Does reliance on reason require an unreasonable faith in reason? In The Reasonableness of Reason, Professor Hauptli argues that naturalized epistemology enables us to explain the reasonableness of the rationalist commitment. Examining different forms of rationalism in turn, the author exposes their limitations. Traditional (justificatory) rationalists are indeed caught in a paradox, and those contemporary rationalists who simply affirm that we should be rational without attempting to argue for it (kerygmatic rationalists, as Hauptli terms them) cannot successfully defend rationalism. Another school of rationalists (realistic rationalists) manages to avoid the paradox which besets justificatory rationalism but, Hauptli shows, this approach rests on a maxim as arbitrary as that of the kerygmatic rationalists. What of naturalized epistemology? A discussion of several naturalistic orientations yields the distinction between descriptive and explanatory naturalism. While descriptive naturalists are reduced to offering no more than an arbitrary commitment, explanatory naturalists can supply a satisfactory response to the challenges raised by conceptual diversity and change. They offer a therapy argument, designed to show how an understanding of our roles as theory-holders and theory-changers undercuts much of the force of traditional challenges to rationality. Explanatory naturalism can successfully defend the reasonableness of reason.