Michael Bergmann seeks to motivate his externalist, proper function theory of epistemic justification by providing three objections to the mentalism and mentalist evidentialism characteristic of nonexternalists such as Richard Feldman and Earl Conee. Bergmann argues that (i) mentalism is committed to the false thesis that justification depends on mental states; (ii) mentalism is committed to the false thesis that the epistemic fittingness of an epistemic input to a belief-forming process must be due to an essential feature of that input, and, (...) relatedly, that mentalist evidentialism is committed to the false thesis that the epistemic fittingness of doxastic response B to evidence E is an essential property of B–E; and (iii) mentalist evidentialism is “unmotivated”. I object to each argument. The argument for (i) begs the question. The argument for (ii) suffers from the fact that mentalist evidentialists are not committed to the consequences claimed for them; nevertheless, I show that there is, in the neighborhood, a substantive dispute concerning the nature of doxastic epistemic fittingness. That dispute involves what I call “Necessary Fittingness”, the view that, necessarily, exactly one (at most) doxastic attitude ( belief , or disbelief , or suspension of judgment ) toward a proposition is epistemically fitting with respect to a person’s total evidence at any time. Reflection on my super-blooper epistemic design counterexamples to Bergmann’s proper function theory reveals both the plausibility of Necessary Fittingness and a good reason to deny (iii). Mentalist evidentialism is thus vindicated against the objections. (shrink)