Last week U.S. District Judge John C. Coughenour sentenced a defendant to prison for plotting to bomb the Los Angeles airport. In the course of the sentencing, the judge criticized the Bush administration's post-Sept. 11 policies, such as the use of military tribunals and the detention of enemy combatants. He said that "the message to the world from today's sentencing is that our courts have not abandoned our commitment to the ideals that set our nation apart." Some people, the judge said, believe that the terrorist threat "renders our Constitution obsolete. . . . If that view is allowed to prevail, the terrorists will have won."

That's a little hard to follow. That courts can handle terrorists who are caught with explosives in their possession doesn't mean they are capable of handling the terrorists who manage to evade detection until the moment they immolate themselves with their victims. But worse than the judge's logic is the underlying sentiment that yesterday's law enforcement procedures are adequate for today's security threats -- and that any deviation from them is a betrayal of the Constitution.

It recalls the now notorious statement by Lord Hoffman, a British law lord who said, "The real threat to the life of the nation . . . comes not from terrorism but from laws," such as a statute authorizing detention of foreign-born suspected terrorists, which the law lords invalidated under the European human rights charter in December 2004. It also echoes Supreme Court Justice Sandra Day O'Connor's quotation, in the case of Yaser Esam Hamdi, of a precedent stating that it "would indeed be ironic if, in the name of national defense, we would sanction the subversion of one of those liberties . . . which makes the defense of the Nation worthwhile."

All of these have become judicial cliches to be invoked in arguments about how the global struggle against terrorism is to be prosecuted. Many cliches are, of course, true, but these are absurdities.

For example, consider the statement that the terrorists will "win" if legal rules and policies are changed in ways that restrict the package of civil liberties in place before the terrorist threat emerged. Whether such restrictions count as a victory for terrorists depends on what terrorists are trying to achieve. Although al Qaeda's ultimate goals are to drive American troops from the Middle Eastand, more broadly, to establish a Muslim caliphate in the region, its proximate goal is to kill ordinary people to bring pressure to bear on democratic governments. A change in policy that reduces the chance that more people will be killed does not hand the terrorists a victory; it frustrates their plans. A failure to alter any policies in response to a successful terrorist attack is, by contrast, a sign of weakness and paralysis; that would be a victory for the terrorists. Osama bin Laden was right to say that people will back the strong horse. But he was wrong about which horse will prove stronger.

Some theorize that terrorists hope to provoke the target government into cracking down on civil liberties, in the further hope that the crackdown will, in the long run, increase disaffection among the population from which terrorists recruit. This is a remote and uncertain effect that has to be balanced against the immediate security benefits of adjusting civil liberties. A policy of static defense might increase terrorist recruitment as well, by suggesting that the target government lacks the will or capacity to take the fight to the enemy. The best course is to ignore such speculative long-term considerations in favor of choosing policies that make sense in the short run.

A second cliche is this: that a nation that permits incremental reductions in its civil liberties in response to threats to its citizens is not worth defending. The truth is that few people have accepted Patrick Henry's call to "give me liberty or give me death" -- this was a rallying cry, not a policy paper -- and in any event nations are rarely faced with such a stark choice. An incremental reduction in civil liberties is not equivalent to their elimination.

British and American traditions are two-sided: They acknowledge that governments have an obligation to protect people's lives as well as their liberties. No nation preserves liberty atop a stack of its own citizens' corpses, but if one did, it would not be worth defending.

The spurious assumption behind both cliches is that whatever package of civil liberties happens to exist at the time a terrorist threat arises must be maintained at all costs; adjustments that reduce liberty are bad even if they produce greater gains in security, potentially saving people's lives. This is a virulent form of the fallacy of the status quo -- that whatever exists must be good. In fact, the balance between security and liberty is constantly readjusted as circumstances change. A well-functioning government will contract civil liberties as threats increase. A government that refuses to adjust its policies has simply frozen in the face of the threat. It is pathologically rigid, not enlightened.

The two cliches about terrorism are familiar from debates among commentators and politicians. What is new and surprising is their citation by judges as self-evident truths. Judges do badly when they appeal to speculative causal theories about terrorism or to the romantic ideals of civil libertarianism. Both are incompatible with the kind of balancing that is so much a part of the judicial function. That ideals have a tendency to explode on the rock of fact was spectacularly demonstrated in Britain, where terrorist carnage occurred just a few months after the detainees in Lord Hoffman's case were released under legal compulsion. It is too soon to tell whether there was a causal connection between the two events, but Lord Hoffman's casual dismissal of the threat to citizens' lives now appears grotesque.

The day before Coughenour's soliloquy, Prime Minister Tony Blair said that he doubted whether statements such as Lord Hoffman's "would be uttered now." Perhaps that's true in England, but it seems that American judges have yet to learn the lesson.

The writers are law professors at the University of Chicago. Eric A. Posner is co-author of The Limits of International Law. Adrian Vermeule is author of the forthcoming book Judging Under Uncertainty.

Copyright 2005 The Washington Post