Proper function and defeating experiences

Jonathan Kvanvig has argued that what he terms “doxastic” theories of epistemic justification fail to account for certain epistemic features having to do with evidence. I’m going to give an argument roughly along these lines, but I’m going to focus specifically on proper function theories of justification or warrant. In particular, I’ll focus on Michael Bergmann’s recent proper function account of justification, though the argument applies also to Alvin Plantinga’s proper function account of warrant. The epistemic features I’m concerned about are experiences that should generate a believed defeater but don’t. I’ll argue that proper functionalism as it stands cannot account for the epistemic effects of these defeating experiences—or, at least, that it can only do so by embracing a deeply implausible view of our cognitive faculties. I’ll conclude by arguing that the only plausible option Bergmann has for modifying his theory undercuts the consideration that motivates proper functionalism in the first place.