By the end of the week, we’ll probably know whom President Obama plans to nominate as retiring U.S. Supreme Court Justice David Souter’s successor.

With all respect to the crack economic team the president has working overtime to keep as many of us as possible off the unemployment rolls and our 401(k)s off the do-not-resuscitate list, this will be the most important appointment he has made so far. Because he swept to electoral victory on the promise of fundamental change, I would urge him to break with the recent past and nominate someone from outside the federal judiciary, perhaps even someone who is not now a sitting judge.

Souter is the last Supreme Court justice whose opinions really have surprised court watchers. There’s a reason for that: He’s the only justice on the court who took his seat without having his name attached to a string of decisions on federal law that predicted — and in some sense, bound him to — a particular jurisprudential tendency.

When President George H.W. Bush appointed Souter, he’d been a federal appeals-court judge for a matter of months. Most of his legal career had been spent on the New Hampshire Supreme Court and as the state’s attorney general. He brought that experience to bear on the federal cases that subsequently came before him on the high court, and his common-sensical judicial profile emerged as those of the better justices so often have, on a case-by-case basis.

To admire that is to acknowledge the continuing relevance of Justice Oliver Wendell Holmes’ great declaration of judicial realism: “The life of the law is experience.”

Ideologues, however, hate surprises, which is why those on both sides of the Washington aisle took a lesson from the Souter nomination. The safe thing, they concluded, was to nominate only prospective Supreme Court justices who have a track record of written opinions on federal legal questions that can be parsed and scrutinized, line by line. (President George W. Bush’s disastrous attempt to nominate then-White House counsel Harriet E. Miers only reinforced the lesson.)

Thus, the federal appellate courts have become what amounts to the Supreme Court’s farm clubs. The brevity of Souter’s service notwithstanding, the fact remains that every current member of the high court came directly from a federal appellate circuit.

But what the ideological purists gained in predictability, the country lost in experience. The notion that a prospective justice’s only relevant qualifications come from being a member of the federal judiciary may be convenient — in a crabbed sort of way — but it’s flagrantly ahistorical.

Take, for example, the five jurists many legal historians would regard as the most important of the 20th century. In the first rank, you’d have to place Holmes, for judicial intellect; Earl Warren for leadership and vision; and William J. Brennan Jr. for courage, conscience, and the political skill to run a brilliant rear-guard action through the Burger court years that solidified and extended the Warren court’s legacy. Just a bit behind those three come the great defenders of the First Amendment, William O. Douglas and Hugo Black, although much of their most admired work was iconoclastic and delivered in dissent.

Not one of these five justices served on the federal bench before joining the high court.

Holmes and Brennan came from the Massachusetts and New Jersey Supreme Courts. Black sat briefly — and very early in his career — on an Alabama “police court” but was appointed because of his tenure in the U.S. Senate. Neither Warren nor Douglas ever had donned a judicial robe before being appointed to the high court.

Neither, for that matter, had justices Robert H. Jackson or Felix Frankfurter, who weren’t exactly judicial slouches.

Obama knows all this well, which is why he should have the courage to reach beyond the narrow strictures of the recent past and look to the private bar, the statehouses, state courts, and, perhaps, legal academia for the next nominee. It would be a salutary event, if his own election could free us to consider an accomplished life’s experience, along with sex, ethnicity and sexual orientation, when we weigh a nominee’s contribution to the court’s “diversity.”

Doing that might also free us from some of the worst rancor that has marked so many recent Supreme Court confirmation hearings. While nominating exclusively from the federal appellate bench gives the ideologues among us — depending on which side of the aisle they occupy — either a comforting certainty or a clear target, it also powerfully enables the kind of single-issue litmus-test confirmations that now seem standard operating procedure in the Senate.

It’s hard for even the most partisan senator to arrive with an interest-group-approved checklist of issues on which to interrogate a nominee if he or she doesn’t have a string of prior decisions to defend.