If people know any theologians of Christology from church history, those tend to be Athanasius and Cyril of Alexandria. The former famously defended the full divinity of Christ between the Council of Nicaea (325) and the First Council of Constantinople (381); the latter is famed for defending the oneness of Christ’s person in the hypostatic union prior to the Council of Chalcedon (451). Reformed Christians attuned to church history today view themselves as the heirs of these great figures, whose theology was largely assumed and handed down to us by the Reformers.
Yet at least equally important in Reformed Christology is Leo the Great (Bishop of Rome, 440-461), whose great Tome was endorsed alongside some of Cyril’s writings at Chalcedon.
I doubt any readers caught it, but in March 2022, I had the joy of seeing the publication of my book, The Manuscripts of Leo the Great’s Letters: The Transmission and Reception of Papal Documents in the Middle Ages. I confess it is not not the catchiest title, but the book was the fruit of four years of Ph.D. work and six further years of research and revision. Its 469 pages describe how over 170 letters associated with Leo the Great came to us today, examining almost 400 manuscripts ranging in date from the sixth to the sixteenth century. After an introduction to the life and work of Leo, focusing on the letters, I delve into a detailed discussion of the reception and transmission of Leo throughout the Middle Ages. A major argument that I advance is that, whether people were reading his canon law or his theology, “every time there was a cultural mixture of reform, renewal, and ‘Renaissance,’ Leo was amongst the authors copied, quoted, and compiled.”
However, my analysis stops short in the fifteenth century. In the Middle Ages, one can trace the transmission of writers through specific manuscripts. The advent of mass printing in the 1400s, however, transformed the nature of transmission with its ability to produce identical copies of any work in bulk. It also, therefore, made it possible for a popular author, such as Leo, to become even more popular and expand his impact. If you read my book, you will learn about how and why Leo was important in the later patristic era, among the Carolingians, and in the High Middle Ages, at the Council of Ferrara-Florence. But you will not catch a glimpse of Leo the Great among the Reformers.
Consider this article, then, an extra chapter, introducing the place of Leo the Great among Protestants of the Reformation era. Despite the question once posed to me by the guest-master at a Benedictine monastery—“Isn’t it hard for you, as a Protestant, to study a pope?”—it is the case that the Magisterial Reformation (Lutheran, Reformed, Anglican) was rooted in the Fathers, Leo the Great among them. His two-nature Christology was as important to the reformers of the sixteenth century as it had been to reformers in the eleventh. We will see this first in a brief discussion of how the two-nature Christology of Leo and Chalcedon is a given throughout the formularies of the Reformation era, and then, after a brief mention of sixteenth-century editions of Leo, we will consider the influence of Leo upon John Calvin (1509–64), Peter Martyr Vermigli (1499–1562), and Richard Hooker (1554–1600). These are not the only sixteenth-century Protestants I could have chosen, of course (Martin Chemnitz will surely be at the forefront of any future investigation),but I take them as being exemplary, at the least.
Leo the Great’s Christology is a clear synthesis and presentation of traditional, Latin, two-nature Christology, drawing on Hilary of Poitiers (c.314–c.367), Ambrose of Milan (c.339–c.397), and Augustine of Hippo (354–430), as well as being in line with Cyril of Alexandria’s (c.376–444) and John of Antioch’s (d. 441) formula of reunion of 433 and other statements in the Greek Fathers—particularly Gregory of Nazianzus (c.329–390). The prime locus for Leo’s Christology was his so-called Tome, a letter sent to Flavian of Constantinople in 448 in response to the deposition of the Constantinopolitan archimandrite Eutyches on Christological grounds.Leo’s Tome was embraced as the official orthodoxy of the imperial church at the Council of Chalcedon in 451, and a definition of the faith was articulated by the council that distilled the essential components of Leo’s teaching into a short span. Later, after Leo’s Christology formally won the day at the Council of Chalcedon in 451 (which was part of the fallout of Eutyches’s deposition), he wrote a letter to the monks of Palestine (Ballerini Ep. 124). This letter was revised later and sent to the Emperor Leo I; the revised version is the so-called Second Tome. This second letter reframes the same Christology in different phrasing and terminology due to Leo’s realization that he faced a hostile audience after the council.
The heart of Leonine-Chalcedonian Christology is the affirmation that Christ exists in two natures but is, nevertheless, a single person. The two natures are united, as the council members were at pains to repeat, “according to hypostasis,” which is Cyril of Alexandria’s way of phrasing the “hypostatic union”—an indivisible union of the human and the divine in a single hypostasis, or person. On the one hand, the hypostatic union means that anything Jesus Christ does can be predicated of the God-Word or the man Jesus Christ. Thus we can say that God was crucified and died and that Jesus of Nazareth is the Lord of glory and Creator of all. This interchangeability of who can be made the subject of a sentence involving Christ is called the communicatio idiomatum—the idiomata, or properties, of one nature are shared or communicated with the other. Nonetheless, the natures themselves remain indivisible and unmixed. Four adverbs are famously included in the Chalcedonian definition of the faith to preserve the two natures and their full unity: without confusion, without change, without division, without separation. This is the Christology of the Reformation formularies, to which we now turn.
As we consider the role of Leo in the thought of the Reformers, let us begin with Martin Luther. The Small Catechism of 1529 is indicative of the formularies at large, stating, “I believe that Jesus Christ, true God, begotten of the Father from eternity, and also true man, born of the Virgin Mary, is my Lord.” The Large Catechism of the same year is essentially the same, asserting the full divinity and humanity of Christ. In both texts, I would maintain that a two-nature Christology is assumed. Both texts, however, are more interested in soteriology than in the technical aspects of Christological doctrine; soteriology and Christology are intimately linked in Luther—as, in fact, is also the case with Leo himself. Throughout his various writings, moreover, Luther continually affirms and, when necessary, explicates a two-nature Christology in line with Chalcedon. Thus, his two catechisms share this affirmation when they state that Jesus is both God and man. The Lutheran tradition, through Melanchthon’s Augsburg Confession (1530), embraces the two natures of Christ in the confession’s third article, and, in Lutheran fashion, spends more time on soteriology than the two natures. Such a concern makes sense, given the theological stakes of the first half of the sixteenth century.
Turning to the Reformed confessions and catechisms, two natures of Christ are affirmed throughout the sixteenth century. The Belgic Confession (1561), Articles 18 and 19, even cites Leo’s proof text for the two natures, Philippians 2:5–11. The Heidelberg Catechism (1563), Q. 35, affirms the fullness of the deity of the Son of God and his assumption of a complete human nature, explaining in Q. 36 that this was undertaken for our salvation. The Second Helvetic Confession (1562) goes into more detail than most on this point in Chapter XI with words that echo very strongly the Chalcedonian definition of the faith, saying that the two natures “are bound and united with one another in such a way that they are not absorbed, or confused, or mixed, but are united or joined together in one person the properties of the natures being unimpaired and permanent.” This confession, moreover, goes on to accept the communicatio idiomatum, whereas most confessions and catechisms, due to their terse nature, do not go into such details.
The formularies of the English Reformation sound a similar note as on the continent—a general embrace of two-nature Christology without a thorough engagement with the niceties of the doctrine. Again, this is understandable given the nature of the texts. Thus, The Bishops’ Book (1537), in its interpretation of the second and third articles of the Apostles’ Creed, affirms both the fullness of Christ’s deity, in the discussion of Article 2, and his taking on of a full (yet unfallen) human nature under Article 3. Unsurprisingly, The King’s Book of 1543 is much the same.
The evolution of the English Reformation compels us to consider the 39 Articles of Religion (1571), the Elizabethan revision of Cranmer’s 42 Articles (1552). Article II states Chalcedonian Christology quite clearly: “that two whole and perfect Natures, …the Godhead and Manhood, were joined together in one Person, never to be divided, whereof is one Christ, very God, and very Man.” The catechism as included in the 1549, 1552, and 1559 Book of Common Prayer does not deal with the natures of Christ, but the two natures are embraced, for example, in the Holy Communion of 1552 stating “the redempcyon of the worlde by the death and passyon of our Saviour Chryst, both God and man.” In the Books of Homilies, no single passage or phrase could be taken to demonstrate their embrace of Chalcedon, but two-nature Christology is part of the fabric of the homilies, especially the “Homily of the Salvation of Mankind.” By the sixteenth century, the teachings of Leo and Chalcedon were simply in the blood of Latin Christendom and their soteriological import was never passed over. Nevertheless, the Reformers still turned explicitly to Leo in their own research and articulation of doctrine, especially as more of his letters became more available throughout the sixteenth century.
The “sacred philology” of the sixteenth century made an increasing number of Leo’s letters available in print as the century drew on, beginning with reprintings of Giovanni Bussi’s 1470 edition of five letters in 1505 and 1511, but really moving forward in 1524 when Merlinus produced an edition of Pseudo-Isidore with ninety-four of Leo’s letters. An edition devoted to Leo alone would come with Pierre Crabbé in 1551. Seven more editions of Leo’s letters would follow up to the year 1591. These sixteenth-century editions of Leo’s letters were printed throughout Europe, at Paris, Cologne, Leuven, Antwerp, Venice, Rome, and elsewhere. Given the references to Leo in sixteenth-century Protestant writers, we know that copies of his letters were available to them. The number of such writers is vast; some prominent names, besides the three discussed below, are Heinrich Bullinger, Martin Chemnitz, Thomas Cranmer, John Jewell, and Philip Melanchthon. Of these, Chemnitz is the one with the greatest likelihood of fruitful future research.
John Calvin, throughout his discussion of Christology in The Institutes of the Christian Religion 2.12–17, maintains, defends, and upholds through Scripture and reason the Chalcedonian doctrine of the two natures of Christ. Straight out of the gate in 2.14, where this topic is discussed most intensively, Calvin sounds a Chalcedonian note, citing the post-Chalcedonian Athanasian Creed: “the Son of God became the Son of man, not by confusion of substance, but by unity of person.” Calvin, like Leo and the Council of Chalcedon, seeks to articulate the fullness of the unity of Christ’s person on the one hand, and the lack of mingling of the two natures on the other. After making the soul-body analogy from Augustine, Calvin discusses how the divine and human natures in Christ operate, saying that each retains its own properties, which lies at the heart of Leo’s famous passage that begins, “For each form does what is proper to it.” Just as Leo includes in that passage the statement that the natures operate “in communion with one another,” so does Calvin go on to say, “This combination of a twofold nature in Christ they express so carefully, that they sometimes communicate them with each other, a figure of speech which the ancients termed idiomaton koinonia (a communication of properties).” Leo drives at this point in the Tome, saying, “For although in the Lord Jesus Christ there is one person of God and man, nevertheless the injury common to both is from one, and the glory common to both is from the other. For from ours he has a humanity less than the Father, and from the Father he has a divinity equal with the Father.” Although Calvin does not here explicitly cite Leo, the Christological doctrine is the same.
Calvin does cite Leo elsewhere in the Institutes. In 3.5.3, he cites Ep. 124.4 to the monks of Palestine where Leo argues that the deaths of martyrs are not efficacious for the salvation of anyone as evidence of the Fathers being against indulgences and merits of the martyrs. While this final passage from Leo was being used in a context beyond Christology, it is clear that Leo’s main legacy in Calvin, as in the Church at large, lies in Christology, for Leo’s letter to the monks of Palestine is one of his major Christological texts. Calvin’s Institutes do not engage with Christology at length, given its nature as a broad overview of Christian theology. For a more thorough treatment of Christology and richer engagement with Leo, we turn to Peter Martyr Vermigli.
In the Reformation era, Christological questions arose as part of the Reformers’ attempts to articulate a philosophically coherent, biblically faithful eucharistic theology as an alternative to the Roman doctrine of transubstantiation. This, however, led to the intramural Protestant dispute between the Lutherans and Reformed over “the doctrine of ubiquity.” This doctrine, taken up by certain Lutheran theologians, held that, along with his divine nature, the human body of Christ was present everywhere, allowing his body and blood to therefore be present in the elements of the Lord’s Supper. An inability to find agreement upon the sacraments lay behind Luther and Zwingli’s infamous parting of the ways at the Colloquy of Marburg in 1529, and lay at the root of Lutheran-Reformed division throughout the Reformation era and to this day.
Peter Martyr Vermigli’s final work, Dialogue on the Two Natures in Christ (1561), was part of this debate, being a response to Lutheran Johannes Brenz’s De personali unione duarum naturarum in Christo. Throughout the Dialogue, the protagonist representing Vermigli, called Orothetes, debates one Pantachus. Many of Pantachus’s arguments are taken directly from Brenz’s work, and many of the patristic passages discussed by Orothetes are likewise drawn from Brenz. At a simple, surface level, the aim of the Dialogue is to refute Brenz’s De personali unione. However, if all Vermigli did was demonstrate that ubiquity was false, taking 203 pages to do so would perhaps be beating a dead horse. Whilst refuting Brenz, Vermigli simultaneously lays out an orthodox, Protestant exposition of the doctrine of two natures in Christ, discussing the fullness of the humanity and of the divinity, the maintenance of their properties as per Chalcedon, and a thoroughgoing discussion of the communicatio idiomatum, the primary disputed point between the Reformed and the Lutherans.
Because of the breadth of space available to him, Vermigli goes beyond the more basic engagement with Chalcedonian Christology found in the formularies and Calvin’s Institutes. Taking such theology as (mostly) agreed between Orothetes and Pantachus, his discussion is largely taken up with the interpretation of the Church Fathers’ Christology. Scripture itself plays an important role, but since the interpretation of Scripture is part of the matter under dispute, the Fathers are also important, as both Lutherans and Reformed muster them in support.
Vermigli explicitly cites Leo on the communicatio idiomatum, using the same passage that we earlier saw only paralleled in Calvin: “Each nature in communion with the other carries out what is proper to it.” Immediately after marshalling this passage of Leo’s, Vermigli draws on another Leo passage, from Leo’s “Second Sermon on the Resurrection,” to show that the communicatio idiomatum does not destroy either nature but leaves them intact, and then uses later passages in the same sermon to show that, although the properties of the natures are intact, nevertheless, they are fully united in a single, undivided person. Vermigli’s discussion then proceeds with the Second Tome, in which it is shown that the communicatio idiomatum enables us to say that the Son of God suffered, even though God himself is by nature impassible.
The final Leo passage in this stage of Vermigli’s argument is from Leo’s letter to Theodoret after Chalcedon, which Vermigli uses to vindicate Theodoret of Cyrrhus as an orthodox Father for appeal in this matter. Vindicating Theodoret is necessary because Vermigli frequently turns to Theodoret even though he opposed Cyril of Alexandria—and Cyril was a favourite of Brenz’s. A critique of Leo’s Tome that gains its most pointed form in Severus of Antioch in the 500s but persists to this day is that he is insufficiently grounded in the hypostatic union and the communicatio idiomatum. Severus even uses the aforementioned passage from the Tome (“Each nature in communion…”) to prove that Leo does not truly believe in either of these doctrines. In other words, Vermigli is disarming a 1000-year-old criticism of traditional, Latin Christology as he makes his way through the controversies of his own day.
Vermigli cites Leo a second time, referencing one of his many letters to Julian of Cos, showing that Leo rejects the implication of assumptus homo language that the human person of Jesus took up God—“rather it was created by the assumption itself.” That is to say, the hypostatic union of human and divine is thoroughgoing and, temporally speaking, coexistent with the entire incarnation of the God-Word. Vermigli even goes on to show how this statement of Leo’s works in tandem with the work of Cyril of Alexandria, the great exponent of Christ’s complete and utter unity. Vermigli’s final citation from Leo is not only part of the clinching patristic argument against ubiquity but also part of the implications of the historic Christology of the Fathers: Christ’s ascension enables all Christian disciples to receive the blessings of the incarnation.
Vermigli’s use of Leo goes beyond prooftexting and is itself a deft display of the historic, Latin view of Christology, unpacking the implications of Leo’s teaching not simply for the two natures but also for the hypostatic union, the communicatio idiomatum, and the benefits we receive from Christ, besides finding contemporary application in Vermigli’s opposition to the doctrine of ubiquity. Furthermore, Vermigli is not simply “Leonine,” but draws richly from across the Greek and Latin Fathers in his argumentation and interpretation of Scripture, using Fathers from before and after Chalcedon, as well as those who highlight the unity of Christ such as Cyril and those who emphasize the reality of the two natures such Theodoret. In other words, Vermigli not only stands within the tradition but consolidates and synthesizes it for his own generation.
Hooker’s discussion of Christology comes in The Laws of Ecclesiastical Polity, Book V, Chapters 50–55, beginning in chapter 50 with sacraments in general, then moving into the good and necessary consequences for the Christian and the Church in 56–57. Only after discussing Christology and its wider implications does Hooker consider the two dominical sacraments in particular. Christology is part of his discussion of sacraments because “the Sacraments do serve to make us partakers of Christ” (5.50.3). Answering the question of how they do so necessitates an analysis of traditional, Chalcedonian Christology. Like Vermigli, Hooker draws from a broad range of Fathers in his discussion of Christology, pre- and post-Chalcedon. Among the fifth-century Fathers we find Augustine of Hippo, Cyril of Alexandria, Theodoret of Cyrrhus, Vincent of Lérins, and Leo the Great. Again, like Vermigli, Hooker seeks to balance the concerns of unity found in the arguments of Cyril and of duality found in the works of Theodoret and Leo. However, unlike in Vermigli, most patristic quotations are in the notes, and the argument itself primarily uses Hooker’s own words with the Fathers to back him up. Of course, Hooker’s intentions were different from Vermigli’s, although both discuss Christology in a sacramental context.
Hooker writes, “These natures from the moment of their first combination have been and are forever inseparable” (5.52.4). Besides arguing for the Chalcedonian indivisibility of the natures, Hooker also argues, in 5.53.1, that there is no commingling or confusion of the natures, then affirms the reality of the hypostatic union, which he discusses for the rest of Chapter 53. He also addresses the communicatio idiomatum. Hooker closes Chapter 54 with a discussion of the Council of Chalcedon’s four adverbs relating to the union, which he translates as truly, perfectly, indivisibly, distinctly: “Within the compass of which four heads, I may truly affirm, that all the heresies which touch but the person of Jesus Christ, whether they have risen in these later days, or in any age heretofore, may be with great facility brought to confine themselves” (5.54.10). It is perhaps noteworthy that Hooker brings forth Chalcedon from his arsenal when he has already made his argument—it is a conclusion, not a premise. That said, Chalcedonian Christology is not the end goal in the Laws—the corollary of union with Christ is a corollary found throughout the post-Chalcedonian Fathers, such as Leontius of Byzantium, Maximus the Confessor, and John of Damascus. Hooker is right on track with the tradition.
In 5.56.10, Hooker gives us the great payoff for the spiritual life that is ours as a result of the hypostatic union, the communicatio idiomatum, the fullness of the two natures in the one person of Christ:
Christ is whole with the whole Church, and whole with every part of the Church, as touching his Person, which can no way divide itself, or be possessed by degrees and portions. But the participation of Christ importeth, besides the presence of Christ’s Person, and besides the mystical copulation thereof with the parts and members of his whole Church, a true actual influence of grace whereby the life which we live according to godliness is his, and from him we receive those perfections wherein our eternal happiness consisteth.
Richard Hooker is not simply parroting patristic Christology. Like Vermigli, he synthesizes it and finds for us corollaries and consequences. As a consequence of the hypostatic union, we ourselves are able to be united to Christ in baptism and in holy communion. We are partakers in the divine life. This is the practical reality that is at stake in orthodox Christology. It is the same reality pressed for by Leo.
In the essay that introduced me to Christology, Robert W. Jenson argues that Western Christology is ultimately deficient because it relies too heavily on Leo and never moves beyond him to address the concerns of the Miaphysite movement. However, what I hope I have shown in the above is that, while Leo’s two-nature Christology is prominent in the theology of the Reformation, early Protestant theologians engage with Leo and his teaching in the context of a wide array of other Fathers, from East and West, and address the concerns of the Miaphysite movement by showing the unity of the single hypostasis of Christ as articulated by Leo and interpreted by Cyril, the Scholastics, and the Reformers’ own logical analysis of both the Fathers and the Scriptures. In this way, the foundational authors of Protestantism show themselves to be heirs of the tradition who are actively and consciously engaging it as they produce coherent articulations and syntheses of the tradition for their own time. Their Christology is neither incoherent nor deficient, and we would do well to internalize their teachings and their approach as we seek to bring the riches of classic, orthodox Christology to light in our own day.
Matthew J. Hoskin teaches ancient and medieval Christian history for Davenant Hall, and theology for Ryle Seminary in Ottawa, Ontario. His research focuses on manuscripts, monks, popes, canon law, and councils, which all feature in his book The Manuscripts of Leo the Great’s Letters (Brepols, 2022), and he blogs about the historic faith at Classically Christian. He lives on Superior’s northern shore in Thunder Bay, Ontario, with his wife and sons.
 Matthew J. J. Hoskin, The Manuscripts of Pope Leo the Great’s Letters: The Transmission and Reception of Papal Documents in Late Antiquity and the Middle Ages (Turnhout: Brepols, 2022), 466.
 Not that printed books were produced in such a way all the time. Ariosto, for example, would actually modify the text of Orlando Furioso during printings, which means that a critical edition of the poem must take into account not only each printing but even each copy, treating each copy like a manuscript.
 I leave open the question of how “Reformed” the Church of England was or is. That it has historically been rooted in the Fathers from the Reformation to the nineteenth century, however, should be uncontroversial. For more, see Jean-Louis Quantin, The Church of England and Christian Antiquity (Oxford: Oxford University Press, 2009).
 See Martin Chemnitz, The Two Natures in Christ, trans. Jacob A. O. Preus (Saint Louis: Concordia Publishing House, 2008).
 Leo’s Tome is officially numbered as Epistle 28, in the standard Latin edition by the Ballerini brothers, and thus in Patrologia Latina vol. 54; Nicene and Post-Nicene Fathers, Series2 (henceforth NPNF2), vol. 12; and Edmund Hunt’s translation of the letters in the series The Fathers of the Church. I use the edition of Carlos Silva-Tarouca, Textus et Documenta: Series Theologica 9, S. Leonis Magni Tomus ad Flavianum Episc. Constantinopolitanum (Rome: Pontificia Universitas Gregoriana, 1932), 20–33.
 Eutyches has become infamous for the heresy that bears his name, Eutychianism—the belief that Christ has one nature in which his humanity is swallowed up by his divinity. Whether Eutyches really held to this view is contested. He seems to have been a well-meaning but confused thinker, a lifelong monk ill-equipped for theological precision.
 For my own translation of this definition of faith, see “Chalcedonian Definition of the Faith,” Classically Christian, accessed December 1, 2022, https://thepocketscroll.wordpress.com/classic-christian-texts/the-chalcedonian-definition-of-the-faith/.
 The revised version is “Ep. 165” in the Ballerini, PL 54, NPNF2, and Fathers of the Church; Silva-Tarouca, Series Theologica 9, 44–58.
 For a summary of this reframing, see Philip L. Barclift, “The Shifting Tones of Pope Leo the Great’s Christological Vocabulary,” Church History 66, no. 2 (June 1997): 221–39, https://doi.org/10.2307/3170655. In Ep. 165, Leo shifts away from naturae to formae, using Philippians 2:5–11 as his terminological cue.
 In Greek: ἀσυγχύτως, ἀτρέπτως, ἀδιαιφέτως, ἀχωρίστως.
 Martin Luther, Small Catechism, accessed December 1, 2022, https://catechism.cph.org/en/creed.html.
 This is the thesis of Bernard Green, The Soteriology of Leo the Great (Oxford: Oxford University Press, 2008).
 See Matthieu Arnold, “Luther on Christ’s Person and Work,” in The Oxford Handbook of Martin Luther’s Theology, ed. Robert Kolb, Irene Dingel, and L’ubomír Batka (Oxford: Oxford University Press, 2014), https://doi.org/10.1093/oxfordhb/9780199604708.013.005.
 Second Helvetic Confession, accessed December 1, 2022, https://www.ccel.org/creeds/helvetic.htm.
 See “The Bishops’ Book: The Institution of a Christian Man,” in Confessional Documents Issued by Henry VIII and Thomas Cranmer, ed. Charles Lloyd and Andrew Raines (Galesburg: Seminary Street Press, 2022), 47, 49–50. The Bishops’ Book (the popular name for The Institution of a Christian Man) was the official interpretation of the Ten Articles, the Church of England’s first confession after the break from Rome.
 See “The King’s Book” in Confessional Documents, 212. The King’s Book was a revised version of The Bishops’ Book, published after Henry VIII expressed concerns to Thomas Cranmer about the latter’s more explicitly Protestant theology (in contrast to the more circumspect Ten Articles).
 Hoskin, Manuscripts, 72–74.
 John Calvin, Institutes of the Christian Religion, trans. Henry Beveridge (Peabody: Hendrickson, 2008), 2.14.1, 309. Italics mine.
 In Latin: Agit enim utraque forma. Leo the Great, “Ep. 28.4,” in NPNF2 12.40.
 Calvin, Institutes, 310.
 Leo the Great, Tome, Ep. 28.4–5 (trans. author). For the Latin edition, see Silva-Tarouca, Series Theologica 9,122ff.; see also NPNF2 12.41.
 Agit enim utraque forma. Leo, Ep. 28.4, quoted in Vermigli, Dialogue on the Two Natures in Christ, trans. John Patrick Donnelly (Kirksville: Northeast Missouri State University, 1994; repr. Landrum, SC: Davenant Press, 2018), 53.
 Severus, “Ad Nephalium, Oratio 2,” in Severus of Antioch, trans. Pauline Allen and C. T. R. Hayward (New York: Routledge, 2004), 62. For this critique’s persistence to this day, see the conclusion of this essay.
 Vermigli, Dialogue on the Two Natures, 59–60.
 Vermigli, Dialogue on the Two Natures, 164.
 Richard Hooker, Laws of Ecclesiastical Polity,ed. Ronald Bayne (London: J. M. Dent & Co, 1907), vol. 2.
 R. W. Jenson, “With No Qualifications: The Christological Maximalism of the Christian East,” in Ancient and Postmodern Christianity: Paleo-Orthodoxy in the 21st Century, ed. K. Tanner and C. A. Hall (Downers Grove: InterVarsity Press, 2002), 13–22.