I am delighted and honoured by the fascinating and wide-ranging responses to my book, and grateful for the welcome challenge of responding. As a scholarly book, mine was written in the first instance for a specialist readership, focusing on detail rather than the big picture. In reconstructing four centuries of ancient Christian philosophical reflection in late antiquity, I examined many, often obscure, Greek and Syriac sources, contextualising them within their own world–an emergent Christian Mediterranean which, over the period I studied, underwent fundamental mutations and profound crises. Yet I am excited to see my interlocutors explore the wider significance of the book’s narrative in their different ways. Derrick Peterson reads it against the backdrop of John Zizioulas’ classic Being as Communion; Joseph Minich raises the question of how to write a “biography” of theology, asking what method should be used in such an undertaking; and Rhys Laverty explores how a theological philosophy, a “theory of everything”, is relevant for today’s Church. I will seek to briefly address all these broad questions as far as is possible. Rather than following them one by one, however, I shall begin by using Laverty’s point about a Christian metaphysic as a point of departure to set out my own understanding of Christian philosophy. From there, I move on to consider how we can best approximate the historical development of this kind of idea. Then, I discuss the controversies engendered by the notion of a Christian philosophy, before finally inscribing my book into debates about genealogy and the Christian contribution to discussions of modernity.
I. WHAT IS CHRISTIAN PHILOSOPHY?
Theology, we say, is faith seeking understanding. But the application of reason to the Christian faith is not a simple exercise. We can identify at least three layers in it.
The first layer is faith as articulated in Scripture. Some think of it as pure faith, but its New Testament presentation centers on basic theological concepts regarding Jesus of Nazareth who is recognized as the Christ. Jesus’ teaching, death, and resurrection are of unique importance insofar as they reconcile humanity with the God of Israel, creator of heaven and earth. The New Testament authors never doubt that faith in this sense is needed for salvation. It is, furthermore, arguable that Christians throughout history have been in nearly complete agreement on the existence and necessity of faith as understood along these lines. Most have also, however, held that this scriptural faith needs further elaboration and elucidation in order to avoid misunderstanding and error.
This has led to the emergence of a second layer in reason’s application to faith: the doctrines of the Church. These doctrines clarify, for example, that Christian belief in God is belief in the Trinity; that Christ is fully divine and human; that the world was created from nothing; that the resurrection is a bodily one. While there has been broad consensus on the need for doctrines, none of them was adopted without controversy, and disagreement on them has led to schism throughout church history. Part of the intensity of these conflicts was due to the general view that these doctrines, in defining the correct faith, were also necessary for salvation.
A casual student of theology might conclude that these two layers are all there is to Christian teaching. But, historically at least, a third layer is also evident: theoretical assumptions adopted to interpret and make intelligible the doctrines of the Church. As much as the second layer (doctrinal teaching) is based upon Scripture, as much is this third layer developed in aid of the officially recognised Church doctrine. Or perhaps more correctly: of the churches. As I mentioned, doctrines were not accepted unanimously by all Christians of all times. Rather, a plurality of Christian communities who define their differences partly in doctrinal terms has long persisted. Total unanimity was never or hardly ever accomplished, and so doctrines were nearly always debated.
These disagreements led to doctrinal controversies whose literary products make up much Patristic theological writing. Their importance has not always been clearly perceived. While some only see the heroic effort of orthodox Fathers in their struggle against heresy, others bemoan their polemical treatises. Yet, polemics aside, the participants in these debates advanced genuine arguments. Such arguments took different forms including appeals to Scripture, authoritative Patristic sources, and doctrines considered settled. Frequently, however, these methods proved inconclusive, and consequently the combatants also argued from reason–or, we might say, philosophically. They would point out that a given doctrinal claim, if universally applied, would result in nonsensical or outright heretical conclusions. In response, the other side would seek to show how their doctrines could be justified based on a philosophical foundation of their own making.
Such philosophical arguments were often applied ad hoc, especially in the early centuries of doctrinal development. As Christian orthodoxy took shape, however, they became more systematic, and attempts were made to connect them so that a single theory could be adduced to explain and rationalise the whole doctrinal edifice of the Christian faith.
My primary intention in writing The Rise of Christian Theology and the End of Ancient Metaphysics was to narrate the history of this process from the fourth to the eighth century. I show how such a “theory of everything”, as Rhys Laverty calls it, was first developed by the so-called Cappadocian fathers with a special interest in defending Nicene trinitarianism. Their subtle theory was so successful in tying together a variety of doctrines, from creation and fall to salvation and restoration, that it soon enjoyed quasi-universal acceptance across the Greek-speaking Church. I therefore call it the “classical theory.” Problems within that theory, however, began to appear once Christology moved to the fore of doctrinal debates, especially in the centuries following the Council of Chalcedon (451). This synod opened deep and seemingly irreconcilable divisions in Eastern Christendom. In the ensuing debates, numerous attempts were made to adapt the classical theory in line with the evolving needs of doctrinal clarification.
This third layer is what I call Christian philosophy. It has existed since early Christian history and it was inseparable from the Church’s adoption of doctrine. I call this aspect of Christian thought a philosophy because it is rational in nature, dependent on intellectual justification, and open to critical debate. Unlike Scripture or doctrine however, this philosophy does not require faithful acceptance, nor was it considered necessary for salvation. This philosophy, moreover, is “Christian” insofar as it grew alongside the emergence of doctrine and from the outset served the justification and defence of doctrinal orthodoxy.
II. METHODOLOGICAL PROBLEMS
Before considering some problems inherent in the conception of this Christian philosophy, let me discuss my historical approach. Joseph Minich raises the intriguing question of how to “write a realistic history of, for lack of a better phrase, “understanding God””. He suggests we might understand the history of theology as a kind of biography, analogous to the narration of a human life. I like this analogy, in particular if we manage to avoid the use of overly teleological categories. The point is not to show how all developments led to an apex in our own understanding, but rather to appreciate how each period can be “immediate”unto God’, to borrow a famous phrase coined by Leopold von Ranke.
How do we go about researching and writing such a history though? I would once again extol the neglected potential of polemical writings. From the way certain theological ideas were opposed and defended, we can often gain a particularly vivid sense of how ideas were understood. My guiding assumption is that all truly big ideas are to a point controversial, because they express an insight that is new, unusual, or even paradoxical. This is true whether we think of “God” as per Minich’s question, or more specifically of the way the Church’s teaching about God was expressed in the language of the Trinity or the Incarnation. In one sense, the controversial or provocative nature of these ideas has not changed throughout history, but the objections raised to them have. Past believers may have found something unobjectionable that strikes us as implausible, while balking at something we take for granted. It is therefore invaluable to pay close attention to the process in which doctrinal debates play out in their time. This admittedly involves a methodological imperative too rarely heeded. We cannot simply cheer every argument advanced by an orthodox Father and pooh-pooh every counter argument made by their opponents. We must step back and adjudicate these claims on their own merits–not to advocate doctrinal relativism, but to understand what was intuitively theologically plausible and implausible at the time.
We can, moreover, observe these theologians “at work” refining their conceptual apparatus and ultimately providing solutions that gained broad acceptance. We can then perceive how problems besetting generations of thinkers can also be left behind as they appear satisfactorily solved. The most impressive such case in the Eastern church, arguably, was the Cappadocians’ “settlement” of the trinitarian controversy. This accomplishment more than anything else earned them their unique place in later theology. Given the significance of their specific philosophy in this, it is hardly surprising that its use in doctrinal disputes was taken for granted by the Eastern church in subsequent centuries.
III. CHRISTIAN PHILOSOPHY AS CONTROVERSIAL
This does not mean that the latter point was settled for good. As Laverty rightly observes, the need for a Christian form of philosophy has often been denied. It is not difficult to see why. Even the brief characterization given above indicates some fundamental tensions at the heart of such an enterprise. One key question is how Christian such a Christian philosophy can be. Is it not inevitable that the adoption of a philosophical discourse within Christianity eventually leads to modifications or even critique of doctrine? It seems a difficult balancing act to ensure that such a Christian philosophy is neither Christian at the expense of being philosophical nor philosophical at the expense of being Christian.
But this is not all. I have above referred to Christian philosophy as the “third layer” of Christian theology, which would seem to suggest an existence on the margins of theology–a mere tool adopted in aid of doctrinal clarification. But the third layer can often present itself as if it were the truly first one. Once philosophical argument moved from ad hoc illustrations into the kind of coherent system found in Gregory of Nyssa, the temptation arose to consider it the true center of theology, a kind of control room in which the detailed meaning of doctrine is determined. Once this possibility is taken seriously, why not focus all theological work on this field in the assumption that, once these questions have been satisfactorily settled, the rest will follow quite easily?
These are not abstract speculations. Rather, the history of theology shows how often and how easily this shift occurs. We can think here of late medieval Scholasticism, or strands of modern theology in the wake of German idealism. This tendency then produces the opposite extreme: rejection of any philosophical reflection in Christian theology, such as in Martin Luther’s early work, or to an extent in Karl Barth.
Part of the problem is that the use of philosophy in theology is often not seen, as I suggest here, as a germane development within Christianity but as an import or an adoption of existing philosophies, for example that of Platonism in the early church, that of Aristotle in the Middle Ages or, that of Kant, Hegel or Heidegger in modernity. In fact, the protest against Christian philosophy has often taken the form of a rejection of the alleged infiltration of Christianity with unsuitable, foreign influences. The idea that Platonic philosophy exerted an undue influence on Christian thought goes back to the Patristic period from which it was adapted by historical theologians in early modernity.
There are several reasons why, in my view, this theory is wrong. First of all, the emergence of Christian philosophy historically follows the evolution of doctrine. Philosophical ideas were adopted in order to defend and justify doctrinal decisions, not to establish them. Second, my own research suggests that much of the development of Christian philosophy, at least in the Patristic period, can be explained from within the Church. This does not mean that Christian theologians of the period did not somehow share in ideas that were more generally en vogue. But the motivation for innovations in Christian philosophy were, by and large, provided by the need to clarify existing doctrines, not by an attempt to make Christianity palatable to pagans; it was doctrinal, not primarily apologetic.
This development of Christian philosophy from within the Church also makes me critical of any view which affirms Christian philosophy as the real nerve center of theology, and which ascribes erroneous theological views (and other problems) to the adoption of the wrong type of philosophy. Most influentially, John Milbank has argued that Duns Scotus’s critique of the theological use of analogy is the most fundamental heresy of Western Christianity, one shared by both Reformation theologians and Tridentine Catholicism. Milbank’s own version of “orthodoxy” (which he calls Radical Orthodoxy) is, consequently, principally philosophical, a view of the world supposedly held universally prior to the late thirteenth century.
As little, however, as there was a version of Platonism that illegitimately underwrote the emergence of doctrines in the early church, as little was there an underlying philosophical orthodoxy. The increasingly elaborate forms of Christian philosophy developed by Christian thinkers were developed in service of the explication of doctrines the Church had already adopted. In many ways, Radical Orthodoxy offers something like the mirror image of the Hellenization thesis: both wrongly consider philosophy the root of Christian doctrine.
Moreover, as I pointed out above, there is little evidence that the Church ever moved to make the adoption of a certain philosophy mandatory in the way faith in certain doctrines was required of the believer. Such a decision was taken, perhaps for the first time, by Leo XIII in Aeterni patris (1879), which prescribed a form of Thomism as normative for Roman Catholic theology. No such attempt was made in the Patristic age. The fact that the classical theory, which came with the authority of the Cappadocians, was adapted and changed when this proved necessary in the context of the Christological debates shows quite distinctly that the adoption of philosophical theories was not as such a matter of orthodoxy. This is further confirmed by the observation that these later adaptations of the classical theory did not lead to the establishment of a single form of Christian philosophy by the end of the Patristic era.
IV. CHRISTIAN PHILOSOPHY AND THE GENEALOGY OF MODERNITY
My disagreement with Milbank and Radical Orthodoxy, however, goes further, and here I must touch on Derrick Peterson’s essay. He reminds us of the work of John Zizioulas, who argued that the Cappadocians developed, along with their clarification of trinitarian doctrine, an ontological revolution bringing the notion of the person into the center of philosophical reflection on being. Peterson rightly sees my own work as an attempt to develop this insight, while trying to avoid some of its problematic aspects. I agree with Zizioulas in his observation that Patristic thought in its philosophical connotations cannot simply be understood as continuing an earlier metaphysical tradition. Rather, it represents a rupture. The universally shared assumption was that being is primarily general and universal; Christian philosophy, however, emphasised the ontological dignity of the individual.
In opposition to Zizioulas, however, I do not consider fourth century trinitarian theology the origin of this. The “ontological revolution” in Patristic thought, therefore, was not the work of the Cappadocian fathers. Rather, it arose from the need to give a precise account of the Incarnation, the belief that God became fully human in one, historical person, Jesus of Nazareth. Peterson intriguingly suggests that my restatement of Zizioulas’ position may also help correct another controversial aspect of his thought, namely, his insistence that Western theology lost its way with Augustine, whereas the Eastern tradition (by continuing along the path of the Cappadocians) preserved a more helpful philosophical and theological perspective. This suggestion was eagerly picked up by a number of prominent Western theologians such as Colin Gunton, but it has, more recently, been sharply and rightly criticized. Peterson now suggests that my insight that the Cappadocian classical theory needed corrections in light of the Christological controversy could also build a bridge to Augustine and the Eastern tradition. I am sympathetic to this idea, but cannot currently take a decisive stand on its validity. One well-known historical fact, however, may serve to confirm Peterson’s theory: the Western reception of John of Damascus’s De fide orthodoxa, an important eighth century work codifying many earlier Eastern developments. Upon translation into Latin by Burgundio of Pisa in the twelfth century, the Damascene’s Christology became the gold standard of further medieval and early modern Western theology. Considering how influential Augustine was on all these thinkers, it seems intuitively plausible that they recognised in the Damascene something not at all incompatible with the kind of theology they had traditionally studied.
Both Zizioulas and Milbank share a genealogical interest in seeking to demonstrate how Christianity is related to modernity. In fact, genealogical accounts are another context in which the problem of Christian philosophy has recently gained significance. The question here is less how Christian philosophy is related to Christian doctrine or the Christian faith, but rather how philosophy embedded in the Christian tradition (or its rejection) can explain non-theological developments during the modern period. Rhys Laverty has, rightly, pointed out the connections between my work and genealogical narratives, referencing the work of Carl Trueman.
One way we can (roughly) divide these narratives is between those who see fundamental continuity between pre-Christian and Christian philosophy with a philosophical “rupture” occurring later to pave the way for modernity, and those that see the rupture as being between Christianity and everything before it. Milbank and Trueman belong to the former group, locating the rupture in the thirteenth century and Enlightenment respectively. Zizioulas, however, belongs in the latter group, alongside rather different thinkers such as Jean-Luc Marion and René Girard. The research I did for The Rise of Christian Theology tends to support the latter of the two views. Admittedly, my work did not touch on medieval and modern thinkers, but the evidence of the Patristic debate I surveyed makes it undeniable that Christian philosophy, in a sense, led to the end of ancient metaphysics. In particular, the idea that Christ could be fully human without being a human individual distinct from the Logos, adopted to explain how Christ’s human nature didn’t require a second (human) hypostasis, directly contradicted the standard Greek assumption that possessing all human properties and being a human person amounted to the same thing. Essence and existence could be seen as separable from each other; the world in which we live became less stable and could, over time, be considered one of several possible ones. These, to be sure, were mere seeds in the Patristic period, but they must be taken seriously. The notion of Christianity as simply continuing an age-old intellectual consensus, cannot be squared with the evidence we have for the rise of Christian philosophy in the Patristic period.
This, finally, brings me to the question of how the history I narrate in my book can aid with the Church’s challenges today. I can answer this question by way of summarizing my main points so far. First, Christian faith as found in Scripture and expounded in the Church’s doctrines tends to develop out of itself philosophical reflection. There is good reason to think that such reflection is as much needed today as it was fifteen hundred years ago.
Second, while such a Christian philosophy is needed, it should not be turned into the center of the faith. It is only a tool, albeit a necessary one, to elucidate, clarify, and deepen the faith of the Church. It is the third layer, not the first, and so rightly subject to debate, disagreement, and critique. This seems especially pertinent when current fault lines within the Church seem principally cultural and ethical rather than doctrinal, as their evaluation inevitably depends on philosophical reflection. The Church is well advised to encourage dialogue and debate rather than apodictic judgments and condemnations.
Third, as much as Christian philosophy in late antiquity pushed against what was permissible within the constraints of traditional metaphysics, as much should the same task be undertaken today by boldly following the insights of the Christian faith. The example of the early church shows, however, that this is not the same as adopting a conservative attitude. References to a universal cultural consensus and a supposedly natural law at that time were regularly made by the opponents of Christianity. Today’s Christian philosophy, then, ought to be prepared to be innovative and open-ended as much as it was in the fourth, sixth, or eighth centuries.
Professor Johannes Zachhuber (D.Phil, University of Oxford) is Professor of Historical and Systematic Theology and a Fellow and Tutor in Theology at Trinity College, Oxford. His publications include The Rise of Christian Theology and the End of Ancient Metaphysics (OUP, 2020) and Theology as Science in Nineteenth-Century Germany: From F. C. Baur to Ernst Troeltsch (OUP, 2013). The Rise of Christian Theology and the End of Ancient Metaphysics is available now in paperback.
 John Zizioulas, Being as Communion: Studies in Personhood and the Church (New York: St Vladimir’s Seminary Press, 1985).
 Johannes Zachhuber, The Rise of Christian Theology and the End of Ancient Metaphysics (Oxford: Oxford University Press, 2020).
 John Milbank, Theology and Social Theory: Beyond Secular Reason, 2nd edition (Oxford: Blackwell, 2006); Catherine Pickstock, ‘Duns Scotus: His Historical and Contemporary Significance’, in Modern Theology 21/4 (2005), 543-74.
 Carl R. Trueman, The Rise and Triumph of the Modern Self: Cultural Amnesia, Expressive Individualism, and the Road to Sexual Revolution (Wheaton: Crossway, 2020).