Brian Daley recounts in his acknowledgements that, in an Oxford pub in the 1970s (probably The Bear, during the Sixth International Patristic Conference in 1971), when he was a young Jesuit, Abbé Marcel Richard suggested to him that he should edit the works of Leontios of Byzantium. And so he did, under the supervision of Henry Chadwick, submitting an edition of the works as his D.Phil. thesis later in the decade. This thesis has now been published as the book under review – I suppose about forty years on from its submission. It is an edition of enormous importance, for Leontios of Byzantium is a towering figure in the debate over Chalcedon that dominated (Greek mostly) theology in the sixth century. Interest in post-Chalcedonian theology is a relatively recent phenomenon, a development signalled when an expanded English translation of Aloys Grillmeier's work, known in English as Christ in Christian tradition, appeared in 1975 with the addition of ‘volume i’ to the title, heralding its continuation; a little more than ten years later, vol. ii/1 appeared in German. By that time research in the post-Chalcedonian period was already well under way: Lorenzo Perrone's book on post-Chalcedonian controversy in Palestine was published in 1980, and in the same year an important symposium on Maximos the Confessor, the greatest of all post-Chalcedonian theologians, took place in Fribourg en Suisse, in which Daley participated.

Leontios himself, though central to post-Chalcedonian theology, is largely lost in the shades of history; there has been much speculation about who he was and what he represented. In the clarification of this, Daley has played a major role; the results are summarised in the long introduction (about 100 pages) to this edition. Daley argues that he is almost certainly the same as the Leontios of Byzantium, who appears as a hated Origenist in Cyril of Skythopolis's Lives of the Fathers of the Palestinian desert. While writing his thesis, Daley had already tackled the question of Leontios's Origenism, arguing against the then strongly held view that he in some serious way embraced Origenist Christology, since there is no trace of such views in the works attributed to him. Rather the author of these works comes over as a ‘strict Chalcedonian’, defending the Chalcedonian Definition as it stands. Further articles and papers appeared, elucidating the way in which Leontios developed an understanding to the union of nature in Christ – a ‘richer union’, as Daley put it in a paper at the Eleventh Oxford Patristic Conference (incidentally, a collection of Daley's articles, not just on sixth-century Christology, would be a boon to scholarship). In these articles, and especially in one still not published (see p. 73 n. 414), given at the Eighth Patristic Conference in 1979, Daley attempted to put to rest a long-running misunderstanding of Leontios, put forward by the German scholar Friedrich Loofs in 1887: the notion of enhypostasia. Throughout his works, Leontios applies the Greek term enypostatos to the human nature of Christ (it had already been used by the early sixth-century defender of Chalcedon, John of Caesarea). Loofs took this to signal a development in Chalcedonian Christology, the idea being that Christ's anypostatos human nature found its hypostasis in the Word who had assumed it. Daley pointed out that the en- prefix did not necessarily imply any sense of inwardness, but was opposite to the alpha privative (an- before a vowel), and simply meant that Christ's human nature really existed. Loofs's theory (itself picking up the use of enhypostasia and anhypostasia in Christology by the Protestant scholastics, something later revived by Karl Barth) still has its defenders; the most detailed study of the term enypostatos, by the German scholar Benjamin Gleede (2012), is not mentioned by Daley, though it seems to me that Daley's position still stands, and that objections still raised relate, not to the meaning of the term enypostatos, but to different philosophical ideas about what constitutes reality.

Such precise analysis of terms is of a piece with the intellectual climate of Leontios's day: the sixth century saw the apogee of commentary on Aristotle's works. Right at the beginning of the first treatise edited here, Contra Nestorianos et Eutychianos, Leontios uses enypostatos of Christ's human nature as part of his response to what seems to have been allowed as a premiss on all sides: that οὐκ ἔστι δὲ φύσις ἀνυπόστατος, in Daley's translation: ‘there is no such thing as an anhypostatic nature’. Daley remarks in his introduction that he can find no parallel to this apparently accepted principle in contemporary philosophical sources (p. 28 n. 159). I wonder, however, if Daley is not being misled by his translation. Given how much of the discussion in the sixth century is about the terms used in the Chalcedonian Definition – ousia, physis, hypostasis, prosopon – it is easy to slip into a kind of technical jargon. But these words had an existing life in current Greek: in late-classical Greek discourse, as a glance at Liddell and Scott shows, anypostatos could well mean insubstantial, non-existent. Maybe this premiss had been advanced by opponents of Chalcedon, whether Nestorian or monophysite, arguing that if there were one hypostasis and two natures in Christ, then one of the natures (obviously the human) would be anypostatos, unsubstantial (= merely adjectival?) or non-existent: a reduction ad haeresim, reducing Chalcedonian Christology to docetism. Monophysites, by maintaining that there was one hypostasis and one (composite) nature in Christ, Nestorians, by maintaining two hypostaseis and two natures, avoided this conclusion. In Leontios's response, enypostatos is opposed to anypostatos, that is, the real particular existence of Christ's human nature is affirmed, for it has been assumed by the hypostasis of the Word of God. The fact that we have little evidence of such a strategy on behalf of opponents of Chalcedon is perhaps less of a problem that it might seem, for we know little, at first hand, of the arguments against Chalcedon. Another example of what seems to me Daley's ‘over-translation’ occurs throughout. Severos and his disciples argued that the realms of theologia and oikonomia were distinct and that Chalcedon had no right to assume that terminology developed in relation to theologia could simply be applied to the realm of oikonomia, in which the ‘natures are made new, and God becomes human’, as Gregory Nazianzen had affirmed (Oratio 39.13; I think the allusion here is to Nazianzen, not Nyssen, as Daley has it: p. 276, apparatus): nature, physis, could then mean different things in the two realms. Leontios maintained that concepts as such remain what they are, but he shared this sharp sense of distinction between theologia and oikonomia, which is disguised (at least to those who use the translation only) by Daley's consistent rendering of theologia as the ‘realm of Trinitarian theology’ and oikonomia as ‘in the Incarnation’. There is no misrepresentation – that is what is meant – but the distinction between theologia and oikonomia is, it seems to me, blurred. However, niggling dissatisfactions like this should not be allowed to dim the huge achievement represented by the eventual publication of this critical edition of a little-known, but immensely influential, theologian.