A commenter on the Usage and Marriage thread perfectly illustrated what I see as the One True Inherent Meaning error as applied to sexual practices. Someone else had written, "I think that gay sex is in fact natural for gay people. Therefore, I think that gay sex, and gay marriage, would not violate natural law." The commenter responded, "You are simply wrong based on human biology. Tab P goes into slot V not slot B."

Well, tab P goes into slot V, except when it doesn't. My guess is that, as a purely descriptive matter, tab P goes into the P-owner's hand many more times, on average, than it goes into slot V. If the most common use (i.e., the norm) defines the One True Inherent Use, then any sex other than masturbation is unnatural.

Ah, the commenter might respond, but that's not the purpose of the penis. The purpose of the penis, either in the sense of what its biological function is, or in the sense of how God designed it (I don't know the commenter's philosophy, so I'm not sure which he'd focus on), is to be inserted into a vagina so as to procreate.

But biology doesn't have "purposes," except in a metaphorical sense. Biology has developed the penis into a multi-functioned organ — it can be used for urination, for sexual pleasure, for emotional bonding, and for reproduction (I list these in what I guess to be decreasing order of actual frequency of use). Likewise for the multi-functioned vagina, though replacing urination with delivery of babies. More broadly, the sexual act is likewise a multi-functioned act. Likewise, biology has developed the mouth into a stunningly multi-functioned organ: It can be used for (among other things) breathing, communicating, consuming sustenance-producing substances, tasting substances to see whether they are wholesome, expelling vomit, kissing, licking stamps, and at least four different kinds of production of pleasure in oneself and others — singing, eating tasty food, stimulating others' nongenital erogenous zones, and stimulating others' genitals.

The anus is a less multi-functioned organ. Still, it can be used not just for elimination of wastes, but also for prostate exams, for gynecological exams, for the administration of medicine to people (often babies) who can't easily keep it down when the medicine is administered orally, and for the relatively accurate determination of body temperature. The latter four functions are of course artifacts of modern medicine, but I doubt that any of us would condemn them as violations of natural law, especially since learning, thinking, and developing new processes is natural for humans. Likewise, the anus can be used for sexual pleasure, and has been used that way by humans for millennia (and is used that way by some animals). Why then treat the anus, the mouth, or the penis as having One True Inherent Purpose rather than recognizing that they can be used in multiple ways, each of which is fully consistent with our biology.

Likewise if one sees the human being as part of God's design, and tries to deduce proper conduct from such design. (I set aside the separate argument that proper conduct should be deduced from supposedly authoritative religious works, such as the Bible — that's not the argument I'm responding to here.) God seems to have designed the human body in such a way that the penis, the mouth, and the anus can be used in lots of different ways; why should we infer, simply from the fact that one use (penile-vaginal sex leading to reproduction) is so important, that it's the One True Proper Use of genitalia? Likewise, God has designed humans in a way that allows some of them to be attracted to members of their own sex; even if you believe that this preference isn't innate, but is caused in part by upbringing or by personal choice, it's clear that the possibility of this preference is indeed present in humans (and, as I said, other animals). This too casts doubt on the theory that penises or the sexual act have One True Inherent Purpose or One True Inherent Mode Of Employment.

Words can have many functions (in the sense of many meanings). Institutions, like marriage, can have many functions. Parts of the body can have many functions. Human practices can have many functions. One can certainly argue that some functions are beneficial and some are harmful. But I see little reason to assume that there can only be one true inherent metaphysical natural function, or to infer that just because one function is very important, all other possible functions are improper or violations of natural (or linguistic) law.

I also commented on the broader "unnaturalness" argument three years ago, here.