New York Times

WASHINGTON — The world will be watching when the Supreme Court hears arguments this month about same-sex marriage. But will the court be watching the world?

Two impressive friend-of-the-court briefs have urged the justices to look abroad before deciding whether there is a nationwide right to same-sex marriage. The briefs agree that there is something to be learned from the experiences of the rest of the world. But they differ about what the lesson is.

To hear one side tell it, there is “an emerging global consensus among liberal democracies” in favor of same-sex marriage.The other side responds that most of the world, including nations with otherwise strong support for gay rights, rejects same-sex marriage.

Both briefs are aimed primarily at a single reader: Justice Anthony M. Kennedy, who may be more interested in both international law and gay rights than any other member of the court. Justice Kennedy has cited the decisions of foreign tribunals in Supreme Court rulings limiting the death penalty and other harsh punishments for juvenile offenders and, notably, in advancing gay rights.

The brief urging the court to find a constitutional right to same-sex marriage was filed by six prominent American law professors, including Harold H. Koh, a former dean of Yale Law School who served as the State Department’s top lawyer in the first term of the Obama administration.

The brief on the other side was filed by Lynn D. Wardle, a law professor at Brigham Young University, on behalf of 54 experts in international law from 27 countries.

The two sides share some common ground. They agree on the obvious point that foreign decisions are not binding precedent and on the more contested view that what foreign courts have said may nonetheless be instructive.

The briefs also agree on the basic facts, saying roughly 20 countries allow same-sex marriage. Professor Koh’s brief lists Argentina, Belgium, Brazil, Canada, Denmark, England, Finland, France, Iceland, Luxembourg, the Netherlands, New Zealand, Norway, Portugal, Scotland, South Africa, Spain, Sweden, Uruguay and Wales. Professor Wardle’s brief counts England, Scotland and Wales only once, as the United Kingdom, and says same-sex marriage in Finland has been approved, but in a law that takes effect in 2017.

Is that, as Professor Koh said, evidence of a growing consensus among liberal democracies? Or does it demonstrate that, as Professor Wardle wrote, “any form of same-sex marriage has only been adopted by 17 of the 193 member states of the United Nations”?

Laurence R. Helfer, a law professor at Duke and a member of the team that submitted the brief supporting same-sex marriage, said “a simple head count of countries is beside the point.”

“The U.S. Supreme Court,” he said, “should be guided by those nations, whatever their number, that invoke core U.S. constitutional principles of equality, liberty and due process to recognize same-sex marriages.”

The math was clearer in earlier Supreme Court decisions. The United States was all but alone, for instance, in allowing the execution of juvenile offenders when the justices banned the practice in 2005.

“The opinion of the world community, while not controlling our outcome, does provide respected and significant confirmation for our own conclusions,” Justice Kennedy wrote for the majority at the time.

In dissent, Justice Antonin Scalia called the majority’s approach illegitimate. “The basic premise of the court’s argument — that American law should conform to the laws of the rest of the world — ought to be rejected out of hand,” he wrote.

He added that the court seemed open to foreign views only when they supported liberal outcomes. It ignored, he said, conservative foreign decisions on criminal procedure, religion and abortion.

“To invoke alien law when it agrees with one’s own thinking, and ignore it otherwise, is not reasoned decision making, but sophistry,” Justice Scalia wrote.

In 2003 in Lawrence v. Texas, which struck down a Texas law making gay sex a crime, Justice Kennedy cited three decisions of the European Court of Human Rights and said a right to “intimate, consensual conduct” had been accepted as “an integral part of human freedom in many other countries.”

But the European Court of Human Rights is of less help to gay rights this time around. Just last year, the European court surveyed the Continent and concluded that “it cannot be said that there exists any European consensus on allowing same-sex marriages.”

The recent briefs may tend to confirm an observation from Chief JusticeJohn G. Roberts Jr. in 2005 at his confirmation hearings.

“Foreign law, you can find anything you want,” Chief Justice Roberts said. “Looking at foreign law for support is like looking out over a crowd and picking out your friends.”

Peter J. Spiro, a law professor at Temple University, said the recent briefs may not be terribly influential “precisely because there are good arguments on both sides.” Indeed, he said, “it might undermine a decision in favor of same-sex marriage to hang it in any respect on the weak peg of international practice.”

But he added that the briefs “show that citing international law is no longer the marker of a weak case.”

“It’s here to stay as a part of constitutional argumentation,” Professor Spiro said. “It’s only a matter of time before it makes its way back into the court’s reasoning.”