During the hiatus between Supreme Court confirmation battles, we may as well settle the clash between the conservative and liberal approaches to constitutional interpretation. The battle lines are familiar. Conservatives, led by Justices Antonin Scalia and Clarence Thomas, say that the sole legitimate approach is to follow the literal text and original meaning of constitutional provisions and amendments. Justices' policy preferences should play no role, assert conservative "originalists." But the claim is undercut somewhat by the consistency with which the conservatives' votes on abortion, religion, race, gay rights, and many other big issues happen to fit their policy preferences.

Liberals and many moderates prefer the "living-Constitution" approach, which has been dominant at least since the Warren Court. It involves using ancient but conveniently vague constitutional phrases to enforce "evolving standards of decency," to promote equality, and to vindicate what sometimes-liberal Justice Anthony Kennedy likes to call "the right to define one's own concept of existence, of meaning, of the universe, and of the mystery of human life." Not surprisingly, constitutional evolution in the hands of liberals supports liberal policies.

Each school of thought is most persuasive in debunking the other. Justice Stephen Breyer skewers originalism in his 2005 book, Active Liberty: "Why would the Framers, who disagreed even about the necessity of including a Bill of Rights in the Constitution, who disagreed about the content of the Bill of Rights, nonetheless have agreed about what school of interpretive thought should prove dominant in interpreting the Bill of Rights in the centuries to come?"

Even when the original meaning is undisputed, it is often intolerable to conservatives as well as liberals. Many Framers did not see the flogging or even the execution of a 12-year-old for theft as "cruel and unusual punishment," for example. And nothing in the text or original meaning of the Constitution was designed to bar the federal government from discriminating based on race (or sex). This has not stopped Scalia or Thomas from voting to strike down federal racial preferences for minorities. Nor have they hesitated to invoke debatable interpretations of the Constitution to attack laws regulating campaign finance and imposing monetary liability on state governments.

The living-Constitution approach may be even more problematic, because it has cut a wider swath through democratic governance with even less basis in the written Constitution.

If the Constitution is an "invitation to apply current societal values," as Scalia has asked, "what reason would there be to believe that the invitation was addressed to the courts rather than to the legislature? ... A democratic society does not, by and large, need constitutional guarantees to ensure that its laws will reflect 'current values.' Elections take care of that."

Consider Roper v. Simmons, last year's decision barring the death penalty for any murder committed before the killer's 18th birthday. This would have been good legislation, in my view. But it was bad constitutional law.

Justice Kennedy's claim for the 5-4 majority that modern Americans had reached a "consensus" that no juvenile murderer should ever get the death penalty was bogus: A majority (20) of the 38 states with the death penalty still allowed such executions. Kennedy's reliance on the laws of almost all foreign nations against the juvenile death penalty was a fig leaf for his personal moral preferences. So was his twisting of the relevant literature on juvenile psychology to suggest misleadingly that minors are incapable of mature moral reflection. And as Judge Richard Posner of the federal appeals court in Chicago points out, Kennedy was tellingly selective in his attention to social-science literature: He ignored the studies suggesting that the death penalty may deter some would-be killers and thus save lives.

In a variation on the living-Constitution approach, Breyer argues in Active Liberty for interpretations designed to promote "participatory self-government" by voters. But Breyer's support for the 1973 decision that ended participatory self-government on abortion—Roe v. Wade—casts doubt on his seriousness. Especially since his book does not even mention this, the biggest and most controversial decision of the past 60 years.

The bottom line is that nonadherents understandably see originalism and living constitutionalism alike as smoke screens for imposing the justices' personal policy preferences.

This is not healthy. How might we avoid the worst excesses of each approach?

The best answer is judicial modesty, in the sense of great hesitation to second-guess decisions by other branches of government. Embraced in general terms by then-Judges John Roberts and Samuel Alito during their Supreme Court confirmation hearings, the judicial-modesty approach is expounded more fully in a November 2005 Harvard Law Review article by Posner, a prolific and ideologically eclectic legal scholar.

Posner begins by puncturing the myth that judging can ever be completely apolitical. In constitutional cases, he shows, the Court is unavoidably "a political body ... exercising discretion comparable in breadth to that of a legislature." The most sincere attempt at "lining up the facts alongside the constitutional text" usually provides no more objective a basis for preferring one outcome to another than for "preferring a margarita to a cosmopolitan."

Next Posner explains that the justices would look and act less like political manipulators if they "acknowledged to themselves the essentially personal, subjective, and indeed arbitrary character of most of their constitutional decisions." Such self-awareness is rare among justices, Posner says, because it "would open a psychologically disturbing gap between their official and their actual job descriptions."

Instead, "cocooned in their marble palace, attended by sycophantic staff, and treated with extreme deference wherever they go, Supreme Court justices are at risk of acquiring exaggerated opinions of their ability and character."

The path of wisdom would be to acknowledge that "the law made me do it" is usually no more than a "rationalization for the assertion of power" of an essentially political nature, Posner adds. Justices who understood this would probably be "less aggressive upsetters of political and policy applecarts than they are."

Judicial modesty also converges with a pragmatic focus on what will be the actual consequences of a proposed decision. Three of Posner's examples—cases in which "the law" did not dictate any particular outcome—are illustrative.

First, he applauds the 5-4 decision (over a liberal dissent) in 2002 to allow Cleveland to finance vouchers enabling low-income children to leave failed public schools for mostly Catholic private schools. The major disputes underlying the case—over whether the Cleveland experiment would work well for children and whether it would lead to sectarian conflict—turned on factual projections beyond the Court's competence.

"Actual social experiments are necessary to generate the data needed for intelligent constitutional rule-making," explains Posner. "The pragmatist wants to base decisions on consequences, and it is very difficult to determine the consequences of a challenged policy if you squelch it at the outset."

Second, Posner deplores as "injuriously unpragmatic" the unanimous 1998 ruling against President Clinton in the Paula Jones lawsuit: "It should have been obvious to the justices that forcing the president to submit to a deposition in a case about his sexual escapades would be political dynamite that would explode and interfere with his ability to perform his duties."

Third, Posner shows sympathy for Justice Breyer's solo, split-the-difference approach in two 5-4 decisions last June involving displays of the Ten Commandments. In one, Breyer joined liberals in invalidating the recent, locally controversial installations of Decalogue plaques in two Kentucky courthouses. ("I have no settled view" on that decision, Posner notes.) In the other, Breyer joined conservatives in upholding a Ten Commandments monument on the grounds of the Texas state Capitol, where it had stood for 40 years, amid various secular monuments, with little ado.

Many critics (including me) have faulted Breyer's hairsplitting for leaving the law unclear. Not so Posner: "Compromise is the essence of democratic politics and hence a sensible approach to dealing with indeterminate legal questions charged with political passion.... To give a complete victory to the secular side of the debate (or for that matter to the religious side) could be thought at once arrogant, disrespectful, and needlessly inflammatory."

Amen. Or, if that offends you, right on.