Religious scholars who agree on little else have been virtually unanimous in their reaction to the Sept. 11 attacks: They have denounced them.
Yet Muslim and Christian thinkers -- working with centuries of teaching on moral use of force -- have found less common ground on the appropriate response to terrorism.
For guidance, Muslim scholars have turned to classical Islamic teaching while Christians have looked to the Just War doctrine, whose venerable precepts have been dusted off in think-tank panel discussions, scholarly articles and church pronouncements. There is considerable overlap between the two faiths.
Many early Christians were pacifists, and elements of that view survive.
The social-issues board of the United Methodist Church, President Bush's denomination, released a statement Tuesday that terrorists must be brought to justice but "war is not an appropriate means of responding to criminal acts against humanity." The board also asserted that "military actions will not end terrorism."
However, Christianity has a long tradition -- through the Just War doctrine -- of permitting societies to take up arms to establish justice or protect the innocent.
As formulated by St. Augustine (354-430), Thomas Aquinas (1225-1274) and subsequent theologians, Just War has two aspects.
The first, "jus ad bellum" ("justice concerning war") lists all the tests that must be met for war-making, including proper purposes and motives -- for instance, self-defense rather than aggression -- and declaration by proper governing authority, not private vigilantes.
Islam enshrines the same criteria.
While the Prophet Muhammad was a military leader at times, a prominent U.S. Muslim scholar, Muzammil H. Siddiqi of California State University in Fullerton, says passages in the Quran that justify combat involved self-defense for early Muslims.
People in that community "were subject to constant terrorist attacks," Siddiqi explains in a forthcoming article for Islamic Horizons magazine. Respect for the holy writings requires proper understanding of the context, he writes.
In another similarity between Islam and Christianity, war must be declared by the proper authorities.
Osama bin Laden, the suspected terrorist mastermind who has proclaimed a holy war against Americans, is neither a recognized ruler nor a religious jurist qualified to do so under Muslim tradition.
One jurist who is, Sheikh Yusuf al-Qaradawi of Qatar, joined four colleagues from Egypt and Syria in issuing a religious ruling, or fatwa, on the United States' military action last week.
It stated that "all Muslims ought to be united against all those who terrorize the innocents, and those who permit the killing of noncombatants without a justifiable reason."
Such thinking among scholars may have influenced the foreign ministers of the 56-nation Organization of the Islamic Conference, who declared last week that "such shameful terror acts are opposed to the tolerant divine message of Islam, which spurns aggression" and "prohibits killing of the innocent."
Killing the innocent, strictly forbidden in the Hadith -- the authoritative traditions from the Prophet Muhammad and his successors -- is another reason Muslim traditionalists oppose bin Laden's tactics.
The death of innocents is also addressed in the second part of the Just War doctrine, "jus in bello" ("justice in war"), which sets out rules for conduct of war, such as avoiding direct harm to innocent civilians and limiting destructive tactics.
Many Muslim and Christian pronouncements on American military action have made protecting civilians a priority.
It hasn't always been so. Theologians paid little attention to such matters in the World War I era, says Rutgers University religious historian James Turner Johnson. But civilian slaughter became a major moral issue in World War II, with Germany's blitz of London, Allied carpet bombing of Dresden and Tokyo and the use of atomic bombs on Hiroshima and Nagasaki.
"One reason the United States wearied of the Vietnam War was the realization that fighting that war meant that we could not -- given the nature of that war -- distinguish combatants from noncombatants," says Jean Bethke Elshtain, a University of Chicago political philosopher.
As the United States began its bombing campaign against Afghanistan, the World Council of Churches objected precisely because of the loss of life to civilians.
"We do not believe that war, particularly in today's highly technologized world, can ever be regarded as an effective response to the equally abhorrent sin of terrorism," said the council, made up of 342 Protestant and Orthodox denominations.
But Johnson thinks technology actually enhances morality, making possible tightly targeted missile strikes and action by smaller military units that can distinguish between combatants and civilians.
Other religious thinkers say the times require a whole new approach.
"The Just War tradition falls short of our needs," writes George A. Lopez of the University of Notre Dame peace institute in America magazine. He suggests that the Sept. 11 attack was a "crime" that needs presentation of evidence equivalent to a grand jury indictment.
But Elshtain thinks no such international justice system exists.
The Rev. J. Bryan Hehir of Harvard Divinity School, a Roman Catholic who advised the U.S. bishops on their 1983 letter "The Challenge of Peace," is worried whether there will be any limits when America proclaims the sweeping goal of ending terrorism.
"Against how many states can the U.S. declare war without being itself defined as a threat to international order?" he asks.
Yet another real-world problem is that one person's terrorist is another's freedom fighter. In their statement against Sept. 11 terror, the foreign ministers of the Organization of the Islamic Conference championed the right of Muslims in Palestine and Lebanon to employ "self-defense" against "the state terrorism practiced by the Israeli government."