Since Andrew Sullivan brought it up, I guess I’ll reiterate what I’ve said before on the subject.

One of the old talking points against same-sex marriage is that it will lead to legal recognition of polygamy. The reasoning is simple: if erotic desire is the basis of legal rights, then how can you deny said rights to people whose preferences run to plural marriage?

Sullivan’s usual rejoinder is that people who want to live in plural marriage arrangements aren’t denied any fundamental rights by a rule that says you can only marry one person, because you are still able to marry a person that you love. Moreover, so long as adultery is a private matter – potentially relevant to divorce proceedings, but not a criminal matter – there’s no legal bar preventing a married couple from living non-monogamously. By contrast, a gay person doesn’t have a place at the table in the absence of legal recognition of same-sex relationships as marriages.

This always struck me as a non-answer. If the question is a right to marry whom you love, then the polyamorist can say: yes, indeed, my rights are violated if you prevent me from marrying a second time simply because I am already married. Forcing me to choose between loves is no different from forcing a gay person to choose between, say, a desire for a family and a desire for erotic satisfaction.

There are other answers, however. Whether they are sufficiently satisfying may be debated, but I think they are better grounded.

The simplest answer is that the Burkean case for same-sex marriage looks at the lived reality of gay lives and says: gee, there are significant numbers of gay couples living in marriage-like relationships: pair-bonded for extended periods of time, sharing a household, raising children together, committed to mutual support, etc. Given this reality, the question is why the law should not grant equal recognition to these relationships – assuming the law does not deem the erotic relationship at the core to be fundamentally anti-social.

A variety of answers to that question may be given, but the first thing to note is that there are not, similarly, large numbers of people in the United States living in long-term, stable polygamous relationships. If there were – if fundamentalist Mormonism were to really take off, or if a large Muslim immigrant population stuck to traditional polygamous practices, or if communal polyamorous unions became common among young hipsters, then the law would need to figure out what to do about it. The law could decide to stamp out such practices – as it did when Utah sought admission to the Union – to engage in social engineering to force people to conform to a certain standard. Or the law could change to recognize such unions as legitimate. But that choice would only be forced on the law by society. The law is in no way obligated to lead society through application of abstract principles to obscure test cases. It is obliged to respond to society as society changes, organically.

This, by the way, is one reason why I strongly feel that the legislature, rather than the courts, is the proper venue for recognizing same-sex marriage: because the courts do need to articulate abstract legal principles so that the law can be understood, and they do use obscure test cases to establish such principles.

Returning to the question of “why not” to grant this recognition to marriage-like same-sex relationships, as I said there are a variety of answers that have been given, but the most fundamental justification for a negative answer relates not to those qualities of the relationship that I delineated, but to the essentiality of male-female complementarity. If marriage is not, fundamentally, about mutual support or raising children – and, more to the point, about yoking erotic desire to these social goods (which is the only reason why the state should care at all) – but rather about defining proper reciprocal sex roles, then same-sex marriage is indeed absurd.

This is why I have said in the past that the case against same-sex marriage is “Schlafly in reverse.” Phyllis Schlafly argued against the Equal Rights Amendment in part on the grounds that if it passed it would lead inevitably to same-sex marriage, because preventing a woman from marrying another woman on the grounds that she isn’t a man would be sex discrimination; the case against same-sex marriage is, fundamentally, the case that recognizing such a thing would make it impossible, going forward, to talk about men and women as being essentially complementary; it would cement a regime of legal androgyny.

How does this play into the polygamy question, though? Well, here it’s important to distinguish between traditional polygamy – which is clearly a form of marriage, indeed, the dominant form for much of human history – and modern polyamory. Traditional polygamy is rooted in a fundamental asymmetry between male and female: it’s called “polygamy” because it’s a system under which a man can have many wives (a multiple-husband system would be called “polyandry”). Marriage in this system is understood fundamentally as an acquisition by the male of rights to erotic access and to the offspring of such access. If that’s what marriage essentially is, then there’s no logical reason why a man can’t have multiple wives. Again, this was the normative understanding of marriage for much of human history; the radical feminist case against marriage is rooted in the conviction that this understanding, and hence patriarchal dominance and female subordination, is fundamental to the institution.

Regardless of whether you view this traditional understanding as abhorrent or attractive, it should be clear that it is radically incompatible with a regime of legal androgyny that would best-harmonize with same-sex marriage. It is not an accident that the religious traditions with the closest ties to their polygamous roots – traditional Islam, Orthodox Judaism, Mormonism – have been the most resistant to the normalization of same-sex relationships. Polygamy depends upon a fundamental asymmetry between male and female, which these traditions also valorize. (Not, I should stress, because they are necessarily committed to female subordination; there is a whole argument that “different doesn’t mean unequal” which you may find persuasive or not, but which I don’t mean to dismiss without engaging with it.) That fundamental asymmetry is challenged by same-sex marriage.

Remove the asymmetry between male and female, and we’re no longer talking about polygamy; we’re talking about modern polyamory. But I’m not sure it’s possible to “assimilate” polyamory to marital norms. Forget about who gets the social security checks and the like (money, after all, is easily divided), and let’s talk about children and divorce. In a polyamorous relationship, who has parental rights with respect to children? The biological parents? The entire collective? If a member of the collective wants to leave, how and with whom is that departure to be negotiated? With the entire collective? What about erotic exclusivity, which is presumed in the case of marital relationships (though it’s always up to any individual couple to choose to depart from that norm at their discretion) – if a member of a polyamorous collective has sexual relations with an outsider, does the law care? Is the collective financially implicated in any children born of that illicit union?

(Note that none of these questions are difficult at all in traditional polygamous marriage: the father has all the rights to the children, and the sole unilateral right to initiate divorce; erotic exclusivity is imposed on the wives but not on the husband; and the collective is financially implicated in the offspring of any extra-marital liaisons by the man inasmuch as such a liaison implies a promise to be included in the collective.)

I don’t presume that there are no possible answers to these questions in the case of polyamorous unions – and if such unions formed and persisted in large numbers over time, the collectives would develop, of necessity, answers to these questions. But they haven’t, and I don’t think they will, in part because I don’t think there are good answers to these questions; I think the math quickly becomes unworkable. Collective living experiments have not tended to last when they have been tried, but I’m sure they will be tried again anyway. In the meantime, the difficulty of these kinds of questions are perfectly good reasons for the law to say: we’re not going to try to answer them until such time as sheer weight of numbers forces us to.

Meanwhile, the radical gay case against same-sex marriage is precisely that the promulgation of a marital norm to homosexual couples progressively narrows the social space for more radical modes of living. Once gay couples can marry, the argument goes, they will increasingly be expected to marry – at least eventually. I don’t know whether this will or won’t happen, but the question turns on how influential the law is in shaping social expectations. And if the law doesn’t shape social expectations much, then why worry about same-sex marriage either way?

So where does that leave the question of polygamy?

There is no Burkean case for recognizing polygamy comparable to the case for recognizing same-sex marriage – not in our society as it actually exists. And both the radical gay case against and the traditionalist case against same-sex marriage suggest that same-sex marriage has negative implications for the social acceptance of plural unions.

It seems to me that the most likely way in which same-sex marriage might lead to legal recognition for polygamy would be through the back-door of a robust religious exemption for traditional marriage. I can imagine, for example, a traditional imam or a fundamentalist Mormon elder arguing that their tradition of plural marriage is just as deserving of special protection as any other religious tradition’s objection to same-sex marriage. I don’t know whether such an argument would prevail, but it does seem to me that the stronger and broader the language of such a legal carve-out, the harder it will be to argue that it doesn’t cover such a case.

Something for the defenders of traditional marriage to ponder as they prepare such language for legislation.