This article seeks to demonstrate the influence of Saint Augustine’s thought on the work of John Henry Newman, especially on the doctrine aimed at clarifying the relations between the act of faith and the other operations of the intellect. To this end, the concepts of auctoritas and ratio are presented as they appear in De vera religione. Subsequently, certain passages in Newman’s work are discussed in which the ascendancy of this doctrine is clear, particularly as regards the subject of doubt and that of the conscience. Finally, a comparison is established between the overall thought of both authors.