The Arians of the Fourth Century

As a major contribution to theological history, it was in the course of composing "The Arians" that Newman first conceived his theory of the development of Christian Doctrine, which stimulated his conversion to Catholicism. This emerges from the book's in-depth study of Trinitarian doctrine in the Early Church and in the councils of the fourth century.

Most important, however, is Newman's deeply influential, concluding essay "On Consulting the Faithful, " which takes up the apparent problem that the Church proper seems to have fallen into heresy during the Arian ascendancy. In answer, Newman provides historical evidence that the faithful of Christ maintained orthodox doctrine even in the Church's darkest hour. He argues for the indefectibility of the Church and a nuanced theology of the "sensus fidelium" that impacted the Second Vatican Council's ecclesiology.