I will first make a few introductory comments pertaining to the development of doctrine. Second, I will treat the patristic and conciliar dogmatic development concerning the conception and articulation of the Incarnation. I will then, briefly, provide St. Thomas Aquinas’s understanding of the incarnational union as a mixed relation. Lastly, I will address the enduring dogmatic significance of the hypostatic union. In one sense, I will not break new theological ground. Much of what I say will not be new to most of you. Nonetheless, I hope that what I say is new in the sense that I hope to demonstrate the permanent doctrinal significance of the theological and conciliar development concerning the hypostatic union.
Initial Comments Regarding the Church’s Understanding of the Incarnation
When treating the doctrines of the Church, or what I like to term, the mysteries of the faith, what is often forgotten is the inherent dynamism within faith itself that compels doctrinal development, that is, faith’s desire to understand more fully the divine mysteries. St. Augustine (354–430), and later St. Anselm (1033–1109), termed this innate dynamism “faith seeking understanding.” The Holy Spirit impels faith to grasp more comprehensively what has been revealed. The absence of such a Spirit-induced doctrinal inquisitiveness testifies to a lifeless faith. What is believed lies dormant within the person, and such dormancy testifies to the person’s lack of love for the faith that he or she professes. The Church possessed such a doctrinal dynamism from its onset, as exemplified in the faithful and in the early bishops and theologians. This faith-seeking-understanding is particularly seen with regard to the Incarnation and the Trinity.
Second, although the Church progressed in its understanding of the Incarnation and the Trinity, various heresies, as we will see, did arise. Importantly, these heresies often became a catalyst for doctrinal development. The Fathers of the Church and the early councils were forced to defend, clarify and proclaim who Jesus truly is and the nature of the one God as a trinity of persons. This demanded that the Church conceive more coherently and articulate more intelligibly the mysteries of the faith. It was not that the Church was unsure as to what it professed. Rather, it was precisely because she did know the mysteries of faith that she wanted to ensure that they were properly understood and confessed.
Third, although the Fathers of the Church and the early councils (Nicaea, 325; Ephesus, 431; and Chalcedon, 451) would not have expressed the following in the manner that I am about to, they would have instinctively known that such must be the case. Because of faith’s demand, the Fathers and councils ardently defended and dogmatically defined three truths that must be simultaneously affirmed of Jesus if one is to conceive properly and articulate accurately the Incarnation: (1) it is truly the Son of God who is man, which highlights that the Son is God as the Father is God. (2) It must be truly man that the Son of God is, which emphasizes the Son’s authentic humanity. (3) The Son of God must truly be man, which demands that the Son of God actually exists ontologically as man. Every Christological heresy, then and now, denies one of these three incarnational truths.
Fourth, taken together, the three incarnational truths then sanction and mandate the predication of divine and human attributes to one and the same person of the Son. To declare, for example, that “God is born,” or that “God suffers and dies” accentuates that it is truly the Son of God who actually exists as a real man, and so is born and dies as man. Such incarnational predication came to be known as the communication of idioms (communicatio idiomata). Significantly, as we will presently see, heretics denied one of the three incarnational truths precisely because of the use of the communication of idioms. Conversely, the Fathers and councils defended its use and in so doing fostered a doctrinally authentic understanding of the Incarnation, again, specifically because the communication of idioms contained within it all three incarnational truths.
It Is Truly the Son of God Who Is Man
With the New Testament as the basis of her teaching, the early Church proclaimed that Jesus is truly God. Ignatius of Antioch (c. 107), for example, in his seven extant letters, calls Jesus simply “God,” fourteen times, and on eight of those occasions affirms him to be ho theos (the God). Inevitably the question arose: how can God be one and the Son be God? If the Father is God and the Son is God, does this not demand that there be two gods, which is obviously contrary to the faith? Various attempts were made to reconcile this seeming doctrinal conundrum.
Sabellius, a third-century Roman theologian, promoted the view that the Father, the Son, and the Holy Spirit were merely different modes or expressions of the one God, and thus they were not distinct persons or subjects in their own right. In becoming man, God modally expressed himself as “Son.” While this may preserve the oneness of God, it is contrary to the New Testament proclamation that the Father, the Son, and the Holy Spirit each possessed a distinct identity. Moreover, it implicitly denied that the distinct person of the Son actually became man, for there really is no Son to do so. Ultimately, Pope Callistus excommunicated Sabellius for teaching heresy. The issue, nonetheless, remained—how to conceive properly the one God as a trinity of persons.
Origen (185–254), in contrast to Sabellius, underscored the distinct identities of the three divine persons. He is the first to state explicitly that, since the Father is eternally the Father, the Son is eternally the Father’s Son, and so a distinct person (hypostasis) from the Father. Origen conceived the Trinity as the Son and Holy Spirit emanating from the Father and so sharing in his one divine nature. Although such an understanding ensures the unique integrity of each divine person, it implies that there is an ontological hierarchy within the Godhead—the Son and Holy Spirit are not as divine as the Father, for only the Father alone possesses the whole of the Godhead. The early theologians, such as Origen, wanted to uphold the Church’s faith concerning Jesus’ divinity. However, they were struggling to maintain Jesus’ divinity while simultaneously upholding God’s oneness.
The issue of Jesus being truly the Father’s divine Son came to a climax with the teaching of Arius (d. 336), a priest of Alexandria. Previous attempts failed at reconciling the oneness of God with the Son being God, so Arius concluded that the Son must be a creature—the first and most divine like of all creation, but a creature nonetheless. If God is unbegotten and the Son of God is begotten, then the Son must be made as is all of creation. Moreover, since the Son became man, he must have changed in so becoming, and he, therefore cannot be God, for God is immutable. Likewise, being human, the Son must experience human weaknesses: thirst, hunger, suffering and death. These frailties are also unbecoming of God since God is impassible. The predicating of human attributes to the Son—the communication of idioms—demands, for Arius, that he not be God but a creature.
In response to Arius’s denial of the full divinity of the Son, the bishops held a Council at Nicaea in 325. The problem that confronted the majority of the bishops was not whether Jesus was truly God—that was what the Church always believed. Rather, the issue that lay before them was how they could simultaneously conceive the divinity of Jesus and the oneness of God. The result of their deliberations was the Nicene Creed, which dogmatically declared that the Son of God is “begotten from the Father, only begotten, that is, from the substance of the Father, God from God, light from light, true God from true God, begotten not made, consubstantial (homoousios) with the Father.” The Council Fathers make a definitive distinction, one that was previously not clearly made. The Son is begotten of the Father and not made. What is begotten is always of the same nature as the begetter. What is made is always of a different nature than the maker. Ants make anthills, but beget other ants, etc. God, therefore, created the world but begot his Son, and the Son, therefore, possesses the same divine nature as the Father—the Son is God as the Father is God. Now, homoousios could be interpreted in diverse ways, as the raucous post-Nicene history clearly bears witness. However, Athanasius (c. 296–373), the great defender and interpreter of the Nicene Creed, perceived that for the Son to be homoousios with the Father demanded that the Son not simply possess the same divine substance of the Father after the manner of two copper coins being made of the same substance, but that the Father and the Son are one and the same God. The Godhead does not reside in the Father alone, as was often formerly presumed, which he shared, to a lesser degree, with his Son. Rather, the one nature of God is the Father eternally begetting his Son (and spirating his Holy Spirit, but that is a later development). The one God is the eternal act of Father begetting his Son, and in so doing sharing with the Son the fullness of his divinity. In this light, contrary to Arius, the oneness of God and the distinction of persons is properly conceived and clearly articulated. Likewise, in full accord with the New Testament proclamation that God is one and that the one God is the inter-relationship of the Father, the Son, and the Holy Spirit. The Nicene Creed, then, establishes the enduring doctrinal tradition of the Church—past, present, and future.
Moreover, I would argue that homoousios is the most important word in the whole of human history, and that it will forever be so. It preserves, irrevocably, the full divinity of the Son within the Trinity, while preserving, irrevocably, the full divinity of the Son within the Incarnation. In so doing, it preserves, irrevocably, the guarantee of humankind’s salvation. Only if Jesus is the Father’s incarnate divine Son, homoousios with the Father, can he adequately enact the Father’s saving work. Moreover, as we will see, the divine Son, who is homoousios with the Father, must also be homoousios with us who are human, for only then can he save humankind as an authentic man. Thus, having declared that the Son is God as the Father is God, Nicaea immediately professed that the same divine Son, “because of us men and because of our salvation came down and became incarnate, becoming man, suffered and rose again on the third day, ascended into heaven, and will come to judge the living and the dead.” With this declaration, the communication of idioms comes dramatically into play. By becoming man, the Son is able to suffer, die and rise. Thus, once the divinity of the Son was dogmatically declared, further Christological issues arose—that of Jesus’ full humanity and the manner in which the divinity and humanity were united.
It Is Truly Man That the Son of God Is
Few, if anyone, today deny that Jesus was a man. However, one of the earliest heresies did so. Docetism (coming from the Greek word dokeo, meaning “to seem”) held that the Son only “seemed” or “appeared” to take on human flesh. Thus, the Son only “appeared” to be born, eat, suffer, and die. The Docetists concluded falsely, based on the communication of idioms, that if Jesus is the divine Son of God, he could not actually be united to human flesh and so suffer and die. As Arius denied the Son’s divinity in view of his becoming flesh, and so suffering and dying, so the Docetists denied the Son’s humanity in view of his being the Father’s divine Son. Ignatius of Antioch strenuously argued against the Docetists. He declared that if Jesus only “seemed” to be man and, therefore, only pretended to suffer, die and rise as man, then our salvation is a mere pretense as well. For Ignatius, only if the Son of God actually existed as an authentic man could we, as real human beings of flesh and blood, be saved.
A more sophisticated undermining of Jesus’ humanity arose in the fourth century with the teaching of Apollinarius of Laodicea (c. 310–c. 390). Along with his friend Athanasius, Apollinarius was a staunch defender of Jesus’ divinity. Likewise, he realized that the Son of God could not have adopted an existing man, but needed to be ontologically united to his flesh. Here Apollinarius perceived a twofold problem. If the Son of God was complete in his divinity and the man Jesus was complete in his humanity, there would be two whole substances and, thus, they could not be ontologically united so as to become one. In order to resolve this conundrum, Apollinarius argued that as the soul is united to the body so as to form a human being, so the Son of God was united to flesh so as to form the one reality of Christ. Thus, Jesus did not have a human soul, and so he was not like us, but rather he was a “heavenly man.” Moreover, Apollinarius argued that if Jesus possessed a soul, with its defective intellect and will, he would be prone to sin. It is, therefore, salvifically advantageous that Christ did not have a human soul, for he would always be obedient to his Father’s will. The Son, then, became the sole governing principle of his flesh. The Son of God is, therefore, not an authentic human being.
The Cappadocians, Basil the Great (330–379), Gregory of Nyssa (330–395), and Gregory of Nazianzus (330–390), vehemently condemned Apollinarius. They immediately recognized that his Christology was inherently Docetic, for Jesus lacked an essential aspect of his humanity—a human soul, with its human intellect and will. The primary argument against Apollinarius’s position was soteriological. Whereas Apollinarius held that Jesus could not have had a human soul, which would necessarily have been defective, Gregory of Nazianzus astutely argued that it is precisely because the human soul was sinfully defective that the Son of God needed to assume it in order to save it. Gregory declared that anyone who has placed his hope in a human being who lacks a human mind is himself truly mindless, for he does not deserve a complete salvation. For Gregory, what was not assumed was not healed. What is saved is that which was united to God.
If it was half of Adam that fell, then half might be assumed and saved. But if it was the whole of Adam that fell, it is united to the whole of him who was begotten and gains complete salvation. Then, let them not envy us this complete salvation, nor equip the Savior only with bones and sinew, with mere representation of a man.
With the vibrant Cappadocian defense and proclamation of Jesus’ full humanity, a humanity like unto our own, the Church doctrinally set in place the second incarnational truth—it is truly man that the Son of God is. However, the metaphysics of how Jesus, the incarnate Son of God, can be fully divine and fully human, without jeopardizing either his divinity or his humanity, has yet to properly addressed. This will be the noble work of the Alexandrians—Athanasius and Cyril.
It Is the Son of God Who Truly Is Man
The early Church, having doctrinally declared that Jesus is truly God and truly man, was next confronted with the need to properly conceive the nature of the incarnational “becoming,” a “becoming” that must terminate in an incarnational “is.” The communication of idioms demanded such clarity, for it postulates that the Son of God actually existed as man, and so it was truly the Son who was born, suffered, and died as man. Ignatius of Antioch, who as noted earlier opposed the Docetists, speaks graphically of “divine blood,” and “the passion of my God.” God as God does not have blood, nor does he suffer as God, but if God actually did come to exist as man, then he truly does have blood and can actually suffer.
For Athanasius, if the Son is to save us, he needed to assume an authentic humanity. He states:
Just as we should not be delivered from sin and the curse of death if the flesh taken by the Word were not human flesh, so likewise man would not be deified were he who became incarnated not the true and real Word of the Father.
Such an understanding demanded that the divine Son ontologically unite humanity to himself. Athanasius declares that the Word “became man and did not come into man.” The Son’s existence as man differs in kind from the manner in which he dwelt in the prophets or saints in the past. Adoptionism—“coming into a man”—is not a viable option for a true understanding of the incarnational “becoming.” For Athanasius, the Word “has become flesh not by being changed into flesh, but because he has assumed on our behalf living flesh and became man.” Thus, “become” means neither “come into a man” nor “change into a man.” Rather, it singularly, in a manner never before used, means “comes to exist as man.” There is neither a change in the Son’s divinity nor in his assumed humanity. What has changed is that the eternal Son of God now exists as man, whereas before he did not.
Such an incarnational understanding of the term “become” is witnessed in Athanasius’s use of the communication of idioms:
When he [the Word] is said to hunger and thirst and to toil, and not to know, and to sleep, and to weep . . . and in a word to undergo all that belongs to the flesh . . . let no one stumble at what belongs to man, but rather let a man know that in nature the Word himself is impassible, and yet because of the flesh which he puts on, these are ascribed to him, since they are proper to the flesh, and the body is proper to the Savior.
For Athanasius, because the Son of God actually came to exist as man, all that pertains to being human is rightly attributed to him.
What was inherent within the progressive Christological development from the time of Ignatius of Antioch to Athanasius, and what was doctrinally professed in the Nicene Creed, now comes to its dogmatic maturity. Not surprisingly, this was occasioned by a heretical understanding of what it means for the Word to become man and the nature of the ensuing incarnational union between the Word’s divinity and his humanity.
In 428, Nestorius (d. 451), the patriarch of Constantinople, was asked whether it was appropriate to call Mary Theotokos, Mother of God. He replied that it was of doubtful validity, for it implied an erroneous understanding of the Incarnation. If Mary is the Mother of God, then the Son of God changed in becoming man, and, in so doing, he would then endure human experiences, all of which were incompatible with his impassible divinity. For Nestorius, the incarnational becoming gave rise to a moral union between the Son’s divinity and his humanity wherein they remained separate, though closely aligned, thus protecting the Son’s divine immutability and impassibility.
Cyril, the patriarch of Alexandria (375–444), found Nestorius’s understanding untenable. Cyril recognized that the traditional Marian title protected a proper understanding of the Incarnation. If Mary is not the Mother of God, then the Son of God did not actually come to exist as man, and so could not actually be conceived within her womb and be born of her. Moreover, if the Son did not truly exist as man, the Son could not truly suffer and die for humankind’s salvation. Again, the entire controversy centered on the validity of the use of the communication of idioms and the proper understanding of the Incarnation that it validated. Cyril’s positive conception and articulation of the Incarnation gave rise to what we today term the hypostatic union. He stated:
We do not mean that the nature of the Word was changed and made flesh or, on the other hand, that he was transformed into a complete man consisting of soul and body, but instead we affirm this: that the Word personally (kath hypostasin—according to the person) united to himself flesh, endowed with life and reason, in a manner mysterious and inconceivable, and became man.
The ecumenical council held in Ephesus in 431, confirmed Cyril’s Second Letter to Nestorius as an authentic expression of the faith, and in so doing dogmatically sanctioned Cyril’s notion of the hypostatic union, namely, that the humanity was united to the person of the Word.
With the death of Cyril in 444, the more radical Alexandrian theologians, Dioscorus and Eutyches, came to the fore. Eutyches (378–454) stated that before the incarnational union there were two natures, but after the union there was only one. Such an understanding became known as Monophysitism, which held that the divinity completely inundated the humanity whereby it lost its authentic humanness. Eutyches was accused of inciting a new form of Docetism and Apollinarianism wherein Christ was no longer fully human. Pope Leo the Great condemned Eutyches (449) in his Tome to Flavian, and called for a council, which was held in Chalcedon in 451. Chalcedon confirmed Leo’s Tome and Cyril’s Second Letter to Nestorius as expressions of the true faith. It also promulgated a creed. The Chalcedon Creed accentuated that “one and the same Son, the same perfect in Godhead and the same perfect in manhood, truly God and truly man [was] . . . consubstantial (homoousios) with the Father in Godhead, and the same consubstantial (homoousios) with us in manhood.” The same Son became man for our salvation “begotten from the Virgin Mary, Theotokos.” The Son was, therefore, “made known in two natures without confusion, without change, without division, without separation, the difference of the natures being by no means removed because of the union, but the property of each nature being preserved and coalescing in one prosopon and one hypostasis—not parted or divided into two prosopa, but one and the same Son, only-begotten divine Word, the Lord Jesus Christ.”
How is it possible that the natures are united such that they are not confused or changed and yet not divided and separate? The answer to this question is extremely important. The difference between the natures is not removed because the incarnational union, the “becoming,” is not the compositional union of the natures—a union wherein the integrity of each would be destroyed. Nonetheless, they are not divided or separated precisely because they are united to one and the same person of the Son—the union is hypostatic. The incarnational “becoming” is the uniting of the humanity to the one person, the one prosopon or one hypostasis, of the Son such that the Son exists both as God and as man. Because the one Son exists as God and man, divine and human attributes are both rightly predicated of one and the same Son. The Council of Chalcedon, therefore, conceived properly and articulated clearly what the Fathers of the Church and the previous councils had instinctively defended and professed—the hypostatic nature of the incarnational “becoming” and the ensuing personal ontological union. In dogmatically defining the hypostatic union, the council also doctrinally sanctioned the threefold incarnational truth manifested in the communication of idioms—that it is truly the Son of God who is man; that it is truly man that the Son of God is; and that the Son of God truly exists as man. Jesus is, then, truly the Son of God truly existing as a true man, and, therefore, all that pertains to his divine and human existence is predicated of him.
Thomas Aquinas (1225–1274) provided greater philosophical and theological depth to the Chalcedonian definition, and to that I now turn.
Thomas Aquinas: The Incarnation as a Mixed Relation
First, in the light of Cyril of Alexandria and the Council of Chalcedon, Aquinas held that the Son of God “subsists,” that is, exists as man. He likewise insisted that the human nature was united to the Son in a hypostatic manner in that the human nature was united to the Son as the Son personally existed as God, what he termed the Son’s esse personale. Here, Aquinas employs his understanding of a mixed relation.
Such a relationship is established when the two related terms exist in different ontological orders. For example, in the act of creation, what comes to be is related to God as God actually exists as ipsum esse, and in so being related creation comes to be. There is no change in God, for he acts by no other act than the pure act that he is, and there is no change in creation since it simply comes to be. Similarly, within the incarnating act, the incarnational “becoming,” the humanity simultaneously comes to be and is united to the person of the Son as the Son personally exists as God. Again, there is no change either in the Son’s personal existence, since the humanity is ontologically united to him as he personally exists as God. Nor is there a change in the humanity since it simply comes to be in being ontologically united to the Son. Aquinas states:
Since the human nature is united to the Son of God, hypostatically or personally . . . and not accidently, it follows that, by the human nature, there accrued to him no new personal being (esse personale) but only a new relation of pre-existing personal being (esse personale) to the human nature, in such a way that the person is said to subsist not merely in the divine nature but also in the human nature.
Moreover, because the humanity is hypostatically united to the person of the Son as he personally exists as God—that is, to his esse personale—and because the Son comes to exist as man, all that pertains to his human existence is rightly predicated of him, for that is the manner in which the Son newly exists. Thus, Aquinas provides new doctrinal depth to the Chalcedonian understanding of the hypostatic union and, in so doing, additional Christological precision of and confirmation for the use of the communication of idioms.
The Enduring Doctrinal Significance of the Hypostatic Union
By way of conclusion, I would like to make two interrelated points.
First, although I have spoken of the hypostatic union as a progressive doctrinal development within the writings of the Fathers of the Church and in the dogmatic definitions and creeds of the early ecumenical councils, as well as in the Christological thought of Thomas Aquinas, the nature of this development must be properly understood. At times the impression is given that the New Testament, because of its literary genre, does not proclaim fully or unambiguously the Incarnation, and that although it may not contain an erroneous understanding of the Incarnation, it does not offer an understanding that one would classify as doctrinal. Thus, the Fathers of the Church and the early ecumenical councils doctrinally developed what was latent, but not fully present, within the scriptural proclamation and so brought it to dogmatic maturity.
Such an understanding of the development of doctrine is mistaken. The New Testament does not present a theology of the Incarnation in a systematic manner, and it does not address the theological issues that arise from within such a proclamation, such as how the Son can be truly divine and yet God can be one, or how Jesus can be both fully God and fully man. Nonetheless, it does proclaim what is to be believed with the assurance of faith—that the man Jesus is the Father’s divine Son. Thus, the Fathers of the Church and the early councils should not be thought of as supplementing or completing some revelational lacuna in the New Testament kerygma.
What must be noted is that if it is held that the apostolic kerygma did not contain the fullness of revelation, then the theological development that followed upon it could take various equally valid forms, a notion that is frequently found in some contemporary Christologies. Here, the New Testament is seen simply as the source from which various incarnational “models” can be offered; none of which can be declared dogmatically true, for the New Testament itself does not provide one inerrant doctrinal understanding. The Fathers of the Church and the early ecumenical councils, then, merely proposed one particular “incarnational model,” allowing for other incarnational models to be equally advanced. However, the Fathers and councils did not simply offer one “incarnational model” among other possible “models.” Rather, using the New Testament as their foundation, they did something entirely different, and that is now my second point.
The New Testament proclamation of the Incarnation, by necessity, contains within it a metaphysics, an incarnational ontology. The Fathers of the Church brought to the fore, especially in the light of various heresies, the incarnational metaphysics inherent within the scriptural kerygmatic proclamation. The early ecumenical councils dogmatically affirmed this trinitarian and incarnational metaphysics. The Son of God is ontologically homoousios with the Father. Moreover, he is ontologically homoousios with us as a man. He ontologically truly exists as a man, and therefore, all that pertains to his divinity and humanity is rightly predicated of him. Such a doctrinal metaphysical definition is not, then, simply an incarnational “model” alongside other possibilities. Because it is metaphysical in nature, it professes who Jesus truly is—he is the one person of the Son who exists as man. Thus, we perceive the enduring nature of the doctrine of the hypostatic union. The hypostatic union expresses and confirms a metaphysical reality, a reality that is absolutely and utterly true, a reality that actually exists, and so it can never be altered or changed. It endures forever. We may never fully comprehend—not even in heaven—this most sacred mystery of faith, but we know what the mystery is, and before the mystery of Jesus, the Father’s incarnate Son, we bow in praise.
EDITORIAL NOTE: This was delivered as a talk at a symposium in honor of Cardinal Gerhard Mueller, the title of which was What It Means to be Catholic: The Incarnation and the Life of the Church.
 Many of the points in the following presentation can also be found in T.G. Weinandy, “The Incarnation,” in The Oxford Handbook of Catholic Theology, edited by L. Ayres and M.A. Volpe (Oxford: Oxford University Press, 2019), 167–182.
 See T.G. Weinandy, “The Apostolic Christology of Ignatius of Antioch: The Road to Chalcedon,” in Trajectories Through the New Testament and the Apostolic Fathers, ed. by A. Gregory and C. Tucket (Oxford: Oxford University Press, 2005), 71–84.
 For a fuller critical examination of Sabellianism and Origen’s trinitarian and Christological thought, see J.N.D. Kelly, Early Christian Doctrines (London: Adam & Charles Black, 1968 (fourth edition), 119–123.
 Translation of the Nicene Creed taken from Kelly, Ancient Christian Doctrines, 323.
 For a fuller critical examination of the Arian controversy, the Nicene Creed and Athanasius’s defense, see Kelly, Ancient Christian Doctrines, 226–251; T.G. Weinandy, Does God Change?: The Word’s Becoming in the Incarnation (Still River, Massachusetts: St. Bede’s Press, 1985), 3–25; T.G. Weinandy, Athanasius: A Theological Introduction (Washington, DC: reprinted Catholic University of American Press, 2018), 48–80.
 See, for example, Ignatius of Antioch, Letter to the Trallians, 9 and Letter to the Philadelphians, 1–5 in Early Christian Writings: Apostolic Fathers, trans. By M. Staniforth (Baltimore: Penguin Books, 1978).
 Pseudo-Athanasius, Against Apollinarius, 1:2; and Apollinarius, Fragment, 45 in H. Lieztmann, Apollinaris von Laodicea und seine Schule (Tubingen, 1904), 214.
 See Apollinarius, Fragment, 107 (Lieztmann, 232).
 Gregory of Nazianzus, Epistle 101, in Christology of the Later Fathers, ed. E. Hardy, (Philadelphia: The Westminster Press, 1954), 218–219. For a fuller critical examination of Appolinarius and the Cappadocian response, see Weinandy, Does God Change?, 25–29.
 Ignatius of Antioch, Letter to the Ephesians, 1 and 7 and Letter to the Romans, 6.
 Athanasius, Against the Arians, II, 70 in Athanasius: Select Works and Letters in Nicene and Post-Nicene Fathers, ed. A. Robertson (Edinburgh: T&T Clark, 1987).
 Athanasius, Against the Arians, III, 30.
 Athanasius, Letter to Epictetus, 8.
 Athanasius, Against the Arians, III, 34. For a fuller examination of Athanasius’s Christology, see Weinandy, Athanasius, 81–101.
 Cyril of Alexandria, Second Letter to Nestorius, 3 in Cyril of Alexandria: Selected Letters, edited and translated by L. Wickham (Oxford: Clarendon Press, 1983).
 For a fuller critical examination of Cyril of Alexandria’s Christology, T.G. Weinandy, “Cyril and the Mystery of the Incarnation,” in The Theology of St. Cyril of Alexandria: A Critical Appreciation, edited by T.G. Weinandy and D.A. Keating (London: T&T Clarks, 2003), 23–54. See also, T.G. Weinandy, Does God Suffer? (Edinburgh: T&T Clark, 2000), 172–206.
 Translation taken from Kelly, Early Christian Doctrines, 339–340.
 For a fuller theological exegesis of the Chalcedonian Creed, see T.G. Weinandy, Does God Change?, 63–66.
 Thomas Aquinas, Summa Theologica, III, q. 2, a. 6, ad. 2. Translation taken from Summa Theologica, Fathers of the English Dominican Province (Benziger Brothers: New York, 1947).
 Thomas Aquinas, Summa Theologica, III, q.17, a. 2.
 For a fuller examination of Aquinas’s Christological thought, see T.G. Weinandy, “Aquinas: God IS Man – The Marvel of the Incarnation,” in Aquinas on Doctrine: A Critical Introduction, edited by T.G. Weinandy, D.A. Keating, and J.P. Yocum (London: T&T Clark, 2004), 67–89.
 For the doctrinal significance of the early ecumenical councils, see T.G. Weinandy, “The Doctrinal Significance of the Councils of Nicaea, Ephesus, and Chalcedon” in The Oxford Handbook of Christology, edited by F.A. Murphy and T.A. Stefano (Oxford: Oxford University Press, 2015), 549–567.