This week I'm thinking about Laurence Bonjour's In Defense of Pure Reason. In §4.4, Bonjour offers what he takes to be a very straightforward argument against the infallibility of rational insight: just look, he says, at all the examples of alleged cases of rational insight that are false — some have been empirically refuted, and some been shown a priori to be incoherent, and some are just inconsistent with others in a way that guarantees that at least some are false.
He qualifies the charge of fallibility, recognizing that it's open to deny that such cases of seeming rational insight into something that ends up being fall are genuine rational insights at all; this, he says, is a "mere terminological or conceptual stipulation" and "fails to secure infallibility in any epistemologically useful sense".
I don't see what infallibility was ever going to amount to if it was to be something stronger than what Bonjour thinks is an uninteresting sense. Did or could anybody ever have thought that anything that seemed to be a rational insight thereby guaranteed its truth? Descartes, for example, recognized the possibility that human reason might be deceived by a God or demon, or imperfectly designed, such that it led into error.
What is the correct characterization of a strong form of infallibility?