When legal scholars talk about a pragmatic justice, they’re talking about someone who isn’t bound by the law as written. In rendering a decision, he or she considers the context of the case and outside factors, like the greater social good.

But as is always the pitfall with social engineering, somebody has to pick what’s good and what’s bad.

It was pragmatic for Chief Justice Earl Warren to find a way to outlaw school segregation through Brown v. Board of Education in 1954. Most Americans came to see it as the right thing to do, even if Warren had to stretch the law to do it.

But folks were less happy 16 years later when Chief Justice Warren Burger used a similarly pragmatic approach to require some black students to be bused out of their neighborhoods.

Burger’s court was acting to remedy educational inequality caused by black families predominantly living in poorer neighborhoods than their white counterparts. But as pragmatic as his approach and as noble his aims, Burger’s decision came to be seen as ineffective, heavy-handed social engineering.

Since the days of Jefferson, there has always been the concern that judges who consider more than the law and the facts of a case would become powerful, unelected legislators.

So Obama, who lectured on constitutional law at the University of Chicago, knows what he means when he says he wants a pragmatic justice to succeed David Souter.

The president, who is keen for an appointee with “empathy,” said last week his pick would know “that justice isn’t about some abstract legal theory.”

“It is also about how our laws affect the daily realities of peoples’ lives — whether they can make a living, care for their families, whether they feel safe in their homes and welcome in their own nation,” Obama said.

That is a fine description for what legal pragmatism is all about — stretching the law in the name of the social good. But despite the workaday concerns the president used to illustrate the concept, pragmatism and practicality are not the same thing.

Robert Jackson was President Franklin Roosevelt’s eminently practical attorney general and eventual appointee to the Supreme Court. President Harry Truman thought so much of Jackson’s legal acumen that he asked him to take a leave of absence from the court to prosecute the Nazis at Nuremburg.

When Justice Hugo Black and the other activists on the Supreme Court were castigating the city of Chicago for stopping a racist speech that was causing a riot, Jackson dissented, famously saying:

“If the court does not temper its doctrinaire logic with a little practical wisdom, it will convert the constitutional Bill of Rights into a suicide pact.”

Practical jurists, like Jackson and current Chief Justice John Roberts, apply their own legal views in light of the limitations of real life — the commonsensical application of the law by judges who believe in divided federal powers.

Contrast that with legal pragmatism, which holds that the pursuit of social justice requires the law to sometimes be subordinated or expanded by decree.

Obama knows how distracting confirmation fights can be. And given the massive agenda Obama is pushing, he doesn’t want to derail his global warming plan or health care initiative over an old-fashioned ideological fight.

One way to avoid that kind of showdown would be to appoint a practical liberal who agrees with Obama’s views but is still bound by the law.

But instead, it appears that Obama will attempt to pass off legal pragmatism — the essence of the activist approach to law — as a moderate view.

Obama doesn’t just want one nominee of his liking confirmed. He wants to redraw the boundaries of the legal debate and blur the lines between pragmatism and practicality.

Conservatives may not be that worried about seeing one liberal justice replaced by another. But if Obama succeeds in making activism a mainstream value, the debate, and the courts, could be lost to them for good.