The argument of this lucid, erudite and original study is that the East and the West are closer than many suppose to agreement on the Filioque, so long as it is understood that those who affirm it and those who deny it have the same catholic goal. The seminal theologian of chapter i is Origen, the first to assert the discrete and eternal existence of the three hypostases. Maspero finds that Origen favours a linear succession of Son to Father and Spirit to Son, which does not entail that the Spirit is created, but implies the superiority of that which engenders to that which is engendered, notwithstanding his maxim that in the Godhead there is no more or less. Chapter ii begins with a contrast between Eusebius of Caesarea and Marcellus of Ancyra, the former of whom dwells chiefly on the procession of the Spirit from the Father at John xiv.26, while the latter holds this verse in dialectic conjunction with John xvi.14, ‘he shall receive from me’. At the centre, however, is Athanasius, who is able to maintain the full divinity of the Spirit because he credits the Father with a physis or nature which is communicable without change. The sequence Father-Son-Spirit is retained, yet there is no ontological subordination of the Spirit. The same may be said of Basil the Great, whose tract On the Holy Spirit defends the worship of the Spirit ‘with’ the Father and the Son, to whom he is therefore equal in honour, against those who prefer to honour him ‘in’ the other two, as though he were not so much a person as a power. The parity of the Spirit and the Son is proved by texts in both Basil and Origen (whom Basil cites with approval) which ascribe to the Spirit the act of creating which John ascribes to the Logos. Gregory of Nyssa is a corroborative witness when he characterises the Son as the power through which, and the Spirit as the power in which the creative purpose of the Father is fulfilled.

Because it opens so many trails that have not been followed in previous studies, Maspero's discussion of the period before the Cappadocians suggests a number of new questions which I shall note here as possible topics for further inquiry. It might be asked, for example, how new it was for Athanasius to posit a common nature, rooted in God the Father, as the basis of unity between the three persons, when Origen had already maintained that the Son is by nature the only-begotten (monogenês) of the Father and compared their relation to that of Adam and Seth. Again we may wonder whether Athanasius' dictum that it is not the Son who receives from the Spirit but the Spirit is an endorsement or a correction of the exegesis of John xvi.14 by his friend Marcellus. Does Basil appeal to Origen because he thinks him orthodox or because he assumes that Origen, like the heretical Dionysius of Alexandria, is an authority for ‘those who make war on the Spirit’? And why, having gone so far as to inculcate parity of honour and worship, is Basil not prepared to call the Spirit God?

His reticence is thrown into relief in chapter iv by the appropriation of the Nicene formula ‘God from God’ in Epiphanius, who defined the Trinity as one Holiness in three existences, and reconciles John xv.26 with John xvi.14 in the formula ‘proceeding from the Father and receiving from the Son’. A treatise falsely ascribed to Athanasius points out that it is not fatherhood and sonship that the Church venerates, but the shared nature of the one Father and the one Son. This work invites comparison with Nyssen's letter to Ablabius in its argument that a single energy or activity implies a single nature, and that however many artefacts we produce from gold the gold itself is one. The review of Nyssen's pneumatology in chapter iv concludes that, while he assigns no cause to the Spirit other than the Father, he assigns to the Spirit an eternal role in the anointing of the Son as king, and therefore confers in him a distinctive property as the bond between the two kingships. While the Spirit is active in creation, as in Athanasius and Origen, his relation to the Son no longer mimics that of the Son to the Father, and because the glory which he returns to the Father and Son is not, as Origen taught, inferior to that which the Father bestows on him, he reveals them fully to us while he himself is manifested in the Son. It is in this exchange of glory for glory that Gregory, according to Maspero, grounds the equality of the three persons, according to the Spirit the same ubiquity of action that he accords to the other two persons, in contrast to Origen's doctrine that he works only in the elect.

In chapter v, enticingly titled ‘Another surprise: a Greek Filioque?’, Maspero adduces texts from Nyssen and Nazianzen which might be thought to distinguish the generation of the Son from the procession of the Spirit by making the Father the cause of the first while assigning some agency in the latter to the Son. His own conclusion is not that these texts anticipate the Latin Filioque but that we ought to construe them, as the authors write them, with a circumspect consciousness of the ineffability of the divine. At the same time, noting that Gregory Thaumaturgus spoke before Nyssen of the Son as the one who manifests the Spirit, he also quotes passages from both Nyssen and Nazianzen in which the Spirit appears as a meson, or intermediary between the Father and the Son. These conceits would perhaps invite comparison with the speculation of Marius Victorinus that the Spirit may be the mother of the Son in the higher as in the lower realm, and also perhaps with the obscure reflections in the meson in Synesius of Cyrene. Maspero takes for comparison the Syriac writers contemporary with the Cappadocians, who are willing to say more openly that the origin of the Spirit suffers from that of the Son in that he has two sources whereas the Son has one. In preparation for the final chapter on Augustine, chapter vii discovers psychological analogies for the Trinity in Gregory Nazianzen's observation that humans also possess an intellect, a logos and a spirit, and in a treatise by Anastasius Sinaita, which contends that we are a fitting image of God because our soul has the property of being ingenerate and the power to generate logos, while the procession of mind from soul mirrors that of the Spirit. The implied anthropology is neither Christan nor Platonic (cf. Plotinus, Enneads 5.1.3), but is surely too eccentric to be heretical.

We come in chapter viii to Augustine's theory that the three persons are distinguished by their mutual relations. The precedent is set by Nyssen's letter to Ablabius, in which the rigorous denial of any distinction in activity or nature between the three persons is balanced by an equally rigorous choice of prepositions to determine the relation between the two dependent persons, and the relation of each to the Father. In Maspero's view Augustine and Gregory are not quite as one because the former brings the relations into the substance of the Trinity while the latter upholds the Aristotelian contrast between a substance and its predicates, affirming that the relations are extrinsic to the substance yet eternal. He also maintains that, whereas Gregory's chief concern is to demarcate the terms in which we speak of the Godhead, Augustine has also grounded his understanding of the Spirit, as the gift of the Son and Father, in an ontology of love. The Spirit is both of the Son and the Father, but at the same time the bond of love between Father and Son and thus the precondition of that unity which produces him. There is thus no basis for the complaint that the Spirit in Augustine is an addendum to the Father and Son, explicable only by reference to a psychological model which he himself pronounces inadequate. Nor, as Maspero shows in the ‘ecumenical proposal’ which completes this remarkable book, is the double procession merely a shibboleth to differentiate the generation of the Second Person from the procession of the Third. All catholic pneumatology in the fourth century is inspired by the recognition that, if the mystery of the Godhead is to be preserved against its Arian detractors, the difference of the three persons must be brought within the sameness, and a theology of relations must succeed the Athanasian theology of nature, as this succeeded the logos-theology of Origen and his precursors. In summary we might say that this it is pre-eminently true of this ancient logomachy – without asking whether it may not be true of all – that ‘the letter killeth but the spirit giveth life’.