The story of the christological controversy from the First Council of Ephesus till Chalcedon is a familiar topic, but one that has suffered from too selective a reading of the sources and dubious presumptions about what the main actors thought they were about. This new monograph cannot offer comprehensive coverage, but pursues a particular question to give coherence: how did the rival factions interpret and attempt to exploit the Nicene Creed? This captures what the two sides were actually trying to do: not to ‘develop’ doctrine, but to interpret the tradition correctly. What Mark Smith offers is not a systematician's analysis and evaluation of the options, but an historian's mapping of the stages in the debate. This he does with a minute attention to the texts (the proceedings of conciliar sessions and related correspondence) and a subtle interpretation of how they were formed and for what purposes.

Smith neatly contrasts Cyril's and Nestorius’ readings of the creed, Nestorius claiming that the initial ‘one Lord Jesus Christ’ implied a reference to his humanity as well as his Godhead, enabling the subsequent statements about Christ to be apportioned out between his two natures, while Cyril read the creed's description of Christ in purely divine terms as making the Godhead the subject of all the human experiences. Both readings made the creed answer questions it had not intended to address.

The discussion that follows of the various sessions and documents of the two rival councils, one chaired by Cyril, the other by John of Antioch, into which the Council of Ephesus (431) divided, offers an analysis that shows full awareness that the published ‘records’ of sessions were carefully tailored documents that selected and rearranged the material they included. Particularly ground-breaking is the discussion of the session of Cyril's council on 22 July, which issued the famous Canon 7 of Ephesus that set up the Nicene Creed, in its original form, as the only authoritative one. Smith points out that no mention of this ‘session’ appears in any subsequent document until a full year later, and that its polemical purpose places it there rather than in July 431. Smith does not go so far as to say that the session was a fiction, but his argument points in this direction.

After a similarly perceptive analysis of the ‘Formula of Reunion’ (433), showing that it ‘postponed rather than resolved’ the issue of the proper interpretation of Nicaea, the book proceeds to the Eutychean controversy and the Council of Chalcedon (448–51). Readings of the Chalcedonian Definition have treated its initial quotation of the Nicene Creed as no more than a pious preliminary. Smith shows that on the contrary the creed was central to the whole conciliar debate, which focussed on what fidelity to Nicaea implied, with the opponents of the emperor Marcian's demand for a new definition appealing to Canon 7 of Ephesus as excluding such an innovation. The response of Marcian's representatives at the council was to use Ephesus’ formal approval of Cyril's Second Letter to Nestorius and his acceptance of the Formula of Reunion as precedents for a new, yet authoritative, reading of the Nicene Creed. The Chalcedonian Definition concluded, with remarkable bravado, with actually reaffirming the Ephesan Canon 7, interpreted not as excluding new doctrinal formulae, but as justifying them, when they were needed to preserve the ‘authentic’ Nicene teaching against novel and false interpretations of it.

The book's ‘Conclusion’ brings out how the debate over the true meaning of Nicaea was not a simple ‘Nicene fundamentalism’ that took the creed on its own, but involved the placing and reading of the creed within a particular tradition, whether this was patristic or the series of councils including Constantinople (381), Ephesus I and (for some) Ephesus II. As Smith points out, this implied that the meaning of the creed was not static and given once for all. In this way it created scope for new readings of the creed in new contexts.

In all, this book provides an analysis of the christological controversy of 431–51 that outdoes all others in its study of a full range of contemporary documents and scrupulous fidelity to how the competing factions understood and conducted the debate. It will be necessary reading for all students of the meaning and history of this central topic in the history both of the church politics of the period and of the development of Christian doctrine.