How Can I Understand St Thomas Aquinas? (Part 1: Structure)

St. Thomas Aquinas is widely considered one of the greatest Catholic theologians who ever lived.
His writings were so profound that he earned the unique title Doctor Angelicus, the Angelic Doctor.
At the Council of Trent, his masterpiece, the Summa Theologica, was placed on the altar right next to the Bible. They were showing that, other than the Bible, St Thomas Aquinas is one of the most useful guides in theology.

Pope Leo XII calls this St Thomas’ “greatest glory.”

There’s no getting around it. St Thomas Aquinas is a spiritual genius. Whenever university professors start studying Catholic theology, they always go to Aquinas.

For those wanting to develop a more mature understanding of the faith, St Thomas is the go-to person.
But here’s the tension:
  • I want to read Aquinas because I know I’ll grow smarter and holier.
  • But… he’s way too smart for me to understand.

And this problem makes complete sense.

Aquinas’ writings are so valuable, but written in a way that can feel intimidating.

There are a few problems people have when reading the Summa Theologica, St Thomas’ masterpiece. One of these issues is that they don’t understand how it’s structured or supposed to be read.

Understanding the structure of the Summa is not your golden ticket to becoming a philosopher. But it can give you some backbone to make your journey easier.

Why Structure Matters So Much

St Thomas Aquinas wanted to write a book to teach his university students. However, something he disliked was authors repeating themselves and having scattered thoughts.

His goal was to create a hyper-organised text, so his students don’t have to put up with that.

Removing the repetitions in his masterpiece, the Summa Theologica, is great for saving time. But it also means that it became very dense.

St Thomas was very particular about how we wrote his book. That’s why structure is more important in St Thomas’ writings than in many other authors.

It’s like having a super-efficient train line. You can stumble around the station and end up at your destination. But it makes it a lot easier to have a map.

The Big Picture

The Summa Theologica unfolds in three main parts (with a later supplement). Each part builds upon the previous section, creating a very sophisticated and holistic understanding.

Prima Pars

St Thomas Aquinas wrote in Latin, so all the Latin names for the parts have been preserved. But it’s straightforward because Prima Pars literally translates to ‘First Part’.

The first part of the Summa or Prima Pars in Latin starts off from the beginning. It first considers if God exists. If so, what is he like? Here, St Thomas explains the Trinity, God’s omniscience, and simplicity.

After that, Aquinas focuses on God as creator. The rest of Prima Pars discusses creation as a whole, but especially of humans and angels.

One famous insight from Prima Pars is Aquinas’ Five Ways’. Although it makes up only a small space, it is often used to prove the existence of God, just using logic. Philosophers like Dr. Edward Feser have simplified these arguments and helped repopularise them.

Prima Secundae


Part two is divided into two sections. It’s a bit like having 2a and 2b.

Prima Secundae, or 2a, is the first of these sections. It focuses on the question of ‘what do I have to do so that I can become moral?’

It is in this section that Aquinas discusses law, sin, and grace.

There is one idea of Aquinas that stands out to many readers. The first is what he calls natural law. It’s the reason people know it’s wrong to murder, even if they weren’t taught. God inscribes his eternal law into our human hearts.
Aquinas’ clarification of natural law really helped later theologians develop more nuanced ideas on a whole range of topics. Even the recent St. Pope John Paul II, makes mention of natural law.

Secundae Secundae


The end section, or Secundae Secundae, focuses on the specifics of moral life.

Instead of discussing virtue generally, he dives into specific ones. Aquinas spends most of Secundae on the theological (faith, hope, charity) and cardinal virtues (prudence, justice, fortitude, temperance).

Aquinas’ discussion on justice is a long but commonly read part of the Summa Theologica. Since justice relates to many other legal and political issues, many people find this section most appealing.

Tertia Pars


In the third part, or Tertia Pars, he begins talking about Christ.

Tertia Pars goes into the mystery of the Incarnation and then the Sacraments which Christ left us. It is in the Tertia Pars, which Aquinas explains the doctrine of Transubstantiation, where the Eucharist changes substance to God.

What many people don’t realise though, is that Aquinas never finished the section on the Tertia Pars. It was left incomplete.

And this is why we have the last part.

Supplementum Tertiae Partis

This section of the Summa Theologica wasn’t intended to be included in the book. After Aquinas died, his secretary got sections of St Thomas’ commentary and compiled a supplement to the third part.

Finally, the Summa ends with the last sacraments of penance, extreme unction, holy orders, matrimony, and the resurrection.

Breaking That Down

I know that this is a lot of information. I’ll show you a brief way of looking at it;

1. Prima Pars: God, Trinity, and creation

2. a. Prima Secundae: The basics of the moral life

     b. Secundae Secundae: Specific theological and cardinal virtues
3. Tertia Pars: Jesus and the Sacraments
4. Supplement: Additions to the Summa from his secretary, finishing the sacraments and resurrection

St Thomas Aquinas starts off focusing on God, as the creator of everything. Then, he goes deeper into man and his moral life. Finally, by becoming holy, he can become united to the God-Man.

It’s a bit like a boomerang that starts off being held by its owner. Then it is thrown, going further and further. However, at the end, the boomerang returns to its creator.

This is how the book as a whole was organised. But what about each individual page?


The Micro-Level: How Each Question Works

Not only is the Summa neatly arranged on a grand scale, it’s also highly structured throughout the whole book. Here’s the pattern you’ll see over and over again:

Questions and Articles

Each “Question” covers a big topic. Aquinas then breaks this down into smaller subtopics, called “Articles.”

For example, in the Secunda Secundae, Question 110 is about lying generally. Article 3 asks a more specific question: “Is every lie a sin?” Article 4 follows: “Is every lie a mortal sin?”

Objections

Here’s where Aquinas shines. Many debaters today distort their opponents' arguments to win a debate. Aquinas does the opposite. He creates the strongest possible counterarguments and even quotes Scripture, philosophers, and Church Fathers against himself. It’s like he argues against his own view first.

People who don’t understand Aquinas can completely misunderstand this. Some people read the objections and think it’s his answer to the question.

The objections are the opposing view to what Aquinas really believed.

On the Contrary

He briefly states an authoritative position that supports the truth he will argue.

I Answer That…

This is the heart of the article. Here Aquinas unfolds his reasoning in full. This is what most readers focus on since it directly addresses the article.

Replies to Objections

Finally, Aquinas goes back to each objection and explains why it doesn’t ultimately hold.

Aquinas Made Easier

This was a lot of information. But understanding at least vaguely how the Summa Theologica works can make it easier to understand.

Some people can just jump into the deep end, and try to figure it out. But if you want to really understand Aquinas, you need to know his structure.

When you grasp both the large-scale layout and the article-by-article method, the Summa Theologica becomes not only readable but exciting. You see Aquinas’ brilliance in action and start to realize why the Church continues to hold him up as a model for all theology.

As St. John Paul II put it:

“The Church has been justified in consistently proposing Saint Thomas as a master of thought and a model of the right way to do theology.”

So if you’ve ever felt intimidated by Aquinas, don’t give up. Once you understand his structure, you’re one step closer to becoming a Thomist. And, more importantly, grow deeper in love with God, just as Aquinas himself did.

Nevertheless, reading the Summa Theologiae is a difficult but rewarding task.

If you want to ease into the Summa, the ‘Tour to the Summa’ can help you with Aquinas before you dive right in. Aquinas’ works are invaluable to those wanting to learn more about God .

May you grow in love and knowledge of the Lord,

God Bless,

Virtue Books and Gifts
Back to blog