Aquinas and Homosexual Sex – Part 1: A Thomist Argument


Back in August, I posted a meme on my personal Facebook page that challenged the Christian argument that sex between two men is morally wrong because this is allegedly prohibited in the Old Testament book called Leviticus.

The basic objection in the meme is that there are several things that Leviticus prohibits that Christians seem to have no moral objections against.

Eating ham or bacon or pork ribs or pork chops or pork roast or pork sausage:

7 The pig, for even though it has divided hoofs and is cleft-footed, it does not chew the cud; it is unclean for you. 8 Of their flesh you shall not eat, and their carcasses you shall not touch; they are unclean for you. (Leviticus 11:7-8)

Eating shrimp, crayfish, crab, lobster, clams, scallops, oysters, or mussels:

10 But anything in the seas or the streams that does not have fins and scales, of the swarming creatures in the waters and among all the other living creatures that are in the waters—they are detestable to you 11 and detestable they shall remain. Of their flesh you shall not eat, and their carcasses you shall regard as detestable. 12 Everything in the waters that does not have fins and scales is detestable to you. (Leviticus 11:10-12)

Planting a mixture of two different kinds of seeds or wearing clothes made from two different kinds of material or fabric:

19 You shall keep my statutes. You shall not let your animals breed with a different kind; you shall not sow your field with two kinds of seed; nor shall you put on a garment made of two different materials.  (Leviticus 19:19)

Trimming your sideburns or beard:

27 You shall not round off the hair on your temples or mar the edges of your beard. (Leviticus 19:27)

Getting a tattoo:

28 You shall not make any gashes in your flesh for the dead or tattoo any marks upon you: I am the Lord. (Leviticus 19:28)

Having sex with a woman when she is on her period:

19 “‘Do not approach a woman to have sexual relations during the uncleanness of her monthly period. (Leviticus 18:19)

  • Christians have no interest in passing laws against any of these other things prohibited by Leviticus.
  • Christians don’t condemn or criticize people who do these other things prohibited by Leviticus.
  • Christians themselves often openly practice these other things prohibited by Leviticus, and feel no shame in doing so.

One of my Facebook friends is a Catholic, a philosophy student, and an admirer of Aquinas.  He made this comment in response to my posting of the meme:

I asked Christopher how reason alone could show that sex between men was evil, and he responded by pointing me to an article that presented a Thomist argument against homosexual sex.

So far I have written ten posts arguing that we should ignore the teachings and laws of the book of Leviticus:

Although I plan to continue publishing posts that provide more good reasons to reject the argument that we should condemn homosexual sex because the book of Leviticus allegedly condemns homosexual sex,  the reasons I have already provided are enough to demolish this WEAK and IDIOTIC argument.  So, I’m going to begin to examine the Thomist argument against homosexual sex, at least the Thomist argument presented in the article that Christopher pointed out to me.


The argument that I will analyze and evaluate comes from an article by Timothy Hsiao published in The Heythrop Journal in 2015: “A Defense of the Perverted Faculty Argument against Homosexual Sex“.  The main argument is summarized in section III of the article:

Here are the main premises/claims of the argument as stated in the above summary:

  1. It is always immoral to misuse a bodily faculty.
  2. Misusing a bodily faculty always involves rejecting the human good.
  3. Sexual activity exists for the sake of procreation and unity.
  4. All sexual activity that is not open to the creation of new life is immoral.
  5. Those who engage in homosexual conduct bring their sexual faculties to bear on a member of the same sex.
  6. Those who bring their sexual faculties to bear on a member of the same sex direct the function of sex to an end that is intrinsically unfit for the direction of sex towards the generation of new life. 
  7. Homosexual activity is immoral.

In the next post on this subject, I will attempt to clarify these claims and the logic of this Thomist argument against homosexual sex.