3 Terms about the Trinity You Should Know & How We Got Them

A graphic featuring a triangle representing the Trinity

Sometimes theology can appear daunting. That is especially the case when it comes to the doctrine of the Trinity. Many of us—even those who have studied the Trinity for years—appeal far more often to “mystery” when it comes to knowing and delighting in the Trinity than we do in other doctrinal areas. While there is indeed a great mystery to be acknowledged in the Trinity, there remain important conceptual tools to master. The necessary terms to know, like homoousios, can be intimidating; so it’s tempting to assume we can do away with them. What do they have to do with the gospel, after all? Homoousios isn’t in the Bible; it’s not even in English. Is it really necessary?

Technical terms like homoousios matter. They matter not only for the theologian or the pastor but for the layperson who is seeking to know the God they worship. Ask any medical doctor about whether technical terms have a place. They will tell you that while much of the jargon may be unnecessary for the patient to remember, the complex ideas named by technical terms are crucial for medical professionals. Knowing the ideas behind the terms can even be the difference between life and death. Likewise, it benefits us to know the ideas and the terms that have safeguarded our knowledge of God and his actions for us and our salvation.

Crucial trinitarian terms

Before explaining some of the crucial trinitarian terms, I should warn you that there is much to explain precisely because these terms are embedded in an exhilarating history. There is debate, persuasion, craftiness, political intrusion, and more. And such doctrinal “development” shouldn’t worry the Christian. It is not as if the doctrine of the Trinity is “invented” or “innovated” beyond what Scripture says. It is the process all Christian theology undergoes through the tutelage of the Spirit as he guides us into all truth. It is a clarifying process as we begin to experience and know more of the divine mystery.

I should also be clear: these terms alone do not make for a fully robust trinitarian theology.1 To focus only on the technical terms would result in a misshapen trinitarian doctrine. While they are a crucial aspect of the trinitarian home, they are but one room in it.

Khaled Anatolios suggests that trinitarian terminology is “not the inner shrine of the meaning of trinitarian doctrine, but a set of logical regulators that safeguard the contents of that meaning.”2 So it ought to be remembered from the outset of our exploration of trinitarian terminology that it is designed to protect and preserve the divine mystery found in Holy Scripture.

Terminological precision: What do these words mean?

Several key trinitarian terms have been enshrined in creedal formulas as time-tested ways to describe and understand God. They aren’t all biblical words in the sense that they can be found explicitly in the Bible, but they do describe biblical ideas. Just as we can’t find the word “Trinity” in the Bible despite its biblical meaning, these words won’t always be literally in our Bibles. That’s okay. We need extra-biblical words to communicate what is actually in the Bible. This shouldn’t scare us. What matters is not whether the words we use are found in our Bibles but whether the ideas we believe are there.3 The fathers of the early church certainly thought that words like homoousios safeguarded and extrapolated biblical ideas. It was the biblical terminology of Christ as Word, Wisdom, and Image that fundamentally motivated their dogmatic claims.4

Below are several key trinitarian terms I think all Christians should know. Many of the terms whose meanings were hammered out throughout the early church era have overlapping—though not always identical—meanings. This is because of the language differences between the Latin West and Greek East. For example, confusion can be had because what the West calls substance is labeled ousia (or essence) by the East; and what the West calls person is labeled as hypostasis by the East—but this term is quite literally substance.5 However, it’s well attested that the theological differences between these terms are overblown; though the way the terms sound to each ear can certainly provide different inflection points.6

Let’s begin.

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Homoousios = The same essence (e.g., A divine person shares the numerically identical essence; consubstantial)

Homoousios is probably the most famous trinitarian technical term coming out of the doctrinal debates in the early church. Whatever is homoousios is of the same essence or substance as something else. In our case, the Father, Son, and Spirit are all of the same substance or essence. They all have the attributes necessary to count as God in the fullest sense.7 Whatever the Father has, the Son has it. For example, as Origen says, “There is no other second goodness existing in the Son, besides that which is in the Father.”8 Similarly, Gregory of Nyssa says, “we behold all the [attributes] of the Father in the Son, and all the [attributes] of the Son are of the Father, since the Son remains wholly in the Father and contains the Father wholly in himself.”9So, there is no distinction to be made here in any sense. There is no junior God. There is no mediating figure in God. The Son and Spirit were not created but exist eternally as God. But the essence is not a fourth “thing” over and above the three persons of the Trinity. The essence only “exists” by subsisting in particular divine persons.10

I should note that it may not be immediately obvious that substance and essence can be used interchangeably as I’ve suggested here. If you feel this conceptual unease, it is mainly due to the language differences between regions in the early church and the later development of these terms in other contexts. While most Christian theologians depended on Aristotle’s Categories to understand the notion of substance, Aristotle had different senses of substance in that work, and his other metaphysical works have even more. So, this terminology can become confusing. Suffice it to say, by the time of Augustine, terms like “nature” (natura), “essence” (essentia), and “substance” (substantia) are thought to be identical terms. However, we must exercise caution since God is only properly being but improperly substance.11


Homoiousios = Like in essence

Homoiousios is similar to homoousios but is less rigid. It means that something is of like essence. So, the Son is like the Father in essence. This likeness does not require identity (e.g., the Son may share some of the same properties as the Father but lack others), though it could be used in a way to mean what homoousios communicated—as long as the appropriate modifiers are added (for example, “like in all things”). Without getting into the details of development just yet, this term was thought to be less forceful than homoousios and was ultimately rejected as deficient as a descriptor for the Persons of the Trinity.

However, prior to formally codifying the Nicene Creed as the standard of orthodoxy alongside homoousios, some such as Athanasius—in an effort to build support for the shared belief that the Son is of the same ousia as the Father—argued that homoiousion theology was better expressed and secured against faulty interpretations by homoousios. In other words, those that preferred homoiousios to homoousios could retain their own theology in its essentials but had a better term available to communicate those same things.12

It is important to remember, though, that these evaluative judgments were made at distinct periods in time as the doctrine was debated. The sort of argument Athanasius uses here was made against the backdrop of the creed of Nikē which came through much imperial pressure in 360. The creed brazenly denied the likeness of essence between Father and Son in “all things” and outlawed any and all talk of ousia. Athanasius saw in that viewpoint an opportunity to gain support for the Nicene Creed and homoousios. Athanasius likely would not have shared the same opinion in the same manner after 381. More of the story here will be detailed as we progress. But understanding this term remains relevant for the overall shape of the trinitarian debates in the fourth century even though it ultimately will fade into the background for orthodox trinitarian formulas.


Hypostasis (or persona) = an independent subsistence of a rational nature

The way I define hypostasis here is how the term came to be codified in later doctrinal development. It is a subsisting reality of a rational nature.13 Early in the 350s and 360s it could be used in reference to the three persons or the one essence.14 The term was quite elastic. It only gradually came to be identified with the terminology of person (e.g., what there is three of in the Trinity).15 Until the early church came to agreement that ousia referred to the divine oneness and hypostasis referred to threeness, confusion abounded.16

Gregory of Nyssa was a key figure important for assisting with the clarity of distinction between the terms; he argues that “the principle of commonality refers to the essence, while the hypostasis is the particularizing sign of each.” He also provides some of the key imagery that assists in understanding the relationship between the two terms. He compares the terms to the function of a rainbow: “That which radiates the many-colored ray is one essence, refracted by the sunbeam, while the hue of the phenomenon is multiform.”17 The idea here is not that the Trinity is exactly like a rainbow. Gregory has already been careful to note how such analogies can subvert rather than assist our knowledge of the Holy Trinity.18 Rather, the point is that in trinitarian doctrine, while the hypostases of the Trinity are distinct, there is no gap between them. They all possess the fullness of the divine essence.

But even in more mature patristic writing, like that of Augustine, there remains little clear definition of what the term “Person” (hypostasis) means. Augustine merely thinks it is better than nothing.19 However, centuries later, Boethius gave us a classic definition that has been received and used throughout church history; and Richard of St. Victor clarifies it further. At bottom, it means an independent subsistence.20 “Subsistence” is another technical term for a substance that exists in and through itself and not in another.21 So, for example, Clifford the Big Red Dog is red. But the color red does not subsist because it doesn’t exist in and through itself. It inheres in Clifford. Whereas Clifford subsists since he exists in and through himself.

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Terminological development: How did we get these words?

Here’s the fun part of our tour through trinitarian terminology: its development really is an epic tale. It is a story of defeat and triumph. There are twists and turns. Your child’s favorite mythical figure gets slapped in the face (probably). Throughout there are key figures and heroes, such as Athanasius and the Cappadocian fathers. While there isn’t space to paint the entire picture, the main highlights can help frame how these terms came about and obtained the meaning they have today. What you’ll notice is that much of the debate and development centers on homoousios and how precisely it is to be understood.

The story typically begins with Arius and the conflict with his bishop, Alexander, in 318. This is no doubt a fine place to start. But Arius was really a catalyst for a theological conflict that had been brewing for decades.22 Pastors were grappling with developing a consistent framework for understanding the revelation of Jesus Christ in light of the monotheism of the Old Testament. These were not dry and arid concerns; they cut to the core of the church and its confession. Therefore, when Arius began to teach that the Son is distinct from the Father and is dependent on him the stage was already set for debate. Arius taught that the Son was a created being. Only the Father could be eternal, because only the Father was unbegotten. Such a view did not sit well with bishop Alexander, and controversy began to erupt throughout the region. Make no mistake: Arius was developing his arguments based on exegesis of important biblical texts like Proverbs 8. The debates, however esoteric they may look centuries later, were founded on competing exegetical frameworks. Notwithstanding, Arius was eventually expelled, but Arius was no fool, and he began to solicit his own coalition to support him.

Enter Constantine, who conquered the East in 324. The Arian controversy ebbed and flowed for years, but it flared to chaos at a crucial moment in which Constantine sought peace and uniformity.23 The Council of Nicaea was called to address the growing confusion in 325. It is at the Council of Nicaea that the terminology of homoousios was first invoked in the creedal formula. The terminology was not a touchstone at this point, however. It was designed merely to rule out the Arian interpretation that Christ was of a different essence than the Father. It defended the claim that the Son is “from the ousia of the Father.”24 Therefore, the Son is eternal and fully divine. It did not have the hold—the same commitment and weight—as it would over the next several decades.

The Council in 325 did little to resolve the trinitarian discussion, debate, and dissension. The Nicene Creed, without robust supplementary interpretation, was liable to misinterpretation and confusion. It took nearly sixty years to consolidate support for the standard understanding of the Nicene Creed and its usage of homoousios. In the meantime, there remained an overall suspicion of the term homoousios and little terminological uniformity otherwise.25 The general reason for this discomfort was that homoousios is not literally found in the Bible (that is, there isn’t a verse you can show that contains this word applied to God) and it is taken from deeply pagan origins with materialistic overtones. In other words, many found the idea of appropriating a term that was popular among pagan groups like the Gnostics as scandalous. But even if one were to overlook such connections there was a general sense that homoousios, when used in other contexts, assumed a material entity. Therefore, it would suggest that God himself were material, another outrageous idea. Ayres, Nicaea and Its Legacy, 94.[/note]

Even more, the word is “notoriously slippery” in its early development, which no doubt contributes to the mayhem that ensued in the decades that followed.26 It could mean either a generic unity of kind (that is, two different beings in the same genus), an identity of matter, or a strict numerical identity of substance (that is, there is no real distinction).27 The term was primarily used prior to Nicaea in the generic sense. Therefore, many have argued that it likely meant a generic form of unity—sharing the same nature—at this time. Indeed, it would be unlikely for the Council to introduce a novel sense of a term without any clarification.28 But it should be noted that its usage was primarily non-Christian prior to Nicaea. Christians have often pillaged non-Christian terms and infused them with different meanings to their own benefit. (For example, the Apostle John grandly opens his gospel with both the use of logos as both an echo of Genesis and a re-appropriation of the Greek concept of Logos.)

But no matter how the framers of Nicaea would have understood the term homoousios—whether as generic or as strict numerical identity, it defended the uncreated and divine status of the Son and anathematized the theology of Arius. As time went on it, the term came clearly to have a more specific meaning about numerical unity of indivisible essence rather than mere generic sameness.29 By 681 at Constantinople III, Nicene theology was understood to require that the persons share the numerically same divine nature and not a mere generic one.30

But what is fascinating in our story is that from 328 to 373 the deck was stacked against the Nicene Creed and homoousios. Some completely rejected the terminology and others sought to use more mediating terms like homoiousios. The theology and status of the Nicene homoousios as a hallmark of orthodoxy was kept alive due in large part to Athanasius.31 But during this period, you wouldn’t think Athanasius was ultimately successful. The terminology of homoousios was actually made formally illegal for the general public in 360.32 Ossius of Corduba banned such terminology in 357 on the grounds that they weren’t terms you could find in the Bible. A public ban of this magnitude threatened to destroy any further reliance on such terms.33 But the emperor Constantine II died in the following year, and by 365 Nicene theology was on the move again in large part thanks to the theological work of the Cappadocian fathers, being restored as law by 381 with the council of Constantinople.34 It was the events of 357–61 and the creed of Nikē that breathed fresh air into Nicene theology and birthed what some have called the Pro-Nicene alliance.35

Ecclesial reception: Is there room for deviation?

This history may be all fine and good, but do we really need these technical terms for our trinitarian doctrine today? Is there space to deviate from the past? Such questions are expansive and require significant defense. So, I’m only going to focus on one aspect: If there was so much contested debate over terms like homoousios, why should anyone believe that they are required today?

I’d like to give two reasons. First, the patristic fathers thought it was a crime to doctrinally innovate beyond the Nicene faith.36 The fathers at Chalcedon were clear: “[He is] accursed who innovates.”37 Cyril of Alexandria is representative when he explains that there is a tacit refusal to go beyond Nicaea even in the slightest respect.38 While the creeds were intentionally minimalistic to gain widespread support, the early church still saw it as necessary for supplementary documents to be used as guides to faithful interpretation of the creeds.39 Athanasius at the Council of Alexandria (362) issued a letter that quite clearly outlaws those who “pretend to cite the faith confessed at Nicaea” but “do nothing more than in words deny the Arian heresy while they retain it in thought.”40 For Athanasius and company, it is not sufficient for language alone to guard the faith once delivered to the saints—the meaning underlying it must be affirmed too. So, for the early fathers, homoousios is necessary in name and content. The Son must be of the same substance or essence of the Father.

Second, the fathers also provide ample biblical evidence in favor of the term. For them, the only way to safeguard the sense and meaning of the scriptural text is by using the terminology of homoousios. So, while it does not reflect explicit scriptural language, it remains necessary.41 It functions as a sort of bodyguard to the biblical terms ascribed to the persons of the Trinity. It protects the claims of Scripture wherein the persons of the Trinity perform the same divine actions and are ascribed the same divine characteristics.


The payoff for understanding terms like homoousios is more than being able to impress your friends with your knowledge. It is to safeguard our confession: “There is one Lord, one faith, one baptism, one God and Father of all, who is over all and through all and in all” (Eph 4:5–6). Without the bedrock theological belief that the Son and Spirit share the same essence as the Father, the mission of the Son through the Spirit for us and our salvation is lost.42

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  1. John Behr, The Nicene Faith: Part One True God of True God, vol. 2, The Formation of Christian Theology (Crestwood, NY: St. Vladimir’s seminary Press, 2004), 10.
  2. Khaled Anatolios, Retrieving Nicaea: The Development and Meaning of Trinitarian Doctrine (Grand Rapids: Baker Academic, 2018), 212.
  3. Jordan L. Steffaniak, “What Does Scriptural Sufficiency Mean?,” The Gospel Coalition Canada, May 3, 2022.
  4. Anatolios, Retrieving Nicaea, 283.
  5. Richard Cross, “Two Models of the Trinity?,” in Oxford Readings in Philosophical Theology, ed. Michael C. Rea (New York: Oxford University Press, 2009), 112.
  6. Cross, “Two Models of the Trinity?”
  7. D. Glenn Butner, Trinitarian Dogmatics: Exploring the Grammar of the Christian Doctrine of God (Grand Rapids: Baker Academic, 2022), 32.
  8. Origen, Origen: On First Principles, trans. John Behr (New York, NY: Oxford University Press, 2019), 1.2.13.
  9. John Behr, The Nicene Faith: Part Two One of the Holy Trinity, (Crestwood, N.Y.: St. Vladimir’s seminary Press, 2004), 425.
  10. Behr, The Nicene Faith: Part Two One of the Holy Trinity, 417.
  11. Augustine, The Trinity, VII 5, 10.
  12. Mark DelCogliano, “The Emergence of the Pro-Nicene Alliance,” in The Cambridge Companion to the Council of Nicaea, ed. Young Richard Kim (New York: Cambridge University Press, 2021), 265.
  13. Gilles Emery, The Trinity: An Introduction to Catholic Doctrine on the Triune God, trans. Matthew Levering (Washington, D.C.: Catholic University of America Press, 2011), 102.
  14. DelCogliano, “The Emergence of the Pro-Nicene Alliance,” 267.
  15. Leo Donald Davis, The First Seven Ecumenical Councils (325-787): Their History and Theology (Collegeville, MN: Liturgical Press, 1990), 63; Lewis Ayres, Nicaea and Its Legacy: An Approach to Fourth-Century Trinitarian Theology (Oxford: Oxford University Press, 2009), 209.
  16. Davis, The First Seven Ecumenical Councils (325-787), 48.
  17. Behr, The Nicene Faith: Part Two One of the Holy Trinity, 423.
  18. Anatolios, Retrieving Nicaea, 224.
  19. Augustine, The Trinity, VII 9.
  20. Davis, The First Seven Ecumenical Councils (325-787), 44.
  21. Michael Gorman, Aquinas on the Metaphysics of the Hypostatic Union (New York: Cambridge University Press, 2017), 16.
  22. Behr, The Nicene Faith: Part One True God of True God, 2:31, 61.
  23. Behr, The Nicene Faith: Part One True God of True God, 2:65.
  24. Ayres, Nicaea and Its Legacy, 96.
  25. Behr, The Nicene Faith: Part One True God of True God, 2:25.
  26. Davis, The First Seven Ecumenical Councils (325-787), 61.
  27. J. N. D. Kelly, Early Christian Doctrines, Revised Edition (San Francisco: Harper Collins, 1990), 234; Butner, Trinitarian Dogmatics, 28.
  28. Kelly, Early Christian Doctrines, 235, 267.
  29. Richard A. Muller, Dictionary of Latin and Greek Theological Terms: Drawn Principally from Protestant Scholastic Theology, Second edition (Grand Rapids: Baker Academic, 2017), 152–53.
  30. Scott M. Williams, “Discovery of the Sixth Ecumenical Council’s Trinitarian Theology: Historical, Ecclesial, and Theological Implications,” Journal of Analytic Theology 1(October 21, 2022): 341, https://doi.org/10.12978/jat.2022-10.180219220818.
  31. Sara Parvis, “The Reception of Nicaea and Homoousios to 360,” in The Cambridge Companion to the Council of Nicaea, ed. Young Richard Kim (New York: Cambridge University Press, 2021), 254.
  32. Parvis, “The Reception of Nicaea and Homoousios to 360,” 225.
  33. Parvis, “The Reception of Nicaea and Homoousios to 360,” 247.
  34. Parvis, “The Reception of Nicaea and Homoousios to 360,” 252.
  35. DelCogliano, “The Emergence of the Pro-Nicene Alliance,” 265.
  36. Richard Price and Michael Gaddis, trans., The Acts of the Council of Chalcedon, vol. (Konzil, Liverpool: Liverpool University Press, 2007), 22.
  37. Price and Gaddis, The Council of Chalcedon, 1:170.
  38. Cyril of Alexandria quoted in Price and Gaddis, The Council of Chalcedon, 1:182.
  39. DelCogliano, “The Emergence of the Pro-Nicene Alliance.”
  40. James Stevenson and W. H. C. Frend, eds., Creeds, Councils, and Controversies: Documents Illustrating the History of the Church, AD 337-461, 3rd ed. (Grand Rapids: Baker Academic, 2012), 80.
  41. Anatolios, Retrieving Nicaea, 22; Parvis, “The Reception of Nicaea and Homoousios to 360,” 246.
  42. My thanks go to Garrett Walden and Hunter Hindsman for comments, feedback, and edits on an initial draft of this essay. Hunter proved especially helpful in several rounds of comments on important sections. Whatever errors remain are solely my own.
Written by
Jordan Steffaniak

Jordan L. Steffaniak (ThM, Southeastern Baptist Theological Seminary) is a PhD candidate in Philosophy at the University of Birmingham, UK. He is married with three children. He is President of the London Lyceum, Research Fellow for the L. Russ Bush Center for Faith and Culture, and teaches at various institutions. He has published in numerous academic journals and is working on two monographs, one related to the classical doctrine of God. He also works full-time in the finance industry.

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Written by Jordan Steffaniak