In March of this year (2023), Joseph Strickland, Bishop of Tyler, Texas, long a vocal critic of Pope Francis, accused the bishops behind the German ‘synodal way’ of using Newman’s concept of the development of doctrine as a vehicle to push false teaching forward. In his support, he quoted a 2017 First Things essay by Michael Pakaluk, Professor of Ethics and Social Philosophy at the Catholic University of America. Newman’s theory, Pakaluk wrote, had its origin in the Commonitorium of St Vincent of Lérins, the main preoccupation of which was to show that the contents of the faith are unalterable. The Commonitorium, written in the 430s, was the first sustained theological effort to establish criteria by which the true development of doctrine could be distinguished from heresy. It was hugely influential, especially for the two principles at its core: firstly, that the Church must ensure that it holds ‘that faith which has been believed everywhere, always, and by all’ (quod ubique, quod semper, quod ab omnibus creditum est – often called the Vincentian canon);4 and secondly, that development in the teachings of the Church must be an advance of established teaching (profectus), not a reversal (permutatio).