After the First Vatican Council defined the dogma of papal infallibility in 1870, the liberal statesman William Gladstone accused British Catholics of a forfeiture of their mental freedom and a disloyalty to their Queen. John Henry Newman responded with A Letter Addressed to the Duke of Norfolk, which by all accounts capably defended British Catholic freedom and loyalty. The Letter’s famous account of the rights of conscience is credited with laying the groundwork the apparent reconciliation of the church with modern political philosophy and political rights of religious liberty. But the Letter contained a more profound teaching than has been appreciated. The almost-unspoken conclusion of the Letter was an inversion of Gladstone’s original accusation: partisans of liberal principles were the true forfeiters of mental freedom, and liberal principles were a betrayal of the non-liberal British constitution. The document most often cited as Newman’s reconciliation with political liberalism is in fact an indictment thereof. This dissertation will argue that the failure to appreciate the teaching of the Letter to the Duke of Norfolk is the result of an insufficient political philosophy. Analyses which presuppose modern or liberal principles distort Newman’s project. The first chapter will distinguish between classical natural right and modern natural rights, emphasizing the conscience as the locus where the modern rupture with the past is most evident. The second chapter will summarize the shortcomings of contemporary readings of Newman’s Letter and conclude with a provisional account of Newman’s “Alexandrian hermeneutic,” an elliptical method of communication derived originally from the Alexandrian Church Fathers. Then, the dissertation will analyze Newman’s relationship to three modern political doctrines where scholars have permitted the hegemony of modern natural rights to obscure Newman’s suspicion of those principles as principles or solid foundations for political life. The third chapter argues that the Letter grounded itself in non-modern natural right. The “right of conscience” Newman advocated within the Letter was a selective and restricted right, not a foundational or universal guarantee. The very attempt at founding politics on a set of inalienable rights was a result of self-will. Chapters four treats corporate “personality,” a concept which appeared in the Letter but developed over a long period of Newman’s writings. Personality asserted the permanence of certain theologico-political issues and allowed sacred history to re-emerge as a hermeneutical framework for the interpretation of contemporary political events. Chapter five argues that the Letter was an instance of what Ernest Fortin called “theology in a political mode,” in both content and style. While Newman consistently advocated prudential toleration, he perceived that the modern doctrine of toleration was inimical to the life and personality of the Church. Newman’s “Alexandrian hermeneutic” gently insinuated what could not be said aloud and moved his audience from a liberal to a scriptural account of history. The Letter to the Duke of Norfolk was the culmination of a life’s work in how to think and speak about the relationship between spiritual and political authority.