A significant and interesting part of the post-Gettier literature regarding the analysis of propositional knowledge is the attempt to supplement the traditional tripartite analysis by employing a fourth condition regarding the defeasibility of evidence and thus to preclude the counterexamples displayed in Gettier’s original article. My aim in this paper is to critically examine the sort of externalism that accompanies the most promising of the proposed fourth conditions, due to Pollock, in order to offer some fresh insights on this old epistemological issue. I argue that Pollock’s paradigmatic treatment of the matter gives rise to a critical problem with regard to the exact role of the fourth condition and its relation with the onto-semantic or alethic condition of propositional knowledge, to wit, truth. In the light of this discussion, I draw certain conclusions about epistemic externalism and point out some of its theoretical shortcomings.