The strongest argument for homosexual sex is also one of the simplest: two consenting adults should be free to do what they want with each other.

This episode asks whether that principle can actually bear the weight we put on it. We already accept limits on what consenting adults may do—to their bodies, to one another, and even in private relationships. So why?

The argument leads beyond homosexuality to a much bigger question about freedom itself. If every sexual desire becomes legitimate simply because it is freely chosen and consensual, then what remains to tell us that some desires should not be acted upon? And if our laws begin treating our changing feelings as the ultimate authority, what happens to the stable principles on which a society depends?

Read the relevant article of the Summa here:

Summa Theologica. Part 2 of 2. Question 154. Article 11. Whether the unnatural vice is a species of lust?

A thought appears. A feeling follows. Pleasure kicks in. Did you just sin?

Not necessarily. And this is where the argument gets much more interesting.

The distinction explored in this episode is between experiencing a pleasure and consenting to it. You don’t necessarily choose what enters your imagination, what catches your eye, or what your body reacts to. But you do have a choice about whether you turn toward it—or turn away.

That sounds simple until you start applying it to real life: the unexpected scene on your screen, the person who catches your attention, the fantasy that suddenly appears in your mind. The question isn’t whether temptation happened. It’s what you chose to do once it did.

Read the relevant article of the Summa here:

Summa Theologica. Part 2 of 2. Question 154. Article 4. Is there mortal sin in touches, kisses and such like seduction?

“I love God. I go to Church. I pray. I help people. Surely God will forgive me for living with my partner?”

Aquinas takes that argument seriously—and gives it a much harder answer than we might expect. Good works matter, but not because they earn us a place in heaven. They prepare us to receive something we cannot manufacture for ourselves: the grace to repent.

That distinction changes everything. You can surround yourself with religious practice while still clinging to a way of life you have no intention of leaving. And if you persist in it until death, Aquinas argues, your good deeds do not magically make the refusal to repent disappear.

The episode ultimately asks a deeply uncomfortable question: are our religious practices actually leading us toward conversion—or helping us feel comfortable without it?

Read the relevant article of the Summa here:

Summa Theologica. Part 2 of 2. Question 154. Article 2. Is simple fornication a mortal sin?

If children need years of guidance and formation, then another question follows: what kind of relationship is capable of sustaining that responsibility?

Aquinas’s answer is marriage. His argument is not simply that parents should ideally stay together, but that human nature itself points toward a stable, lasting union because raising a child is a long-term project. From there, he makes a further move: when something is essential to the common good, it cannot remain merely a private arrangement—it becomes something society has reason to protect through law.

That takes Aquinas’s argument into more controversial territory. What should we make of exceptions? What if a father does take responsibility for a child born outside marriage? What if an arrangement happens to work? Aquinas’s answer is that laws have to account for what generally happens, not merely what is possible in individual cases. And that raises a much bigger question: should our social rules be built around exceptional cases, or around what human beings generally need to flourish?

Read the relevant article of the Summa here:

Summa Theologica. Part 2 of 2. Question 154. Article 2. Is simple fornication a mortal sin?

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“If two consenting adults want to have sex, and they’re not hurting anyone, what’s the problem?”

It’s one of the most familiar objections to the traditional Christian view of fornication. Aquinas’s answer takes the argument somewhere unexpected: look at the child.

A human child needs far more than food, shelter, and schooling. Children need years of guidance, example, imitation, discipline, protection, and formation. And that raises a question Aquinas thinks we can’t simply ignore: what responsibilities do we have toward the person our actions may bring into existence?

In this episode, we follow Aquinas’s argument from fornication to parenting, education, and human development—and discover why he thinks the consequences of sex cannot be measured only by asking whether the two adults involved have harmed each other.

Read the relevant article of the Summa here:

Summa Theologica. Part 2 of 2. Question 154. Article 2. Is simple fornication a mortal sin?

An elderly couple can’t have children. Is their sexual relationship therefore sinful? If not, why would contraception be different?

Part 2 takes that apparent contradiction seriously and follows Aquinas’s reasoning all the way through. The key turns out not to be whether conception actually happens, but whether we deliberately stand in its way.

That distinction—between nature withholding an outcome and the will deliberately preventing it—opens up Aquinas’s entire argument about sex, pleasure, reproduction, and what it means to accept an action for what it actually is.

A note from the author: The article discussed in this episode is my own attempt to formulate how St. Thomas Aquinas might respond to some of the modern objections raised against his argument. It is not a text written by Aquinas, but a contemporary reconstruction written in the style of his Summa Theologica. Read the full article along with me via the link in the show notes.

I also encourage you to read Humanae Vitae (“On Human Life”) by St. Paul VI, which is also linked in the show notes. Whether or not you agree with its conclusions, it is worth reading the argument in its own words rather than relying on second-hand summaries.

NOTES

* The source article: Whether sexual acts that cannot result in child-bearing are sinful?

* On Human Life by Pope Paul VI

* Read the relevant article of the Summa here: Summa Theologica. Part 2 of 2. Question 154. Article 1. Into what parts is lust divided?

If a sexual act cannot result in child-bearing, is it sinful? What happens when you ask AI to produce the strongest possible case against St. Thomas Aquinas?

That’s exactly what this episode does. Starting with a modern philosophical critique, we explore the claim that sex has many legitimate purposes, that biology doesn’t create moral obligations, and that Aquinas’s reasoning simply doesn’t hold up.

Instead of avoiding these challenges, we follow them to the heart of the debate, where one overlooked distinction reveals why Aquinas’s position is often misunderstood—and why it still provokes such fierce disagreement today.

This goes right to the heart of the most common present-day objection that is made against Aquinas’s arguments regarding the morals of sex, as discussed in the last two episodes.

In this episode, I use an article that I wrote in the style of St. Thomas Aquinas, with the assistance of a large language model to generate present-day objections, find current sources and get the structure right.

NOTES

* The source article: Whether sexual acts that cannot result in child-bearing are sinful?

* The opinion poll mentioned: Catholic Conformity Poll

* Read the relevant article of the Summa here: Summa Theologica. Part 2 of 2. Question 154. Article 1. Into what parts is lust divided?

Modern debates about sex often begin with personal choice. Aquinas begins somewhere else entirely: with purpose.

In this episode, he continues his exploration of lust by asking why different sexual acts belong in different moral categories. His answer isn’t based on emotion or social convention, but on what each act frustrates or damages. Some separate sex from its life-giving purpose. Others place children at a disadvantage. Others violate bonds of family, marriage, or personal dignity.

It’s a challenging framework, and many listeners will disagree with parts of it. But before rejecting it, it’s worth understanding the careful reasoning behind it. This episode unpacks that reasoning step by step and shows why Aquinas thought moral distinctions should correspond to real human goods.Read the relevant article of the Summa here:

Summa Theologica. Part 2 of 2. Question 154. Article 1. Into what parts is lust divided?

Why does Christianity distinguish between different kinds of sexual sins? Is it just tradition, or is there a coherent way of thinking behind it?

In this episode, Aquinas argues that morality isn’t built on arbitrary commands. It’s built on understanding the purpose of sex. Before examining six different forms of lust, he explains the principle that makes those distinctions meaningful.

Whether or not you agree with his conclusions, his method offers something rare in modern debates: a serious attempt to explain why sexual ethics should follow reason rather than instinct, preference or the crowd.

Read the relevant article of the Summa here:

Summa Theologica. Part 2 of 2. Question 154. Article 1. Into what parts is lust divided?

“Hidden pride? Manifest lust.” - St. Josemaria Escriva.

In Part 3, we answer the four challenges raised at the start, and discover something new: lust doesn't just wreck your thinking and your will. It takes over your speech. Saint Thomas walks through four kinds of broken speaking that come from lust.

Obscene words spill out because a lustful heart fills the mouth. Scurrilous words rush out without thought — you don't deliberate before speaking, you just let it fall. Wanton words aim for pleasure — sexting and catcalls are lust speaking through you. And foolish words show total blindness — when you can only talk about sex, even while the world burns.

You'll also learn the hidden link between pride and lust: pride tells you that you deserve every pleasure, and lust does the work.

Finally, you'll see why Saint Thomas loves controversy: objections force you to think harder and find truths you'd miss otherwise. By the end of the series, you'll understand lust as a complete corruption — it breaks how you think, what you want, and even what comes out of your mouth.

Read the relevant article of the Summa here:

Summa Theologica. Part 2 of 2. Question 153. Article 5. Whether the daughters of lust are fittingly described?