During oral arguments over same-sex marriage, Justice Samuel Alito asked about a hypothetical relationship involving two men and two women. PHOTOGRAPHY BY MARK WILSON/GETTY

Judging from Justice Samuel Alito’s contributions during Tuesday’s oral arguments in Obergefell v. Hodges, the same-sex marriage case before the Supreme Court, he is a little hung up on polygamy. Over the course of two and a half hours, he asked about little else—other than sibling marriage and the sexual relations of the ancient Greeks. "Suppose we rule in your favor in this case and then, after that, a group consisting of two men and two women apply for a marriage license," he said to Mary Bonauto, one of the lawyers arguing against state bans on same-sex marriage. "Would there be any ground for denying them?" She explained that there would be many grounds: the structures of marriage are designed around two people, and polygamy raises questions of coercion and consent. So Alito gave it another try: imagine, he said, "four people, two men and two women—it's not the sort of polygamous relationship, polygamous marriages that existed in other societies." It’s one that exists in Alitoland, and it looks like this:

Alito: And let's say they're all consenting adults, highly educated. They're all lawyers.

[Laughter.]

Alito: What would be the ground under the logic of the decision you would like us to hand down in this case? What would be the logic of denying them the same right?

Bonauto gave the same answer, emphasizing that the distance of polygamy from both heterosexual and same-sex marriage, which are in the same class, was so great as to make it another institution. (For example, the things that a marriage helps authorities clarify, like who gets to make decisions in a medical emergency, would instead be muddied.) Alito liked that less than the reply from the lawyers on the other side, which fanned his fears. He asked John Bursch, the lawyer arguing against gay marriage, "Do you see a way in which that logic can be limited to two people who want to have sexual relations?” Bursch replied, "It can't be." (When Alito elaborated by bringing up the group "I mentioned earlier, two men and two women," Bursch replied with a hypothetical involving a putative close friendship between himself and Justice Elena Kagan, which was even more confusing.)

Alito was making two points, which had to do with the two separate questions that the Supreme Court is considering in Obergefell. Question One (which I wrote about on Tuesday) is whether the Fourteenth Amendment gives same-sex couples a constitutional right to marry in all fifty states. Polygamy, for Alito, seems to epitomize the tradition-destroying force and absurdity of granting that right—if gays can marry, who can't? And what will the world come to? Question Two asks whether states that do not allow same-sex marriage must regard as valid same-sex weddings performed in other states. Here, Alito was using polygamy to ask what else might be foisted on a state if it couldn't draw a line at same-sex marriage.

Question Two is moot if the answer to Question One—marriage equality everywhere?—is yes. But, for now, Question Two is very relevant to many people's lives. A number of states not only ban same-sex marriage but explicitly forbid the recognition of out-of-state same-sex marriages, even when it means refusing to recognize things like adoption orders granting parental rights, or to put a widower's name on a death certificate. For example, Sergeant Ijpe DeKoe married Thomas Kostura in New York. When the Army transferred DeKoe to a base in Tennessee, he suddenly became, in the eyes of that state, a single man—his marriage was dissolved when he crossed state lines. DeKoe and Kostura are among the plaintiffs whose suits are now before the Supreme Court.

It is also an unusual question. Under Article IV, states give "full faith and credit"* to one another’s marriages, even if, say, a seventeen-year-old married in a state where that is the minimum age moves to a state where the age is eighteen. One of the few historical counter-examples to that standard involves the refusal to recognize interracial marriage—“not a precedent on which I think the Court would want to rely in this instance," Douglas Hallward-Driemeier, the lawyer arguing that same-sex marriages should be recognized, said. (A 1970 case cited by Tennessee turns out, on closer examination, to involve a marriage between a stepfather and stepdaughter that was invalid in both the state where the wedding was held and the one to which the couple moved.)

And here is where the full irony of Alito's polygamy fixation becomes clear. If one is looking for a route to polygamy in the United States, the surest, quickest way is to allow states to keep refusing to recognize same-sex marriages legally performed elsewhere. If, as Tennessee and its cohort insist, a man married to a man is actually single, then what’s to stop him from marrying a woman in those states? He probably wouldn’t want to—but the legal oddity suggests the incoherence of the anti-marriage-equality position.

I asked Roberta Kaplan, the Paul, Weiss, Rifkind lawyer who argued and won United States v. Windsor—which overturned the central parts of the Defense of Marriage Act—if such a scenario was plausible. "The Tennessee statute defended in the Supreme Court yesterday provides that marriages between gay people are 'void and unenforceable' in Tennessee," she wrote. "Thus, at least theoretically, a gay man married in New York could move to Tennessee—with his husband—and then get married for a second time to a woman in Tennessee. And he could not be prosecuted for bigamy since his first New York marriage is void."

Perhaps Alito could even get his four lawyers together. Two men married to each other in New York and two women married to each other in New York could all move to Tennessee, where they would be rendered single again, and the women could marry the men. What would the relation of each to each be? How about if they moved back to New York? These are, indeed, confusing questions, but there is a simple way to avoid them. Find that there is a right to same-sex marriage, and that those marriages, between two people, are as real, and as solid, as any in any state. They involve husbands and wives, not single people who are play-acting. They can survive a cross-country trip.

* Correction: The clause was previously attributed to the Fourth Amendment.