New York Times

WASHINGTON — The Supreme Court issued a remarkable number of unanimous decisions last term, and in their public remarks the justices seemed unanimous in saying that unanimity was a good thing. But is it?

A new study from Cass R. Sunstein, a law professor at Harvard, concluded that all of the usual reasons for seeking common ground were open to question. “The arguments in favor of higher levels of consensus,” he wrote, “rest on fragile empirical foundations.”

One of the standard justifications is that closely divided rulings may be perceived to be less legitimate than united ones. Justice Ruth Bader Ginsburg endorsed that view last month.

“I don’t think that 5-4 decisions have the same clout as a unanimous decision,” she said.

That sounds plausible. The public may be less likely to accept and follow decisions that would have gone the other way with the switch of a single vote. A divided opinion, Judge Learned Hand once wrote, “cancels the impact of monolithic solidarity on which the authority of a bench of judges so largely depends.”

That is why Chief Justice Earl Warren worked hard to deliver a unanimous opinion in Brown v. Board of Education, the 1954 decision that declared segregated public schools unconstitutional. He feared that a divided decision would produce a backlash.

As it happened, the unanimous decision in Brown was met with determined resistance in the South. “Perhaps the opposition would have been even worse if the court had been divided,” Professor Sunstein wrote. “But perhaps not.”

Or consider two examples from June. The court was unanimous in striking down buffer zones near abortion clinics in Massachusetts andwas divided 5 to 4 in saying some employers could refuse to provide contraception coverage. The different vote counts did not seem to figure in the reactions of women’s groups opposed to the rulings.

Michael F. Salamone, a political scientist at Washington State University, has designed experiments to test whether the public is more apt to accept unanimous decisions than divided ones.

In one, he asked subjects what they thought of the court’s 2005 decision in Kelo v. City of New London, which allowed the government to use the power of eminent domain to take private property for business development. His descriptions of the decision, based on a USA Today article, were similar, but he gave differing accounts of the vote.

He told some subjects the truth, which was that the vote was 5 to 4. He told others that the decision was unanimous or that it had a single dissent. A fourth group was told only that the court had ruled.

It did not matter. People disagreed with the decision at essentially the same rate.

In a second study, Professor Salamone asked questions about three contrived Supreme Court cases modeled on real ones concerning same-sex marriage, workers’ privacy and alternative dispute resolution.

Here, the results varied with how much those surveyed cared about the issues in the first place. But the bottom line, Professor Salamone wrote, was that “5-to-4 rulings in widely reported cases do not appear to significantly detract from popular acceptance.”

Professor Sunstein, for his part, concluded that “the idea that 5-4 decisions pose a serious problem of credibility or legitimacy remains an unproven hypothesis.”

Justice Ginsburg offered a second reason to think less of closely divided decisions: They are more apt to be overruled or modified.

This appears to be true, according to one leading study, which found that closely divided decisions were about 54 percent more likely to be overruled than the average ruling and unanimous ones 47 percent less so. But those numbers should be taken with “many grains of salt,” Professor Sunstein said.

“The court overrules very few of its decisions,” he wrote, “and hence the risk that any particular decision will be overruled is exceedingly low.”

In the past decade, for instance, the Supreme Court has decided about 80 cases a term, which is low by historical standards, and it has overruled fewer than two precedents a term.

The third reason generally offered for seeking consensus is the establishment of clear legal principles. “Unanimity, or near unanimity, promotes clarity and guidance for the lawyers and for the lower courts trying to figure out what the Supreme Court meant,” Chief Justice John G. Roberts Jr. said in 2006, not long after he joined the court.

But it is hardly obvious that consensus produces clarity. Supreme Court opinions are the product of negotiation and compromise, which is why they can read as if written by a committee. A nine-member committee does not seem likely to produce crisper prose than a five-member one.

Research bears this out. A 2011 study that used linguistic software to analyze the usage and concepts in 5,800 Supreme Court rulings found that unanimous opinions were the most complex. Ones decided by slim majorities were the clearest.

How hard, then, should the justices work to achieve unanimity?

“The court’s legitimacy might be at risk if it rules in ways that deeply offend the American public, or if large segments of that public perceive themselves as consistent losers,” Professor Sunstein wrote. “But separate opinions, as such, are unlikely to threaten the court’s legitimacy, certainly not in specific cases, and probably not even across a wide range of cases.”