Skip to content

The Angelic Doctor’s Heavenly Doctrine of God

Aligning with Aquinas on the Trinity is aligning with orthodoxy

What role should historical theology play in private interpretation of scripture? This issue has been debated since the time of the Reformation. Today, many people confuse the Reformed mantra sola scriptura (scripture is the sole, infallible authority for faith and practice) with solo scriptura (one’s own, independent interpretation of scripture is the sole, infallible authority for faith and practice). In turn, they have reverted to an elevation of private interpretation devoid of the richness of history.

This overemphasis on private interpretation has bred an overconfidence in personal conclusions on many doctrinal matters. As a result, our present age is one in which “contemporary” is the only characteristic that seems to matter. Many pastors and seminarians—and in turn laymen—only read books that have been printed in the last couple decades. They have virtually no place for historical theology in their private interpretation of scripture. The theological well from which they drink is little more than stagnant water from their peers. Consequently, they only read people who agree with their particular epistemological viewpoint on issues, rather than reading broadly and, most importantly, historically. It should greatly concern you if the doctrine of the Trinity you espouse would be unrecognizable, or—even worse—condemned, by a standard of historic orthodoxy. Click To Tweet

For example, it should greatly concern you if the doctrine of the Trinity you espouse would be unrecognizable, or—even worse—condemned, by a standard of historic orthodoxy. Especially in a modern culture of “hot takes,” students should be slower to spout off their opinions until they have read more vastly than their contemporary books. After all, how do you know your interpretation of a text or a doctrine is accurate if you have no historical context? Have you inadvertently become a “mini-pope,” making yourself the arbiter of orthodoxy? In truth, theology should be a process of study, evaluation of presuppositions, reformulation, and clearer articulation, all against the backdrop of doctrinal precedent.

Sadly, what passes for research these days is little more than reading a contemporary author and then hitting CTRL+F on the keyboard in order to find an agreeable point! Such an approach has produced increasingly shallow Christian thinkers. This shallowness then breeds more of the methodology that produced it, forming a vicious circle. The end result? Doctrines like the Trinity, which have been well-defined in history, are victimized by those who want to redefine them according to their own self-styled nuances.

So how should we incorporate historical theology into our private interpretation?

Doctrinal harmony

One way is by recognizing doctrinal harmony, advancement, and agreement in the Church. Here, as an example, I appeal to someone who is often seen as an enemy of Protestantism: Thomas Aquinas. At the outset, let me clarify that this is not an attempt to baptize Thomas, but rather to demonstrate a vital appreciation of the historic doctrine of the Trinity from one whom many Protestants might consider hands off. Far too often students are quick to commit the Genetic Fallacy when they come to Aquinas. They look to the man, or his body of doctrine, or even the Counter-Reformation at Trent (which appealed to Aquinas to build much of their doctrine of sacramentalism), and conclude that any theological claim from him must be bad. Consequently, they never give his doctrine of the Trinity a fair assessment. Another mistake made out of misplaced disapproval (and, quite frankly, chronological snobbery) is to commit the Composition Fallacy: “Well, Thomas got these other things wrong, so everything from him must be wrong.”Out of chronological snobbery we commit the Composition Fallacy: “Thomas got these things wrong, so everything from him must be wrong.” Click To Tweet

Instead, Christians should be noted by their charity, fairness, and objectivity in their assessment of past theologians. We see this modeled well in Herman Bavinck. In Book 2, Aquinas seems to be his dearest friend; he cites him approvingly numerous times. Yet, in Book 3, Aquinas is one of his fiercest foes. Many Protestants have long recognized Aquinas’ accuracy in Theology Proper. Following Bavinck’s lead, we will examine Aquinas’ doctrine of the Trinity showing (1) how it is Nicene orthodoxy, (2) how Protestant Scholastics retrieved not only Nicaea, but appealed to Thomas at points on the Trinity, and (3) why Protestants today can benefit from Aquinas on the Trinity.

Defining the Trinity of Nicaea

In the first few centuries of the Church we see interesting developments in Trinitarian language, even though the official term Trinity isn’t used until Tertullian. What we find, primarily in the apologists, is a focus on unity in the Godhead, and that “persons” were commonly referenced, though not with the specificity that would later be termed relations of origin.[1] In the fourth and fifth centuries, we see an establishment of appropriate terms when discussing God that have shaped theological formulation (grammar) to this day.

It is only appropriate to start with Athanasius since he was the assistant and deacon to Alexander of Alexandria at the First Council of Nicaea.[2] Athanasius eventually succeeded Alexander as Bishop, all the while defending Trinitarianism against the much more popular Arianism, even when it was held by Constantine’s son, Emperor Constantius II. That first council read,

We believe in one God, the Father almighty, maker of all things visible and invisible; And in one Lord, Jesus Christ, the Son of God, begotten from the Father, only-begotten, that is, from the substance of the Father, God from God, light from light, true God from true God, begotten not made, of one substance with the Father, through Whom all things came into being.

The key to the debate, stressed by Athanasius, was that Jesus is homoousios (of the same substance) with the Father, in contrast to Arius who wanted to settle for Jesus as homoiousios (of like substance) with the Father. Such an important distinction was made using one letter in a Greek philosophy term, yet the difference was monumental.

While the groundwork was laid by Athanasius in 325 at Nicea, consensus was not reached in his lifetime. In fact, Arianism and its ugly stepchild Semi-Arianism was revived many times by men such as Aëtius and Eunomius after Athanasius and Arius died. It took the Cappadocian Fathers (Basil the Great, Gregory of Nyssa, and Gregory of Nazianzus), with their contributions in the First Council of Constantinople (381), to produce the final version of the Nicene Creed that remains a monument of orthodox Trinitarianism. The creed became known as the Nicene-Constantinopolitan Creed. The contributions of these men, along with Athanasius beforehand and Augustine afterward, provide a unity for doctrinal definitions regarding the Trinity that remains without a doubt the litmus test for Trinitarian taxonomy by which all measures of controversy have been measured.

Among these contributions was a theological grammar properly conveying Scripture’s teaching regarding the oneness and threeness in God. The harmony demanded by the biblical text drove these Nicene and post-Nicene fathers to develop proper language when discussing the Trinity. The divine unity was best encapsulated by the terms ousia (along with phusis meaning nature) for what is one in God. This was later referred to as God’s substance, essence, nature, or being. In like manner, the threeness of God was distinguished by the term prosopon, which was later referred to as person(s) or subsistence(s).

These two categories of how God is one in a certain respect and three in another respect were necessary for the Church to maintain and articulate the harmony of Scripture (cf. 2 Cor. 13:14; 1 Cor. 12:4–6; Eph. 4:4–6; 1 Pet. 1:2; Rev. 1:4, 5). Additionally, these terms were developed to keep aberrant views at bay. Therefore, any view that misunderstood the category of essence, or person, or both, was examined and rejected. Naturally, in a text like Matthew 28:19 or Deuteronomy 6:4, you do not see the terms ousia and hypostasis, or even the proper way to define the hypostasis of the Father, Son, and Spirit. So the proper taxonomy to describe the Trinity (essence and persons) is something we have inherited from the Early Church. We are in its debt.

When you harmonize these texts allowing the exegetical data of each to remain, without removing or distorting other texts, you are engaging in what is known as theologia (in contrast to oikonomia). Theologia refers to the mysteries of God’s nature as he is in himself, sometimes called God’s incommunicable attributes or nature—archetypal theology in the Reformed theologian Franciscus Junius. This would be how we define the ousia. On the other hand, oikonomia is referring to the manner of revelation or how God has made Himself known. We have to be careful not to collapse these categories or confuse them. The Cappadocians were wonderful in preserving just that delicate balance and precision.

Basil wrote, “The term ousia is common . . . while hypostasis is contemplated in the special property of Fatherhood, Sonship, or the power to sanctify” (Letter 214.4). Gregory Nazianzus explained, “The Godhead is one in three, and the three are one, in whom the Godhead is, or to speak more accurately, who are the Godhead” (Oration 39.11). Gregory Nyssa similarly reasoned, “Each of the three persons possess unity . . . by reason of the identity of essence and power” (Against Eunomius, 1.36).

What we see here is that essence (ousia) is what is common, while person (hypostasis) is how we specify a relation. Essence is a generic term for deity, whereas hypostasis is a specific characterization used to refer to one of the persons. Basil was very helpful with this. His example would be “man,” which is a generic term for humanity, whereas “Peter” is a specific person.

Augustine’s Pro-Nicene Trinitarianism

Continuing this rich tradition, Augustine furthered Pro-Nicene Trinitarianism against—you guessed it—lingering Arianism. In, On the Trinity, he writes, “Whatever . . . is spoken of God in respect to himself, is both spoken singly of each person, that is, of the Father, and the Son, and the Holy Spirit; and together of the Trinity itself, not plurally but in the singular” (On the Trinity, 5.8.9).

What we also find in Augustine is that more categorical definitions become normalized. Augustine helped set trajectories for Classical Theism with his focus on God’s essence, in that God is simple, timeless, and immutable. In this respect, Augustine helped set a standard in hermeneutics that still functions as a guardrail in Christian Theism. It is the concept of accommodation: that things which are true of creatures are “accidents” in us while “inherent and necessary” in God. For example, consider that God’s love is categorically different from ours. God is love, so it is predicated of God by necessity, whereas in creatures it is something we happen to have to one degree or another though it is not our essence. Furthermore, when it comes to these properties in creatures, they are different from one another, while in God they are one and the same divine essence.

Being the master theologian he was Augustine applied this concept to the question concerning the terms “Father” and “Son.” God cannot be “Father” and “Son” accidentally. It is difficult to prove this as an essential feature, so Augustine suggested that the “persons” Father, Son, and Spirit are differentiated by relations.[3] The Son is in relation to the Father with begetting/begotten language. Augustine presented the Spirit’s dual procession from both the Father and Son as well (On the Trinity, 15.17.29). He argues that the Bible implicitly teaches this kind of Trinitarianism.

From the time of Augustine to Aquinas, Trinitarianism was guarded well. The ecumenical centralization of Christianity ensured that the boundaries of cardinal doctrines, such as the Trinity, were kept in check by the creeds until the Reformation. Those Creeds continued to guide the magisterial reformers and Puritans as well. In fact, the early ecumenical creeds are restated in the Protestant confessions with very minor additions. Those additions were largely based on Aquinas’ contributions, as they sought to codify and define that which Augustine presented in his sermons.

Thomas Aquinas’s many contributions

Thomas Aquinas’ contributions on the Trinity are many, but are found predominantly in Summa Contra Gentiles 4.1–26 and Summa Theologiae I.27–43. Aquinas built upon the “relations” development of the hypostases in Augustine, as well as the strong doctrine of simplicity and immutability. Building on the “accidents” and “essential” qualities treated by Augustine, Aquinas helpfully deduced the doctrine of pure actuality, meaning God has no passive potential. God can act, so he has active potential, the ability to do other things, but he does not have a potential that is passive and might be actualized. With simplicity (that God is not composed of parts or properties) and now with pure actuality (no passive potential) the reflexive relations between the three persons can be better articulated: the Word eternally generated by God is a hypostasis[4] which shares the essence of God but is nonetheless “relationally distinct.” This harkens back to Basil’s observations.Aquinas says the persons are distinct per relationes (as to their relations with one another) but not different per essentiam (as to their ousia or essence). Click To Tweet

For Aquinas, the relations “Begetting,” “Begotten,” and “Proceeding,” are real and distinct things “in” God. Drawing from Augustine and Basil, Aquinas says the persons are distinct per relationes (as to their relations with one another) but not different per essentiam (as to their ousia or essence). So if the persons are not different from the essence (they are not something other than God) but they are distinct from one another, how does one avoid falling into modalism? If the Father (person) is identical to God (ousia), and the Son (person) is identical to God (ousia), how is the Father not also the Son?

To answer these issues, Aquinas, in Summa Q.28 and 29, utilizes the medieval concept of sameness (identitas). For Aquinas there is a difference between secundum rem (sameness of thing) and secundum rationem (sameness of concept): different kinds of “sameness” that are mutually exclusive from one another. God is one (secundem rem) in one respect (essence) and three (secundum rationem) in a different respect (person). This explanation helps avoid modalism and other Trinitarian issues because the persons are categorically distinguished from the essence.[5]

Continuing, he raises the same question posed to Aristotle: “Is the road to Thebes the same as Athens?” He then answers the question: “Yes,” in that they have the same properties, but they have those properties differently. For example, the route may be uphill one-way, and downhill the other, yet not two roads but one. So the persons of the Godhead have the same properties, but they have them differently. The Father possesses the essence as Father, the Son as Son, and the Spirit as Spirit.

The Reformed Scholastics appreciate Aquinas

If you have come up with an interpretation that has escaped the notice of every other Christian for two thousand years, you had better abandon your interpretation. -R.C. Sproul Click To TweetThough it may be surprising, the Reformed Scholastics had an appreciation for Aquinas on the doctrine of God. The Reformed Scholastics and Puritans had such high appreciation for the development of Trinitarian taxonomy that they borrowed from the Great Tradition in forming the confessions. For example, the Second London Baptist Confession says, “The Lord our God is but one only living and true God; whose subsistence is in and of Himself . . . a most pure spirit, invisible, without body, parts, or passions.” Here we see simplicity, pure actuality, oneness of subsistence—all drawing from the Great Tradition. In another example, Chapter 3 of the Second Helvetic Confession reads,

Notwithstanding we believe and teach that the same immense, one and indivisible God is in person inseparably and without confusion distinguished as Father, Son and Holy Spirit so, as the Father has begotten the Son from eternity, the Son is begotten by an ineffable generation, and the holy Spirit truly proceeds from them both, and the same from eternity and is to be worshipped with both.

Thus there are not three gods, but three persons, consubstantial, coeternal, and coequal; distinct with respect to hypostases, and with respect to order, the one preceding the other yet without any inequality. For according to the nature or essence they are so joined together that they are one God, and the divine nature is common to the Father, Son and Holy Spirit.

All this verbiage was chosen to tether and demonstrate their dependence upon the early Church and subsequent orthodox trinitarinism. Finally, the Belgic Confession Article 1 reads, “Article 1: The Only God We all believe in our hearts and confess with our mouths that there is a single and simple spiritual being, whom we call God.”

In short, the reformers built their ministries upon the truths articulated at Chalcedon and Nicaea. Luther, Calvin, and many others all wrote catechisms and confessions for their people, seeing the anti-confessionalism of the radical Anabaptists as anti-Christian. Thus, the mantra sola scriptura must be understood historically not as anti-tradition or anti-creed, but as acknowledging them as vital insofar as they accurately reflect Scripture. In that way, confessionalism is true and helpful, but only as subordinate to scripture.

The late R.C. Sproul helpfully stated it this way: “Although tradition does not rule our interpretation, it does guide it. If upon reading a particular passage you have come up with an interpretation that has escaped the notice of every other Christian for two thousand years, or has been championed by universally recognized heretics, chances are pretty good that you had better abandon your interpretation.”[6]

Laziness can manifest itself through inattentiveness to the exegetical work of great minds who have gone before us. Click To TweetIn light of this, what should the Church do? Principally, we must be slower in conflating private interpretation with conclusive meaning before doing the hard work of mining the text and the history of the Church. It has been well said that “no verse of Scripture yields its meaning to lazy people.”[7] Truth be told, such laziness can manifest itself not only through inattentiveness to our own exegetical work, but through inattentiveness to the exegetical work of great minds who have gone before us. Seminary students, pastors, and scholars alike should spend time reading broadly and deeply—and of course, eating the meat and spitting out the bones of men such as Thomas Aquinas.


[1] Sometimes called modes of origin not to be confused with modalism. See: J. Warren Smith “The Trinity in the Fourth-Century Fathers,” eds. Giles Emery and Matthew Levering, The Oxford Handbook of The Trinity (Oxford: Oxford University Press, 2014), 116.

[2] He served for 45 years and of those 45 years spent 17 years in exile on five different occasions by four emperors for his, at the time, seemingly controversial positions.

[3] It’s interesting to note that Augustine, considers but ultimately rejects the idea that all truth claims about God must be relational  (Books V-VII). This is something the Mutualistic Theist/Relational Theist/Biblical Personalism groups would do well to pay attention to.

[4] This is the notion Aquinas borrows from Aristotle for what he would call a first substance.

[5] Summa Theologica, #27–43 and Summa Contra Gentiles #1–26.

[6] R.C. Sproul, The Agony of Deceit: What Some TV Preachers are Really Teaching (Chicago: Moody Press, 1990), 34–35.

[7] A.W. Pink, “Saving Faith,” Studies in the Scriptures – 1932-33 (Lafayette, IN: Sovereign Grace Publishers, 2001), 6:132.

Peter Sammons

Peter Sammons (PhD, The Master’s Seminary) is director of academic publications at The Master’s Seminary and managing editor of The Master’s Seminary Journal. He is the author of Reprobation and God’s Sovereignty: Redeeming a Biblical Doctrine (Kregel, 2022).

Back to Top