The Supreme Court could rule on same-sex marriage next year. Here's what you need to know.

When the Sixth Circuit Court of Appeals on November 6 upheld four states' same-sex marriage bans, it created a rift between the federal appeals courts over whether states should be required to marry gay and lesbian couples — a split only the Supreme Court has the judicial authority to resolve.

Supporters and opponents of same-sex marriage have long argued that the Supreme Court needs to settle the issue. But now, with the federal appeals courts split and same-sex marriages recognized in 35 states, the legal stakes are much higher. And it's very likely the Supreme Court will take a case. Then what?

"I'm optimistic and hopeful," said James Esseks, director of the LGBT and AIDS Project at the ACLU. "The landscape for marriage for same-sex couples has changed and matured in a sense."

It's still unclear when or whether the Supreme Court will decide to hear an appeal on the Sixth Circuit Court's decision. But here's a rundown of how the country got to this point, the legal arguments surrounding marriage equality, and how the nation's highest court could rule.

How did we get to this point?

Same-sex marriage supporters wave an LGBT flag in front of the Supreme Court. (Jewel Samad / AFP via Getty Images)

A flurry of same-sex marriage cases began when the Supreme Court in June 2013 struck down the Defense of Marriage Act, the federal ban on same-sex marriages. Since then, lower courts have invoked the ruling to strike down states' same-sex marriage bans under the argument that they violate the 14th Amendment's Due Process and Equal Protection Clauses.

As the lower court rulings piled up, the chances of a case being taken by the Supreme Court appeared to increase. But in October, the Supreme Court declined to take up appeals from cases originating in Utah, Oklahoma, Virginia, Wisconsin, and Indiana.

The Supreme Court's decision not to hear the cases was in some ways a victory for LGBT advocates, since it let lower courts' pro-LGBT rulings stand, effectively legalizing same-sex marriage in 11 states. But the Supreme Court's decision also left the legal debate about marriage equality unresolved in 20 states, 15 of which still don't allow gay and lesbian couples to marry.

So why is the Supreme Court likely to take these recent cases?

Kevork Djansezian/Getty Images News

Justice Ruth Bader Ginsburg previously said that the Supreme Court would decide the issue of same-sex marriage if federal appeals court decisions conflicted, as they do today. (Kevork Djansezian / Getty Images News)

There is now a disagreement between the federal appeals courts on whether states' same-sex marriage bans are unconstitutional, and the Supreme Court is the only judicial body with the authority to decide which side is right.

Until October, federal appeals courts were unanimous in their rulings that states' same-sex marriage bans are unconstitutional. But the Sixth Circuit Court of Appeals on November 6 upheld same-sex marriage bans in Ohio, Michigan, Kentucky, and Tennessee, making it the first federal appeals court in the country to come down against marriage equality since the 2013 Supreme Court decision.

The Sixth Circuit Court's decision made it so there's now a split on the legality of same-sex marriage bans among the federal appeals courts. Justice Ruth Bader Ginsburg has said that type of split usually forces the Supreme Court to intervene.

"[W]hen there's no disagreement among the courts of appeals, we don't step in," Ginsburg said at the 92nd Street Y event on October 19. "The major job that the court has is to keep the law of the United States more or less uniform. So when courts of appeals disagree about what the law of the United States is, then we are obligated to grant review."

What are the differences between the states' same-sex marriage cases?

A couple marries in San Francisco. (Justin Sullivan / Getty Images News)

There are six cases from Ohio, Michigan, Kentucky, and Tennessee under appeal following the Sixth Circuit Court's decision. The Supreme Court could take one of them, all of them, or anything in between, explained Paul Smith, one of the nation's leading attorneys on LGBT issues.

These six cases fall under two categories: recognition and licensing. Recognition cases only address whether a state has to acknowledge — but not license — same-sex marriages from outside the state. Licensing cases deal with the broader issue of whether a state must grant marriage licenses to gay and lesbian couples.

Ohio has two recognition cases, Michigan has a licensing case, Kentucky has both types of cases, and Tennessee has a recognition case.

Which of these cases the Supreme Court takes up could be crucial to the scope of the justices' final decision. If the Supreme Court only agrees to hear a case about whether states should recognize same-sex marriages from other places, that could indicate the court wants to focus on the more narrow issue of recognition. If the Supreme Court takes a case about whether states should be required to grant same-sex marriage licenses, that could show the court's intent to decide the issue once and for all.

When and how could the Supreme Court rule?

The Supreme Court, where same-sex marriage rights could be decided. (Chip Somodevilla / Getty Images News)

If the court accepts an appeal on the Sixth Circuit Court cases, there are three possibilities that legal experts consider the most likely. The court could hand down these decisions as soon as June 2015, but 2016 is also a possibility.

The Supreme Court could decide that all states' same-sex marriage bans are unconstitutional. Except for some potential procedural hurdles and delays at the state level, this ruling would allow gay and lesbian couples to legally marry across the country.

The Supreme Court could, on the other side, decide that states' same-sex marriage bans are constitutional. This ruling would effectively reinstate same-sex marriage bans in dozens of states. Based on previous court rulings, Esseks of the ACLU doesn't expect that currently married same-sex couples will be unmarried in these states. But he acknowledged that there will likely be a legal battle to decide whether states have to recognize same-sex marriages that occurred prior to a Supreme Court ruling.

The Supreme Court could also decide that states have to recognize same-sex marriages from other states, but they don't have to grant marriage licenses to gay and lesbian couples. This could also reinstate same-sex marriage bans in dozens of states, but same-sex couples could marry in other places, such as Massachusetts and Washington, DC, and have their marriages recognized.

"They could do that and not formally decide the freedom to marry question," Esseks said. "But the rationale that they would have to adopt in deciding the recognition question is certainly related to the doctrine around the freedom to marry. If we won a recognition case, that would certainly put us in good stead to win the freedom to marry case down the road."

Okay. But how is the Supreme Court expected to rule?

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Justice Anthony Kennedy consistently acts as a swing vote in the US Supreme Court. (Chip Somodevilla / Getty Images News)

Following the Supreme Court's decision in United States v. Windsor to strike down the federal ban on same-sex marriages, LGBT advocates are fairly confident that the court will rule at least 5-4 in favor of same-sex marriage rights across the country, based on constitutional rights set by the Fourteenth Amendment's Due Process and Equal Protection Clauses.

Justice Anthony Kennedy, who could act as the fifth vote that decides the issue, wrote the majority opinion that struck down the federal ban on same-sex marriages in 2013 with a legal rationale that could apply to states' bans. He argued that the federal ban violated constitutional protections and discriminated against same-sex couples by preventing them from fully accessing "laws pertaining to Social Security, housing, taxes, criminal sanctions, copyright, and veterans' benefits."

Since a similar legal argument applies to state-level programs and benefits attached to marriage, many court watchers expect Kennedy to rule against states' same-sex marriage bans as well.

"The court was so focused on the tens of thousands of children being raised by same-sex parents and so sensitive to the ways those children are being disadvantaged and harmed and stigmatized," said Shannon Minter, legal director at the National Center for Lesbian Rights. "It's hard to see how those same considerations wouldn't end up applying equally or even more forcefully to state marriage bans."

Those considerations are particularly important, LGBT advocates argue, since the Supreme Court in October effectively legalized same-sex marriages in 11 states by refusing to hear appeals from cases originating in Utah, Oklahoma, Virginia, Wisconsin, and Indiana.

Hulton Archive via Getty Images

Chief Justice Earl Warren's Supreme Court struck down states' interracial marriage bans. (Hulton Archive via Getty Images)

"It is almost inconceivable that having allowed so many couples to marry and so many families to gain the legal security and protection of marriage, the court would then roll back the clock," Minter said. "That would be not only cruel but chaotic."

Opponents of same-sex marriage rights argue the Supreme Court will allow states' bans to stand to protect states' rights. "The US Supreme Court has determined that states have the right to define marriage and we remain confident that they will uphold all the various traditional marriage laws and constitutional amendments that have been wrongly invalidated by federal judges," said Brian Brown, president of the National Organization for Marriage, in a statement. "We look forward to the US Supreme Court taking one or more of the … marriage cases now pending before them, and ultimately ruling that defining marriage as the union of one man and one woman is entirely constitutional."

But there is a precedent for the Supreme Court not allowing states to define marriage when it violates a person's constitutional rights. In Loving v. Virginia in 1967, the Supreme Court deemed states' bans on interracial marriage unconstitutional. "This case presents a constitutional question never addressed by this Court: whether a statutory scheme adopted by the State of Virginia to prevent marriages between persons solely on the basis of racial classifications violates the Equal Protection and Due Process Clauses of the Fourteenth Amendment," wrote Chief Justice Earl Warren. "For reasons which seem to us to reflect the central meaning of those constitutional commands, we conclude that these statutes cannot stand consistently with the Fourteenth Amendment."

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