It is tempting to overstate the differences between St. Thomas Aquinas and the Church Fathers.

Aquinas is indelibly associated with Aristotle. The Fathers, on the other hand, especially St. Augustine, are thought of as Neoplatonists. (This too is overstated, but that’s another story.) Aquinas produced a systematic theology whose stiffness and rationalism can seem a world away from the brilliant streams of consciousness that poured out from the pens of the Fathers. And in the eyes of many Protestants, Aquinas is more Catholic than the Fathers.

But anyone who has spent real time with the writings of Aquinas knows how deeply indebted he is to the Fathers. This is readily apparent in his most famous work, the Summa Theologica. Read the Summa, and one begins to realize that Aquinas is in constant dialogue with the Fathers, organizing, explaining, and sometimes charitably correcting them.

A search through a PDF of the whole text reveals just how enmeshed Aquinas’ thought is with theirs. Aquinas cites Augustine the most of all at 3,156 times. That’s even more than Aristotle, who garners a total of 2,095 mentions—including references by name and by title, as ‘the philosopher.’ Not counting the supplement, the Summa has a total of 521 questions, meaning that Aquinas turns to Augustine as an authoritative guide on average six times for each question. Hardly any topic is broached that does not in some way bear the influence of Augustine.

Today, Augustine looms as large as ever for us. We owe our understanding of the doctrines of the Trinity, grace, and original sin to him. Augustine’s account of personal conversion, in The Confessions, his understanding of the role of the church in history, in The City of God, and his commitment to the authority and inerrancy of Scripture have left a lasting impression on Western Christianity. Aquinas both reflects and reinforces Augustine’s enduring authority.

But Aquinas’ engagement with the Fathers extends well beyond Augustine. Here are the Fathers he cites most often after him. Each number represents number of times cited by name in the Summa: 

1. Gregory the Great — 761     
2. Dionysius —607
3. Jerome —377
4. Damascene —367
5. John Chrysostom —309
6. Ambrose —284     
7. Isidore —162     
8. Origen —84
9. Basil —56
10. Gregory of Nyssa —53
11. Athanasius —45
12. Cyril —28

The list is both expected and surprising. It makes sense that St. Gregory the Great, as a Latin Father, would figure prominently in the Summa. The same goes for St. Ambrose, the teacher of Augustine, and St. Jerome, the translator of the Vulgate. It is impressive to see the Greek Fathers well-represented, particularly St. Basil the Great, and St. Gregory of Nyssa.

But then there are the surprises. Dionysius, better known today as Pseudo-Dionysius, is not a Church Father well-known even to many Catholics who read up on their theology. But he is nonetheless an immensely important writer in the patristic era. His work on The Celestial Hierarchy is both a formal theology of the angels and also an extraordinarily rich devotional work. The Divine Names is a classic work of apophatic theology. Aquinas draws upon Dionysius in his treatment of biblical metaphors and typology, the infinity and ineffability of God, and the nature of the good, among others.

Another surprise is the Damascene, or St. John of Damascus. This is another Church Father who is not as familiar to us today. St. John lived from 676 to as late as 787 and is known as the ‘last of the Greek Fathers.’ One of his most significant works is the Fountain of Wisdom, which The Catholic Encyclopedia describes as “the first attempt at a summa theologica that has come down to us.” The third part of this treatise is better known to us today as The Exposition of the Orthodox Faith.

As with Dionysius, Aquinas mines St. John’s writings for insights on what we can and cannot know about God, the divine attributes, and the three persons of the Trinity and a range of other topics, encompassing the Eucharist, death, and the general resurrection.

Probably the least known on the list is St. Isidore of Seville, a Father who lived in present-day Spain, from 560 to 636. His works include the Etymologies, which is often described as a sort of encyclopedia of not only theology but also a survey of natural knowledge, including math, astronomy, and medicine. He also produced a book of sentences—a series of questions or propositions about theology, a style that was to become quite popular in the Middle Ages.

Aquinas pulls in a wide variety of citations from Isidore—everything from the nature of angels and demons and the sacraments to facts from astronomy and biology.

Today, perhaps more so than before Vatican II, we read and study the Fathers directly—and we should. But even here Aquinas has a lot to teach us about how to read the Fathers. And through Aquinas we may even meet Fathers who we otherwise would have overlooked.

Rather than obscuring them, Aquinas amplifies the importance of the Fathers for us today. And the Summa is one of our best windows into their world. 

This article originally appeared Feb. 8, 2018, at the Register.

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