Way back on May 22nd, my brother posed this dilemma for natural law advocates:

If anything would be unnatural and contradictory to the function of sex, it would be castration, the severest form of male birth control. Yet it is approved by Jesus, perhaps echoing the text of Isaiah 56:4-5, which affirms that eunuchs have a special place in God’s heart.

The discussion on natural law began with this post by Ed Feser, which is an excellent introductory essay on traditional natural law theory. America’s most prominent natural law theorist, Robert George, articulates and defends a slightly different form of natural law than Feser’s. Since I claim to be a natural law theorist, I will outline the view here before addressing my brother’s complaint. In this I will lean heavily on Feser’s excellent summation. If you are already familiar with the natural law theory or already read Feser’s post, then I would encourage you to skip the following. If not, then you may find it enlightening.

Feser begins by pointing out that traditional conceptions of natural law theory begin with the notion that “things” have forms, which might be understood as ‘natures’ or ‘essences.’ In other words, there is a ‘human nature’ that all humans have.

Goodness, then, is the actualization (what Aquinas calls a ‘second actualization’) of the form or essence. Feser’s example is of a squirrel: “A good squirrel is one which flourishes in the sense that it realizes its squirrel nature to the fullest: it scampers up trees and avoids predators, gathers its food, rests when it needs to, and in general does well all the things that squirrels by their nature tend to do.”

Important to this concept is the notion of ‘natural ends’ of forms or essences. Natural law theory has always suggested that natures have specific functions or purposes that stem from the sort of things they are. For instances, kitchen knives have the purpose of cutting vegetables. A “good knife” is one that cuts vegetables well, since it is performing it’s ‘natural end’ or acting like the sort of thing it is (i.e. a knife).

Yet this is obviously too simplistic with regard to humans. Aquinas is very clear that ‘natural law’ is an extension of reason and that humans have the unique ability to rationally deliberate about their ends, and to choose which ends to bring about, unlike the case of the knife (or squirrel). Again, Feser says it better:

A fully good human being, in the not-yet-moral sense of “good” used above, is one who has fully realized his natural potentials. And a morally good human being is just one who tends to choose to act in a way that will lead him to realize those potentials. By the same token, just as a bad human being, in the not-yet-moral sense, is one who fails to realize those potentials, a morally bad human being is one who tends to choose to act in a way that keeps him from realizing them.

Now to the interesting stuff. Feser extends his discussion of natural law into sexual ethics, and it’s his discussion here that later commenters latched on to (see here and here, as well as my brother’s post).

The money quotes from Feser:

Since it’s the natural law theory example that critics of the theory always get the most worked up over, let’s look at sex. One way to understand the traditional natural law view of the matter is this. If you consider the sexual drives that human beings have, then it is blindingly obvious that if those drives have any natural purpose at all – if they were, say, designed with a certain end in view – then that purpose is to get people to use their sexual organs. And if you consider the sexual organs themselves, then it is also blindingly obvious that if they were designed with any purpose in mind, then that purpose is procreation. More specifically, the purpose of a penis – again, if you assume that it was indeed designed with a purpose in mind – is quite obviously to deposit semen into a vagina (and also, of course, to urinate). That’s what it’s for, if indeed it is for anything, and whether or not it can be used for other purposes.


It must also be emphasized that, contrary to another common misunderstanding, “unnatural” in the context of the view I’m describing does not mean “using something other than for its natural purpose.” It means “using it in a manner contrary to its natural purpose.” To borrow an example from Michael Levin, there is nothing unnatural about merely tapping out a little song on your teeth, even if that’s not what teeth are for. But there is something unnatural about painting little pictures on your teeth and then refusing ever to eat again lest the pictures be rubbed off, or pulling them out so as to make a necklace out of them. The former sort of act does not frustrate the natural end of teeth, but the latter acts do. And part of the idea in the traditional natural law understanding of the sexual act is that ejaculating into a Kleenex, or a condom, or into any bodily orifice other than a vagina, doesn’t just involve using an organ other than for its natural purpose (which is not necessarily “unnatural”) but that it uses it in a manner contrary to its natural purpose. For the “aim” or point of arousal and ejaculation, if they have an aim or point at all, is to get semen into a vagina, and the acts just described frustrate that aim.

For the same reason, not every human intervention in the natural order counts as “unnatural.” Putting eyeglasses on doesn’t “interfere with nature” in a sense that traditional natural law theory would take exception to, because what glasses do is remedy a defect that keeps eyes from performing their natural function. The point of glasses is not to interfere with an organ’s performance of its natural function, but rather to aid it in performing that function. By contrast, the point of birth control devices is to stop an organ from performing its natural function. So such devices do “interfere with nature” in a sense that is illicit from the traditional natural law point of view.

Now, the lengthy summary of the discussion is perhaps superfluous, but the scholar in me made me treat this more like an essay than a blog post. Hopefully my brother’s dilemma is a bit more forceful (if you’re still reading). In short, it is this:

Natural law tradition (as Feser explains it) deems using sexual organs in a manner contrary to their intended purpose (procreation) illicit.

Jesus (allegedly) sanctions (following the OT) ‘using’ the sexual organs in a manner contrary to their intended purpose, i.e. destroying them (see Matthew 19:11-12).

I have two replies to the dilemma, one to Feser and the other to my brother. In reverse order:

1) My brother claims that Jesus sanctions castration, which (quite obviously) would be contrary to the intended purpose of the sexual organs. However, he takes no thought of the surrounding context of either Isaiah 56:4-5 or Matthew 19:11-12. Regarding the former, it’s not clear at all what Jewish ‘eunuchs’ actually were. It seems marriage was highly regarded in Jewish culture, especially since the blessing of Abraham is to his descendants as well (Genesis 17:6-7). It’s not clear that Israel had any real ‘eunuch’ culture where they intentionally castrated themselves. Jesus’s words, though, are much clearer since we don’t need to rely at all on extra-biblical knowledge of the culture.

In suggesting that Jesus is sanctioning castration in these passages, my brother glosses over the fact that Jesus is answering a worry from his disciples about marriage: “If such is the case of a man with his wife, it is better not to marry” (19:10). Jesus replies by identifying three levels of ‘eunuchs’–some are born that way (which doesn’t seem like castration at all), some are made that way by men (castration) and some ‘have made themselves eunuchs for the sake of the kingdom of heaven.’ Given that Jesus has already used the term ‘eunuch’ to refer to a group of individuals who have not been castrated, then it’s not at all obvious that he is suggesting castration for this third group. Rather, he is commending a lifestyle of celibacy and continence, of deliberate singlehood for the sake of the kingdom of heaven. In other words, he is describing the monastic tradition.

So there is nothing in this verse that contradicts the traditional natural law tradition. Jesus and His followers do not misunderstand each other so badly as my brother thought.

2) However, this underscores for me a complaint I have with Feser’s characterization of sexual ethics within the natural law tradition. Fundamentally, Feser reduces the ‘purpose’ of the sex drive to the purpose of the sex organ, a reduction that I am not comfortable with. What it entails is a view of the sex drive that is more physical than personal. My rejoinder would simply be to view the ‘sex drive’ as an expression of the whole person, of the whole human nature, which means that it may find expressions outside the sex act or any sexual act. Fundamentally, the physical ‘sex drive’ is a physical manifestation of a deeper desire to create, what the Greeks called ‘eros’ which comes from the whole person, body and soul. On this view, the aforementioned monastics are simply directing their eros and all the energy therein (which most often comes out as sexual energy) toward a different object–the Church.

In other words, Feser’s suggestion that “it is blindingly obvious that if those [sex] drives have any natural purpose at all…then that purpose is to get people to use their sexual organs,” is, I think, not so ‘blindingly obvious.’ “Sex drives” are not onlybiological, and so its expression is not only biological. A purpose of the sex drive is clearly the use of sexual organs, but that is not the only purpose.

In sum, my brother’s dilemma for the natural law tradition evaporates in light of a clearer understanding of the words of Jesus. I’ve also offered a reappraisal of the natural law position on the sex drive and it’s relationship to sex organs.

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Posted by Matthew Lee Anderson

Matthew Lee Anderson is the Founder and Lead Writer of Mere Orthodoxy. He is the author of Earthen Vessels: Why Our Bodies Matter to our Faith and The End of Our Exploring: A Book about Questioning and the Confidence of Faith. Follow him on Twitter or on Facebook.


  1. Matt writes: “Sex drives” are not only biological, and so its expression is not only biological. A purpose of the sex drive is clearly the use of sexual organs, but that is not the only purpose.

    I agree that the “castration” objection isn’t very solid, although I note the parallel construction of “made (themselves) eunuchs” in the latter description that might argue against your position.

    Francis Beckwith’s comments to Feser’s post lines up with your thoughts. But see Max Goss’s objection below it. That, I think, summarizes the fear of traditional natural law theorists–no ‘foot in the door’ for homosexuality must be allowed.


  2. Interesting! Bookmarked for more reading; a LOTR fan…


  3. Jim writes:
    Francis Beckwith’s comments to Feser’s post lines up with your thoughts. But see Max Goss’s objection below it. That, I think, summarizes the fear of traditional natural law theorists–no ‘foot in the door’ for homosexuality must be allowed.
    Let me attempt to clarify. I think that ‘sex drives’ are one manifestation of a deeper desire known as ‘eros.’ Eros can be directed toward individual persons (sex) through sexual acts, or it can be directed toward ‘culture’, in which case something like deliberate celibacy might obtain.

    So I actually think I’m saying something different than Beckwith, though I might agree with his claims about sex organs and the sex act.

    Regardless, to describe the natural law position regarding homosexuality as driven by fear fails to take seriously the intellectual robustness of the tradition, and the intellectual ability of it’s current proponents (I would commend John Finnis or Robert George to you as articulating a VERY defensible natural law theory). In short, I am not afraid of homosexuality getting a “foot in the door.” I do think that there are good reasons to not engage in homosexual practices or to allow state sanctioned homosexual marriages.


  4. Hello,

    You mentioned that sex has personal as well as physical purposes. You may be interested in Humanae Vitae, a Generation Later, edited by Janet E. Smith, and Love and Responsibilty, by Karol Wojtyla.



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