Same-Sex Marriage Hearing at the Supreme Court: What You Need to Know

— -- This coming week, the Supreme Court will hear arguments on the highly controversial issue of same-sex marriage. But what does that mean exactly? And what are the potential national implications? We've asked Kate Shaw, an ABC News contributor and an assistant professor of law at the Benjamin N. Cardozo School of Law in New York, to provide some clarity.

1) OK, let’s start with the basics. Very simply, what is the constitutional explanation for why same-sex couples in Massachusetts can get married but why same-sex couples in Texas can’t? Why is the law different in different states?

SHAW: States have a lot of freedom to structure their laws in ways that reflect the preferences of their citizens; that’s one of the unique features of our federal system. Some states can allow 16-year-olds to drive while others set the driving age at 18; and some states have the death penalty, while others don’t.

But the principle that each state can tailor its laws to its citizens’ preferences has limits, and those limits come from the U.S. Constitution. The Supreme Court has made clear, for example, that the Constitution prevents states from prohibiting interracial marriage. So the question in this case is whether prohibiting same-sex couples from marrying is within the states’ regulatory power, or whether it violates the U.S. Constitution.

2) Got it, so how many states in the United States currently allow for same-sex marriage? What’s the story with D.C. and Alabama?

SHAW: Right now, 36 states and D.C. allow same-sex couples to marry. Alabama’s situation is unique: Earlier this year, a federal judge found the state’s ban on same-sex marriage unconstitutional, but the Alabama Supreme Court then ordered Alabama officials to stop performing same-sex marriages. A number of couples got married in the period between the federal and state court decisions, but right now no new same-sex marriages are being performed in that state.

3) Remind us why there was a rapid increase in the number of states that allow for same-sex marriage in recent years. What happened in the courts?

SHAW: In June 2013, in a case called United States v. Windsor, the Supreme Court struck down part of the federal Defense of Marriage Act (DOMA) -- the part that prevented the federal government from recognizing same-sex marriages for purposes of everything from federal taxes to Social Security benefits. Although the court in that case didn’t explicitly rule that state bans on same-sex marriage were unconstitutional, lower courts in the wake of Windsor concluded almost uniformly that state marriage bans couldn’t survive. Windsor had held DOMA unconstitutional on the grounds that it harmed gay couples and their children without any permissible purpose, and most federal judges concluded that state marriage bans fell on the same logic. So that’s why you’ve had this cascade of decisions in the last two years. The number of states with same-sex marriage has jumped from 12 to 36.

4) OK, so what exactly is happening Tuesday at the Supreme Court, and who is involved?

SHAW: Cases from four states -- Kentucky, Michigan, Ohio and Tennessee -- have been consolidated into one marathon argument session on two distinct questions: first, whether the Constitution allows states to deny gay couples the right to marry; and second, whether the Constitution requires states to recognize valid same-sex marriages performed in other states.