In this work Gilles Emery aims at his first systematic presentation of St Thomas' treatment of the Trinity as a whole, concentrating on this in its most developed form, namely as it appears in the Summa Theologiae. (The Trinitarian Theology of Saint Thomas Aquinas is not to be confused with his two collections of his essays on topics related to the Trinity, despite the similarity in title.)

His discussion sets St Thomas' treatment of the Trinity in the Summa in relation to the treatment he offers in other works, both those closest to the Summa (the Disputed Questions de Potentia and his commentary on St John's Gospel) and earlier works distinct in aim and less developed in thought. He situates St Thomas' position in relation to the approaches of those who preceded him, Anselm, Richard of St Victor, Bonaventura and a multiplicity of others. At every point, he reveals how deeply St Thomas' thought is rooted in that of the Cappadocians and Greek tradition, while avoiding treatment of later controversies such as that with Palamism. He shows how the avoidance of Arianism and Sabellianism, along with Aquinas' reflection on scripture, compels Aquinas to consider the distinctions between the Persons of the Trinity as arising from actions immanent to the Trinity and not matters of the workings (‘economy’) of God towards the world in creation and salvation. Fr Emery judiciously draws upon his detailed study of a very large range of patristic and mediaeval authors in such a way as to show how St Thomas' presentation disguises his remarkable capacity to steer through a maze of controversy of which the modern reader knows little, so many problems so exactly dealt with, without prejudicing the limpid clarity and order which enables us to profit from him today.

For St Thomas, it is only by understanding the immanent Trinity as fundamental that we can get a true understanding of the economy. In Emery's view, people tend to have a false conception of the structure of the Summa, thinking of it only in terms of the treatment of separate topics in separate questions and treatises, whereas its whole structure is to treat of God in Trinity from beginning to end, first considering what concerns God's essence, second what concerns the distinction of persons and third what concerns the procession of creatures from God (ST I, q. 2, prologue), so that strategically the Summa is divided into Part I, qq. 2–26, Part I, qq. 27–43 and then the whole of the rest from Part I, q. 43, to the end of Part III. Although it is vital that, in all the works of God ad extra, the Trinity works together as a unity, nonetheless each of the Persons has a different role within the acts ad extra, so that the processions of the Persons from the Father are the cause and the rationale of the different roles of the Persons in the working of God ad extra (pp. 344–7, 350–3).

In particular, his last Quaestio on the Trinity, ST I, q. 43 on the sending of the Son and the Spirit, looks forward to the main body of the rest of the Summa, I, qq. 62, 73, 93–4 and the whole of Parts II and III. Aquinas' account of these temporal missions prepares the way for his account of how intellectual creatures through grace return to God as adopted sons in glory and union with him (p. 359 and ch. 15), by the Word providing knowledge and by the love coming by the Spirit, each present in creatures in a new way.

By contrast, in the immediately previous question Quaestio 42, Aquinas' theory of appropriation has a retrospective function, looking backwards over qq. 27–41, as a reflection upon how scripture's subsidiary ways of speaking of the Persons reflect our avenues towards understanding its principal ways of speaking of them. Emery's account of how Aquinas explains how the scriptures appropriate many terms to particular Persons which are also applicable to all of them explains how this arises. It shows how many of these appropriations arise from their links with the psychological analogies connected with speaking and understanding and with loving which give us what understanding we have of the properties of the individual Persons. The presence of this Quaestio is in its way a further indication of St Thomas' preoccupation with using theology to help us understand the scriptures. For him, in the Summa the authority of scripture always comes first, the Fathers and Councils second and reason third, but the task of theology is to allow reason to aid us in understanding Revelation.

St Thomas' treatment of the Trinity may seem rather abstract because of its explicit reflection on the logical distinctions (often referred to by Emery as ‘linguistic’) on which it relies. Each of the Trinity is distinguished only by its relations to the others, a difference in relation being the only type of difference, which does not involve differences in quality or nature, so that the three persons can be and are, one in esse (this is stated most precisely in ST I, q. 28, art. 2, ad. 1).Footnote ¹ The concept of ‘property’ applies to the things which belong to only one person, while the concept of ‘notion’ also includes attributes belonging to more than one of the Trinity but not to all three and so still not to God as such (cf. pp. 96–102, 168–71). Meanwhile, the logical distinctions he makes between concrete and abstract uses of terms (q. 39, arts. 3–6, and q. 40, art. 1) and between substantival and adjectival uses of concrete names (q. 39, art. 3), enable him to provide modern readers who know nothing of Gilbert of Poitiers and Joachim of Fiore (pp. 142–6) to escape the same traps. (Here to translate concretum by Geertz's anthropological term ‘thick’ on p. 149 is tempting, suggesting fruitful further meditations, but has no relevance to Aquinas' actual argument.)

Aquinas' account presents the view that Revelation is the sole source of a knowledge of the Trinity, the Father alone begetting the Son, alone begotten by the Father alone, while the Spirit is spirated by the Father through the Son and so by the Father and the Son. There is no possibility of deducing the Trinity from any analogies which theology may offer and to present these analogies as if they provided proof would be to invite contempt. Yet, this would seem to make the difference between being begotten and being spirated the merely logical difference, that begetting is from the one person alone, but spirating from one person through another and, without any analogies by which we might understand the difference between begetting and spirating, turning the doctrine of the Trinity, so far as our understanding of the terms is concerned, into a kind of mathematical consequence of the incomprehensible mystery, a matter of the order amongst the persons (p. 206). And the Eastern Tradition has been reluctant or opposed to seeking to go further than this, with the result that it puts more accent on the monarchy of the Father, an accent reflected in Bonaventura (p. 125 with nn. 109 and 110, and pp. 169–72) and refuses to connect its thought about the relation of Persons within the Trinity in itself with its thought about the relation of the workings of the Son and the Spirit in the economy of salvation (p. 274).

However, in St Thomas' conception, certain psychological analogies have been given to us in Revelation as we find it in the scriptures as appropriate helps to understanding, in particular, first of all, the analogy between the way a person who understands goes beyond mere understanding to express this understanding in a Word, not an external word, but a word of the heart, an inner word. And it is by reference to this that we are to understand how it can be that the begetting within the Godhead is not to be conceived by analogy with human or animal begetting, but by analogy with this speaking of a word inwardly (pp. 61, 62, 178, 182–4, 186–7), going beyond being wise to expressing this wisdom inwardly (pp. 192, 238). And second, the loving by a person who loves goes beyond mere disposition to an active movement towards the object of love, an object itself personal in the case when it is love by a person and so has a fruit in a person (p. 68, with n. 81, and pp. 240, 243). Here Emery works through St Thomas' labours, coming to some clarity in the end, pp. 66–8, 229 (Lonergan's 1949 discussion reprinted in pp. 201–5, Verbum, 1968, suggests that the Holy Spirit as Goal stands to love somewhat as the Word stands to understanding). This loving is a movement of will formed through the expression of understanding in the Word (pp. 287–8) and so the Holy Spirit is not mutual as between the Father and the Son, but as from the Father through the Son (a correction of the common idea of how the Holy Spirit as amor is the nexus between the Father and the Son, p. 237). These processions of intellect and will are not to be conceived by analogy with physical movements, but as actions whereby a reality is drawn out from a principle (pp. 53–4), i.e. a principium or arche.

All this illustrates the truth of Emery's conception of how, for Aquinas, these psychological analogies do not prove the Trinity, but supply ‘likely reasons’ (rationes verisimiles), so that, after we have taken the doctrine to be true, such reasons confirm it (pp. 22–31) – so that ‘by faith we arrive at cognitio, but not conversely, as Augustine says’ (ST I, q. 32, art. 1, ad 2). It is only in explaining this and not in any modern sense, that Aquinas or this book provide a ‘theory of knowledge’.

These psychological analogies given by Revelation enable us to understand how it is that, in using such terms as Person, Father, Son, begetting and proceeding, we are not relying upon mere metaphors or images, but using the terms in their proper sense, something which Aquinas is most anxious to demonstrate (pp. 53–4, 60–1, 106, 153, 187, 352, 397) and his method has followed Basil (p. 81). They make it plain that we use such terms as Father, Son, begetting and proceeding in respect of the Trinity in their proper sense (proprie),Footnote ² as Ephesians 3:15 implies (pp. 161–2) and not metaphorically, so that they satisfy the criteria for being used analogically given in ST I, q. 13.

However, although Emery constantly speaks of our uses of these terms as ‘analogical’, there is absolutely no case of this in Aquinas. Indeed, in the case of what the schoolbooks later call ‘intrinsic analogy’, where we have a term used proprie of God or one of the divine Persons which is also used of creatures, Aquinas almost invariably speaks of its being used of creatures in virtue of likenesses. In Aquinas' text (ST I, q. 42, art. 2 ad 1), Emery's ‘analogical representation’ on p. 60 is ‘a representation gathered from many modes of likeness (similitudo)’ and one may remark that all the important cases of analogical use in ST I, q. 13, arise out of the likenesses referred to in q. 4.

The translator has achieved a remarkable self-effacement, showing no trace of her own personal style of writing but perfectly synergising with Fr Emery's own thought.

This book is the fecund fruit of Emery's learning. Often one seems to be going over the same ground again, albeit in a different way, where what is in fact accomplished is a widening of the circle, drawing in more connections with other writers and other controversies of the time and advancing to throw light on further aspects and elements within the structure of St Thomas' thought. As a result, it is sometimes difficult to retrace points of interest, which are therefore worth marking as one reads in order to make up for the poverty of the index. The passages cited from the Summa contra Gentiles are always traceable directly in readily available Latin texts – the details of the references given are taken from the most recent Marietti edition, 1961–7.

This work is invaluable to work through and reflect upon, showing how in St Thomas logic serves piety and aids contemplation, the intimate connections between the Summa and his reflections on scripture, especially St John's Gospel, being unmistakable.