When Justice Anthony M. Kennedy spoke for the Supreme Court in 2013 in striking down part of a federal law that denied benefits to legally married gay couples, he cited two reasons: states' rights and equal rights.
Throughout American history, Kennedy said, states had "full power over marriage and divorce," including "the definition and regulation of marriage." He referred to the act of Congress as a federal intrusion on state power that discriminated against gay couples and denied the equality of same-sex marriages.
His opinion for a 5-4 majority in United States vs. Windsor striking down a key provision of the Defense of Marriage Act may have been read as endorsing a two-track approach: one that provided full rights for legally married gay couples while preserving a state's right to decide on the definition of marriage.
Now, after the justices agreed Friday to take up the issue again, Kennedy and the other justices must reconcile what they left unresolved two years ago. Is marriage for gays and lesbians a matter of equal rights and individual liberty guaranteed by the Constitution? Or is it a matter left to the states?
Despite its ambiguity, Kennedy's opinion in Windsor was heralded as a major victory for the "marriage equality" movement, reflecting a powerful social change that had swept across the nation. It came on the same day that the high court, with Kennedy in dissent, dismissed an appeal from California, which had the effect of restoring gay marriages in the state.
Since then, federal judges from Utah to Florida have read the Windsor opinion as implicitly endorsing a constitutional right for same-sex couples to marry.
At the same time, defenders of state laws that limit marriage to a man and a woman also cited Kennedy's words in their appeals.
In his appeal in DeBoer vs. Snyder, one of four cases that will be heard in April, Michigan Atty. Gen. Bill Schuette said the Windsor opinion had reaffirmed the view that the definition of marriage was, in Kennedy's words, "within the authority and realm of the separate states."
He also cited Kennedy's opinion last year that upheld the Michigan ballot measure barring race-based affirmative action at the state's universities. He noted that Michigan's voters in 2004 had adopted a ballot measure limiting marriage to a man and a woman and argued that this decision, like affirmative action, should rest with the people.
If this year's decision on gay marriage turned only on court precedents and legal logic, it would look to be a toss-up. The justices, all of whom were appointed after the Roe vs. Wade abortion decision, have been wary of forcing major changes in social policy. They also believe in deferring to the states.
But Kennedy and four of his colleagues have given signals in recent years that they are inclined to lean in favor of gay couples seeking to marry. Kennedy has said in several opinions that the government may not "demean" loving couples who are gay.
He has also taken special note of children who are being raised by same-sex couples. During arguments in the California case, he said it would be hurtful to tens of thousands of children if their same-sex parents were denied the right to marry.
The Michigan gay marriage case was brought by two nurses raising four adopted children who were abandoned by their mothers. The judge who heard their case said he could not justify the state's decision to discriminate against such a committed couple.
And Kennedy, unlike Justice Antonin Scalia, also believes the law must evolve and change based on "a new perspective and a new insight," as he said in the Windsor case. In decades past, legal marriages for gay couples might have struck many people as unusual, he said, but not today.
The best clue to the outcome may be seen in the court's recent actions. Last summer, the justices had appeals from five states with bans on same-sex marriage that had been struck down by federal judges. State officials from red states such as Utah, Oklahoma and Indiana were anxious to defend their laws at the high court. And it takes the votes of only four justices to hear such an appeal.
But the court denied all the appeals in October, clearing the way for gay marriages to begin in at least 35 states. That action was seen as a signal that the ultimate decision had been made, even if the justices had yet to formulate an opinion to explain the result.