At the heart of the English Reformation was a debate over what defined catholic orthodoxy: scriptural warrant alone or also ancient church praxis? In the 1530s Philipp Melanchthon argued that the Scripture-versus-tradition argument was a false dichotomy, since the fathers defined the church’s consensus fidelium as nothing other than the apostolic witness as found in sola scriptura. At the invitation of Thomas Cromwell, Alexander Alesius, an exiled Scot who had taught both at the University of Wittenberg and at Cambridge, injected this argument into the discussions of the vice-gerential synod of 1537. Since the resultant Bishops’ Book was a compromise which failed to resolve the fundamental issue, the question was taken up again two years later during the debate over the Act of Six Articles. Grounded in a close comparison between the scholarship of Alesius, who by then had become a close friend of Cranmer, and ‘The Writings of Authorities’, a pamphlet incorporated into ‘Cranmer’s Great Commonplaces’, this essay shows how thoroughly Cranmer made the Lutheran approach to defining catholic orthodoxy his own. The essay argues that ‘The Writings of Authorities’ records some of the specific arguments, long thought to have been lost, which Cranmer made against the Act, and traces how these teachings on the Bible, derived as they were from the Lutheran construal of the ancient orthodoxies of Scripture and the Fathers, eventually became the basis for an enduring Anglican orthodoxy through their incorporation into the Edwardian formularies and the Elizabethan Thirty-Nine Articles.