Externalist Evidentialism: Sufficient and Nessesary Conditions for Epistemic Justification

Some contemporary epistemologists claim that there are two different kinds of epistemic defeat that are respectively called evidence undermining and judgment undermining. Using a thesis called two streams of justification thesis, they argue that in the first case one's justification is completely undermined while in the second case, despite the fact that one loses some part of her justification, she is justified to believe in P to some degree. In this paper, after focusing on the argument proposed in Rotondo's (2013) (as an instance of this camp of epistemologists), I show that different articulations of the thesis should be distinguished. I call them the first articulation and the second one and then I show that the second articulation is more plausible. Then I introduce a specific formulation of the evidentialism thesis and argue that despite its own problem, it has an advantage over the second articulation. I introduce my preferred justificatory thesis to rectify the problem at the end. The preferred justificatory thesis determines the necessary and the sufficient conditions for a person to be justified in believing a proposition. Accepting the preferred justificatory thesis is equal to rejecting Rotondo's claim.