I’m working on Duncan Pritchard’s book, writing a substantial notice of it for PPR. One of the central elements in Duncan’s thinking is the idea he gets from Wittgenstein that there are bedrock propositions that fall outside standard epistemological assessment (he calls them “hinge” propositions). They don’t count as known or justified or rational, or something in that neighborhood.
It struck me, in noting this feature, the growing sentiment in this direction in recent epistemology. Gil Harman is defending a version of assumptional epistemology, and one way to understand Schaffer’s contrastivism is along the same lines (Jonathan uses the neat encapsulation phrase “what is presupposed rather than proved” in describing his view). And, of course, these views share a lot in common with the denials of closure found in Dretske’s work and in Nozick’s as well. I haven’t seen what Duncan has to say about closure yet, but I expect something akin to Dretske’s idea that closure is fine so long as the entailed claim isn’t a “heavyweight” one (though Duncan would likely call it a “hinge proposition” instead).
Contextualists like to claim that they hold the middle ground between skeptics on the one hand and Mooreans on the other, but they also can claim to hold the middle ground between assumptionalists and non-assumptionalists (of which Moore is a paradigm example). They are not alone on this middle ground, of course–there are also the invariantists who espouse pragmatic encroachment into the epistemic realm (e.g., Stanley, Hawthorne, McGrath&Fantl).
For those of us not the least inclined toward being sucked into the black hole of skeptical epistemology, this taxonomy is more congenial to our philosophical temperaments and not discussed as much as it deserves. There is the literature on closure, which may be the Achilles’ heel of assumptional epistemology, but the jury is still out on this question. But there is little direct discussion in mainstream epistemology addressing the primary and substantive commitment of assumptional epistemology. Or perhaps I’ve missed a body of literature on the subject?