Given that there is an infallible magisterium, all Catholic theologians affirm that what the magisterium may teach infallibly (the Object) includes propositions revealed by God (the Primary Object). But does the magisterium have divine authorisation to teach infallibly what God has not revealed, propositions which the magisterium judges to be useful or necessary for the defence of Revelation – those constituting the Secondary Object?

If the magisterium is divinely authorised to teach infallibly the contents of the Secondary Object, what response does the magisterium require of the faithful? The response cannot be faith because that response is owed to revealed truths only. It cannot be mere human faith, the credence we give to people whom we judge likely to be expert and truthful. In answer to the question, theologians have developed a third concept of faith –“ecclesiastical faith”, the response of believing because the Church's magisterium says so.

This book answers the questions: (1) how did the notion of a Secondary Object unfold in Catholic theology? and (2) what characterises the set of propositions which constitute the Secondary Object? and (3) what is the strength of the claim that the magisterium may be infallible in teaching matters of the Secondary Object?

Jean‐François Chiron, a priest of the Diocese of Chambéry (France) who teaches at the Faculty of Theology and the seminary of Lyon, holds that a clear notion of the Secondary Object arose during controversies over the writings of Cornelius Jansen in France and the Lowlands during the 17^th century. Popes condemned some teachings of Jansen. When Jansenists replied that Jansen's works did not contain the condemned doctrines, Pope Innocent X replied in Cum Occasione(1658) that they did. A fierce dispute broke out regarding whether a pope could infallibly teach a matter of fact (fait), e.g., that a book contained certain statements, as well as a matter of droit(that the statements were true or false).

The Archbishop of Cambrai, François Fénelon, supported with elaborate arguments the position that matters of fact are included in the Object. Clearly, that Jansen wrote something is not revealed by God, so if a pope can teach this fact infallibly, there must be a Secondary Object. Fénelon's arguments furnished the foundation for the next three centuries of debate about whether the magisterium can teach infallibility matters belonging to the Secondary Object.

Chiron meticulously tracks the debates through the writings of the manualists and the documents of Vatican I, including Gasser's famous relatio(report), concluding that the Council supported the view that the proposition the pope (Church) can teach infallibly matters of the Secondary Object was not defined by the Council but remained theologically certain (theologice certum).

The history of the treatment of the subject at Vatican II, and in the Roman magisterial documents issued since this Council, including Humanae Vitae, Ordinatio Sacerdotalis, and the texts of oaths and professions of faith, as also the criticisms of these documents by theologians – all this history is recorded in detail and evaluated.

Chiron exhibits two interesting facts:

1. (1) Councils, popes, and Roman congregations have proved to be very deferential to the views supported by a majority of theological manualists;

2. (2) Magisterial documents themselves are the cause of confusion and uncertainty amongst theologians and the rest of the faithful because terms lack a consistent meaning across documents. For example, the Annexe to the book explores the use of the term “definitive” and shows that a reader of the documents has to work out the meaning of the term by close study of the context in each document.

It is impossible to praise too highly this magnificent work of erudition. The author has read almost everything on the topic. Chiron delicately dissects the wording of magisterial documents, always presenting the contexts in which they are published, resulting in carefully nuanced judgements. A Catholic ecclesiologist will live in peril if he has not read it.