 In his discussion of this cosmological saga, Eriugena always appeals to dialectic and the order of reasons in order to mediate between the various sources. For Eriugena, true philosophy is vera ratio and indeed, all appeal to authority is nothing other than an appeal to right reason (Periphyseon, I.511b). Vera ratio underlies both the cosmos and reason. Eriugena is therefore a strongly rationalistic (in the Medieval sense of the word) philosopher, attempting to make sense of divine revelation in scripture and nature in terms consistent with the evidence of reason based on the rules of Dialectic. Dialectic, moreover, is not just about the organization of words and thoughts but also describes the structure of reality itself. Thus, in the Periphyseon IV.781c–d, he makes the bold claim that one need only introduce the “opinions of the holy Fathers” where 