Answers needed

[emjay]

1. Human thought: When I believe that my thoughts are valid, I implicitly recognize supernatural reality. The problem is, I can’t not believe in the validity of my thoughts. Even if I say, “My thoughts are not valid,” I am trusting that my lack of trust in my thoughts is valid. (!?) If I say, “My thoughts are the result of chemical interactions,” I’m essentially saying, “My thoughts are not valid,” since what basis do I have to think that chemical reactions would produce rational thought?
   

I think that is the argument used by CS Lewis (though please correct me if I'm wrong), which I'll quote here for reference (from C.S. Lewis, Miracles, 1947):

All possible knowledge, then, depends on the validity of reasoning. If the feeling of certainty which we express by words like must be and therefore and since is a real perception of how things outside our minds really 'must' be, well and good. But if this certainty is merely a feeling in our own minds and not a genuine insight into the realities beyond them - if it merely represents the way our minds happen to work - then we can have no knowledge. Unless human reasoning is valid no science can be true.

It follows that no account of the universe can be true unless that account leaves it possible for our thinking to be a real insight. A theory which explained everything else in the universe but which made it impossible to believe our thinking was valid, would be utterly out of court. For that theory would itself have been reached by thinking, and if thinking is not valid that theory would, of course, be itself demolished. It would have destroyed its own credentials. It would be an argument which proved that no argument was sound - a proof that there were no such things as proofs - which is nonsense.

Thus a strict materialism refutes itself for the reason given long ago by Professor Haldane: 'If my mental processes are determined wholly by the motions of atoms in my brain, I have no reason to suppose that my beliefs are true... and hence I have no reason for supposing my brain to be composed of atoms.' (Possible Worlds)

I have to be honest it makes no more sense to me when you say it than when he does. I'm not trying to be obstinate here - I genuinely don't get it and accept that that may make me an idiot. I would like to understand it though so can you or anyone tell me a) what this means and b) if it's a valid argument. Thanks