C.S. Lewis: An excerpt from: Religion Without Dogma (1946)

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 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 judgement of fact or a judgement 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.

“The validity of rational thought… is the necessary presupposition of all other theorizing.”
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 reasoning 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.
Holding that science has not refuted the miraculous element in religion, much less that naturalism, rigorously taken, can refute anything except itself, I do not, of course, share Professor Price’s anxiety to find a religion which can do without what he calls the mythology.

On Kant’s philosophical justification of human autonomy:
“Kant’s philosophy explicitly presupposes human autonomy. It adopts human autonomy as the root idea to which every other idea must conform.”

http://struth-his-or-yours.blogspot.com/2011/08/bastion-of-secular-mindset.html

On the idea of physical determinism some comment by Richard Tarnas and C.S. Lewis:

http://struth-his-or-yours.blogspot.com/2011/10/irony-of-modern-intellectual-progress.html