When George W. Bush delivered his address to Congress on Sept. 20, he referred to the terrorists who attacked the World Trade Center and Pentagon nine days earlier as "enemies of freedom" who had "committed an act of war." He called al-Qaeda a collection of "murderers" who "plot evil and destruction." They are "the heirs of all the murderous ideologies of the 20th century," he said in the speech's best passage. "By sacrificing human life to serve their radical visions ... they follow in the path of Fascism, Nazism and totalitarianism. And they will follow that path all the way to where it ends -- in history's unmarked grave of discarded lies."

Terrorists. War criminals. Murderers. Islamofascists. Which labels fit al-Qaeda best? The group seems to blur the lines between terror, war, crime and genocide. But where the U.S. response was concerned, it did not matter. "Evildoers," the general term Mr. Bush eventually settled on, reflected the way ordinary people felt about al-Qaeda. The strong moral case for destroying the group through military action was irrefutable.

Now that al-Qaeda's Afghanistan hub has been overrun and its operatives seized, however, it is important for the West to classify the threat with greater precision. Despite a dozen conventions that mention terrorism in some way, international law on the subject is poorly developed -- Ottawa and Washington are, even now, debating how to deal with the prisoners in Cuba -- and so critics of the United States have been left to exploit the ambiguity of captives' status in an attempt to whipsaw the Pentagon.

Witness Amnesty International, which argues the Sept. 11 attacks were "human rights abuses." The group says both that the United States should treat captured terrorists as presumptive prisoners of war under Articles 4 and 5 of the applicable Geneva Convention; and that they should subsequently be afforded all the rights and procedures reserved for domestic criminal suspects. The former proposition would prevent the United States military from interrogating al-Qaeda suspects about future attacks. The latter would limit the use of military tribunals, threaten to free human time bombs on technicalities and dilate legal proceedings to the point where they resemble the Lockerbie trial, which cost more than $300-million and succeeded only in convicting a single low-level operative 12 years after the fact.

The United States has contributed to the ambiguity surrounding the classification of terrorism. Washington has generally used criminal prosecutions to deal with attacks on U.S. targets, and has only occasionally offered an ad hoc military response, as when Ronald Reagan bombed Libya in 1986. The August, 1998, bombing of two U.S. embassies in Africa produced a sheaf of indictments (and, last year, several convictions), but only a limited and unsuccessful set of missile attacks against targets in Sudan and Afghanistan.

Sept. 11 changed attitudes. Mr. Bush used the word "war" a dozen times in his Sept. 20 speech and compared the attack to the 1941 blitz on Pearl Harbor. Yet, even though attitudes changed, little else did in a formal sense -- for the United States stopped short of declaring war. Indeed, there was no sovereign nation to declare war against: At no point did the Taliban, with whom al-Qaeda enjoyed a symbiotic economic and military relationship, constitute the internationally recognized government of Afghanistan. The closest Congress came was a Sept. 14 resolution that authorized "all necessary and appropriate force against those nations, organizations, or persons [who] planned, authorized, committed, or aided the terrorist attacks."

As for Zacarias Moussaoui, the only man in U.S. custody accused of having a direct role in the Sept. 11 hijackings, he has been treated, in procedural terms, as a garden variety criminal defendant and will be tried in a civilian court.

In other words, although the United States has developed a clear moral and military agenda in the wake of Sept. 11, the legal context surrounding the campaign against terrorism is muddled. For good reasons, Mr. Bush is using a hybrid strategy, but it remains unclear where war ends and domestic law begins.

The confusion stems from an anachronism: The major authorities that would appear to govern the status and treatment of terrorists were drafted in an age when catastrophic terrorism was unknown. Consider, for instance, the claim of Donald Rumsfeld, U.S. Secretary of Defence, that captives being held in Guantanamo Bay, Cuba, are "unlawful combatants." Mr. Rumsfeld is correct as a matter of law: The category has been defined by the U.S. Supreme Court to include an "enemy combatant who without uniform comes secretly through the lines for the purpose of waging war by destruction of life or property." But that precedent was laid down 60 years ago in a case relating to German saboteurs. It was an age when the important wars were ones fought between sovereign European states, and "unlawful combatants" were a freakish exception to the rule of the uniformed soldier. The idea of a whole globetrotting army of unlawful combatants was unthinkable. The same goes for the 1949 Geneva Conventions; and for the 1945 Nuremberg Charter, under which al-Qaeda operatives might theoretically be charged with crimes against humanity.

What is needed is a new legal rubric for fighting terrorism -- one that properly accounts for the hybrid military/criminal nature of terrorism and that does not encumber Western governments with a confusing welter of overlapping legal precedents. While, fortunately, Western nations will prosecute the war against terrorist groups regardless of what roadblocks international lawyers seek to erect, it would be better if an obsolete legal baseline did not offer NGOs and other nations -- each with their own diplomatic and political biases -- a platform from which to criticize, erode support for and otherwise hobble the just prosecution of a wholly new type of war.