But if the reason something cannot be explained is not about ontology but about limits in explanation then I don't think that is an argument against physicalism. If information processing is a physical thing based on particular architectures then it is plausible that there are limits on what it can explain just like how a cat brain cannot explain things a human brain can. You might not expect some kind of machine learning architecture to explain itself without the right kind of structure either. If a physicalist thinks that our brain does all the information processing then if there are plausible reasons to suggest that there are limits on the kinds of reports a brain can generate about the information it processes or things it does, then it might seem reasonable from a physicalist point of view to say that they believe everything is physical - because thats what all the scientific evidence suggests - but my brain architecture is just physically incapable of producing the kinds of reductions, explanations or descriptions that you might want and perhaps should not be capable of doing that if it needs to be representing veridical information about the outside world.

To me, it might just be required that a physicalist believes everything is physical. You might expect everything should be describable in physical terms but what if there are good reasons that they cannot be? That doesn't necessarily stop them being physical just that our ability to explain or describe things doesn't come for free. Maybe we are what its like to be physical things.. we just can't explain it or describe properly the relation.

Thank you for the welcome. The point I try to make is that if experiences are representations of things in the outside world then maybe they can never be reduced to brains. Yes, you can say - "well I have experiences and that is that" - but a physicalist could just say that his experiences are his brain. You would tell him he is wrong because experiences don't reduce to brains but if this irreducibility is something a physicalist expects or is consistent with physicalism then the argument wouldn't work.

I feel like he does reject that idea about propositions. I seem to remember a whole section where he is criticising the way a picture is entailed by a proposition or something like that.

well said but we can go deeper than that. all of these fields are expressed through math. ultimately our descriptions of the brain and consciousness are just math. mind is math. then look at important findings in math like godel incompleteness amongst others all suggestions on limits to self reference. paradox is inherent in any (self)description of the mind.