I can also talk about weuisfdyhkj. It's a label. In itself not more meaningful than the label you use. You think that you know what the label means but if your brain can't simulate a reality behind the label it has no meaning. According to Wittgenstein we should therefore not speak about it.
I think I know my answer to this- I've realised my definition of "rational" subtly differs from LessWrong's. When you see mine, you'll see this wasn't my fault.
A set of rules is rational, I would argue, if that set of rules by it's very nature must correlate with reality- if one applies those rules to the evidence, they must reveal what is true. Even if skepticism is false, then it is a mere coincidence that our assumptions the world is not an illusion, our memories are accurate etc happened to be correct as we had no rational rule that would sho...
I've raised arguments for philosophical scepticism before, which have mostly been argued against in a Popper-esque manner of arguing that even if we don't know anything with certainty, we can have legitimate knowledge on probabilities.
The problem with this, however, is how you answer a sceptic about the notion of probability having a correlation with reality. Probability depends upon axioms of probability- how are said axioms to be justified? It can't be by definition, or it has no correlation to reality.