The series of which this is the second volume owes its inspiration to the call for renewed attention to the classic patristic authors uttered by de Lubac and Daniélou in the 1940s; it was later reinforced by discussions amongst those ecumenists for whom the Fathers and the conciliar decisions of the ancient Church are in some sense authoritative and relevant. Thomas Guarino presents here a theological analysis and evaluation of Vincentius’ Commonitorium, a work much debated and, almost equally he believes, misunderstood. Properly and sympathetically interpreted, he thinks, the Commonitorium not only allows for but encourages the notion of Christian doctrine as living articulation of saving truth expressed in Scripture and interpreted consistently by councils and the authoritative thinkers of the Church. It is not, he stresses in particular, the mere crabbed appeal to antiquity imputed to it by a hostile criticism which would render vain its application to contemporary issues. An introduction sketches the literary history: written about 434, perhaps echoing the current semi-Pelagian debate but not anti-Augustinian in tone, the work was unnoticed in the Middle Ages but once printed and circulated it became an important standard in the debates of the sixteenth century. Chapter i sets out well the message, as Guarino understands it, of the work: the Faith is a given, a ‘deposit’ held semper ubique ab omnibus; but its appropriate development is also a necessary requirement in the face of inappropriate innovation. Newman's elaborate gloss on this message, his Essay on the development of Christian doctrine, is the subject of a useful chapter ii and a predictably weaker chapter iii looks at its contemporary application. ‘Predictably’, because though Vincentius with wonderful clarity lays out the conditions for legitimate development it is precisely their instantiation on which Copts disagree with Orthodox, Baptists with Calvinists and Roman Catholics with everybody else. The book is plainly written and certainly useful. The main point, that Vincentius is a subtle and careful thinker, is here well made and validated. It would make a good starting point for an undergraduate church history seminar.