Incest – The Surprising Thomistic Objections

Eamonn Clark

*WARNING: Put on your Charity Goggles*

A disappointing article appeared recently in the Chicago Sun-Times entitled, “Archbishop not backing gay marriage – yet.” (See Phil Lawler’s commentary here.)

While one might argue there are several problems in the article, I want to focus on His Eminence’s explanation of consanguinity in marriage. I think he is off-base and risks coming across as a consequentialist.

The Angelic Doctor lists four reasons why consanguine marriage is illicit – and guess what? The risk of birth defects is not one of them. To me, it seems unlikely that Thomas was altogether ignorant of the likelihood of sickly kids coming from kissing cousins, but suppose he was… He is still against it, and with today’s rapid advances in genetic manipulation, the “problem” of incestuous birth defects could eventually be overcome. We should see the causal link between incest and sickness as a sign that something is wrong with the act, not as a random feature of an otherwise virtuous behavior. Thomas gives us a more principled account of why consanguinity (and affinity) is such a big deal.

With that, the four reasons are:

  1. Shame (in its proper sense) before one’s parents – and those closely united with them by blood and law – is good on account of the special respect owed to them on account of one’s special relationship with them.
  2. Families often live together, and this would provide an untold number of occasions to lust if there were not a clear, strong, and constant prohibition against incest.
  3. Inter-family marriage increases the social good of individual human beings, and in so doing it also builds up the community.
  4. We already have a natural inclination to love family members, and if this had the possibility of intercourse added to it then there would be an occasion for too great a sexual desire for that person.

So, for St. Thomas, it is about filial piety, intemperance in itself, and the good of the commonwealth, not scoliosis or clubfoot.

Again, it is not that birth defects are irrelevant to the discussion, but it is a symptom of the problem rather than the problem itself – and it is a symptom which theoretically could be eliminated. If we are to win the battle of the minds against secular culture, then we need to do better. Going back to Thomas is almost always a good idea, and I suggest that this is one of those moments. Incest is one of the last sins against chastity that Western society actually considers immoral… Let’s be sure not to lose that ground.

St. John the Baptist – pray for us.

6 thoughts on “Incest – The Surprising Thomistic Objections

    1. Hi Father,

      If you’re asking about incest among the first descendants of Adam and Eve, you may find an indirect answer to this in the Supplementum, Q. 65, which discusses polygamy. (“Theft” in case of urgent necessity would also be related.) There are hints, too, in Q. 94 in the I-II.

      In short – it was completely necessary, and the natural law provides for such circumstances through admitting of degrees or levels, though, interestingly Fra Rainaldo writes that breaking such a precept would require inspiration from God to do lawfully. A curious discussion indeed.

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  1. I am guessing his Eminence made this statement in the context of pointing out that the logic that made “gay marriage” legal would extend to legitimizing both polygamy and incestuous unions, but am I correct? It certain follows from Justice Kennedy’s opinion in Obergefell, though I doubt he recognizes that it is so.

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