Short of a major scandal or a serious blunder during his confirmation proceedings, federal appellate judge Samuel Alito will take his place on the Supreme Court. What kind of justice will he be? If media reports are to be believed, he is likely to support abortion restrictions, if not the reversal of Roe v. Wade, and to join Justices Antonin Scalia and Clarence Thomas in efforts to end affirmative action plans, dismantle the wall of separation between church and state, expand states' rights and limit Congress's ability to regulate under the Constitution's commerce clause.

In short, even before Judge Alito becomes Justice Alito, pundits have branded him as ideological rather than independent-minded; they also believe they know how he will vote on a range of legal, cultural and economic issues.

But are they right? If recent history is any indication, the answer is "Yes, but . . ."

The "yes" comes from our research comparing the ideological labels assigned by commentators to Supreme Court nominees with their voting records on the court. As it turns out, those labels often convey useful information about how nominees, upon ascending to the high court, approach the cases before them. At the time of Scalia's nomination in 1986, virtually all the commentary -- on the left and the right -- predicted that he would be quite conservative. That forecast proved accurate. Scalia now reaches right-of-center decisions in almost seven out of every 10 cases he considers. Likewise, Ruth Bader Ginsburg, assessed as moderate-to-liberal when she was picked in 1993, votes precisely as that label would suggest, reaching liberal outcomes in about two-thirds of the court's cases.

So, yes, Samuel Alito, in all likelihood, will be a conservative justice and will reach decisions in accord with that label. But there's a "but" -- actually several, all recent or current justices: David Souter, Harry Blackmun, John Paul Stevens, Anthony Kennedy and Sandra Day O'Connor, to name five justices for whom, to greater or lesser extent, ideological labels proved misleading. The "but" offers important insights into why some nominees, once they become justices, sometimes don't behave as predicted and how the court's dynamics can affect their views.

In the case of Souter, initial judgments about how he might vote were downright wrong. The clear expectation, based largely on his lower court record, was that Souter would be a rather consistent conservative voter -- even more to the right than Reagan appointees Kennedy and O'Connor, at the time of their nominations. Souter, of course, is a rather consistent voter -- on the court's liberal wing.

In retrospect, we probably should not be surprised by this turn of events. Lower court records can actually provide disinformation about a nominee's true preferences. Judges on lower courts, after all, are bound by Supreme Court precedent, and that constraint may explain why Souter -- thought to be moderately conservative as a state and federal appellate court judge -- emerged as liberal once on the high court. The Supreme Court that Judge Souter was bound to follow was somewhat conservative or, at least to the right of Souter's actual preferences. While Supreme Court nominees "respect" precedent, as they unfailingly tell the Senate Judiciary Committee, once elevated they are not compelled to follow it. Freed from that constraint, the "real" Souter came into view.

Even when commentators correctly anticipate a justice's political leanings, time can wreak havoc with any predictions we might make on the basis of a nominee's presumed political values. As the years wear on, new issues will test the strength and breadth of those commitments. When President Ronald Reagan appointed Anthony Kennedy in 1987, criminal law was a far more salient political matter to the president than, say, gay rights. Nonetheless, it was Kennedy who (16 years later) wrote the opinion striking down a Texas law that prohibited same-sex sodomy -- an opinion that belied his generally moderately conservative approach to judging, not to mention one that the very conservative Reagan would likely have condemned. We might make educated guesses as to Alito's views on abortion and states' rights, but what about genetic fingerprinting and stem cell research?

The passage of time also enables even hard-core liberals or conservatives to rethink their jurisprudence. Witness Harry Blackmun, who served from 1970 to 1994. Early in his tenure, he joined the other three conservative appointees of President Richard Nixon to uphold the death penalty. But just before he retired, Blackmun declared that "no sentence of death may be constitutionally imposed" and that "from this day forward" he "no longer shall tinker with the machinery of death." John Paul Stevens, too, has become increasingly liberal with each passing administration, while Byron White (who served from 1962 to 1993) became more and more conservative.

Then there's O'Connor, the swing justice during her last few terms on the court. Over time, this moderate-to-conservative Reagan appointee grew more liberal -- and with that movement came a change in her voting behavior. So, based on our calculations, the odds of the court upholding an affirmative action program just 10 years ago were no more than one out of three; but by the time the court heard a challenge to the University of Michigan law school's affirmative action plan in its 2002 term, the odds had increased to more than 50 percent -- largely because of O'Connor's move to the left. In the end, O'Connor did provide the key vote to uphold the law school's program (while also joining the 6-3 majority in striking down a different affirmative action plan governing Michigan's undergraduate admissions).

New issues and a rethinking of old ideological commitments may well have conspired to make O'Connor's voting less predictably conservative. But so too, in all likelihood, did the nature of her job.

Branding nominees as "conservative," "liberal" or something in between, with the expectation that those nominees will act reflexively in accordance with those labels, ignores the nature of judging. While O'Connor's preferences may have grown more liberal over time, it is equally likely that her vote in the Michigan law school case reflected her belief in the value of making changes incrementally. The lesson here is that Alito will be more likely to chip away at abortion rights and affirmative action practices than to vote to overrule them immediately. Limiting -- even severely limiting -- case law is one thing; overturning well-entrenched precedents is quite another.

Then there is the matter of internal dynamics on the court. Despite the size of its building, the court is a small office -- with all the attendant politics of a small office. If we believe that most members of this office, the justices, hope to move the law in ways that reflect their own ideological commitments, then they engage in ideological fanaticism to their own peril. To produce a decision with the force of precedent, a majority must subscribe to the opinion's rationale. Unless five of the justices are quite conservative or quite liberal, extremism can cost votes, depriving the opinion author of a majority. In seeking to overturn Roe, Chief Justice William Rehnquist overplayed his hand, losing O'Connor's crucial vote in the process. The extremely conservative nature of Scalia's views, to say nothing of his take-no-prisoners style, may have needlessly antagonized potential allies.

Extremist justices can miss opportunities to pull the law toward their preferences in more subtle ways as well. By custom, the senior justice voting with the majority (or the chief justice, if he is part of the majority) is responsible for choosing someone to write the majority opinion. In closely divided cases, the justice assigning the opinion may be less inclined to ask an extremist to write out of fear that his or her majority may dwindle to a minority. This may well explain why Stevens assigned the Michigan law school case to the most moderate (and fragile) member of the majority, O'Connor, and not to the far more liberal Ginsburg. It also may explain why O'Connor has seemingly relished and indeed maintained her place as a key player on the court. Like Lewis Powell before her, she seemed to recognize that moderation -- perhaps even modulation -- can work to the advantage of a policy-minded justice.

Where does this leave us with Judge, likely-to-be Justice, Alito? History provides little reason to question predictions that Alito will cast right-of-center votes, and reliably right-of-center votes at that. On the other hand, if that same history is any indication, even his thick judicial record may provide less insight into his future votes than we might imagine.

Moreover, neither Alito nor anyone else can know whether his current conservative leanings are a reliable indicator of how he might vote 20 or even 30 years from now, when he'll be just three weeks older than the moderate-turned-liberal Justice Stevens is today.

Nor can Alito or anyone else predict the political composition of future Supreme Courts. If Alito wins confirmation, he and new chief justice John Roberts would give the conservative faction a firmer basis for forming a majority on many issues, but it is still by no means a guaranteed majority. A Democratic president could alter the balance again. But if a nimble and tactful Alito can adapt to whatever changes the future may hold, he may well emerge as the liberals' worst nightmare: an effective Scalia.

Lee Epstein is a professor at Washington University at St. Louis, where she teaches political science and law. Jeffrey Segal is a political science professor at Stony Brook University in New York. They are the authors of "Advice and Consent: The Politics of Judicial Appointments" (Oxford University Press).

The labels didn't quite fit: Four current justices -- David Souter and Anthony Kennedy, above, John Paul Stevens and Sandra Day O'Connor, below -- have proved more unpredictable than expected. Justices sometimes moderate their views to build a majority, the authors say.