Among proponents of critical thinking, Harvey Siegel stands out in his attempt to address fundamental epistemological issues. Siegel argues that discursive inclusion of diverse groups should not be confused with rational justification of the outcome of inquiry. He maintains that epistemic virtues such as inclusion are neither necessary nor sufficient for rational judgment, and that if we are to avoid falling prey to relativism, criteria are needed to distinguish which of these virtues are indeed rational. However, the author argues that at least some of Siegel's own rational criteria cannot pass the necessary or sufficient standard by which he measures epistemic virtues. Moreover, reliance upon criteria fails to settle conflict in cases of disagreement over what constitutes authoritative evidence. Jrgen Habermas's theory of communicative rationality can help us to overcome this impasse, because it provides a nonrelativistic basis for justifying inclusion and giving it a place of priority in practical reasoning.