simply to have as good a time as possible. The universe is a universe of nonsense, but since you are here, grab what you can. Unfortunately, however, there is, on these terms, so very little left to grab -- only the coarsest sensual pleasures. You can’t except in the lowest animal sense, be in love with a girl if you know (and keep on remembering) that all the beauties both of her person and of her character are a momentary and accidental pattern produced by the collision of atoms, and that your own response to them is only a sort of psychic phosphorescence arising from the behaviour of your genes. You can’t go on getting any very serious pleasure from music if you know and remember that its air of significance is pure illusion, that you like it only because your nervous system is irrationally conditioned to like it. You may still, in the lowest sense, have a “good time”; but just in so far as it becomes very good, just in so far as it ever threatens to push you on from cold sensuality into real warmth and enthusiasm and joy, so afar you will be forced to feel the hopeless disharmony between your own emotions and the universe in which you really live.
         (3) You may defy the universe. You may say, “Let it be irrational, I am not. Let it be merciless, I will have mercy. By whatever curious chance it has produced me, now that I am here I will live according to human values. I know the universe will win in the end, but what is that to me? I will go down fighting. Amid all this wastefulness I will persevere; amid all this competition, I will make sacrifices. Be damned to the universe!”
         I suppose that most of us, in fact, while we remain materialists, adopt a more or less uneasy alternation between the second and the third attitude. And although the third is incomparably better (it is, for instance, much more likely to “preserve civilization”), both really shipwreck on the same rock. That rock -- the disharmony between our own hearts and Nature -- is obvious in the second. The third seems to avoid the rock by accepting disharmony from the outset and defying it. But it will not really work. In it, you hold up our own human standards against the idiocy of the universe. That is, we talk as if our own standards were something outside the universe which can be contrasted with it; as if we could judge the universe by some standard borrowed from another source. But if (as we were supposing) Nature -- the space-time-matter system -- is the only thing in existence, then of course there can be no other source for our standards. They must, like everything else, be the unintended and meaningless outcome of blind forces. Far from being a light from beyond Nature whereby Nature can be judged, they are only the way in which anthropoids of our species feel when the atoms under our own skulls get into certain states -- those states being produced by causes quite irrational, unhuman, and non-moral. Thus the very ground on which we defy Nature crumbles under our feet. The standard we are applying is tainted at the source. If our standards are derived from this meaningless universe they must be as meaningless as it.
         For most modern people, I think, thoughts of this kind have to be gone through before the opposite view can get a fair hearing. All Naturalism leads us to this in the end -- to a quite final and hopeless discord between what our minds claim to be and what they really must be if Naturalism is true. They claim to be spirit; that is, to be reason, perceiving universal intellectual principles and universal moral laws and possessing free will. But if Naturalism is true they must in reality be merely arrangements of atoms in skulls, coming about by irrational causation. We never think a thought because it is true, only because blind Nature forces us to think it. We never do an act because it is right, only because blind Nature forces us to do it. It is when one has faced this preposterous conclusion that one is at last ready to listen to the voice that whispers: “But suppose we really are spirits? Suppose we are not the offspring of Nature...?”
         For, really, the naturalistic conclusion is unbelievable. For one thing, it is only through trusting our own minds that we have come to know Nature herself. If Nature when fully known seems to teach us (that is, if the sciences teach us) that our own minds are chance arrangements of atoms, then there must have been some mistake; for if that were so, then the sciences themselves would be chance arrangements of atoms and we should have no reason for believing in them. There is only one way to avoid this deadlock. We must go back to a much earlier view. We must simply accept it that we are spirits, free and rational beings, at present inhabiting an irrational universe, and must draw the conclusion that we are not derived from it. We are strangers here. We come from somewhere else. Nature is not the only thing that exists. There is “another world”, and that is where we come from. And that explains why we do not feel at home here. A fish feels at home in the water. If we “belonged here” we should feel at home here. All that we say about “Nature red in tooth and claw”, about death and time and mutability, all our half-amused, half-bashful attitude to our own bodies, is quite inexplicable on the theory that we are simply natural creatures. If this world is the only world, how did we come to find its laws either so dreadful or so comic? If there is no straight line elsewhere, how did we discover that Nature’s line is crooked?
(“On Living in an Atomic Age”)

The Abolition of Man:
Nothing I can say will prevent some people from describing this lecture as an attack on science. I deny the charge, of course: and real Natural Philosophers (there are some now alive) will perceive that in defending value I defend inter alia the value of knowledge, which must die like every other when its roots in the Tao are cut.
...
         Perhaps I am asking impossibilities. Perhaps, in the nature of things, analytical understanding must always be a basilisk which kills what it sees and only sees by killing. But if the scientists themselves cannot arrest this process before it reaches the common Reason and kills that too, then someone else must arrest it. What I most fear is the reply that I am ‘only one more’ obscurantist, that this barrier, like all previous barriers set up against the advance of science, can be safely passed. Such a reply springs from the fatal serialism of the modern imagination -- the image of infinite unilinear progression which so haunts our minds. Because we have to use numbers so much we tend to think of every process as if it must be like the numeral series, where every step, to all eternity, is the same kind of step as the one before. I implore you to remember the Irishman and his two stoves. There are progressions in which the last step is sui generis -- incommensurable with the others -- and in which to go the whole way is to undo all the labour of your previous journey. To reduce the Tao to a mere natural product is a step of that kind. Up to that point, the kind of explanation which explains things away may give us something, though at a heavy cost. But you cannot go on ‘explaining away’ for ever: you will find that you have explained explanation itself away. You cannot go on ‘seeing through’ things for ever. The whole point of seeing through something is to see something through it. It is good that the window should be transparent, because the street or garden beyond it is opaque. How if you saw through the garden too? It is no use trying to ‘see through’ first principles. If you see through everything, then everything is transparent. But a wholly transparent world is an invisible world. To ‘see through’ all things is the same as not to see.

That Hideous Strength (fiction):
Frost had left the dining room a few minutes after Wither. He did not know where he was going or what he was about to do. For many years he had theoretically believed that all which appears in the mind as motive or intention is merely a by-product of what the body is doing. But for the last year or so -- since he had been initiated -- he had begun to taste as fact what he had long held as theory. Increasingly, his actions had been without motive. He did this and that, he said thus and thus, and did not know why. His mind was a mere spectator. He could not understand why that spectator should exist at all. He resented its existence, even while assuring himself that resentment also was merely a chemical phenomenon. The nearest thing to a human passion which still existed in him was a sort of cold fury against all who believe in the mind. There was no tolerating such an illusion. There were not, and must not be, such things as men. But never, until this evening, had he been quite so vividly aware that the body and its movements were the only reality, that the self which seemed to watch the body leaving the dining room and setting out for the chamber of the Head, was a nonentity. How infuriating that the body should have power thus to project a phantom self!
         Thus the Frost whose existence Frost denied watched his body go into the ante-room, watched it pull up sharply at the sight of a naked and bloodied corpse. The chemical reaction called shock occurred. ...
         Still not asking what he would do or why, Frost went to the garage. The whole place was silent and empty; the snow was thick on the ground by this. He came up with as many petrol tins as he could carry. He piled all the inflammables he could think of together in the Objective Room. Then he locked himself in by locking the outer door of the ante-room. Whatever it was that dictated his actions then compelled him to push the key into the speaking tube which communicated with the passage. When he had pushed it as far in as his fingers could reach, he took a pencil from his pocket and pushed with that. Presently he heard the clink of the key falling on the passage floor outside. That tiresome illusion, his consciousness, was screaming to protest; his body, even had he wished, had no power to attend to those screams. Like the clockwork figure he had chosen to be, his stiff body, now terribly cold, walked back into the Objective Room, poured out the petrol and threw a lighted match into the pile. Not till then did his controllers allow him to suspect that death itself might not after all cure the illusion of being a soul -- nay, might prove the entry into a world where that illusion raged infinite and unchecked. Escape for the soul, if not for the body, was offered him. He became able to know (and simultaneously refused the knowledge) that he had been wrong from the beginning, that souls and personal responsibility existed. He half saw: he wholly hated. The physical torture of the burning was not fiercer than his hatred of that. With one supreme effort he flung himself back into his illusion. In that attitude eternity overtook him as sunrise in old tales overtakes and turns them into unchangeable stone.

A Grief Observed:
If H. ‘is not,’ then she never was. I mistook a cloud of atoms for a person. There aren’t, and never were, any people. Death only reveals the vacuity that was always there. What we call the living are simply those who have not yet been unmasked. All equally bankrupt, but some not yet declared.
         But this must be nonsense; vacuity revealed to whom? Bankruptcy declared to whom? To other boxes of fireworks or clouds of atoms. I will never believe -- more strictly I can’t believe -- that one set of physical events could be, or make, a mistake about other sets.

The Discarded Image: An Introduction to Medieval and Renaissance Literature:
No Model yet devised has made a satisfactory unity between our actual experience of sensation or thought or emotion and any available account of the corporeal processes which they are held to involve. We experience, say, a chain of reasoning; thoughts, which are ‘about’ or ‘refer to’ something other than themselves, are linked together by the logical relation of grounds and consequents. Physiology resolves this into a sequence of cerebral events. But physical events, as such, cannot in any intelligible sense be said to be ‘about’ or to ‘refer to’ anything. And they must be linked to one another not as grounds and consequents but as causes and effects -- a relation so irrelevant to the logical linkage that it is just as perfectly illustrated by the sequence of a maniac’s thoughts as by the sequence of a rational man’s. The chasm between the two points of view is so abrupt that desperate remedies have been adopted. Berkeleyan idealists have denied the physical process; extreme Behaviourists, the mental.

Update (12 Aug 2009): The Case for Christianity:
Supposing there was no intelligence behind the universe, no creative mind. In that case, nobody designed my brain for the purpose of thinking. It is merely that when the atoms inside my skull happen, for physical or chemical reasons, to arrange themselves in a certain way, this gives me, as a by-product, the sensation I call thought. But, if so, how can I trust my own thinking to be true? It’s like upsetting a milk jug and hoping that the way it splashes itself will give you a map of London. But if I can’t trust my own thinking, of course I can’t trust the arguments leading to Atheism, and therefore have no reason to be an Atheist, or anything else. Unless I believe in God, I cannot believe in thought: so I can never use thought to disbelieve in God.
(This book became part 1 of Mere Christianity, but the above paragraph was not included. Thanks to Victor Reppert for bringing it to my attention.)

Update (2 Jan 2010): Additionally, here are a couple of excerpts where Lewis refers to the AFR without actually expressing it.

God in the Dock
Dr Pittenger thinks the Naturalist whom I try to refute in chapter 3 [of Miracles] is a man of straw. He may not be found in the circles Dr Pittenger frequents. He is quite common where I come from; and, presumably, in Moscow. There is indeed a really serious hitch in that chapter (which ought to be rewritten), but Dr Pittenger has not seen it or has charitably kept silent about it.
(“Rejoinder to Dr Pittenger”)

Surprised by Joy: The Shape of My Early Life
In the second place he [Owen Barfield] convinced me that the positions we had hitherto held left no room for any satisfactory theory of knowledge. We had been, in the technical sense of the term, “realists”; that is, we accepted as rock-bottom reality the universe revealed by the senses. But at the same time we continued to make for certain phenomena of consciousness all the claims that really went with a theistic or idealistic view. We maintained that abstract thought (if obedient to logical rules) gave indisputable truth, that our moral judgement was “valid,” and our aesthetic experience not merely pleasing but “valuable.” The view was, I think, common at the time; it runs through Bridges’ Testament of Beauty, the work of Gilbert Murray, and Lord Russell’s “Worship of a Free Man.” Barfield convinced me that it was inconsistent. If thought were a purely subjective event, these claims for it would have to be abandoned. If one kept (as rock-bottom reality) the universe of the senses, aided by instruments and co-ordinated so as to form “science,” then one would have to go much further -- as many have since gone -- and adopt a Behaviouristic theory of logic, ethics, and aesthetics. But such a theory was, and is, unbelievable to me. I am using the work “unbelievable,” which many use to mean “improbable” or even “undesirable,” in a quite literal sense. I mean that the act of believing what the behaviourist believes is one that my mind simply will not perform. I cannot force my thought into that shape any more than I can scratch my ear with my big toe or pour wine out of a bottle into the cavity at the base of that same bottle. It is as final as a physical impossibility. I was therefore compelled to give up realism. I had been trying to defend it ever since I began reading philosophy. Partly, no doubt, this was mere “cussedness.” Idealism was then the dominant philosophy at Oxford and I was by nature “against Government.” But partly, too, realism satisfied an emotional need. I wanted Nature to be quite independent of our observation; something other, indifferent, self-existing. (This went with the Jenkinian zest for rubbing one’s nose in the mere quiddity.) But now, it seemed to me, I had to give that up. Unless I were to accept an unbelievable alternative, I must admit that mind was no late-come epiphenomenon; that the whole universe was, in the last resort, mental; that our logic was participation in a cosmic Logos.

Update (30 July 2010): Perelandra (fiction)
“That could hardly be the whole story,” said Ransom. “If the whole universe were like that, then we, being parts of it, would feel at home in such a universe. The very fact that it strikes us as monstrous --”
         “Yes,” interrupted Weston, “that would be all very well if it wasn’t that reasoning itself is only valid as long as you stay in the rind. It has nothing to do with the real universe. Even the ordinary scientists -- like what I used to be myself -- are beginning to find that out. Haven’t you seen the real meaning of all this modern stuff about the dangers of extrapolation and bent space and the indeterminacy of the atom? They don’t say in so many words, of course, but what they’re getting to, even before they die nowadays, is what all men get to when they’re dead -- the knowledge that reality is neither rational nor consistent nor anything else. In a sense you might say it isn’t there. ‘Real’ and ‘Unreal,’ ‘true’ and ‘false’ -- they’re all only on the surface. They give way the moment you press them.”
         “If all this were true,” said Ransom, “what would be the point of saying it?”
         “Or of anything else?” replied Weston. “The only point in anything is that there isn’t any point. Why do ghosts want to frighten? Because they are ghosts. What else is there to do?”
(I posted a longer version of this quote with its surrounding context here.)