WASHINGTON — For thousands of years, in societies around the globe, marriage has meant the union of a man and a woman. "And suddenly," declared Justice Stephen G. Breyer, "you want nine people outside the ballot box" to change that by judicial fiat.
History weighed heavily on the nine members of the Supreme Court on Tuesday as they debated whether the Constitution guarantees gays and lesbians the right to marry. That even Breyer, clearly a supporter of same-sex marriage, felt compelled to take note underscored the magnitude of the issue before the court.
With intellectual side trips to Plato's Greece and the land of the Kalahari bushmen, Tuesday's arguments challenged the justices to decide whether they are ready or willing to overturn not just legal doctrine but also embedded traditions in the name of equal rights. At what point do thousands of years no longer determine right and wrong? And if what was wrong is now right, is it up to them, instead of voters and legislators, to say that?
The collision of ancient understandings and modern sensibilities put the court right in the middle of one of the most defining social issues confronting 21st-century America. If the justices seemed eager to avoid a definitive ruling two years ago, when the issue last came before them, they seemed acutely aware on Tuesday that there may be no turning back this time.
The prospect of breaking so decisively from the past struck not just Breyer but also several of his colleagues.
"The word that keeps coming back to me in this case is millennia," said Justice Anthony M. Kennedy, widely considered the swing vote.
"Every definition that I looked up, prior to about a dozen years ago, defined marriage as unity between a man and a woman as husband and wife," said Chief Justice John G. Roberts Jr.
"As far as I'm aware, until the end of the 20th century, there never was a nation or a culture that recognized marriage between two people of the same sex," Justice Samuel A. Alito Jr. said.
"You're asking us to decide it for this society when no other society until 2001 ever had it," added Justice Antonin Scalia.
Kennedy noted that the Kalahari people of southern Africa, without a modern government like that in the United States, defined marriage as between a man and a woman. Alito argued that even ancient Greeks, who engaged in same-sex relationships, did not extend marriage to them.
Against this concern, advocates for same-sex marriage pressed their point that history, by itself, was hardly the only guide. Justice Ruth Bader Ginsburg noted that women were deemed under law to be subordinate in marriage for centuries. Several justices noted that blacks and whites were not allowed to marry in some states until the court intervened in 1967.
"Times can blind, and it takes time to see stereotypes and to see the common humanity of people who had once been ignored or excluded," Mary L. Bonauto, a lawyer representing plaintiffs suing to overturn state bans on same-sex marriage, told the justices.
And Breyer seemed to answer his own concern later in the oral arguments when he argued that history, even thousands of years of it, might not be enough to justify excluding gays and lesbians from what he suggested was a fundamental right. "The answer we get is, well, people have always done it," he said. "You know, you could have answered that one the same way we talk about racial segregation."
Tuesday's hearing reinforced the expectation that the court will find a constitutional right to marry for gays and lesbians, given Kennedy's past writings and the tone of his questions and comments in court. But the court set up the issue in a way that lets it look as if it is responding to changing national norms rather than imposing them.
The court's decision two years ago in Windsor v. United States threw out the heart of the Defense of Marriage Act, a federal law that defined marriage as the union of a man and woman, without finding a constitutional right to marry for same-sex couples. Since that case was argued, the number of states where same-sex marriage is legal has grown to 36 from nine.
But most of those additional states now granting marriage certificates to gays and lesbians did so only after lower federal courts interpreted Windsor to mean that there is, in fact, such a constitutional right. Just 11 states have extended marriage to gays and lesbians through ballot initiatives or legislative measures. So it was the Supreme Court's own partial ruling in 2013 that led lower courts to rule in favor of same-sex marriage in so many states, rulings the court is now being asked to validate.
The opponents of same-sex marriage focused part of their argument on that circumvention of the democratic process. Roberts noted that Maine outlawed same-sex marriage in 2009 and then reversed itself and legalized it in 2012, showing that change can happen through expressions of popular will rather than judicial activism.
"That sort of quick change has been a characteristic of this debate," he told proponents. "But if you prevail here, there will be no more debate. I mean, closing of debate can close minds, and it will have a consequence on how this new institution is accepted. People feel very differently about something if they have a chance to vote on it than if it's imposed on them by the courts."
Other conservative justices echoed that sentiment, suggesting that those who favor same-sex marriage should wait for the democratic process to play out. But the other side said the equal protection clause of the 14th Amendment made it unconstitutional to prevent gays and lesbians from enjoying the same right to marry that heterosexuals enjoy. Waiting, they said, is not a constitutional remedy.
"Gay and lesbian people are equal," said Donald B. Verrilli Jr., the solicitor general, arguing on behalf of same-sex marriage for the Obama administration. "They deserve equal protection of the laws, and they deserve it now."
Now, nine people outside the ballot box will have to weigh the millenniums against the here and now.