James Pereiro provides a new key for a fuller and proper understanding of the Oxford Movement. Although references to ethos constantly surface in the writings and correspondence of the Tractarians, the study of the theory of religious knowledge which it implies has so far been neglected. Pereiro explores the pre-Tractarian historical circumstances, the intellectual roots of the Movement, the formation of the concept of ethos, and the influence it had in the ideological and historical development of the Movement. He also discusses in detail the formation of Newman's theory of development of Christian doctrine: the intellectual clash of ideas from which Newman's theory emerged, and the vital role played by the concept of ethos. The two appendices publish some manuscript sources of great interest for the history of Tractarianism: S. F. Wood's early theory of development of doctrine, and the negative reactions of Newman and Manning; and a long narrative description of the Oxford Movement written by Wood at the request of Newman and Pusey.