Who defines the word 'marriage'?

Michelle Brodie could have just waited one year. Instead of getting married, she could have bided her time until Jan. 1, when California's domestic-partnership law takes effect. Within the state, she would have had nearly all the rights of marriage without the uncertainty of a license signed in defiance of state law.

But she came to San Francisco's City Hall this week because that wasn't enough. In the end, she did not want a domestic partnership or a civil union or any other such legal arrangement with her partner, Susan Barnes. She wanted a marriage.

Friday, city officials here will file a brief with the California Supreme Court, explaining why nothing short of marriage for same-sex couples is acceptable. Their stand points to a shift in the nationwide debate about same-sex unions. Increasingly, the question is not merely about access to equal rights for gay and lesbian couples. It is about the word "marriage" - and who gets to use it.

To those on both sides of the issue, it is far more than just a matter of word choice. Rather, the word marriage encapsulates a long-held vision of society that proponents of the traditional American family are loath to concede - and a history of discrimination that gay-rights groups are desperate to overthrow.

In many ways, the debate is only beginning, as gay-rights activists ride the momentum of recent nationwide events and pursue goals that seemed unattainable even a year ago - leaving state officials to grapple with the legality of those actions after the event.

Last weekend, Jason West, the mayor of New Paltz, N.Y., defied state law and married 25 couples. He now faces 19 criminal counts and possible jail time. In Portland, Ore., County Attorney Agnes Sowle declared refusing gay and lesbian couples to be a form of sex discrimination and began issuing licenses to waiting couples. State officials have yet to respond.

Last month, the Massachusetts Senate asked for clarification of the state's Supreme Judicial Court ruling earlier, which instructed the state to approve marriage licenses for same-sex couples no later than May. The Senate asked the court if it could pass a bill that would give same-sex couples all the "benefits, protections, rights, and responsibilities" of marriage, but call the contracts "civil unions." The justices' response: "No."

To supporters of same-sex marriage, the declaration of marriage is the ultimate statement of equality - not just for the right to file joint tax returns or make hospital visits, but for the message it sends. "When I say, 'I am married," it is a powerful thing in our society," says Matt Foreman, executive director of the National Gay and Lesbian Task Force in Washington.

And some in the gay and lesbian community look at civil unions - even if they hold all the benefits of marriages - as a new incarnation of "separate but equal."

"I'm not going back to the 1940s and '50s," says Ms. Brodie after she married in a City Hall ceremony. "If straights' [unions] are called marriage, then gays' [unions] should be called marriage."

Yet Brodie acknowledges that the word "doesn't mean anything" other than equality. To opponents of same-sex marriage, however, it has a deep and personal meaning beyond the halls of government. It's cultural shorthand for a set of moral values and the conviction that the union of one man and one woman is the basic building block of society.

This dual meaning of the legal and the moral is what make the argument about the purpose of marriage so contentious. "It's unique in that it's very much a public institution, but at the same time it's a private institution," says Nancy Cott, author of "Public Vows: A History of Marriage and the Nation." "I don't think anything else combines these two in this way."

The concern among many who are opposed to same-sex marriages is that the traditional cultural resonances of marriage are dissipating. They see the Massachusetts Senate's effort to keep the word marriage just for heterosexual couples - even while conceding away its benefits - as a last-ditch effort to save the institution.

"Some see the word as politically trivial, but if they do they're missing the point," says Douglas Kmiec, a professor at Pepperdine School of Law in Malibu, Calif. "It was quite insightful to say to the court, 'If you want all the benefits, you can have them. What you can't have is the cultural definition of marriage itself.'"

Marriage, however, is changing - just as it always has been. From antiquity to relatively recent times, marriage was about property and child-rearing. The notion of marriage for romance or happiness has emerged only in the past two centuries.

"If people marry because they feel entitled to find happiness with another person, it's very hard to distinguish heterosexual relationships from homosexual relationships," says Hendrik Hartog, author of "Man and Wife in America."

For now, much of the power to define marriage rests in the courts' hands. Next week, the California Supreme Court could decide whether it will take the case against San Francisco. "What is the equal- protection clause [of the state constitution] designed to protect?" asks Professor Amar. "It is always complicated to decide how far to extend the protections of equality."

• Robert Harbison contributed to this report.