Sonia Sotomayor's critics and backers have spent the last two weeks parsing one line of a speech she gave in 2001 during a conference at Berkeley on Latino representation on the judiciary. "I would hope," she said, "that a wise Latina woman with the richness of her experiences would more often than not reach a better conclusion than a white male who hasn't lived that life."

    The quote prompted cannon fire from Rush Limbaugh and Newt Gingrich, who equated the sentiment with a kind of racism (although Gingrich later dialed back his rhetoric). Equally telling has been the reaction to the reaction - the White House and Sotomayor's Democratic supporters have backtracked on the seemingly simple idea that what she would bring to the Supreme Court is not just her Yale law degree, but also her Bronx-Puerto Rican life narrative.

    "What she said was, of course, one's life experience shapes who you are, but ultimately and completely - and she used those words 'ultimately and completely' - as a judge you follow the law," Sen. Patrick Leahy, chairman of the Judiciary Committee, recounted to the media after he met with Sotomayor last week. "There's only one law. And she said 'ultimately and completely,' a judge has to follow the law no matter what their upbringing has been."

    Leahy's comments, as much as Limbaugh's, put life experience and faithfulness to the law on opposite ends of a spectrum of judicial influence, suggesting a judge can draw from one or the other, but not both. In fact the opposite view - that justices inherently sift cases through their varying worldviews - prevailed throughout the last century (and even in a Supreme Court decision this week), prompting a couple of questions ahead of Sotomayor's confirmation hearings this summer:

    Why is this idea suddenly so thorny? And don't we want a Supreme Court staffed with jurists who have a common deference to the Constitution but a varying set of backgrounds from which to approach it?

    From the 1880s until about 2000, said Harvard law professor and Supreme Court historian Mark Tushnet, the idea that a judge's background would influence how he or she approached cases - and that this was desirable - was conventional wisdom. The court for years even followed a kind of enforced diversity, drawing justices from the geographic regions that captured some of the country's biggest disagreements, with plantation owners in the South, industrialists in the Northeast and ranchers to the West.

    Other types of biography weighed heavily, too. Michal Belknap, a historian and law professor at California Western School of Law, is writing a biography of Justice Tom Clark, who was appointed to the court in 1949 after practicing oil and gas law.

    "As far as I'm aware," Belknap said, "nobody ever asked him whether his background as an oil and gas lawyer would influence his thinking in oil and gas cases. The reason they gave them to him was that he was the only person who could understand those cases."

    That a similar concept would apply now to a justice with a personal understanding of issues of immigration, racism or poverty - "It seems to me like something that's fairly obvious," Belknap said. "And probably the only difference between (Sotomayor) and other people is she actually said in a fairly prominent public context something that I think most lawyers, judges and law professors would think is obvious and self-evidently true."

    The idea that justices should mechanically apply the law through a lens in no way colored by their own experience Tushnet chalks up to a successful conservative political strategy. Opponents say the view ignores two complications: Language is inherently ambiguous, and if the Constitution or statutes held indisputable answers to these cases, they wouldn't be in the Supreme Court in the first place.

    Lani Guinier, a Harvard law professor, also sets the shift inside a broader debate around originalism, the idea that the Constitution is a fixed document judges must read through the eyes of its creators and not with a view toward contemporary society.

    "The idea of originalism makes the notion of a judge relying on anything other than the historical record verboten," she said. "And in fact judges who interpret the Constitution in conjunction with anything else other than the historical record are called judicial activists. What you're really seeing here is the morphing of that debate on judicial activism."

    "A Mathematical Fact"

    Scott Page, a professor of complex systems, political science and economics at the University of Michigan, has been explaining through math this same concept that Belknap accepts as self-evident: that problem-solvers are inherently influenced by their background, and that a multitude of backgrounds helps a group more often arrive at the right answer.

    Sotomayor's supporters - and Sotomayor herself, in the full text of her Berkeley speech - aren't suggesting that she'll apply some Latina brand of law, just as justices Sandra Day O'Connor and Thurgood Marshall didn't read the Constitution differently as a woman and an African-American. Rather, they may have read the facts of a case differently, emphasizing a factor it might not occur to another judge to examine.

    Ruth Bader Ginsburg recently illustrated this in the case of a 13-year-old girl who had been strip-searched at school. The girl's humiliation weighed heavily on Ginsburg but not, she criticized, on her male colleagues, who didn't recognize what such an event might feel like: "They have never been a 13-year-old girl," Ginsburg said of the other eight justices.

    "There's strong evidence that based on ethnicity, training, education, age, we're going to parse things differently," Page said. "I'm likely to say, 'this is like a Brady Bunch episode.' Someone else is likely to say, 'this is like There's Something About Mary."

    Page has tried to study the value of diversity when people with different ways of parsing things work together. No one person can be diverse, he starts by explaining; you can only be diverse relative to other people. Much empirical work on the benefits of diversity have the flaw, he said, of measuring activities people work on side-by-side but not together. The Supreme Court, on the other hand, is the perfect example of a kind of collective problem-solving group where the blind spots of one individual may be filled out by another's expertise.

    "This isn't like the mantra 'two eggs are better than one,'" Page said. "It's a mathematical fact; it's like the Pythagorean theorem, a-squared plus b-squared equals c-squared. You can show the group's error equals the average error of the people in the group minus their diversity, which is just the differences in how they predict outcomes."

    The more highly dimensional the problem, he says - i.e., Supreme Court cases - the more the theorem has bite. "The formula says, 'How different is your prediction than my prediction?'" Page said. "That's mathematical fact. The empirical question is: What would cause us to see the world differently?"

    Belknap might point out that, obviously, it's our different backgrounds - Sonia Sotomayor's childhood raised by a single mother in a Bronx project compared to John Roberts' childhood as a boarding-school student and the son of a steel plant manager.

    In Sotomayor's original quote, she was stressing more the value of her experiences than the novelty of her ethnicity.

    "What's really important about that quote - and I think many of us do this automatically - we assume a false parallelism she was actually not making," Guinier said. Sotomayor was not comparing a wise Latina to a wise white man, although many assumed the word appeared twice in the quote. "She's comparing someone who has a rich set of experiences and can use them to someone who is not wise."

    "You could read into her quote," Guinier added, "the Scott Page view of diversity."

    One Kind of Homogeneity

    That view emphasizes not just the differences apparent in a photo of the potential new Supreme Court, which will have one African American, two women and a Hispanic if Sotomayor is confirmed. Equally important are all the ways in which their biographies differ, contributing to the collective breadth of life experience.

    Sotomayor would actually be contributing to one kind of homogeneity on the court: It is increasingly dominated by former Circuit Court of Appeals judges with Ivy League law degrees. Conservatives championed these criteria during the Bush Administration, in dispatching nominee Harriet Miers and confirming John Roberts and Samuel Alito.

    "The great irony here is they set up these de facto credentials for being a Supreme Court justice that don't exist in the Constitution," said University of Maryland law professor Paula Monopoli. "(Sotomayor) meets now all of the criteria they set up, and they're not talking about it."

    Page's research suggests that as Americans may celebrate later this year the first Hispanic seated on the high court, they should remember the value of all kinds of backgrounds. When Sandra Day O'Connor retired four years ago, for example, she took with her the last remaining perspective of someone who had once been an elected official, one of many lost views Belknap laments.

    He blames Roe v. Wade, a decision that has remained so divisive for the last three decades that he says no president could effectively nominate anyone other than the safest bet who resembles everyone else already sitting on the court. Law professors and politicians - two groups widely represented in the past - today come with a trail of opinions that would likely bar them from confirmation in a climate where Sotomayor has stirred controversy on a single sentence uttered eight years ago.

    In the earliest days of the republic, Monopoli recalls, the court sought geographically representative perspectives to give its opinions legitimacy throughout a diverse country.

    "We still need that," she said, "we just need it in a different way now."