In the midst of the Arian controversy of the fourth century, orthodox Christians struggled over how to best articulate the doctrine of the Trinity in a way that would exclude both Arianism, which regarded Christ as a creature, and Modalism, which regarded the three persons of the Trinity as being a single person. The Nicene Creed ended up serving as a solution; it clearly distinguished between the distinct persons of the Trinity “one God, the Father Almighty”, “one Lord, Jesus Christ, the Son of God”, and “the Holy Spirit”, thus excluding Modalism, while also defining that Christ was “begotten from the Father, only-begotten, that is, from the essence of the Father, God from God, light from light, true God from true God, begotten not made, of the same essence as the Father”, to the exclusion of Arianism.
The language of the Son being begotten “from the essence of the Father” and being “of the same essence” were included specifically to confess the divinity of Christ, contra Arianism. The point of this confession that the Son was co-essential with the Father was that He was eternally of the same divine nature as the Father; thus truly God in nature from all eternity.
While this language was orthodox when used with this meaning, a great many orthodox bishops were weary of the language, especially the language that the Son is “of the same essence” as the Father, since this language had been used by modalists in articulating their heresy. This terminology became the subject of much controversy in the approximately fifty years between the Council of Nicea and Council of Constantinople, where the Nicene Creed was again finally confirmed by the church, not only because the Arians opposed it, but also because many orthodox bishops wanted to avoid the language that had been previously condemned because of its use by modalists. These orthodox bishops worried that such language may be intended to confess modalism by making the Father, Son, and Spirit out to be a single person. For this reason, many did not accept the decision of Nicea for many years, although consensus was eventually reached by the time of the Council of Constantinople in 381, in large part thanks to the efforts of Athanasius in favor of the terminology.
Because the language of essence (ousia in Greek) and co-essentiality (‘homoousias’ in Greek) was the subject of so much controversy, and is not used in scripture, it became the subject of quite a bit of writing by orthodox church fathers such as Athanasius and Hilary of Poitiers. Hilary of Poitiers, writing on the regional synods held by Eastern churches in the intervening period between the Council of Nicea in 325 and the Council of Constantinople in 381, gave an extremely helpful explanation of what the language meant in his work On the Synods of the Easterners.
In this work he goes into detail in explaining what the orthodox framers of the Nicene Creed intended by the language of ‘essence’ and ‘co-essentiality’, as well as the various ways that the language could be misunderstood heretically, which he acknowledged gave some legitimacy to those who opposed such language for fear of it carrying a heretical meaning. Hilary urges that it must be carefully defined, and understood according to the orthodox intention of the Nicene Council, and that so long as it is understood rightly, it must be accepted as orthodox.
Sadly, in later church history, the language and concept of co-essentiality was indeed twisted contrary to its original meaning (see: https://contramodalism.com/tag/fourth-lateran-council/). Semi-modalism thrives off of a twisting of the doctrine of co-essentiality that teaches that ultimately the persons of the Father, Son, and Spirit are together a singular person who exists as all three; the person of “God the Trinity”. The concern of orthodox church fathers like Hilary that such language would be misunderstood if not carefully defined has truly been realized, and needs to be corrected.
In this post, I hope to examine and highlight Hilary’s insightful teaching on this subject. I urge the reader to pay special attention to Hilary’s teaching that co-essentiality understood rightly teaches not that the Father and Son are one concrete “thing”, nor a single person, but that they are of exactly the same and identical divine nature, as two truly distinct persons. Note also the ways in which he says the concept can be misunderstood heretically, and how much this sounds precisely like semi-modalism. To the interested reader, I highly recommend the entire work, available online here: http://www.newadvent.org/fathers/3301.htm.
Hilary of Poitiers writes:
“Many of us, beloved brethren, declare the substance of the Father and the Son to be one in such a spirit that I consider the statement to be quite as much wrong as right. The expression contains both a conscientious conviction and the opportunity for delusion. If we assert the one substance, understanding it to mean the likeness of natural qualities and such a likeness as includes not only the species but the genus, we assert it in a truly religious spirit, provided we believe that the one substance signifies such a similitude of qualities that the unity is not the unity of a monad but of equals. By equality I mean exact similarity so that the likeness may be called an equality, provided that the equality imply unity because it implies an equal pair, and that the unity which implies an equal pair be not wrested to mean a single Person [here he predicts semi-modalism]. Therefore the one substance will be asserted piously if it does not abolish the subsistent personality or divide the one substance into two, for their substance by the true character of the Son’s birth and by their natural likeness is so free from difference that it is called one [note that the substance is one not because it is one existing “thing” which is the Father and Son, but because the Father and Son have an exactly identical nature].
68. But if we attribute one substance to the Father and the Son to teach that there is a solitary personal existence although denoted by two titles: then though we confess the Son with our lips we do not keep Him in our hearts, since in confessing one substance we then really say that the Father and the Son constitute one undifferentiated Person [semi-modalism]. Nay, there immediately arises an opportunity for the erroneous belief that the Father is divided, and that He cut off a portion of Himself to be His Son. That is what the heretics mean when they say the substance is one: and the terminology of our good confession so gratifies them that it aids heresy when the word ὁμοούσιος is left by itself, undefined and ambiguous. There is also a third error. When the Father and the Son are said to be of one substance this is thought to imply a prior substance, which the two equal Persons both possess. Consequently the word implies three things, one original substance and two Persons, who are as it were fellow-heirs of this one substance. For as two fellow-heirs are two, and the heritage of which they are fellow-heirs is anterior to them, so the two equal Persons might appear to be sharers in one anterior substance. The assertion of the one substance of the Father and the Son signifies either that there is one Person who has two titles, or one divided substance that has made two imperfect substances, or that there is a third prior substance which has been usurped and assumed by two and which is called one because it was one before it was severed into two. Where then is there room for the Son’s birth? Where is the Father or the Son, if these names are explained not by the birth of the divine nature but a severing or sharing of one anterior substance?
69. Therefore amid the numerous dangers which threaten the faith, brevity of words must be employed sparingly, lest what is piously meant be thought to be impiously expressed, and a word be judged guilty of occasioning heresy when it has been used in conscientious and unsuspecting innocence. A Catholic about to state that the substance of the Father and the Son is one, must not begin at that point: nor hold this word all important as though true faith did not exist where the word was not used. He will be safe in asserting the one substance if he has first said that the Father is unbegotten, that the Son is born, that He draws His personal subsistence from the Father, that He is like the Father in might, honour and nature, that He is subject to the Father as to the Author of His being, that He did not commit robbery by making Himself equal with God, in whose form He remained, that He was obedient unto death. He did not spring from nothing, but was born. He is not incapable of birth but equally eternal. He is not the Father, but the Son begotten of Him. He is not any portion of God, but is whole God. He is not Himself the source but the image; the image of God born of God to be God. He is not a creature but is God. Not another God in the kind of His substance, but the one God in virtue of the essence of His exactly similar substance. God is not one in Person but in nature, for the Born and the Begetter have nothing different or unlike. After saying all this, he does not err in declaring one substance of the Father and the Son. Nay, if he now denies the one substance he sins.
70. Therefore let no one think that our words were meant to deny the one substance. We are giving the very reason why it should not be denied. Let no one think that the word ought to be used by itself and unexplained. Otherwise the word ὁμοούσιος [co-essential] is not used in a religious spirit. I will not endure to hear that Christ was born of Mary unless I also hear, In the beginning was the Word, and the Word was God. John 1:1 I will not hear Christ was hungry, unless I hear that after His fast of forty days He said, Man does not live by bread alone. Matthew 4:4 I will not hear He thirsted unless I also hear Whosoever drinks of the water that I shall give him shall never thirst. John 4:13 I will not hear Christ suffered unless I hear, The hour has come that the Son of man should be glorified. I will not hear He died unless I hear He rose again. Let us bring forward no isolated point of the divine mysteries to rouse the suspicions of our hearers and give an occasion to the blasphemers. We must first preach the birth and subordination of the Son and the likeness of His nature, and then we may preach in godly fashion that the Father and the Son are of one substance. I do not personally understand why we ought to preach before everything else, as the most valuable and important of doctrines and in itself sufficient, a truth which cannot be piously preached before other truths, although it is impious to deny it after them.
71. Beloved brethren, we must not deny that there is one substance of the Father and the Son, but we must not declare it without giving our reasons. The one substance must be derived from the true character of the begotten nature, not from any division, any confusion of Persons, any sharing of an anterior substance. It may be right to assert the one substance, it may be right to keep silence about it. You believe in the birth and you believe in the likeness. Why should the word cause mutual suspicions, when we view the fact in the same way? Let us believe and say that there is one substance, but in virtue of the true character of the nature and not to imply a blasphemous unity of Persons. Let the oneness be due to the fact that there are similar Persons and not a solitary Person [here classical trinitarianism is vindicated in teaching that God and His Son are co-essential in that they are identical in nature, having the same divine nature, and semi-modalism is refuted for teaching that the Trinity of three persons is itself a solitary person].
72. But perhaps the word similarity may not seem fully appropriate. If so, I ask how I can express the equality of one Person with the other except by such a word? Or is to be like not the same thing as to be equal? If I say the divine nature is one I am suspected of meaning that it is undifferentiated: if I say the Persons are similar, I mean that I compare what is exactly like. I ask what position equal holds between like and one? I enquire whether it means similarity rather than singularity. Equality does not exist between things unlike, nor does similarity exist in one. What is the difference between those that are similar and those that are equal? Can one equal be distinguished from the other? So those who are equal are not unlike. If then those who are unlike are not equals, what can those who are like be but equals?
73. Therefore, beloved brethren, in declaring that the Son is like in all things to the Father, we declare nothing else than that He is equal. Likeness means perfect equality, and this fact we may gather from the Holy Scriptures, And Adam lived two hundred and thirty years, and begot a son according to his own image and according to his own likeness; and called his name Seth. Genesis 5:3 I ask what was the nature of his likeness and image which Adam begot in Seth? Remove bodily infirmities, remove the first stage of conception, remove birth-pangs, and every kind of human need. I ask whether this likeness which exists in Seth differs in nature from the author of his being, or whether there was in each an essence of a different kind, so that Seth had not at his birth the natural essence of Adam? Nay, he had a likeness to Adam, even though we deny it, for his nature was not different. This likeness of nature in Seth was not due to a nature of a different kind, since Seth was begotten from only one father, so we see that a likeness of nature renders things equal because this likeness betokens an exactly similar essence. Therefore every son by virtue of his natural birth is the equal of his father, in that he has a natural likeness to him. And with regard to the nature of the Father and the Son the blessed John teaches the very likeness which Moses says existed between Seth and Adam, a likeness which is this equality of nature. He says, Therefore the Jews sought the more to kill Him, because He not only had broken the Sabbath, but said also that God was His father, making Himself equal with God. John 5:18 Why do we allow minds that are dulled with the weight of sin to interfere with the doctrines and sayings of such holy men, and impiously match our rash though sluggish senses against their impregnable assertions? According to Moses, Seth is the likeness of Adam, according to John, the Son is equal to the Father, yet we seek to find a third impossible something between the Father and the Son. He is like the Father, He is the Son of the Father, He is born of Him: this fact alone justifies the assertion that they are one [this paragraph refutes those who try to make the oneness of the Father and Son, and their co-essentiality, to consist of being one subsisting “thing”; rather, their essential oneness lies in the two persons each distinctly possessing the exact same divine nature, and so there only being one divine nature between the two of Them].
74. I am aware, dear brethren, that there are some who confess the likeness, but deny the equality. Let them speak as they will, and insert the poison of their blasphemy into ignorant ears. If they say that there is a difference between likeness and equality, I ask whence equality can be obtained? If the Son is like the Father in essence, might, glory and eternity, I ask why they decline to say He is equal? In the above creed an anathema was pronounced on any man who should say that the Father was Father of an essence unlike Himself. Therefore if He gave to Him whom He begot without effect upon Himself a nature which was neither another nor a different nature, He cannot have given Him any other than His own. Likeness then is the sharing of what is one’s own, the sharing of one’s own is equality, and equality admits of no difference. Those things which do not differ at all are one. So the Father and the Son are one, not by unity of Person but by equality of nature [contrast this with later articulations of co-essentiality, like that of the Fourth Lateran Council, which redefined it to mean a unity of persons into a single person, only avoiding the term “person”; Van Til would later come out and express the belief frankly, calling the Trinity itself a single “person”. We see from Hilary’s own words here how antithetical this view is to the intention of the orthodox church fathers of the Nicene era].
75. Although general conviction and divine authority sanction no difference between likeness and equality, since both Moses and John would lead us to believe the Son is like the Father and also His equal, yet let us consider whether the Lord, when the Jews were angry with Him for calling God His Father and thus making Himself equal with God, did Himself teach that He was equal with God. He says, The Son can do nothing of Himself, but what He sees the Father do. John 5:19 He showed that the Father originates by saying Can do nothing of Himself, He calls attention to His own obedience by adding, but what He sees the Father do. There is no difference of might, He says He can do nothing that He does not see because it is His nature and not His sight that gives Him power. But His obedience consists in His being able only when He sees. And so by the fact that He has power when He sees, He shows that He does not gain power by seeing but claims power on the authority of seeing. The natural might does not differ in Father and Son, the Son’s equality of power with the Father not being due to any increase or advance of the Son’s nature but to the Father’s example. In short that honour which the Son’s subjection retained for the Father belongs equally to the Son on the strength of His nature. He has Himself added, Whatever things He does, these also does the Son likewise. John 5:19 Surely then the likeness implies equality. Certainly it does, even though we deny it: for these also does the Son likewise. Are not things done likewise the same? Or do not the same things admit equality? Is there any other difference between likeness and equality, when things that are done likewise are understood to be made the same? Unless perchance any one will deny that the same things are equal, or deny that similar things are equal, for things that are done in like manner are not only declared to be equal but to be the same things.
76. Therefore, brethren, likeness of nature can be attacked by no cavil, and the Son cannot be said to lack the true qualities of the Father’s nature because He is like Him. No real likeness exists where there is no equality of nature, and equality of nature cannot exist unless it imply unity, not unity of person but of kind. It is right to believe, religious to feel, and wholesome to confess, that we do not deny that the substance of the Father and the Son is one because it is similar, and that it is similar because they are one.
77. Beloved, after explaining in a faithful and godly manner the meaning of the phrases one substance, in Greek ὁμοούσιον, and similar substance or ὁμοιούσιον, and showing very completely the faults which may arise from a deceitful brevity or dangerous simplicity of language, it only remains for me to address myself to the holy bishops of the East. We have no longer any mutual suspicions about our faith, and those which before now have been due to mere misunderstanding are being cleared away…”
This treatment of co-essentiality is instructive for modern Christians. To those familiar with later articulations of co-essentiality by semi-modalists, it should be clear that they have fallen into exactly the sorts of errors Hilary of Poitiers warned against by conceiving of the essence shared by the persons of the Trinity as a singular personal subsistence; in other words, a person. Hilary’s words make it clear that semi-modalistic misunderstandings of co-essentiality are not faithful to the original meaning of the doctrine and terminology employed by the Nicene Creed and orthodox church fathers. We must reject the later innovations of semi-modalism and return to the classical understanding of co-essentiality articulated by the Nicene church fathers if things are to improve.