Today we find philosophical naturalists and Christian theists both expressing an interest in virtue epistemology, while starting out from vastly different assumptions. What can be done to increase fruitful dialogue among these divergent groups of virtue-theoretic thinkers? The primary aim of this paper is to uncover more substantial common ground for dialogue by wielding a double-edged critique of certain assumptions shared by 'scientific' and 'theistic' externalisms, assumptions that undermine proper attention to epistemic agency and responsibility. I employ a responsibilist virtue (...) epistemology to this end, utilizing it most extensively in critique of Alvin Plantinga's "Warranted Christian Belief". Epistemological externalism presages, I also argue, a new demarcation problem, but a secondary aim of the paper is to suggest reasons to think that 'responsibilist externalism,' especially as glossed in virtue-theoretic terms, provides its proponents with the ability to adequately address this problem as we find it represented in a potent thought-experiment developed by Barry Stroud. (shrink)