Rudolf Otto is often spoken of as continuing the tradition of reflection on the nature of religion inaugurated by Schleiermacher. I argue that, on the contrary, there are important differences between Schleiermacher's and Otto's accounts of religion. Otto opposed naturalistic analyses of religion which threatened Christianity's claims to truth, and saw Schleiermacher as providing insufficient resources for resisting such analyses. Otto's grounding of his own religious epistemology in the work of Jakob Friedrich Fries provided him with an explicitly supernatural ‘religious a priori’, and thus provided a universal legitimating ground for religion which resists naturalistic analysis. Schleiermacher, in contrast, explicitly ruled out the sort of ‘experience of the holy’ postulated by Otto by denying both the ‘givenness’ of God in experience and supernatural intervention in the natural order. Further, Schleiermacher's appreciation of humanity's embeddedness within ‘the system of nature’ led him to embrace the view that religion, like any natural phenomenon, is an appropriate subject for scientific investigation.