[cybernautique]

That's not irrational in the sense of there lacking inherent reasoning or rationalization, it's just a poor deduction. If you mean that rational agents are incapable of flawed reasoning, then I agree that humans are somewhat irrational (and further that no human could ever be rational).

I suppose my biggest gripe is this: how do you construct a notion of rationality which allows for some people to be perfectly rational sometimes, imperfectly rational at other times, and others to be rational never, while allowing for real flaws in reasoning and the absence of perfect information? (this is, to me, a rough sketch of some necessary/sufficient conditions)

[philosopher1234]

I think irrational is something like retaining a false belief despite it being clear that it is false. It’s got something to do with holding on to a point of view despite its inadequacy.

[cybernautique]

Then much of science is irrational; what about those times where it's understood that a belief is false, but it also holds the most explanative power of all other considered beliefs?

And, again, the notion that something is 'clearly false' at some point presupposes perfect information about the context within which the belief is held.