What the justices are saying; key cases on same-sex marriage

Chief Justice John Roberts: "The fundamental core of the institution is the opposite-sex relationship and you want to introduce into it a same-sex relationship. You're seeking to change what the institution is."

Justice Samuel Alito: "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. Would there be any ground for denying them a license?"

Justice Antonin Scalia said the issue is not whether there should be same-sex marriage "but who should decide the point," embracing the states' argument.

Justice Clarence Thomas asked no questions, as is his custom.

Justice Elena Kagan: "It's hard to see how permitting same-sex marriage discourages people from being bonded with their biological children."

Justice Ruth Bader Ginsburg: "You are not taking away anything from heterosexual couples" if the state allows gay couples to marry.

Justice Stephen Breyer: "Marriage is open to vast numbers of people. [Many same-sex couples] have no possibility to participate in that fundamental liberty — and so we ask why."

The Supreme Court has struggled with the issue of gay marriage and gay rights for nearly half a century. Here are some of the key decisions:

Baker vs. Nelson, 1972: The first Supreme Court gay marriage ruling was just a sentence long, saying that the appeal of a gay couple from Minnesota who had been turned down for a marriage license "is dismissed for lack of a substantial federal question."

Bowers vs. Hardwick, 1986: The justices by a vote of 5-4 upheld a Georgia law outlawing sodomy. The case involved a Georgia bartender, Michael Hardwick, who was arrested on suspicion of having oral sex with another man in Hardwick's bedroom. The justices said the constitutional right of privacy did not extend to homosexual sodomy.

Romer vs. Evans, 1996: In a 6-3 decision that became the precursor for later gay marriage rulings, the justices struck down a Colorado voter initiative that said no homosexual could be protected from discrimination based on orientation.

Boy Scouts of America vs. Dale, 2000: The court ruled that the Boy Scouts had a constitutional right to exclude openly gay Scout masters based on the Scouts' freedom of association. The 5-4 ruling reversed a decision of the New Jersey state courts.

U.S. vs. Windsor, 2013: In a landmark 5-4 decision that has been the basis for dozens of federal court rulings striking down gay marriage bans, the justices struck down a key part of the federal Defense of Marriage Act. The court said the federal government could not deny benefits to legally married gay couples.

Hollingsworth vs. Perry, 2013: The justices upheld a lower-court ruling invalidating California's gay marriage ban, Proposition 8. While the 5-4 decision made gay marriage possible for Californians, it was a technical ruling.