James A. Weisheipl, O.P., S.T.M.

I    Brief Note on the Text of Isaiah (6:1) used for the Prologue

II   Proofs for God’s Existence

III  The Concepts of “Nature” and “Person”

“Nature” as a Philosophical Concept
“Person” as a Philosophical Concept

IV  The Mystery of the Triune God

A. Consubstantiality of the Son with the Father
B. Three distinct Persons in one Nature

V   The Mystery of the Incarnation

VI  St. Thomas’ doctrine of the Hypostatic Union



It was customary for medieval sermons to be based on a special text of Scripture, which would be developed phrase by phrase in the course of the sermon. Naturally, every text was adapted to the ultimate purpose the preacher had in mind. Similarly, every book or important treatise in the Middle Ages would be introduced by a Prologue, which was likewise a development of a text chosen by the author from Scripture. The development of this text was not necessarily an explanation of the literal sense of the passage. It was rather an explanation adapted by the author to prepare the reader for the book about to follow. Usually the text chosen was adapted to cover the special range of material to be discussed, and thus served as a division of the matter about to be treated. There is nothing unusual about this.

Since, as St. Augustine says, St. John’s purpose in writing his gospel was “to inform us about the contemplative life,” St. Thomas chose the text from Isaiah (6:1) to show the reader something about John’s own contemplation in that the Lord Jesus is contemplated therein in a threefold fullness: sublime (alta), expansive (ampla), and perfect (perfecta). (See Prologue, n. 1). Hence, St. Thomas adapts the text of Isaiah (6:1) to fit this threefold fullness of John’s contemplation revealed in his Gospel. This is a very normal and ordinary procedure. Indeed almost any text is flexible and adaptable in many ways according to the purpose of the preacher or writer.

St. Thomas, in fact, uses the text chosen for two purposes: first, to explain the threefold fullness of John’s contemplation; second, to divide the following exposition of John’s Prologue into three parts: namely 1 (1-2) concerning the sublimity of the Word, 1 (3- 13) concerning the totality of the universe through the Word, and 1 (14a) concerning the Incarnation of the Word. The first division corresponds to Lecture 1, the second to Lectures 2 to 6, and the third to Lecture 7. Consequently, the tripartite reading of the text of Isaiah (6:1) is essential to Thomas’ development in the Prologue of his explanation of the Gospel.

The Latin Vulgate that Thomas used had this threefold division of the text of Isaiah (6:1): Vidi Dominum sedentem super solium excelsum et elevatum, et plena erat domus a makestate eius, et ea quae sub ipso erant replebant templum. In the commentary we have translated this literally as, “I saw the Lord seated on a high and lofty throne, and the whole house was full of his majesty, and the things that were under him filled the temple,” as required by the exposition of Thomas. Moreover, it is clear from Thomas’ running gloss, which he gave in class some time between 1248 and 1252 as a young cursor biblicus at Cologne under St. Albert the Great, that this was the actual reading of his personal Bible. (See Expositio super Isaiam ad Litteram, in Opera Omnia, ed. Leon. 28 [Rome 19741, 6:1, lines 96-103). What is more, St. Albert the Great himself used this full text from Isaiah (6:1), as above, and adapted it for his own purposes for the Prologue to his Commentary on the Second Book of the Sentences (ed. Borgnet 27:1-3), which he wrote when he was already a Master in Sacred Theology at Paris toward the end of 1245 or the beginning of 1246. (See my Friar Thomas dAquino, Garden City: Doubleday, 1974, p. 45). He too needed all three parts of the text to show the division of Book Two into three parts or three “Treatises.”

The historical and textual problem with all of this is that the Latin phrase, et plena erat domus a maiestate eius, the second phrase, is not found in the ordinary editions of the Latin Vulgate, neither in the old Clementine version nor in the critical edition prepared by Dom Robert Weber in 1975 (Stuttgart: Württembergische Bibelanstalt, 2 vols.). Nor is this second phrase to be found in the Greek Septuagint nor in the Hebrew Massoretic text of Isaiah. The historical and textual problem is to locate the vulgate tradition to which the Bible of Thomas and Albert belonged; this has not yet been done. The text of Isaiah (6:1) in the critical edition simply reads: Vidi Dominum sedentem super solium excelsum et elevatum, et ea quae sub eo erant implebant templum.

The text in Thomas’ Bible was somehow a conflation from Isaiah (6:4), et domus repleta est fumo, “and the house was filled with smoke,” while the reading in the Piana edition of Thomas’ works and all subsequent editions, including the Marietti, is a conflation from Isaiah (6:3), plena est omnis terra gloria eius, “the whole earth is full of his glory.”

The Hebrew author of Isaiah 6 (1-4) wished to say that he saw the splendor of the All High God fill the temple (6:1), the whole earth (6:3), and the house (6:4). This kind of Hebraic development is completely missed in the version Albert and Thomas had before them. But, then, this particular text would not have been suitable for the kind of development Thomas wished to present in his Prologue. Nor would it have been suitable for Albert’s purposes either when he commented on Book II of the Sentences.

Nothing I have said here makes the slightest difference to our understanding or appreciation of St. Thomas’ Prologue. Isaiah 6 (1-4) as St. Thomas had it helps to explicate John’s Gospel in a way that the passage as established by biblical criticism does not. Nevertheless, for the study of the Bible in the Middle Ages, the study of medieval exegesis, and a fuller understanding of St. Thomas and his sources, it would be helpful if we could discover St. Thomas’ Bible or at least the manuscript tradition to which it belonged. (See the editors of Expositio super Isaiam, ed. cit., Preface, pp. 43-47).




Despite the constant teaching of the Catholic Church, many Catholics are surprised to learn that it is reasonable and also a matter of divine revelation that the human mind can arrive at a clear and unshakable conviction of the existence of one God as creator of the universe. Many non-Catholics insist that the question of God’s existence is strictly a personal matter, and one of faith, not reason. Usually what is meant by “strictly a personal matter” is HANDS OFF! It is a religious question, and of concern only to me! This attitude, however, is not only an insult to God, but also to human reason. Man has an intellect by which he can discover truth, all truth, and even the cause of all truth. By his intellect man knows very few things intuitively and easily; his normal path is one of arduous learning, reasoning, discovering, and problem-solving. This winding path by which he comes to see why things are so and not otherwise than they are, is called “proof” or “evidence.” On the basis of the proof or evidence the human mind can readily see the truth or falsity of the claim. “Proof” is always our reason for making the claim; that is, the “proof” contains the cause of the conclusion we have just drawn. As long as the area of investigation is co-natural to man, i.e.., within the ambit of his experience, the “evidence” or “proof” he digs up will very often coincide with the real cause in nature which brought the situation about. That is to say, in all the natural sciences (involving sensible bodies and activities), in the numerous branches of mathematics (involving imagination and consistency), as well as in most human affairs (dealing with right and wrong, responsibility, guilty or not guilty), we can very often amass our evidence from the very causes that produced the situation in question. In that case, the cause of our knowing a truth conclusively coincides with the causes that brought the real situation about. But when, on the other hand, our investigation carries us beyond the realm of human experience, then the only evidence we have is the effects we have in front of us. That is to say, when we raise such basic questions as the efficient designer and creator of our whole being and the totality of the universe, or ask why we ourselves are on this earth, we are asking about causes that transcend all our experience and imagination. But we do have the evidence in front of us all the time that there must exist some cause because of the nature of the effects we behold. That is, the totality of the evidence within ourselves and around ourselves is contained in the effects. Human footprints in the sand indicate that a man has walked this way before, the evidence is the footprint, an effect. That there is a creative God is the most important truth the human mind can reach, because it makes all the difference in our response, our daily lives, our total attitude. To deny human reason the possibility of proving with certitude that there is a First Cause of all within range of human experience is to deny our intelligence.

Modem academicians and politicians are all too ready to leave God out of the picture. Rather than say, “He does not exist,” as atheists, Marxists, and materialists do say, they would prefer to be skeptical, agnostic, or say it is a matter of religion, not of reason and debate. Because of the prevailing agnosticism, or better, indifference, toward the real existence of a creating God, who is the total efficient, exemplar, and final cause of every single reality outside himself, the First Vatican Council (1870) explicitly declared what was always taught: the human mind can prove with absolute certainty that only one creating God exists, from the evidence of his handiwork, his effects within us and around us. This declaration of the First Vatican Council was not a new truth, but the constant teaching of the Scriptures and the living Church. Time and again the Scriptures declare that the glory and love of the Lord are manifest in his handiwork; and St. Paul insists that even the pagans and irreligious men have no excuse for ignoring God, for “whatever can be known about God is clear to them, as he himself made it so. Since the creation of the world, invisible realities, God’s eternal power and divinity, have become visible, recognized through the things he has made” (Rom 1:19-20). St. Thomas did not need the First Vatican Council to tell him that the human mind can arrive at a firm conviction of the existence (an sit) of a First Cause from his effects (Sum. theol. I, q.2, a. 1-2). As to what God is or who he is, we can know very little indeed, because his nature has got to be radically different from anything we experience humanly. Even the most sublime terms in the human vocabulary when applied to God pale utterly: terms such as “love,” “forgiving,” “generous,” “all knowing,” “all powerful,” and the like. It is more honest to say with St. Thomas that we know much more what God is not than what he is (Sum. theol. I, q.3, prol.). Imagination gives an utterly distorted picture of God, this is inevitable. The capacity of the human mind, however. is such that it can not only know that God exists, but also it great deal about what he is not, and a little bit about what we must say he is, even though human words and experience cannot do justice to the reality, as the prophet Isaiah well understood (Is 64:3; 1 Cor 2:9).

It is particularly important today that all Christians acknowledge the fundamental ability of the human mind to know with certitude that God exists. God made man in “his own image and likeness” (Gn 1:26) for this very purpose: that he might know him, love him and serve him on this earth and be happy with him forever in heaven. St. Thomas credits the human mind with far greater potential than would the sceptic and agnostic. What is more, the human mind has every right to know about the existence of God, since our whole manner of life depends upon that knowledge. To deny man the right to know God’s existence, that is, to prevent him from knowing that God exists, is a far greater crime than a simple denial of man’s capacity, for the latter is only an insult, the former adds the perversion of justice. No one today can be complacent about this contemporary insult and injustice presented in the societal game of “important things do not count.”

Despite the fact that man can know by reason that God exists, God still chose to reveal his own existence through the Scriptures. For reason is pushed to her greatest efforts when she seeks the highest truth, Truth Itself. Indeed, to Thomas it seemed remarkable that some philosophers, i.e., those gentiles without the Christian revelation, did in fact arrive at the inevitable conclusion that God exists. That is his actual starting point: a few philosophers, highly gifted, using human reason unaided by revelation did, in fact, arrive at the most important issues concerning man: the first of these being that he has a Creator. Thomas, however, was not only a fighting optimist, but also a factual realist. He knew that only a few men arrived at the really important truths in human life, and only after a long time of persistent struggling against error, and even then, arriving at a few gems of truth mixed with much dross of falsehood. These are the three reasons St. Thomas gives (Sum. theol. I, q.1, a.1) why God in his infinite mercy felt obliged to reveal even these: so that all men, no matter how ungifted, no matter how busy, might know at least the essential truths without any error. In other words, considering the actual condition in this hectic world, God in his infinite goodness revealed even those truths that the human mind can in fact know with its native powers, so that the most important truths of human life “could be known by all men easily, with absolute certitude, and with no admixture of error” (Vat. Council 1: sess. 3, cap. 2, Denz 3005). At the same time, that Council condemned as contrary to the true Catholic faith the outright denial that “the one and true God, our Creator and Lord, can be known with certitude from the things he has made, by the natural light of human reason” (Chap. 2, can. 1, Denz. 3026).

In other words, there are two kinds of truths that God has chosen to reveal to mankind: (1) those that we could never know by any amount of human reason, such as man’s destiny to eternal beatitude, the Word made flesh for our salvation, the triune nature of God, and the final resurrection of the human body; (2) those that “the human mind” can know, and in fact, that some gifted few have discovered, after a long struggle, and even then with a great admixture of error, such as the existence of one Creator of the universe, his providence over all things, and the immortality of the human soul. The first kind God alone could tells us, and he had to tell us, granting that he freely chose to predestine man to a supernatural end: if God decided to give man a home beyond his nature, then he had to tell us how to get there, namely, by following his Son to Calvary. The second kind, however, God had no need to reveal at all, but he did so that all men could come to the essential truths of human life more easily, with absolute certitude, and without any admixture of error. The most important truth in human life is that there is but one God, the Creator and Lord of all.

Thomas always maintained that many philosophers of the past have in fact come to know God’s existence through his created effects. At the same time, he was well aware how few these highly gifted “philosophers” were compared to the totality of mankind, the length of time they devoted to the search, and the great number of erroneous notions these philosophers had about “God,” as they understood him. Nevertheless, Thomas never failed to point out the many different paths philosophers found to God. (See J. A. Baisnée, “St. Thomas Aquinas’ Proofs of the Existence of God Presented in Their Chronological Order,” Philosophical Studies in Honor of the Very Reverend Ignatius Smith, O.P., ed. J. K. Ryan, Westminster: Newman, 1952, pp. 29-64). In Thomas’ own presentation of the various paths the philosophers took, he often simplified, clarified, and strengthened the tortuous paths actually marked out by variousphilosophers. He often saw more clearly what Plato, Aristotle, Avicenna, or John Damascene wanted to say, and said it with greater precision and less admixture of error. In the Summa theologiae I, 2, 3, Thomas gives only five of the simplest and most convincing ways various philosophers actually used. These “five ways,” of course, were not the only ways in which philosophers have come to know the one, true God. Thomas himself enumerated other ways, and in one’s own personal experience one can find many other ways to God. So there is nothing exclusive, sacrosanct, or all-inclusive in the “five ways” (quinque viae) presented to beginners in the Summa theologiae. (See Joseph Owens, “Aquinas and the Five Ways,” The Monist, 58, 1974, 16-35).

In his Prologue to St. John, Thomas indicates “four” especially selected ways, suitable to his purpose in the commentary, that have brought philosophers to the contemplation of God’s existence, and which are most appropriate to point out to the reader of St. John’s Gospel. The contemplative is most easily brought to a knowledge of God’s creative existence by perceiving his authority, eternity, and incomprehensibility.

(i) Here St. Thomas points out that the “most efficacious way” (via efficacissima) for philosophers to know God is through his authority over all things.: We see things in nature that act for an end they do not and cannot know; such is true of the entire universe with all its stars and galaxies. Since such things lack intelligence, they cannot direct themselves to an end, but must be directed and moved by some Intelligence. Since the whole course of nature is most fittingly ordered to a complexity of ends, there must be something beyond nature with intelligence to direct all things as Lord and Master. In the Prologue, Thomas sees all this expressed by Isaiah in the use of the word “Lord,” when he says, “I saw the Lord.” And Thomas notes that John reflects the authority of the Incarnate Word when he says, “He came unto his own,” that is, into the world that belonged to him. This philosophical argument corresponds to the “fifth” of the famous “five ways” in the Summa theologiae. In the Summa contra gentiles (I, c. 13, n. 115), written in Paris early in 1259, this argument is attributed to St. John Damascene (De fide orthodoxa, I, c. 3) and also associated with Averroes’ In II Phys., com. 75. Altogether, St. Thomas uses this argument from “the governance of all things in the world” eight times, and here he calls it the “most efficacious way.” (See Baisnée, loc. cit., p. 63). Surely, this way strikes most scientists and those who contemplate the stars and the world of nature. By way of contrast, it might be noted here also, that in the Summa theologiae Thomas called the “first” way, the argument from change throughout the universe, the “more manifest”—and so it was for Aristotle.

(ii) Thomas goes on to say that some philosophers come to the knowledge of God through his eternity. Many are struck by the constant fluidity, flow, and mutability of everything in our human experience: “Time and tide wait for no man.” But some are struck by the fact that certain things are subject to more change than others. The higher a thing is in nature, the less subject to change it seems to be. Thus terrestrial bodies change in every way, and different living things have longer or shorter life-spans, while celestial bodies seem to us only to change their position in the heavens. Nevertheless, all things in the heavens and on the earth are in the constant flow of time. This “historicity” of all things in time and place would lead us to think that the cause of things in time and place must itself be beyond all time. Thus the contemplation of the temporality of every thing we experience has led some philosophers to a God who is eternal and unchanging.

This argument, it would seem, was never used elsewhere by St. Thomas. It suggests, however, Plato’s famous argument that from contemplating “that which is Becoming always and never is Existent” one is led to “that which is Existent always and has no Becoming” (Timaeus 27D6-28C4)—an idea Thomas could have read in the translation and commentary by Calcidius (early 4th century). A similar argument from the mutability of all creatures to the absolute immutability of God is also suggested in Malachi (3:6): “I, the Lord, do not change”; while the whole universe constantly changes. The theme of the absolute contingency and temporality of creatures in contrast to the constancy and eternity of God runs throughout all the writings of St. Augustine; it is one of his fundamental themes.

In the Prologue to John, Thomas suggests that Isaiah implies this view when he uses the word “seated,” that is, without change and forever. John the Evangelist suggests the same when he says, “In the beginning was the Word.” Some contemporary commentators, however, have reduced this argument to the “first” given in the Summa Q. A. Baisnée, op. cit., p. 63). But this view does not seem tenable, since the argument in the Prologue is cast entirely in terms of temporality and eternity, which is not at all the same as Aristotle’s argument from motion (the first way in the Summa). For Aristotle, both God and the universe are eternal, yet God is its First Cause and Mover.

(iii) Other philosophers, Thomas continues, come to the knowledge of God from his dignity. “And these,” he says, “were the Platonists.” They saw that everything that shares “being” depends on one who has it essentially. That is to say, since everything that exists, diverse as things are, shares in the common act of existing (esse), there must be a first Being, whose very nature must be esse itself ipsun esse subsistens. This same argument is used by Thomas also in De potentia, q.3, a.5, and is there attributed to Avicenna (Metaph. VIII, c,7, IX, c.4). The underlying principle, however, is fundamental lo the whole of Thomas’ metaphysics: “Whatever is possessed by participation (per participationem) is reduced to one that has it by essence (per essentiam). (Cf. Peter of Berganlo, Tahula aurea, s.v. “Participare”). This is the argument Thomas uses to establish the fundamental principle of his existentialist metaphysics: in God alone are esse and quod est (essence, or nature) identical; in all creatures, even angels, they are truly distinct (cf. Sum. theol. I, q.3, a.4). In the Prologue to John, Thomas sees this unique dignity of God as expressed in the phrase of Isaiah when he says, “on a high ... throne.” John implies the same when he says, “The Word was God,” which brings us back to the very name of God as “I am who am” (Ex 3:14), the source of the name Yahweh.

(iv) Finally, there were other philosophers who came to the knowledge of God from the basic incomprehensibility of truth. It is obvious to most people that the human mind is limited in its ability to know the truth. Only the most arrogant “rationalist”—usually the very ones who deny the human mind’s ability to prove God’s existence—would say, “Given time, man will know and be able to explain everything.” The reasonable philosopher, as opposed to the “rationalist,” is fully aware of the mind’s limitations in every sphere of human activity, especially the most important ones. Therefore, those realists have argued there must be some Intellect that not only knows all truth, but is Truth Itself (ipsa veritas) and the ultimate cause of all truth. That is to say, if truth exists in the mind, and human minds come and go in the course of human generation and death, and the foundation of our knowledge is a passing world, then there must be some ultimate ground for all truth, even the truth that “two and two are four.” In the Prologue, Thomas seems to attribute this way of reasoning to St. Augustine, who is quoted at this point (Prol. n.6). In his careful study, J. A. Baisnée found no other use of this argument by St. Thomas (See op. cit., p. 64). Cornelio Fabro, moreover, sees this.,as a “refreshing novelty” in Aquinas, carrying expressly the signature of St. Augustine (see C. Fabro, “Sviluppo, Significato, e Valore della Quarta Via,” Doctor Communis, 7, 1954, 82). In any case, Thomas sees this incomprehensibility of God’s ways in Isaiah’s use of the word “lofty” (elevatum), meaning beyond the understanding of every creature. St. John himself intimates this when he says in 1:18: “No one has ever seen God.” This reminds one very much of St. Augustine’s favorite quotation from St. Paul, “How deep are the riches and the wisdom and the knowledge of God! How incomprehensible are his judgments, and how unsearchable his ways!” (Rom 11:33). Almost anyone who considers even briefly the unfathomable ways of human life and experience comes to one of two conclusions: either there is a God great enough to draw good out of evil or life is “absurd.” But even the “absurdity” of life should be enough to lead men to the Lord of the absurd!

These are only four of the many ways Thomas could have chosen to show how serious, contemplative philosophers have come to a knowledge of God’s existence and his ways. In the Prologue, St. Thomas uses these four paths by which contemplative philosophers have come in order to expand on only one point: the sublimity of St. John’s contemplation (alta). This, for Thomas, was the first aspect of John’s contemplation of the Word that he wished to convey to us in the Gospel. The other aspects of this contemplation—its expansiveness and perfection—are explained and exemplified in the subsequent paragraphs of this Prologue by Thomas.




The eternal salvation to which God has freely ordained mankind is a blessed, consummate happiness that cannot be attained by the powers of sheer created nature itself—much less by fallen human nature—even though in creating human nature “in his image and likeness” God intended, that this nature should partake of the intimate life of his own dynamic being, Life Itself. That such a sublime happiness is in store for those who freely choose to serve the one true God, and him alone, has been revealed to mankind by God himself; man could not otherwise conceive even the possibility of such eternal bliss beyond the grave. “No ear has ever heard, no eye ever seen, any God but you doing such deeds for those who wait for him 15 (Is 64:3, cf. Sum. theol. I, q. 1, a. 1). In order to know that such eternal happiness exists for and can be attained by each individual human being, every person needs the special grace (gratia) of God, a purely unmerited “gift” (the meaning of the word gratia). Only by grace can man know the wonders of that goal, and the way to the goal, as well as obtain the help (auxilium), the actual, daily grace necessary to achieve that goal.

Man receives the message, the “Good News” (Evangelium), about this. salvation through faith (fides) in the God-Man Christ Jesus, “the one mediator between God and men, who gave himself as a ransom for all” (1 Tim 2:5-6). Each person works out his salvation with “fear and trembling” (Phil 2:12), having confidence and hope (spes) in God’s abundant mercy and power. We achieve this salvation, however, through a total, unconditional affirming love of God and neighbor (caritas) exercised daily through all the other virtues required to live a full Christian life as a “pilgrim” passing this way but once to our true home, heaven, “the holy city, the new Jerusalem” (Rv 21:2). “For we do not have here a lasting city; but we are seeking one that is to come” (Heb 13:14). Thus the whole focus of our pilgrim life is the Word-made-flesh, Christ Jesus, who not only merited redemption for us, but is also the true example of the way we must live. He is “the way, the truth, and the life” (Jn 14:6), and only through him can we go to the Father. So, Christian life consists in accepting Jesus as our Lord and Master, and in imitating him, especially in obedience to the will of the Father.

Since God himself freely chose the ultimate goal for man, he alone is free to determine the means to that goal, the road by which we must travel to attain the destined happiness beyond our dreams. God could have chosen any number of ways, but in fact he chose only one. That one way is the person of Jesus Christ, who within himself unites our human nature with his divine nature. For this reason Jesus said, “I am the way, the truth, and the life; no one comes to the Father except through me” (Jn 14:6). That just happens to be the one and only means set for us before we were born, not by nature, but by the grace of God.

In order that man be saved, he must accept as absolutely certain—through the gift of “faith”—two fundamental mysteries of revelation that defy human language and human comprehension. They are the mysteries of the Incarnation.—or “the Word became flesh” (Jn 1:14) and of the Trinity: or the ultimate mystery of God as three Persons in one nature. These are the two basic mysteries, enigmas, puzzles, incomprehensibles, that every person must take on faith, with love, in order to follow the way of Christ to the Father, by the grace of the Holy Spirit.

The fundamental teaching in this matter is expressed quite simply by St. Thomas:

The way for men to arrive at eternal happiness is the mystery of the Incarnation and passion of Christ, for it says. “There is no salvation in any other; for there is no other name under heaven given to men, by which we can be saved” (Acts 4:12). And therefore belief in some way, in the mystery of the Incarnation of Christ was necessary at all times and for all people; but this belief is different according to the different times and persons. (Sum. theol. II-II, q.2, a. 7)

But Thomas goes one step farther:

One cannot believe explicitly in the mystery of the Incarnation of Christ without belief in the Trinity.- because the mystery of the Incarnation of Christ includes that the Son of God [the Father] became man; that he renewed the world through the grace of the Holy Spirit; and that he was conceived [in the womb of Mary] by the Holy Spirit. (Sum. theol. II-11, q. 2, a. 8,- see also Nicene Creed, Denz. 125, among others)

Although neither the mystery itself nor anything affirmative and unpuzzling about the mysteries can be proved by human reason, it is a human intellect that tries to understand the meaning of the terms used by God in revealing himself to us, and tries also to show what the mystery is not, at least by showing that the mystery is not absurd or impossible (See Sum. theol. 1, q. 1, a.8). The English word mystery” comes from the Greek mysterion, meaning what is “secret or hidden from comprehension”; it usually has to do with divine truths, or secrets hidden behind sacred signs and symbols (sacramenta). We sometimes speak of the many natural “mysteries” that are around us, in actual fact, the whole of human life is one big “mystery” beyond our comprehension. But there is one big difference: natural mysteries may some day come to be understood, but supernatural mysteries, such as the Trinity, the Incarnation, and God’s love, can never be understood, much less comprehended by any created mind. The best the human mind can do is recognize that it is rational for a man to believe in the truth of the mystery.

The special role of theology, as St. Anselm and all the scholastics following Augustine knew, comes from the dynamism of faith seeking to understand, insofar as is humanly possible, the revealed word of God: Fides quaerens intellectum (Anselm, Proslogion, prooem. Opera Omnia, ed. F. S. Schmitt, I, 1938, p. 94. See M.-D. Chenu, La théologie comme science au XIII siecle, 2nd ed., Paris: Vrin, 1943 or any of Chenu’s works on theology as a science). For St. Augustine, it was not so much a matter of understanding in order to believe, but a matter of believing in order to understand: Credo ut intelligam. Quoting the Latin wording from the Septuagint, Augustine based his view on Isaiah (7:9): “Unless you believe, you will not understand” (Aug., Sermo 53.7, PL 38:257; Ennar. in A. 118, serm. 18. 3-4, PL 37:1552-53). What little understanding we are capable of having in this life presupposes two things: a lively faith, and a humble inquisitive mind. To understand as well as possible what faith holds, we must employ every bit of learning, especially philosophical learning, which sheds light on what has been revealed. The words “nature” and “person,” each of which has a precise meaning in philosophy, are essential to our understanding of what we believe. For in our Christian faith we assert that Jesus Christ is one person, the Son of the eternal Father, and that he has two natures, the truly human and the truly divine. The Holy Trinity is three persons, and the Father, Son, and Holy Spirit are one in being or nature. Our task then throughout the rest of these notes will be to explain as carefully as we can in “the words of men” what we believe, so that through them we might catch some glimmer of the great mystery that is God himself. To accomplish this task we must first examine the words “nature” and “person.” In this particular note we shall explain the various meanings these terms have in everyday use, the way they must be understood at the crucial juncture where reason meets faith, where reason surrenders to the mystery of revelation.

“Nature” as a Philosophical Concept

“Nature” is a wider and more comprehensive term than “person,” being used of many more things. Thus every person has a nature, but not every nature has or is a person. The various meanings the word “nature” has in common speech and in its philosophical refinements are what concern us here.

The word nature in English today is used in all sorts of loose ways. “Nature lovers” think of the great outdoors; “naturalists” usually think of plants and animals, or else of the great variety of “health foods” that help to make one strong physically. Literary people often use the term “nature” in the sense of “the universe out there,” a meaning more or less synonymous with that of the Greek word kosmos (from which we get our English word “cosmetics”). Intellectuals with a deeper understanding of medicine, sociology, or even law, think of nature as a “normal course of events,” or “behavior that is found among many,” or “laws of behavior” acceptable in civilized society and codifiable. While all these meanings (and many others) can be traced back to ancient usage, none of them focuses fully on the precise philosophical meaning the word had for the ancient Greeks and Latins and on through the Middle Ages as well. Renaissance humanists often distinguished between Nature with a capital N, meaning God acting in the universe (Natura naturans), and nature with a small n, meaning the created universe as an instrument of God (natura naturata). This distinction was also utilized by St. Thomas, St. Bonaventure, and many philosophers of the thirteenth century. Even in that context, a certain dynamic character was thought to belong to the universe as God created it. That is to say, in most of these usages the implication is that there is some innate source within things for their “normal,” “usual,” “codifiable” behavior. In all of these usages derived from antiquity, there is implied an inner dynamism that defies our every attempt to turn them into machines.

Our own thoughts about “nature” have to a large extent been molded and influenced by the mechanistic philosophy dominant in academia since the seventeenth century. Today it is hard for us to avoid thinking in clear and distinct- mechanical terms. We tend to imagine the universe as a big machine, something like a watch, made up of ever smaller and smaller particles that operate according to determined or determinable mathematical laws. All mathematical formulations, even statistical laws of “random probability,” are necessarily mechanical, as Leibniz (1646-1716) saw so clearly; but he ended by acknowledging two parallel worlds—the mechanical and mathematical (the phenomenological), and the “real,” ontological, and metaphysical (the monodological and non-mechanical) world. For Leibniz, the phenomenological world appears to be mechanical and mathematically determinable, but the real world behind the phenomena consists of monads, each of which is self-contained and non-causal. In order that such a parallelism exist at all and make any sense, Leibniz had to postulate a pre-established harmony determined by God, the Lord of both worlds. It was inevitable that Leibniz’s metaphysics, and even Newton’s, passed into oblivion, while their mechanical and mathematically determinable world became the dominant philosophy of modern science.

If we wish, however, to appreciate what the word nature meant to the Greek pagans and Christians, to the Middle Ages and the whole history of Christian thought, we must put aside for the moment any mechanistic notions we may have about the universe in which we live, and try to appreciate a philosophical language that expresses what really lies at the foundation of our human experience, a language that describes a world made up of such principles as potency and act; the four radically different kinds of causality (formal, material, efficient and final); real substances that are things (res); accidental characteristics (nine of them, not counting the post-predicaments and modes), matter and form; essence and actuality of being, or quod est and esse. This philosophical language is difficult for us moderns to grasp precisely because it is non-mechanistic and apparently foreign to our “scientific” minds and “analytic” philosophy. But in fact, the older, philosophical vocabulary is much less difficult to grasp than are modem “scientific” and “analytic” concepts, contrary to what might have been expected. Therefore it is intelligible to more people and is grounded more securely in human experience. Whatever may be said about the Semitic mind and the picturesque language of the Old Testament, the Christian experience in both East and West, in both Greek and Latin, is more deeply rooted in history and in personal experience than any of the fleeting modern systems of thought. There is indeed a chasm of sorts between the modern “scientific” and “analytic” vocabulary on the one hand and the traditional personalist vocabulary of the ancients. But it is not a chasm between East and West. The clash between the Eastern and Western theologies is not a clash between Greek and Latin mentalities, but a clash between Platonic and Aristotelian philosophies—both of which are Greek.

As to the word “nature,” there is an important history of Greek and Latin Philosophical usage (see my “Concept of Nature,” The New Scholasticism, 38, 1954, 377-408; and “Aristotle’s Concept of Nature: Avicenna and Aquinas,” in press. See also, G. S. Kirk, Heraclitus: The Cosmic Fragments, Cambridge, 1954, index).

For our purposes here it is sufficient to note three historical points briefly before zeroing in on the analogical use of the term in Aristotelian and Scholastic philosophy. 1) The Greek seekers of wisdom before Socrates (d. 399 B.C.), the pre-Socratics, are frequently called physiologoi because their whole enterprise was a search for the underlying active “source” (arche) of all natural processes in the world, including the origin and nature of man. This underlying active source they called physis (nature), from which we derive our English words physics, physical, physician, and the like. For most of these pre-Socratics, one or other of the basic elements were sought out as the ultimate, active nature of things, as though the whole universe had to have been made from one single element; they are commonly called philosophical Monists, from the Greek word monos, “single.” 2) Socrates and his disciple Plato (427347 B.C.) gave up the enterprise of the physiologoi as hopeless, Socrates establishing a moral or ethical philosophy, and Plato turning from the world of nature to the world of separated, subsistent Ideas that defined each thing in itself, and establishing the primacy of art over nature, and of mind or spirit over matter (See, Laws X, 884A913D). Plato, responding to Parmenides, established a dualism that enticed a host of eminent Fathers of the Church, mystics, separatists, and modem dualists. This is not the Pauline warfare between the “spirit” and the “flesh,” but the Cartesian separation of mind and body that overflowed into the pseudo-conflict of faith and reason, Church and science, sacerdotium and regnum, Church and State. 3) Aristotle (384-322 B.C.), a disciple of Plato, tried to reinstate the quest of the ancient physiologoi in order to establish a realist foundation for his metaphysics of being. That Aristotle would have wished to re-establish the investigation of nature is not at all surprising, for his father was court physician to Philip of Macedonia and was himself a born naturalist in the pay of Alexander the Great. What is surprising, however, is that he should have found such a simple truth whereby to succeed in his quest. The simple truth was that the word “is” can be used in many different ways, the fundamental distinction being between actually and potentially. While the phisiologoi and the Platonists were rightly busy looking for the actual, Aristotle discovered the potential, that is, primary matter (materia prima), which was capable of becoming actual. For this simple discovery, the Thomistic commentator Cardinal Thomas de Vio Cajetan called him Divus Aristoteles, quia invenit materiam (Divine Aristotle, because he discovered matter).

To physis (nature) in the sense of an active principle, Aristotle gave the name “form”, but to physis (nature) in the sense of a passive or potential principle, he gave the name “matter.” Thus Aristotle could say that the word nature is analogical, i.e., “equivocal by intent” (equivocatio a consilio). For the word nature is used in at least two different senses: primarily as “form,” and secondarily as “matter” (Phys. II, 1). Form as the actual principle is defined as the active “source or cause of being moved and of being at rest in those things to which it belongs primarily (per se) and not incidentally” (192b2l- 23). Matter as the potential principle is defined as the passive “source of being moved and of being at rest in those things to which it belongs primarily and not incidentally” (ibid.). In either case, nature, strictly speaking, is a principle (arche, principium) or a “source” relative to observable and manifest behavior or properties, whether they be movements such as growing or healing, or characteristics more or less static and proper to different kinds of natures, such as size, color, weight, habitat, and anatomy. St. Thomas is very explicit on this very difficult point: “In the definition of nature, the term “source” (principium) is used as a kind of generic classification rather than a term like “thing” (or any other quid absolutum), because the term nature bespeaks of a relationship of origin” (St. Thomas, In II Phys., lect.1, n.5). Thomas rejects every attempt to make absolute Aristotle’s concept by suggesting that it might be “an innate power within things” (vis insita rebus), as some of Aristotle’s commentators have attempted to do. In scholastic terms, the noun “nature” is a nomen relativum, not a nomen absolutum. Thus nature is not really a thing, but an origin or “source” from which (a quo) other things proceed.

One further, somewhat epistemological or psychological observation ought to be made at this point. To understand the “nature” of anything living or non-living in this universe we must study the manifestations or phenomena that are observable to the senses or to the intellect, both static and dynamic. Some manifestations are sensibly observed, as in minerals, plants, and animals; others are only intellectually observed, such as thinking, willing, hating, loving, and other psycho-physical phenomena. In either case, it is the scientific mind that projects the notion of “source” as the root and origin of specific or typical diversities. The more a scientist knows about the observed phenomena, the better he understands the nature of the thing studied. One should not be misled by the logical or the lexicographical simplification of some definitions. The logical definition of “man” as “a rational animal,” while quite good and complete in its way, should not lead us to think we know all there is to know about human nature. The truth is that this marvelous definition of “man” which includes both animality and rationality, is quite elementary and simplistic. It is not likely to carry one very far in understanding “human nature” with all its complexities. While such a definition clearly sets “man” off from “non-thinking animals” and “non-animal thinkers,” it has minimal content. This content can come only from patient study, observation, and experience. An understanding of—let us say—“human nature” is directly proportional to the extent and analysis of one’s experience, personal or vicarious. While it is easier to understand human nature, mainly because we are human and can reflect on ourselves and our inner states with an analytic mind, the same holds true of our understanding of all natures other than man: only through the phenomena can we claim some understanding of the “nature” of anything.

Simply put, therefore, nature is that which makes a thing to be what it is. It is the response to the question, “What is it?” In other words, the nature of a thing is the same as its definition (its quod quid est, or ratio). Aristotle explains that because of this wider meaning of the term, the word nature can be applied to things that have no principle of motion, like the “nature” of a triangle, an idea, ideals, and even spiritual things. Thus, “by an extension of meaning from the original sense of physis, every essence in general has come to be called a nature” (Metaph. V, 4, 1015al 1-12). St. Thomas adds that this latter usage is “by way of metaphor” (In V Metaph., lect. 5, n. 823). In this extended sense, the term is understood in a somewhat static fashion as “whatever a thing is.” In this sense it is identical with the term essence.

Finally, it should be noted that in the technical language of Latin and Greek, nature is not a thing, a quod est, but that by which a thing is what it is (quo est). For this reason, Aristotle can say that “Things ‘have a nature’ which have a principle of this kind” (Phys. II, 1 92b2-3). It is always an it that has a nature, and that it must be substantial, an ousia.

“Person “ as a Philosophical Concept

Since nature is not an it, an existing thing, or supposit, it cannot properly be said to exist. Existence (esse) belongs to things that have a nature, not to nature itself. Aristotle uses two ways to speak of the concrete, existing thing that has a nature. 1 ) In the Categories 5, Aristotle speaks of substance (ousia) in the primary and truest sense as “that which is neither predicable of a subject nor present in a subject, whereas substance (ousia) in a secondary sense is the apprehended substantial nature or essence of a thing, which, in order to exist, must exist in a subject. This subject necessarily is the concrete, uniquely existing individual, “for instance, the individual man or horse” (2a3). Since the Greek word ousia played such an important part in the Christian theology of the fourth century, it is important to remember that for Aristotle, and for all the Greek thinkers, ousia in the primary sense is that alone which has existence. It is the ultimate given suppositum that has existence, but the kind of existence it has depends upon its nature (physis). The Latins simply called it a suppositum, or first substantia, which possessed existence by reason of the “form” making the substance to have the kind of nature and existence it has. The scholastic axiom, “Form gives existence” (Forma dat esse) simply means that the kind of existence a thing has depends on its form, or nature. But ultimately, only the supposit itself can be said “to exist.”

2) Frequently Aristotle speaks of this first ousia as an hypostasis, meaning “that which stands under” all properties and characteristics. Literally, the Greek word was translated as subsistentia, but it always had the sense of substantia in Latin. The Greeks, however, made a very important distinction between ousia, which, in the primary sense, alone had existence (esse), and hypostasis, which, in Christian thought, played the same role as (persona) “person” in Latin. The meaning of these terms must be carefully kept in mind when reading the early Greek and Latin Fathers, as St. Thomas is careful to point out (Contra errores Graecorum, prol. Opera Omnia ed. Leon. XIL A 71, 1-72).

The English word person comes from two Latin words, personare, “to sound through,” as through the mask used in an ancient dramatic performance. Thus we still list the “Dramatis personae” on the program of a play. Because of the influence of the Latin etymology of this word persona, some early Roman theologians, such as Sabellius, thought of God as one substance which spoke through three different masks: the Father, Son, and Holy Spirit. More will be said on this subject later.

An important point to establish here is that in Latin philosophy the term person was applied only to substances that had a particular kind of nature, namely, intellectual. Boethius gave the Latin scholastics the classical definition when he defined a person as “the individual substance of a rational nature” (Contra Eutychen, c. 3). Then he goes on immediately to say, “Now by this definition we Latins have described what the Greeks call hypostasis.” The linguistic difficulty, however, was that the Greeks too had a word they used for the masks placed over the face of the actor playing different roles. As Boethius noted, their word for mask was prosopon, which never lost its original meaning. To convey the Greek reality signified by hypostasis, the Latins had to adapt their word persona to embrace substantial individuals of an intellectual nature. While there is a technical difference between “rational” and “intellectual,” the latter being wider in extension, that difference is not the issue here. Only intellectual substances can be persons, and these intellectual substances must be individual and unique (See Sum. theol., I, q.29, aa. 1-2).

When philosophy demonstrates the existence of a unique First Being, the First Cause of all that exists, it shows him necessarily to be pure spirit, intellect and free volition, the first beginning and last end of all that are created by himself alone. That is to say, philosophy, reasoning from all the effects in the universe, demonstrates that God is a person. When philosophers argue about the existence of a “personal” God, they are really asking whether he is an intellectual being, having knowledge and free will. The question has nothing to do with whether or not God has any personal meaning for me as a person, although this question, too, inevitably follows.

Philosophers, Christian or not, also have grounds for acknowledging the existence of pure spirits, both good and evil. Each such spirit, being an individual intellectual substance, is truly a person. These are not personifications of subsistent forces of good and evil, but subsistent intelligences, each one unique without the individuality and limitations of material substances. They are spiritual intelligences, created by God, that have certain powers over material things, but belong to a vast world altogether different from our own material universe. Some of these personal spirits are irreparably evil because of a free choice made by each one, and hence are the cause of fiendish evil beyond the comprehension of man. Other personal spirits are pure, having made a free choice by the grace of God, and are now messengers of divine governance in the universe. From a Christian point of view, the world of human beings can be considered a kind of battle ground, a plaything or booty to be won over by the good angels in the name of God, or by evil spirits in the name of Satan, Lucifer (see Is 14:12), or Beelzebub, “the Prince of demons” (Mt 12:24; Mk 3:22). The important point here is that each individual spirit is an intelligence having a will that is either perverted or good. Therefore each “individual substance of an intellectual nature” is to be called a person. Each is unique and each has a name, whether we know it or not.

A consequence of what has been said is that each individual substance of, an intellectual nature is a person even though that nature exists only in an embryonic stage and needs a natural course of development to reach its full potential, which for a Christian is eternal happiness with God. Once an individual substance has been constituted by matter and by a form, namely, the “human soul,” it is a true person in the strictest sense of the term. It therefore has certain natural “rights” that belong to it not by any human decree, but by the nature of a person being exactly that, a person. Any violation of those rights is a crime against humanity, not animality.

From this it also follows that no individual substance of a nonintellectual, non-human nature can possibly be a person. Thus a companionate dog, no matter how “loyal” or “intelligent” it may be, is in no way a person. Even if that dog responds to a name or its master’s presence or absence, it is not a person. To use the word person of any individual substance of a non-intellectual nature is a misuse of the term, which cannot be tolerated in philosophy. On the other hand, a group of persons may constitute a legal entity known as a corporation or “moral person,” which may be the subject of legal rights and obligations before the law. But this is merely a legitimate extension of a basically sound definition of person.

Briefly, nature is a reply to the question, “What is it?” It is the ultimate specific “source” of definite, characteristic phenomena, both static and dynamic. The active, automatic “origin” of these characteristics is the form or species of the thing, making it to be what it is, the passive, potential “abilities” of such an individual thing are the matter. The spiritual forms or species are immaterial natures: these may exist solely in the mind (such as “triangles” and “the square root of two”), or they may exist in physical reality, in which case they are necessarily intellectual substances. Person, on the other hand, is a reply to the question, “Who is it?” The person or “who” is an individual substance (material or immaterial) of an intellectual nature. In all creatures there is a distinction between person (as a supposit or quod) and nature, as that by which (id quo) a thing is what it is. That is to say, in all creatures, every person “has” a nature by which he has existence. Thus existence and all actions belong to the person or supposit, but nature is the means by which the person or supposit has existence and its specific actions.

The importance of all of this will become evident when we consider the two great mysteries of our faith: the Trinity and the Incarnation.




According to the Creed attributed to St. Athanasius, whoever wishes to be saved must hold to the Catholic faith whole and entire. “The Catholic faith, however, is this: that we adore one God in trinity and trinity in unity, neither mixing the persons nor separating the substance” (Denz. 75). The Athanasian Creed, dating at least to the fourth century, goes on in great detail to profess that “the Father is God, the Son is God, the Holy Spirit is God, but there are not three Gods, but one God.” All are equal in immensity, eternity, omnipotence, lordship, and creation. They are all one God. But each Person is really and truly distinct from the other two, and these Persons are only three: Father, Son, and Holy Spirit. This is the incomprehensible mystery that God has revealed to us about his inner dynamic life.

When philosophers prove the existence of one God (cf. Note 11 above), they prove that in him his very nature or essence is to be (esse). St. Thomas proves this fundamental truth of his philosophy in many ways (See Sum. theol., I, q.3, a.4 and all parallel places). Simply, in everything that exists, whatever is over and above the essence (praeter essentiam) must be caused either by the essence itself (or nature), as proper characteristics naturally springing forth from it, like risibility in man, or it must be caused by some extrinsic source, like heat in water being caused by fire. But since the very existence of a thing (ipsum esse rei) within our experience is other than its essence, then the thing’s existence must be caused either by its essential principles or by some exterior cause. Its own existence cannot in any way be produced by the essential principles of the thing, for then the essence could not but necessarily exist, since whatever is essential necessarily belongs to it. Therefore, the thing whose esse is other than its essence must have its existence caused by another—and ultimately by one whose very essence is to be. Therefore in God essence and existence (esse) are identical. Thus God is his nature or essence, and he is his esse or existence. Expressed in more Platonic terms, esse is a reality in which different things share or participate in varying degrees, but whatever is had by participation (per participationem) presupposes one who has it essentially (per essentiam).

For St. Thomas the splendor of God’s reality is expressed most fully in the identity of his essence and existence. The very nature of God is to be ipsum esse subsistens, “subsistent being itself.” In human history, God, having chosen a special race of people among all those whom he had created, revealed to the Jews his own name, Yahweh, “I AM WHO AM” (Ex 3:14). This truth, as Gilson has constantly emphasized, is the basic principle of the whole of St. Thomas’ philosophy. He has also noted that St. Thomas himself referred to this insight as haec sublimis veritas (Sum. c. Gent., I, c.32; see E Gilson The Christian Philosophy of St. Thomas Aquinas, trans. L. K. Shook, New York: Random House, 1956, pp.84-95; Le Thomisme, 6th ed.,: Paris. Vrin, 1965, pp.99-112). It belongs to the nature of God necessarily to exist. That is, he cannot not exist.

From this basic truth it follows, first, that God is in every way uniquely and absolutely indivisible, or “simple,” as St. Thomas puts it, having no distinctions within his nature whatever (Sum. theol., I, q.3). Thus in God there is no distinction or difference between his intellect and will, truth and love, justice and mercy, and so forth, even though for us each of these words has a real and distinct meaning (ratio) that must be retained in our talking about God. In our talking about God, human language does not lose its meaning, but it takes on a subtlety and expansion in which we realize that words are being used differently of God and creatures. The difference is radical and absolute (per se), but there is a human reasonableness in using certain words of both God and creatures. This “equivocation by intent,” as Aristotle calls it, is more properly called analogy, which is quite different from simple metaphorical language, such as God’s “walking,” or his “coming down” (Sum. theol., 1, q. 13, etc.). Words such as “good” and “love” can be used properly both of God and man, but in two radically different ways; the reality as it is found in God infinitely transcends our conception of “good” and “love” realizable in man. Thus such statements as “God is love” (1 Jn 4:8), God is truth, God is good, and so forth, are more true and significant than we can possibly realize. The meaning such terms have for us is quite real and proper, but our understanding of those terms is but a shadow of the reality that is in God. Similarly, God’s nature is esse in a way that surpasses our understanding of all the things of our human experience.

The second point is that God has revealed to us through the Law and the Prophets, through Jesus Christ, and through his Church, that he, the Father, “so loved the world that he gave his Only Begotten Son, so that whoever believes in him should not perish, but have eternal life” (Jn 3:16). The Son of God-made-man himself stated time and again that he “was sent by the Father” to do the will of him who sent him, and that all he has is “from the Father.” But he also said that he would “ask the Father, and he will give you another Paraclete, to be with you forever—the Spirit of truth” (Jn 14:16-17), “the Paraclete, the Holy Spirit, whom the Father will send in my name, he will teach you all things, and bring to your mind whatever I have said to you” (Jn 14:26). The Son-made-man also said: “When the Paraclete comes, whom I will send you from the Father, the Spirit of truth who comes from the Father, he will give testimony to me” (Jn 15:26). The last injunction of Jesus to his apostles was “go, therefore, and teach all the nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit” (Mt 28:19). This baptismal formula reflects the Church’s gradual understanding of God as three Persons (See Acts 2:38; 2 Cor 13:13).

The only words God used in revealing himself to us are those of “Father,” “Son,” and “Holy Spirit” (“Spirit” or “Paraclete,” meaning advocate or comforter). And it is only within this context that the theologian must try to understand the inner life of the Godhead. St. John also uses the word logos, Verbum, or Word, as synonymous for the Son. St. Paul speaks of Christ as “the image of God” (2 Cor 4:4- Col 1:15). There simply are no other words given to us for theological understanding. These are common enough terms, but how they are to be understood of the one God, whose nature is his esse is a difficult problem, where “faith seeks understanding” with the help of philosophy, the age-long “handmaid of theology” (the ancilla theologiae) as understood by the Alexandrine theologians, particularly St. Athanasius, and by the Cappadocian Fathers (St. Basil of Caesarea, St. Gregory of Nazianzus, and St. Gregory of Nyssa) in the East, and by St. Augustine in the West.

In this note there are two major points that need clarifying. First, the doctrine of consubstantiality of the Son with the Father, which was the first really crucial development in Christian doctrine. Although the debate over this doctrine reached a climax in the fourth century, still there was the subsequent problem of Filioque, which came to a head in the ninth century. The second baffling mystery was how each of the three Persons is identical with the one nature, yet truly distinct from each other.

A. Consubstantiality of the Son with the Father

Frequently in the New Testament Scriptures, Jesus Christ seems to be presented as somehow less than Yahweh, the one true God of the chosen people, he speaks of himself as “sent by the Father” to do not his own will, but “the will of him who sent me.” He always speaks of himself as having only that teaching, that knowledge, that mission, that will, that judgment which has been committed to him by the Father. Throughout the Gospel of St. John, Jesus seems to acknowledge a subservient position to the Father, depending upon the Father’s acceptance and glorification of him as a loyal Son. In the Gospel according to St. John, Jesus even declares explicitly that “the Father is greater than I” (Jn 14:28). In the end he commends his spirit to the Father.

One of the prevalent assumptions of such ecclesiastical writers as Origen and Clement of Alexandria was that the Son, Jesus Christ, was subordinate to the Father. One form of “subordinationism” insisted that Jesus was no more than a mere man who was “adopted” by God. Other forms, like that held by Arius (c.250-c.336), maintained that the Person of Jesus was created by the Father from nothing in order to be the instrument of the divine plan; and thus that the Person of Jesus had a substance (ousia) different from God’s. This was the extreme form of Arianism that developed from the “subordinationism” of the third century. A second party that developed in the early fourth century, called “Homoeans” (from homoios, “similar”), tried to avoid the very basic commitment of “What think you of Christ?” by saying that there was much similarity between Father and Son “according to the Scriptures.” But the most influential group to emerge was the Semi-Arians, who claimed that the Father and Son were “similar in substance” (homoiousios), but not identical. Although the question of the ousia of Jesus was the central issue that directly occasioned the synod of Alexandria (c.320) in which St. Alexander condemned the teaching of Arius, the Catholic teaching was not universally proclaimed until the Ecumenical Council of Nicaea, convoked by the Emperor Constantine at his summer palace in 325.

At the Council of Nicaea, under the presidency of Hosius of Spain and under the prosecution mainly by Saint Alexander of Alexandria, whose secretary was the deacon St. Athanasius, approximately 235 bishops (318 according to Athanasius) gathered to consider this crucial dogmatic problem and legislate a number of disciplinary decrees. Basing themselves on the texts “In the beginning was the Word... and the Word was God” (Jn 1:1), “The Father and I are one” (Jn 10:30), “That they may be one, even as we are one” (Jn 17:11), “That all may be one, as you Father, in me, and I in you” (Jn 17:21) and similar texts, the conciliar Fathers at Nicaea professed the ancient belief that the “Son is of one substance (that is, homoousion) with the Father.” The Latin rendering is “consubstantial (consubstantialis) with the Father.” This doctrine was directly opposed by the Semi-Arians under the leadership of Eusebius, bishop of Nicomedia. Eusebius and his many followers insisted on the term homoiousion, “of similar substance with the Father,” in place of the orthodox homoousion. Some so-called historians of this controversy of the fourth century have been so insensible and obtuse as to describe it as “a quibble about an iota.” That iota made all the difference in the world between orthodoxy and heresy. As late as 359, St. Jerome could write: “The whole world groaned one day and marvelled to find itself Arian” (Dial. adv. Lucif 19, PL 23, 172C).

The significant point is that the word homoousion is nowhere to be found in the Canonical Scriptures, no more than is homoiusion. But homoousion was a soundly based philosophical term used in response to a Greek philosophical question. Consequently, the crucial question for modern man seeking the Christian truth is not so much “what think you of Christ? Whose Son is he?” (Mt 22:42), but rather, “What think you of homoousion? By what authority do you profess it?” In the earliest ages of Christianity, many thought highly of Jesus as the “adopted son of God,” and accepted him as the “Christus” of faith giving us hope. But, as we shall see, the fundamental question is about the historical Jesus as “consubstantial with the Father,” just as the bishops assembled at Nicaea openly declared to be the true teaching of the Church.

This is one of the earliest examples of the development of Christian doctrine which Cardinal John Henry Newman (1801-90) helped us to understand (See especially his Arians of the Fourth Century (1833), St. Athanasius, 2 vols. (1843), Development of Christian Doctrine (1845) ). The real meaning of the text “The Father and I are one” (Jn 10:30) is that the Son is “consubstantial with the Father” (homoousion toi patri). In theological terms, the ousia (substance) of the Son is identical to the ousia of the Father. From this it is only a short step to the recognition of the Holy Spirit as consubstantial to the Father and Son; that is, the ousia of the Holy Spirit is identical to that of the Father and the Son. Moreover, that unique ousia is “an individual substance of an intellectual nature”; that is, God is a “person” or “personal.”

B. Three distinct Persons in one Nature

Nevertheless, there are three distinct persons (hypostases) identical with the one divine nature (ousia). Because the divine nature is identical with its existence (esse), as explained above, there can he only one God. Thus the person of the Father cannot be distinct in any way from the divine nature which is esse, or ipsum esse subsistens (Sum. theol. I, q.28, a.2). Although none of the three Persons is distinct from the one identical nature or ousia, each is really and truly distinct from the other two, as Father is from Son (Sum. theol. I, q.28, a.3). The only meaning open to our appreciation of the mystery is to be found in the terms God himself used to reveal himself, namely, the relative terms of “Father,” “Son,” and “Spirit” (Sum. theol. I, q.29, a.4).

The role of a father is “to beget,” just as the meaning of sonship is “to be begotten.” The Father, therefore, is unbegotten, but is origin and progenitor of the Son, who himself does not beget, for there is no “Son” in the Godhead other than himself. That is to say, the whole reality of the Father is to beget, to generate, to give all that he has, namely, his whole divine nature, to the Son. And the whole reality of the Son is to be begotten, to be generated, to receive all that he has, namely, his whole divine nature, from the Father. This relation of Father and Son within the Trinity is clearly expressed throughout the Gospel of John: “All that the Father has are mine” (Jn 16:15). “Father, glorify your Son, since you have given him authority over all men” (Jn 17:1-2); “The teaching you gave me, I have given to them” (Jn 17:8); and again, “My teaching is not my own, but of him who sent me” (Jn 7:16). Both St. Augustine and St. Thomas wax eloquent on the precision of this expression. Jesus’ doctrine does not belong to himself as originating with him. Rather it belongs to, it is the possession of, the Father (in the genitive case); it is the Father’s doctrine precisely as received from him by the Son. The life of the Father is an eternal giving of himself whole and entire to the Son. The life of the Son is an eternal receiving of the Father whole and entire. The life of the Father and the Son together is an eternal breathing of the Spirit, while the life of the Spirit is an eternal breath, or gift, whole and entire from the Father and the Son together.

It is obvious that the Spirit must proceed from the Father and the Son (Patre Filioque), and not from the Father alone, for in the latter case another “son” would be generated and there would be no distinction between the Son and the Spirit, as Catholic faith teaches (Sum. theol., I, q.36, a.4; see Sum. contra Gent., IV, cc.126, Contra errores Graecorum, etc.). The Holy Spirit thus possesses the identical nature of the Father and of the Son precisely as breathed (spirata) by Father and Son. He is the “gift” (donum) sent to the Church and into the hearts of all baptized in the Spirit. He is the “uncreated grace” (gratia increata) by whom all those with “created grace” (gratia creata) live the intimate life of the Godhead. He is the Spirit that Jesus breathed on the disciples that they might have his Spirit. In other words, the Spirit belongs to the Father and the Son, just as the Son belongs to the Father. Just as the Son was sent into the world at a particular period in human history “when the fullness of time had come” (Gal 4:4), so the Holy Spirit was sent in a visible way to men at a special time in human history (Sum. theol., I, q.43, a.2 and a.7).

The precise problem where human understanding must give way to belief in a mystery is how can one personal God, who is ipsum esse subsistens and a person, be in fact three distinct Persons and not three gods. If there are three Persons, each “an individual substance of an intellectual nature,” as Boethius and sound philosophy define “person,” then why is not each Person a distinct substance with its own esse? That is to say, why are there not three gods, if there are three distinct Persons? Or rather still, why are there not four persons, a quaternity, as Peter of Poitiers seems to have implied, according to Geoffrey of Auxerre, St. Bernard’s secretary, in his Libellus against the so-called capitula (PL 185, 598; cf. Sum. theol., I, q.28, a.2; N. Haring, The Commentaries on Boethius by Gilbert of Poitiers, Toronto: PIMS, 1966, 3-13). To put the question in a less philosophical context, how can one God be three Persons? Or conversely, how can three distinct Persons be only one subsistent esse and not three? At this point no amount of philosophical analysis and explanation can dissolve the real mystery, something transcending mere human intelligence. All we must insist upon is the absolute identity of person and nature in God and we must not think of the “person” as “an adjunct, or something extrinsically attached,” as Gilbert seems to have suggested (Sum. theol., I, q.28, a.2). Not even when we see God “face to face” and know him as he really is will the mystery dissolve. Only God can comprehend himself. Not even the angels and demons, whose spiritual intelligences far transcend every human intelligence, can understand the mystery.

The importance and sublimity of this mystery of the Trinity becomes more apparent when we prayerfully consider the mystery of the Incarnation: the fact that the Son of God (and only the Son) became true man for our sake, suffered, died, and triumphed over death, that we might have his life. This will be discussed in Note V below.

By way of summary, we can say that the one true God has only one nature, which, of itself, is the total actuality of being (esse), containing no distinctions, potentiality, temporality, or need, having no beginning or end or mutability. This ousia is subsistent truth and love, knowing all things, even what is “future and contingent” to us, and loving all those whom he has freely chosen to love und share in his eternal, dynamic bliss. By faith (and faith alone) we are given a glimpse of the dynamic nature of the Godhead in three distinct Persons: the Father, the Son, and the Holy Spirit. Each Person, though identical with the divine nature, is distinct from the other two by the way in which that nature is possessed. The Father is the divine nature precisely as giving it whole and entire from all eternity to the Son. The Son is that same divine nature precisely as being given it whole and entire from all eternity, himself begotten, but in no way “created.” The Holy Spirit is that same divine nature precisely as breathed by the Father and the Son, himself unbebotten and ungenerated, but simply the Father’s breath of love for the Son and the Son’s breath of love for the Father.

In human history the “Only Begotten Son of the Father” was sent into the world to become man, suffer under Pontius Pilate, die and be raised up again on the third day. Also in human history the Spirit of God, the gift of love, was sent by the Father and the Son into this temporal world to sanctify and to animate the “people of God” in their pilgrimage to their true home, which is eternal bliss with all the saints in seeing God face to face. “Then I shall know even as I am known” (1 Cor 13:12).

In the prologue to his Contra errores Graecorum St. Thomas manifests a fine sense of history, as well as the demands of a good translator. He notes that the writings of our ancient holy Fathers must be seen in their historical context. That is, before the Arian heresy concerning the precise relationship between the person of Jesus and the person of God, ecclesiastical teachers were not as precise in speaking about the unity of the divine essence as were teachers after Arius. Similarly, even St. Augustine, one of the great doctors of the Church, was not as precise about grace and free will when he was writing against the Manicheans in his youth as he was in the face of the heresy of Pelagianism. Thus in his later writings, particularly in his anti-Pelagian works, Augustine speaks most cautiously about man’s free will and the primacy of God’s free gift of grace and final perseverance. And so, St. Thomas says, it is not surprising if modern doctors of the faith, coming after so many new errors, speak more cautiously and more elaborately concerning the doctrine of faith, so as to avoid all heresies. Hence if some things are found in the writings of the ancient doctors that are not as cautiously expressed as the moderns would like, those writings are not for that reason to be disdained or cast aside. Nor should those statements be expanded but reverently explained.

Coming to the main point in his prologue, St. Thomas notes with sympathy the problems of the translator. What might sound good in Greek may not always sound correct in Latin. For this reason the Latins and Greeks profess the same truth of faith in different words. An important example is the mystery of the Trinity itself. For among the Greeks it is correct and orthodox to say that the Father, the Son, and the Holy Spirit are three hypostases. But among the Latins it would not be correct to say that they are three substances, even though hypostasis for the Greeks is the same as substantia for the Latins in literal translation. For among the Latins the term substantia is more commonly taken to mean the essence, which both the Greeks and the Latins admit to be only one in God. For this reason, just as the Greeks say there are three hypostases, we say there are three persons, as even St. Augustine acknowledges in his De trinitate (VII, n.7, PL 42, 939).

Therefore, the question of precise language is extremely important for the preservation and development of the true Catholic faith. One of the most important functions of the Catholic theologian is to know exactly what can and what cannot be said consistent with the revealed Christian doctrine. The history of Christian belief or dogma may seem more like a history of heresies. But it is often the case that an outrageous statement or a view that is “offensive to pious ears,” male sonans, or contrary to the living faith of the Church, occasions a clarification and more exact formulation of the true faith, thus contributing indirectly to the development of Christian doctrine in the history of the Church. Therefore each new formulation, like homoousion, must be understood in the historical context of the speculative problem; in this case it was a Greek philosophical problem that needed a Greek theological solution consistent with divine revelation. The true development of Christian doctrine is never a case of abrogating or denying an earlier profession of faith, but always a more explicit profession of the one true faith in the face of given historical obsessions or preoccupations of a certain time in human history. It is only God himself who has no history. Everything created by God and governed by his immutable providence has a very definite history, one that is irreversibly unique and destined to manifest the glory of God.




The Catholic faith professes a firm belief in the divinity of Jesus Christ, the Word Incarnate, in the literal sense of the word “divine,” meaning God himself. That is:

We believe in one Lord, Jesus Christ, the only Son of God, eternally begotten of the Father, God from God (Deum de Deo), Light from Light, true God from true God, begotten (genitum), not made (non factum), one in Being (consubstantialem) with the Father. Through him all things were made. For us men and for our salvation (propter nos homines et propter nostram salutem) he came down from heaven; by the power of the Holy Spirit he was born of the Virgin Mary, and became man (et homo factus sit).

This is the ancient profession of faith approved by the Council of Nicaea (325), more fully formulated by the First Council of Constantinople (381), and recited weekly by the faithful in their Sunday liturgy. It is a belief that Jesus of Nazareth, “born of a woman, under the law” (Gal 4:4), is in his unique personality the Only Begotten Son of the Father, one in nature with him, truly God and at the same time truly man, and born as we are of a woman, “one tempted in all things as we are, yet without sin” (Heb 4:15). Quite simply, it is a belief that the historical Jesus, born of the Virgin Mary, is one divine Person in two natures, one divine, the other human.

For St. Thomas, John the Evangelist proclaims for us in a special way the “mysteries of Christ’s divinity.” For him, St. John’s Prologue is a canticle of the Word become flesh, “full of grace and truth” (Jn 1:14). The reality of who he is, therefore, is announced in the first strophe of the Prologue:

In the beginning was the Word,
And the Word was with God,
And the Word was God.
He was in the beginning with God.

To Thomas’ Aristotelian mind, the first two phrases declare the existence (an est) of the Word and the other two declare the reality of who he is (quid est). The first phrase declares “when” he was, namely, in the beginning. The second declares “where” he was, namely, with the Father. The third phrase declares who he was, namely, God. The fourth declares the “manner” so as to exclude the two basic errors concerning the Word: (1) the error of gentiles, such as pagan Greeks and Romans, who thought there were many gods, and the Manichaeans, who thought there were two gods, one good, the other evil; and (2) that of the Arians, who thought that the Word was less than the Father, different in substance, and created by the Father. Both of these errors are excluded by the fourth phrase, that the unique Word was with the Father from the beginning and identical with him in nature.

In typical scholastic fashion Thomas sees in these four lines of the first strophe a refutation of all the errors of both heretics and philosophers. As for the heretics, there were (1) some like the Ebionites and Cerinthus, who denied the existence of Jesus Christ before his conception in the womb of Mary; that is, they thought Christ to be no more than “a mere man” who later deserved to be called “divine “ being “adopted” by the Father and “accepted as the Christ” by his disciples. To this group belong Paul of Samosata (3rd cent.), Photius (9th cent.), Rudolf Bultmann and Hans Kung (20th cent.), and in a certain sense, Nestorius, about whom more will be said later. To all of these the Evangelist says, In the beginning was the Word. (2) Then there were those like Sabellius (3rd cent.) who denied the real distinction of Persons, thinking that “Father’ and “Word” are two masks for the one true God (see Note 111). To these the Evangelist says, And the Word was with God, insisting on their distinction in Person. (3) Then there were the heretics like Funomius (d. 394) and the other extreme Arians, who insisted that Jesus, though pre-existent to his incarnation, was very much unlike (anomios) the Father. To them the Evangelist says, And the Word was God. (4) Finally, there was Arius himself and all the semi-Arians, who said that the Word was less than the Father and created by him. To all these the Evangelist says, He was in the beginning with God.

As to the philosophers, there were (1) the pre-Socratics, who all, except Anaxagoras, were pure materialists, whether they acknowledged one or many elements as “nature,” or only atoms in space, for them the universe came about not by Intelligence, but by chance. Against these the Evangelist says, In the beginning was the Word; all things come by his agency, not by pure chance. (2) Plato, however, admitted the reality of things immaterial, but for him these were subsistent, immaterial Forms, or Ideas, separate from God as well as from matter. Against this the Evangelist says, And the Word was with God. (3) The later Platonists, especially Plotinus (c. 205-270 B.C.). acknowledged the existence of’ the One, from which proceeded Mind (Nous) containing all the Ideas, but who was less than the One. Lest anyone think that the Word was “with God” in this sense of being less than him, the Evangelist says, And the Word was God. (4) Finally, Aristotle placed the ideas of all things in God, and acknowledged the identity of intellect, act of intellection, and reality intellected (or known) in God, but he thought that the world was co-eternal with him, that is, created from all eternity by God. For St. Thomas, the word he in St. John (hoc in Latin; houtos in Greek) implies that he “alone” was in the beginning with God, excluding not other Persons, but any other co-eternal nature.

This is a typical example of how much a scholastic theologian like St. Thomas could see in a single strophe of John. Everything St. Thomas says in his commentary on the first strophe is entirely true and correct, but he does not mean to imply in any way that St. John had these ideas in his mind when he or his scribe wrote these opening lines of the Prologue. Here is an excellent example of St. Anselm’s “Faith seeking understanding,” or “an example of meditating on the rationale of the faith.”

The climax of the entire Prologue for Thomas is the direct statement, And the Word was made flesh (Jn 1:14), because taken literally and strictly it excludes all errors concerning the one person and the two distinct natures in Christ, one fully divine, the other as fully human as we are. In this profession of faith lies the mystery of the Incarnation. Everything else in our Christian belief, that God became man “for us and for our salvation,” that “by dying he destroyed our death,” that “by rising he restored our life,” and that “he will come again in glory to judge the living and the dead,” depends upon the basic mystery of the Incarnation, namely, that Jesus of Nazareth, born at a definite time in history of the Jewish Virgin Mary, is one unique person, “the Son of the living God,” who united in his person two wholly complete and distinct natures: human and divine.

In this note we will restrict our analysis to the mystery of the union of the human and the divine in the one person of Jesus Christ. Among the many so-called Christological heresies concerning this central mystery of Christianity, we will restrict ourselves to the three most common ones: (a) Christ was not really “divine” either in his person or in nature; (b) Christ was not really “human” like all the rest of mankind, and not “one tempted in all things as we are, yet without sin” (Heb 4:15); (c) there were two persons in Christ, one human, the other divine. But first we must begin with a preliminary note to focus the real problem.

Today it is common among historians of Christianity and Scripture scholars, at least since the time of H. S. Reimarus ( 1694-1768) to distinguish between the Jesus of history and the Christ of faith (see Sebastian Bullough, O.P., “Scripture Survey: From Wrede to the New Quest,” Blackfriars, 44, 1963, 79-82). Perhaps Rudolf Bultmann more than anyone else today has sharpened the distinction between Geschichte (the existential significance of history) and Historie (the empirical study of historical facts as objectively real). Although there are no two words in English to convey the difference between geschichtlich and historich, the whole of Bultmann’s work manifests the distinction which is fundamental to modern Christian studies and beliefs (see especially the article of Claude Geffré, “Bultmann on Kerygma and History,” Rudolf Bultmann in Catholic Thought, ed. T.F. O’Meara, O.P., and D.M. Weisser, O.P., New York: Herder and Herder, 1968, pp. 167-95). Although the bibliography on this important modern distinction is vast, and although there are many ways to exemplify the distinction between “historical science” (Historie) and “existential history” (Geschichte), we will limit our brief and simple observations to the mystery of the Incarnation.

Simply put, Historie deals with what little we can know of the historical Jesus precisely as a human being said to have been born in Bethlehem of Jewish heritage, whose mother’s name was Mary, and who was put to death. Many Protestant theologians have given up the quest for the “historical Jesus,” claiming that all our knowledge is colored by a later reaction, expressed in a kerygmatic manner, by the so-called evangelists and preachers long after the factual historical events, which had by then ceased to be important. Geschichte, on the other hand, is the Christ event, the impact on a human being of the escatalogical challenge put to each individual today as it was at the end of the first century through the basic kerygma. In other words, many Protestant theologians (and some Catholic ones) do not think that much, if anything, really certain can be known of the historical man known as Jesus of Nazareth. For most of them, the historical Jesus was an ordinary, idealistic Jewish man little different from other Jews at the beginning of the present era; perhaps in his idealism he was a “great man” who came to a tragic death and was buried.

The main thing is that much was said about him after his death and burial. And what was said is the reaction of living men accepting an eschatalogical challenge. Today the challenge made to the early Christians is made to each of us, the challenge of the existential acceptance of Jesus as “the Christ of faith.” Inevitably the acceptance of the Christ event by the early Christians expressed itself in a multitude of “myths” that sprang from the believer. The most important of these “myths” was the “deification” or “divinization” of Jesus by the believer. For Bultmann it is the myths alone that are really important. When Christ is “demythologized” there is nothing left but a tragic life of a man called Jesus. Thus the quest for “the historical Jesus” is not only vain and futile, it is also un-Christian and of no salvific value whatever. It is empty Historie, having no contemporary existential significance.

Bultmann puts the matter simply when he says: “The saving efficacy of the cross is not derived from the fact that it is the cross of Christ: it is the cross of Christ because it has this saving efficacy. Without that efficacy it is the tragic end of a great man” (quoted by C. Geffré, op. cit., p. 181).

This whole approach to the Jesus of history and the Christ of faith seems to be at the root of Hans Kung’s best seller, On Being a Christian (trans. E. Quinn, Garden City: Doubleday, 1976, from Christ Sein, Munchen: R. Piper, 1974).

This preliminary note on the contemporary, mainly Protestant, approach to Christology has been introduced here solely to show how radically different is St. Thomas’ approach to the mystery of the Incarnation. For St. Thomas (and all those before him in the Catholic faith) it is the historical Jesus who is one divine Person, the Only Begotten Son of the Father, who became man by being conceived of the Holy Spirit in the womb of the Virgin Mary, thereby uniting to himself a truly complete human nature, subject to all the natural ills and pleasures that man is heir to, including suffering and death (but not sin).

(a) The most common error concerning Jesus Christ is the one we have just been talking about, namely, that he was not truly divine in his Person as the Only Begotten Son of the Father or in his nature, which is consubstantial with the Father and the Holy Spirit. This heresy has assailed the Catholic faith from its very inception, and, as we have seen, some Protestant theologians embrace it today. The mystery of the Incarnation (or “coming in the flesh,” in carne) does indeed baffle human credulity, and it cannot be accepted without the gift of faith that comes from the Holy Spirit in baptism.

At first, not even the apostles and the immediate disciples of Jesus knew what to make of the Son of Man, the miracles he worked, the doctrine of salvation he preached. Nor did they know what to make of his constant references to God as his Father, to his doing the will of his Father, to the close presence of the Kingdom, to the Father’s Kingdom being already at hand, and to the death he was to suffer and to his ultimate victory over death. It was only with the coming of the Holy Spirit that the disciples began to understand the reality of the historical Jesus they had come to know and love. Even after his death and resurrection, Cerinthus and a large Jewish sect called the Ebionites refused to accept Christ as anything more than “a mere man” (purus homo). Various theories of “adoptionism” were common throughout the second and third centuries. This was the view that Jesus was born a mere man, but later (some put it at the baptism by John) he deserved to be “adopted” by God, much as parents might adopt an attractive boy as their son. Every form of “adoptionism” implies a “subordinationism” of Jesus, at least as a creature. It was inevitable that Arianism of one kind or another should errupt in the fourth century. Every form of “Arianism” from the extreme “anomeanism” of Eunomius to the semi-Arianism of Eusebius of Caesarea (who baptized Constantine as he lay dying on the battlefield) denied the identity of nature in the Father and in the Word, who in the fullness of time became flesh.

It was inevitable that a subdued question raised since the first century should come to a head in the Arians of the fourth century. The question was: What is the relation between Jesus, the Son of Man, and the Father, who is Yahweh? How are Jesus, born of Mary, and the Father “One”? The only possible answer consistent with the biblical writings was the unbiblical term (homoousion) “consubstantial.” The neo-Platonism of Plotinus unmistakably influenced Origen and many other Greek Christians. For Plotinus the Logos or nous emanates from the One and is less than the One, just as the Spirit emanates from the Logos and is less than it. Neo-Platonism together with the natural inability to accept any “man” as “God” inevitably resulted in the widespread Arianism of the fourth century. To appreciate even inadequately the threat Arianism posed for the Church even after the Council of Nicaea (325), one might recall how at one time the great St. Athanasius seemed to stand alone (Athanasius contra mundum), and how even St. Jerome in the West could say that the whole world woke up one day to find itself Arian. The fourth century, beset as it was by various forms of Arianism and the dubious “freedom” of the Church, was the greatest age of the Fathers, both Greek and Latin, in the history of the Church. It was the “golden age of the Fathers.” Through them the Holy Spirit preserved orthodoxy through a development of doctrine and a flowering of heroic sanctity unparalleled since the age of the martyrs.

Possibly the climax of the fourth century came with the Council of’ Rome in 382 under Pope St. Damasus I, in which the whole development of Christian doctrine up to that date was summarized in the Tomus Damasi, and the canonical books of Sacred Scripture were fixed as we have them today (see Denz. 152-180).

The relation of Nestorianism to Arianism will be discussed under heading (c).

(b) The second most common heresy concerning the Incarnation is, in fact, the direct opposite of the first. Just as the first cannot accept a man who is God, so the second cannot accept a God who became man. Just as Arianism (and all forms of adoptionism, subordinationism, and the like) is a kind of naturalism that sees Jesus as a creature, so this second heresy (in its many forms) is a kind of spiritualism that disdains matter as something unworthy of being a creature of God at all. Basically it is a denial that Jesus had a real human body, and that he really suffered and died. In its earliest form it is called Docetism (from the Greek, dokeo, “I seem”) and existed as a tendency rather than a formulated and unified doctrine, which considered the humanity and sufferings of the earthly Christ as apparent rather than real. Evidence of its existence in the early Church is to be found in 1 John (4:1-3) and 2 John (v 7); see also Colossians (2:8-9). But it reached its zenith among the Gnostics of the second and third centuries (see G. Bareille, DTC, IV, cols. 14841501, s.v. “Docetisme”). Besides Gnostics like Serapion, Bishop of Antioch (190-203), there was Marcion (d. c. 160), who claimed that Christ, who was an “emissary” of the Father, suddenly appeared preaching and teaching in the synagogue at Capernaum, and was not born of woman at all, but whose passion and death were the work of the evil Creator God of the Old Testament.

The most complete formulation of this heresy seems to be that of Manichaeism, promulgated by a certain Manes (c. 216-276) from Persian Gnostic sources. Its basic principle is that matter is evil and the creature of an Evil God, or Demiurge. Thus the true God could not have assumed a real human body made up of flesh and bones an ‘ d been born in the manner of men. For them, the body of Jesus was an “apparent body,” a “glorified” body. Manichaeism was established in Egypt before the end of the third century, but here its roots were deeply imbedded in the Egyptian Gnosticism of the second century. Early in the fourth century there were sects in Rome, and by the end of that century, Manichaeism spread through out North Africa. Even St. Augustine himself was a Manichee for nine years before his conversion. Although the details of Manichaeism are complex, as are its subsequent forms as adopted by the Albigensians, Cathari, and Puritans, its basic principle is clear: Jesus Christ could not have been a true man like us. He gave only the “appearance” of joy and tears, suffering and death, since such physical things are unworthy of God. It is fundamentally a dualism unable to reconcile spirit and matter, God and man, divinity and humanity (or even flesh and spirit in man). Together with an irreconcilable dualism in Manichaeian Christology, there is an irreconcilability in its puritanical spirituality, as well as a fundamental inability to accept the human body as a work of God’s art, or man as the “image of God.” St. Thomas combines all the various sects that deny the full reality of Christ’s human body under the heading of “Manichaeian.”

The basic point Thomas insists on is the absolute reality of the concrete, individual human nature of Christ that was begotten of the Virgin Mary (Sum. theol. III, q.5, a.1). In the words of the De ecclesiasticis dogmatibus (c. 2; sometimes attributed to Augustine, but in reality the work of Gennadius), St. Thomas stressed that the “body” (corpus) assumed by the Word “was not putative, as though it were something imaginary” (PL 58, 981). For him, the whole significance and purpose of the Incarnation and Redemption of man would have been frustrated unless the “flesh” (Jn 1:14) assumed by the Word were a true physical and organic human body, made of flesh and blood as we are, possessing all that is needed to constitute a complete human nature without original sin. Apart from Scriptural texts, Thomas relies most heavily on the Council of Ephesus (43 1), which declared the Virgin Mary to be in truth the “Mother of God, from whom that perfect, holy body, informed with an intellective soul, was taken, to which the Word of God is united in his person (secundum hypostasim) and said to be born in the flesh” (Denz. 25 1; cf. Sum. theol. III, q.4, a.3, Sed contra, etc.).

Historically there were opinions, later condemned, that denied that Christ had a human soul; such was the position of certain Arians and later of Apollinaris (cf. St. Aug. De haeres., 49. PL 42, 40; St. Athanasius, Contra Apollinarium, Lib. II, n. 3. PG 26, 1136; St. Thomas, Sum. theol. III, q.5, a.3). For them the place of the human soul was taken by Christ’s divinity. Historically there were some, like the Monothelites, who denied that Christ had a human will, its place being taken by the divine will (on this point consult ODCC, 2nd ed. Oxford 1974, 932-33). But most extensive was the view of the Monophysites, whom we shall discuss later, who held that Christ has only one nature both divine and human. Such a union, according to St. Thomas, would result in a tertium quid that would be less than divine and more than human, which would in effect be a denial of the reality of both Christ’s humanity and his divinity (Sum. theol. III, q.2, a. 1). An extreme form of Monophysitism was condemned in the person of Eutyches (d. 454) at the Council of Chalcedon (451), to which the Monophysites of today have remained implacably opposed (cf. ODCC, 931-32).

The basic view of St. Thomas is that the whole of human nature, past, present, and to come, was united to the divinity in the one, indivisible person of Jesus Christ. In this indivisible unity the eternity of God, which knows no beginning, middle, or end. was joined to the temporality and historicity of man, with all its yesterdays and tomorrows, all its aches and pains, all its grandeur and ignominy. How the eternal instant of God felt, thought, willed, grew, and matured, suffered and died in his human nature is a mystery that is too much for our all-to-temporal being to understand. But we must take consolation in the fact that Jesus fully experienced all the human loves, compassion, loneliness, joys and desires, affection and aspirations that we experience too often in an inhuman and incomplete way. And he endured incredible suffering and death. The same Jesus who could pour out his heart in love for his disciples (Jn 14-17) is the same Jesus who could say, “I am thirsty” (Jn 19:28), and “My God, my God, why have you forsaken me?” (Mt 27:46).

The less we appreciate the true humanity of the historical Jesus, the less we involve ourselves in the divinity that Christ came to give us. One constant theme of all the great Fathers of the Church, especially St. Athanasius and St. Augustine, is that God became a partaker of our humanity that we might become partakers of his divinity. There is only one point in which divinity and humanity meet for all eternity, and that is in the person of the historical Jesus.

(c) The main theological and philosophical difficulty that arises from what has already been said is “Why is the historical Jesus not a human person?” If a person is “an individual substance of an intellectual nature,” as Boethius had said (see above, Note III), then why is not the individual human nature born of the Virgin Mary not a human person, that is, a “man”? Could a divine Person, the Son of God, assume a human person, in which case there would be two persons in Jesus, just as there are two natures? As the Greeks put the question, “Why are there not two hypostases in Jesus?” We do not say that the Word assumed “a man,” but a human nature. Technically, this is a real philosophical problem that has its roots in Aristotelian philosophy. Normally what Mary would have given birth to should have been a human person having an individual human existence (esse). But, in fact, she gave birth to a divine Person, the Only Begotten Son of the eternal Father, in human flesh.

Historically, Nestorius, patriarch of Constantinople (428-3 1), condemned the teaching of some monks concerning the divine maternity of Mary. These monks even went so far as to call Mary, the “Mother of God,” Theotokos (deipara, or Dei genetrix), meaning “God-bearer.” For Nestorius, God could have no mother, for he existed from all eternity; Nestorius therefore insisted that Mary could only be called Christotokos, the mother of Christ, or “Christbearer,” thus teaching that the hypostasis or person of Christ, born of Mary, was other than the divine person begotten of the Father. Thus, while emphasizing the infinite gap between the human nature of Christ and his divine nature as God, Nestorius and his numerous followers (even to this day) also taught that an infinite gap exists between the hypostasis begotten of Mary and the Second Person (hypostasis) of the Holy Trinity. In other words, Nestorius taught not only a duality of nature (physeis) in Christ, but also a duality of substances (hypostases), that is, of persons. We have already touched upon the difficulties of the Greek and Latin terminology in this matter (Notes III and IV above).

The Council of Ephesus was convoked in 431 by Theodosius II at the instigation of St. Cyril, patriarch of Alexandria and representative of Pope Leo I at the Council. Much to the surprise of Nestorius, his views were condemned and the Council declared that the human nature of Christ is united to the divine, not by a fusion of natures (secundum naturam, kata physin), but by an identity of person (kath hypostasin; secundum personam). In other words, the Council of Ephesus declared as a matter of revealed doctrine that there is only one person in Christ—the Divine Word, the Son of the Father, the Second Person of the Blessed Trinity—and a duality of natures that always remain distinct, except by reason of the Divine Person (Denz. 250-264).

One of the monks denounced by Nestorius in his sermons was the archimandrite Eutyches, who taught that in Christ there is an intimate fusion of natures, so that after the Incarnation there was in Jesus only one person and one nature. The Council of Chalcedon was convoked in 541 by the Emperor Marcion under the presidency of St. Flavian to consider the orthodoxy of the extreme view proposed by Eutyches. The Monophysite (one-nature) position held by Eutyches and his followers was condemned outright as contrary to orthodox belief, and the Council declared that Jesus Christ has two distinct natures, in no way “fused or changed into one.”

This historical background is necessary in order to understand St. Thomas’ commentary on John because he refers to these heresies ,ind their condemnations over and over again. Thomas, in fact, was one of the first scholastics to utilize the Latin translations of the Greek acts, decrees, and canons.

St. Thomas’ most important contribution to Christology is his insight into the manner of the union between the divine and the human in Christ (see Friar Thomas dAquino, pp. 307-313). The crux of his profound insight into the fact that the union must be hypostatic is most clearly expounded in the two articles on the unity of Christ’s esse (q. 17). To this problem we must now turn briefly.




The Council of Ephesus (431) declared against Nestorius that there is only one hypostasis in Jesus, and that that hypostasis is the eternal Son of the Father, consubstantial with him in nature (that is, physis), or substance (ousia). The Council of Chalcedon (451) declared against Eutyches that there are two distinct natures in Christ in no way “fused or changed into one,” but are united kath’ hypostasin, that is, by reason of one person. Since the union cannot be between the two natures, divine and human, for the two would become one nature, and since the union cannot be between the divine Person and the human person, for this could only be a union secundum quid and per accidens, the union can only be in the unique Person, that is, secundum hypostasin. Since, as we have already seen, what the Greeks called hypostasis, the Latins called persona, the union of the divine and human in Christ is called “personal” or “hypostatic” (see Boethius, Contra Eutychen et Nestorium).

But the philosophical clarification and possibility of a theological understanding of the mystery did not come to Thomas until he returned to Naples in 1272 and resumed dictating the Tertia Pars. By the time Thomas came to compose question 17 concerning the kind and number of existences (esse) in Christ, he saw clearly the mysterious reality of the Incarnation.

We have already explained that for Aristotle nature is only a quo, that by which a thing is what it is. An individual, specific nature is “had by” a concrete suppositum or ousia (substance) in the primary sense of the term. We also said that existence (esse) belongs only to things, substances in the primary sense of ousia, that is esse belongs to a concrete, individual substance (ousia) having a specific kind of nature, by means of which the thing exists as a specific kind of thing. A thing is one because it has one esse.

Regarding the Incarnation the inevitable question arises as to whether Christ is one or many (a. 1), and whether in Christ there is only one esse or more (a. 2). Prior to q. 17 in the Tertia Pars, for example in the Disputed Question De unione verbi incarnati, debated in Paris earlier that year ( 127 2), Thomas thought that the individual human nature begotten of Mary must have some kind of esse of its own, even if only “in a certain sense” (secunduin quid) “as human.” But this would mean that in the strict sense (simpliciter) Christ is one” because he has only one person, namely, the divine; but in another sense Christ is “two” (secundum quid), because he has two natures. In the Summa (III, q.17, a.2) Thomas in no way allows the human nature of Christ to have an esse proper to it. If the concrete, individual human nature that Christ received from Mary had its own esse in any way, then the union between it and the Divine Person would be accidental, and Christ would not be absolutely and indivisibly one being, one person. Even if the new manner or mode of God’s existence, namely, “as human,” had its own esse secundum quid, as Thomas earlier thought, then the union would not be absolutely and in every way one, but secundum quid many. From this it would follow that the union between the Divine Person and the human nature would be “accidental” an accident in a substance. But the union between Christ’s human nature and his Divine Person cannot be accidental, no more than our human nature can be accidental to our personality. Therefore, St. Thomas concluded, the human nature of Christ and all his natural characteristics and his activities exist by the one esse of the Godhead. Thus the special kind of union that exists between the person of Jesus Christ and his human nature is “personal” or “hypostatic,” that is, secundum personam or kath’ hypostasin.

Thomas’ understanding of the hypostatic union rests squarely on his basic principle that in all creatures esse is other than essence. Only in God are esse and his essence identical (see Sum. theol. I, q.3, a.4, and all parallel places). Fr. Norbert Del Prado, O.P., has called this so-called real distinction between essence and existence in creatures “The Fundamental Truth of Christian Philosophy” (1911). It is only because human nature does not include esse in its definition (nature, or essence) that Christ’s human nature cannot have an esse proper to it as human. It is the real distinction between essence and existence (esse) in creatures that underlies Thomas’ teaching in III, q. 17.

It is clear, therefore, that all other medieval positions that identify essence and esse in creatures—such as the Scotists, Nominalists, Suarezians—must face the question of the hypostatic union in another way. This is not the place to discuss those other views.

This then is our faith, that Jesus Christ, born of Mary at a specific time in human history, is in reality God himself; he is the Only Begotten Son of the eternal Father, identical with him in nature and being (esse), but distinct from the Father as a Son who receives all that he has from the Father. As this Only Begotten Son is identical with his divine nature and as he was truly begotten of Mary by the Holy Spirit, Jesus—the historical Jesus has two distinct natures, one divine by which he is equal to the Father (Jn 17:11), the other human by which he is the Son of Mary, less than the Father Qn 14:28), a man like us in all things except sin—in short, our brother in the flesh. Thus our Lord Jesus Christ, Son of the living God and our brother in the flesh, by the will of the Father and the work of the Holy Spirit, brought life into the world by his death and resurrection. By his death on the cross he destroyed our death of damnation. By his resurrection he restored our life of grace and glory. And we believe that he will come again in glory to judge the living and the dead.

The only point that still needs to be mentioned here is that only the Son, the Word, “became flesh” (Jn 1:14). In the Nicene Creed we profess our belief in one Lord, Jesus Christ, the only Son of God, eternally begotten of the Father ... one in being (that is, homoousion) with the Father. Then we profess our belief in his Incarnation when we bow our heads as we say: “By the power of the Holy Spirit he was born of the Virgin Mary, and became man.” That is to say, only the Son of God became man, not the Father, nor the Holy Spirit. We cannot say that the Father suffered and died for us; nor can we say that the Holy Spirit became man, suffered under Pontius Pilate, died and was buried. Only in the heresy of Sabellius (3rd cent.) where the word person is taken to be a “mask” (persona, or prosopon) through which the one God speaks to us with different masks could one say, “the Father suffered and died.” This heresy in the West has also been known as Patripassionism, meaning that the “passion of Christ” can be attributed to the Father. This heresy, also known as “Modalism,” was condemned in 447 by Pope Leo I in a letter to Turribius, bishop of Asurias (Denz. 284). It had long been battled in the East by St. Basil the Great (c. 330-379).

Thus Christ alone is the mediator between God and man. “There is no other name, under heaven, given to men by which we must be saved” (Acts 4:12). St. Paul expresses the simple truth in the most direct way when he said (1 Tim 2:5-6):

There is one God,
and one mediator between God and man, the man Christ Jesus,
who gave himself as a ransom for all.