The Triablogue article wasn’t written in response to that “King Louis IX” tweet. It was responding to a different Catholic-style argument that masturbation was some form of sex and especially the Onan/prooftext move and the broader tendency to treat tradition as if it settles exegesis. But on the general principle, I agree with something Catholics sometimes say correctly: you don’t “accidentally” sin. If you’re asleep, you’re not exercising moral agency, so you’re not morally culpable for bodily events outside your control.
Divorce is its own complicated discussion, and I’m not pretending it’s easy. But whatever one thinks about divorce, the claim that “you can’t marry someone infertile if you already know” isn’t Catholic teaching. Their own canon law indicates the opposite:
Code of Canon Law (1983), canon 1084 §3:
Can. 1084 §1. Antecedent and perpetual impotence to have intercourse, whether on the part of the man or the woman, whether absolute or relative, nullifies marriage by its very nature.
§2. If the impediment of impotence is doubtful, whether by a doubt about the law or a doubt about a fact, a marriage must not be impeded nor, while the doubt remains, declared null.
§3. Sterility neither prohibits nor nullifies marriage, without prejudice to the prescript of can. 1098. (see below)
And the Catechism makes the same point in plain terms:
Catechism of the Catholic Church, §2379:
“Physical sterility is not an absolute evil.”
Now, obviously fraud is a separate issue, but that’s not what’s being claimed here. If someone lies to obtain consent, Catholic law has a category for that:
Code of Canon Law (1983), canon 1098:
A person contracts invalidly who enters marriage “deceived by fraud … concerning some quality … which can gravely disturb the partnership of conjugal life.”
But again, deception isn’t the same thing as “infertility makes marriage unacceptable.” So if someone claims Catholics forbid knowingly marrying the infertile, they aren’t even representing their own system accurately. Nothing in canon law suggests that two people who know one is infertile (or even that both are infertile) are therefore barred from marrying.
Now, the deeper issue is the natural law style reasoning that often gets smuggled in here. I take natural law arguments seriously in principle, but a lot of them are bad in practice. People argue as if “X has a function, therefore any use not narrowly identical to that function is immoral.” That’s like saying, “cars subvert the function of legs, therefore driving is selfish and against God’s created order.” It’s a cheap move because it treats a function as the function, and then moralizes every non-identical use.
The deeper problem is epistemological: it’s not obvious how you get from how something does operate to how it must operate morally. And in practice, Catholics often seem to pick out whichever “features” of a thing line up with their priors, then declare those features the controlling teleological purpose rather than showing why that purpose is the sole (or governing) end in the first place.
And natural law arguments can be turned right back around on the Catholic position. Sex is pleasurable far more often than it results in conception. Pleasure accompanies sex in the overwhelming majority of marital acts, even when conception is impossible (pregnancy, menopause, infertility, natural cycles). So why assume reproduction is the sole purpose? There’s no argument for that. The biblical picture clearly includes union, fidelity, delight, and mutual giving—not just reproduction.
So if someone wants to say contraception or masturbation is wrong, fine: make the argument. But don’t pretend Scripture directly labels masturbation a sin when it doesn’t.
People keep treating Matthew 5:28 as if Jesus is condemning sexual attraction itself, as if noticing beauty equals “adultery in the heart.” But that reading is just not careful. The text is about a deliberate, chosen look that is aimed at feeding illicit desire. It is not describing the automatic fact of being attracted to the opposite sex.
That matters because heterosexual attraction is part of how God made human beings. Scripture doesn’t treat creation design as sin. The point is what you do with that attraction. Jesus is addressing a purposeful gaze that cultivates forbidden desire, a kind of inward appropriation of another person. So the sin is not that you find someone attractive. The sin is the intentional stare, the mental undressing, the willing indulgence that turns attraction into a settled appetite.
This is also why the common “therefore masturbation is condemned by Matthew 5” move is not straightforward. Even if someone thinks masturbation is wrong, you do not get there just by equating every form of attraction with lust, and then calling lust adultery.
Furthermore, the passage is clearly tied to Jesus’s handling of the commandments and the category of adultery, but we also can’t underread his point. He’s not just tightening up the wording of the law. He’s exposing that outward sexual sins come from inward corruption, from a rotten posture of heart and character. In other words, don’t get so fixated on the letter of the law that you miss the heart of the law. The point is that evil sexual acts are not isolated “events” but expressions of what a person is on the inside. The problem is that if you’re going to treat sexual attraction itself as illicit, you need an argument that there’s no meaningful difference between lusting after or tempting a married woman and desiring a single woman in a way that’s ordered toward marriage. But those are obviously different things.
Jesus addresses lust in a section of the Sermon on the Mount typically styled the “antitheses” (Matt 5:21–48). Though some reject the potential antinomian connotations arising from the term, “antitheses,” most agree that this section contains six examples of the principle Jesus elucidates in Matthew 5:17–20. Since Jesus came to fulfill the law (i.e., “the body of guiding precepts that shape the stipulations of the old Mosaic covenant and that are found within the Law/Torah/Pentateuch, most specifically in Exodus–Deuteronomy”5), he reserves the right to correctly interpret the law. In each of the six examples, Jesus quotes from the law (e.g., Ἠκούσατε ὅτι ἐρρέθη in Matthew 5:27) and then gives his definitive interpretation (ἐγὼ δὲ λέγω ὑμῖν).6 Frederick Bruner notes that the ἐγὼ is fronted in Jesus’s interpretations, which serves to emphasize that Jesus’s words carry greater authority than even the law.7 However, in contrasting the law with his interpretation, Jesus does not mean to put his words in opposition to the law. Rather, he seeks to unveil the heart behind the law, thereby revealing the lofty righteousness of God and the true expectations for those in his kingdom (2 Cor 3:12–18).
In Jesus’s second example (Matt 5:27–30), he addresses adultery (μοιχεύσεις). R. T. France points out that, after quoting the sixth commandment “verbatim” from the LXX (Exod 20:15; Matt 5:21), Jesus here does the same from the seventh commandment (Exod 20:13).8 In other words, Jesus means to tackle fundamental doctrine. Jesus affirms the prohibition against adultery yet takes the matter deeper. No one can claim they have obeyed the law if they have simply avoided sexual contact with a married woman or with someone other than one’s spouse. Instead, even a lustful look constitutes adultery.
Interpreters have long observed that Jesus seems here to connect the seventh and tenth commandments.9 Craig Keener notices that the term used for looking lustfully (ἐπιθυμέω) in Matthew 5:28 is identical to that which we typically translate as “covet” in LXX Exodus 20:17 (οὐκ ἐπιθυμήσεις τὴν γυναῖκα τοῦ πλησίον σου).10 Additionally, Keener cites numerous Jewish texts that link lust to adultery, concluding that Jesus was not informing his hearers of anything new.11 Thus Jesus, in Matthew 5:27–28, draws a seemingly straightforward connection between lust and adultery by way of covetousness.
https://www.thegospelcoalition.org/themelios/article/cut-off-your-hand-save-your-soul-how-the-outer-self-affects-the-inner-self-in-the-fight-against-lust/
I agree with Keener, Carson, and Guelich that Mt 5:28 is blended commentary on both the seventh and tenth commandments. On that interpretation, the issue is one of adulterous sexual covetousness.
Examples would include a married man covenanting a single woman, a single man coveting a married woman, or a husband coveting someone else’s wife or vice versa.
4. Keener notes that “Jewish men expected married Jewish women to wear head coverings to prevent lust (single women were exempt, since they needed to find a husband),” 187.
This suggests that singles were expected to sexually appealing to the opposite sex—within the bounds of modest attire—for purposes of attracting a mate.
5. There is a dispute over whether the construction involves lust on the part of the first party—A is lusting for B–(e.g. Nolland) or whether it involves A provoking B to lust (e.g. Carson, with Blomberg straddling the fence). …
Masturbation is often thought to violate the general principle laid down in Mt 5:28. Possibly so, but the inference isn’t straightforward:a) The traditional interpretation has always been problematic since heterosexual attraction is part of God’s design for human nature. So at best it becomes a matter of degree rather than an absolute prohibition.
b) John Frame defines “lust”, not as sexual attraction, but forbidden desire. Although that’s a good definition, it doesn’t select for what’s forbidden. To insist that masturbation is lustful in the forbidden sense is circular inasmuch as that’s the very question at issue.
c) On a related note, critics condemn masturbation if that’s linked to sexual fantasies. However, that simply pushes the issue back a step. Are sexual fantasies inherently sinful? Are all sexual fantasies sinful? To take a comparison, it would be hard to teach sex-ed without evoking the sexual imagination of the student.
d) In addition, the question of lust cuts both ways. If a bachelor has no outlet for pent-up sexual impulses, then that’s a source of lust. That preoccupies the mind. Masturbation can function as a “lust”-reducing safety value to lease excess pressure, which otherwise continues to build up.
e) Then there’s the question of whether the traditional interpretation is correct:
Klaus Haacker (“Der Rechtsatz Jesu zum Thema Ehebruch,” BZ 21 [1977]: 113-16) has convincingly argued that the second auten (“[committed adultery] with her”) is contrary to the common interpretation of this verse. In Greek it is unnecessary, especially if the sin is entirely the man’s. But it is explainable if pros to epithymesai auten, commonly understood to mean “with a view to lusting for her,” is translated “so as to get her to lust” The evidence for this interpretation is strong (see Notes). The man is therefore looking at the woman with a view to enticing her to lust.
If Haacker (see above) is right in his contention that the second auten is unnecessary on the customary reading of this verse, the problem is resolved if the first auten within the expression pros to epithymesai auten functions as the accusative of reference (i.e., the quasisubject) of the infinite (as in the equivalent construction in Lk 18:1) to generate the translation “so that she lusts” REBC (Zondervan, 2nd ed., 2010), 9:184-85.
If the alternative rendering (“get her to lust after him”) is correct, then I take this to mean that what 5:28 really forbids is seduction, viz. a man seducing a woman. As such, the prohibition would presumably apply to both premarital and extramarital sex–since OT law condemned each form of immorality, although adultery was the graver offense.
https://triablogue.blogspot.com/2007/01/lusting-in-ones-heart.html
The Council 