It's a question that's been addressed about Islam with particular urgency in the past year by people in and outside that faith. Muslims in the United States and around the world have offered a spectrum of answers. Non-Muslims such as President Bush and the Rev. Franklin Graham have offered their own wildly varying responses.
But it's also the question that divides the leadership of the Baptist General Convention of Texas and the Southern Baptist Convention. It's the question raised by the "confessing movement" of the United Methodist Church. It's the center of the debate in Israel over the definition of who is Jewish. And it's a challenge raised by some of the laity movements in the Catholic Church.
Today's multifaith controversy over the nature of Islam is only the latest in a long dialogue, with Christianity offering a redefinition of Judaism, Islam challenging the sacred texts of Christians and Jews, the Church of Jesus Christ of Latter-day Saints discerning errors in other faiths, and so on.
But the question about Islam is now far more than a theological argument, say some contenders in the debate. It's a matter of international security. Or it's a challenge to civil rights. Is Islam a religion of peace, as Bush has said repeatedly? Or is it a violent scam, as the Rev. Pat Robertson said last week on the Fox TV show ``Hannity and Colmes''? Where can anyone go for a definitive answer to questions about whether a particular behavior is or is not true to Islam?
There is no single answer, said Imam Yusuf Kavakci, head of the Dallas Central Mosque in Richardson, Texas. Muslim history has had a hierarchy of scholars and political leaders, starting with Muhammad himself. But unified authority was lost with the end of the Ottoman Empire in 1920, the disintegration of the Muslim world into many nations, and the presence of Muslims as a growing minority of many other countries, Imam Kavakci said.
That means that when Osama bin Laden and his followers - or other groups - claim to act in the name of Islam, there is no universally recognized authority that can say without contradiction that they're wrong, he said. Individual, respected scholars in Muslim nations and the United States can and have issued denunciations. But there is no single forum where consensus can be reached, he said. "It's a problem we Muslims have," he said.
It's not just a problem for Muslims, said Robert Spencer, author of one of several recent books by non-Muslims that seek to critique that faith. Spencer claims no credential beyond 20 years of his own study of Islam. The thesis of his book, ``Islam Unveiled,'' is that Muslim texts and history show that there is no single authority that can define the true nature of modern Islam as a religion of peace.
Judaism and Protestant Christianity have the same problem of not having a recognized single authority that can decide difficult questions of interpretation, said Spencer, who lives in New Hampshire. "That's one reason I'm a Catholic," he said.
Like other non-Muslim critics of Islam, including the authors of a book titled ``Unveiling Islam,'' Spencer pulls verses from the Quran and the collected sayings of Muhammad called hadiths to bolster his claims that Islam has a violent core.
``Unveiling Islam'' was written by brothers who converted to Christianity from Islam while in their teens. Ergun Caner is now a professor at Criswell College in Dallas. Emir Caner is a professor at Southeastern Baptist Theological Seminary in North Carolina.
Ergun Caner said he does not hold himself or his book up as the last word on Islam. He acknowledges that some Muslims will challenge his ability to understand their faith because he does not understand the 1,400-year-old Arabic of the Quran. But he said that he has read many modern Arabic commentaries - for and against Islam - and that his interpretation cannot be dismissed with a blanket statement that Islam is a religion of peace. "Islam doesn't speak with one voice, and neither does Christianity," he said.
But there is a way to hear the strongest voices amid the chorus, said Dr. Jamal Badawi, an internationally known Canadian-based Muslim scholar."There is a difference between a reasonable interpretation and one that is completely out of bounds," he said.
Some of the more radical voices claiming to speak for Islam are doctors and engineers, not Muslim legal scholars whose ignorance of Muslim history has led to impossible interpretations of the Quran, he said.
Shaykh Muhammad Hisham Kabbani is an American-based Sufi cleric, a minority voice within Islam. Sufism is a kind of Islam that stands at an opposite pole in many ways from the version practiced in Saudi Arabia. He says he is frustrated by critics of Islam who say they can understand his faith merely by reading the sacred texts, either in the original Arabic or in translation.
"When you study medicine, there is a book on internal medicine," said Shaykh Kabbani, who was a medical doctor before he became a religious leader. "You can not study it by yourself. You have to go to medical school."
For instance, he said, there are some verses in the Quran that most Muslims understand are no longer in effect, like leaves that fall from a tree, he said. Those verses, some of which are the most militant in the book, applied only to the time of Muhammad, he said. And a simple reading of the book doesn't show that.
But other Muslims have what might be considered a more "Protestant" view of their faith. Just as a series of Christian movements have called for a return to the "fundamentals" of their faith, so have some Muslim movements. The leadership of Saudi Arabia follows such a version of Islam, generally called Wahhabbism after Muhammad ibn `Abd al-Wahhab, a contemporary of George Washington.
Clearly, there are few disinterested parties in such a discussion. One person's jewel of faith is another's flawed understanding, based on the individual's concept of an authentic divine revelation.
So how can people hope to separate the essence from the heretical? "The answer is political in both the best and worst sense of that word," said Rev. George Mason, pastor of Wilshire Baptist Church in Dallas and a nationally recognized moderate Baptist leader.
Controversies have led to councils that reached a consensus about the faith - the Council of Nicea, the Council of Trent. Or politically powerful leaders within the church or a denomination have moved to impose a particular interpretation. Or there has been a third way, he said."Finally there is the politics of the pew, the everyday practice of the faith, which in the end is really the defining essence of it."
Religious revelation is never completely self-evident, he said, so interpretations inevitably produce conflict. The Rev. Richard Land heads the Ethics and Religious Liberty Commission of the conservative Southern Baptist Convention. For him, the interpretation of revelation is a bit more straightforward.
For Christianity, "the only thing you can do is get a clear an concise understanding of what each of these denominations teach and go to the New Testament and see which one squares most with what is taught in the New Testament."
But that still leaves the possibility of serious disagreement, he acknowledged. Some Baptists are Calvinists and some aren't, he said, reflecting a split on whether people's salvation is predestined. As for his opinion of Islam, he asked why religious leaders of predominantly Muslim nations do not condemn terrorism more forcefully if they truly represent a faith of peace.
That's a confusion of politics and religion, Imam Kavakci said. Oppressive political regimes in nations including Egypt, Saudi Arabia, Iraq, Syria and Jordan make it impossible for Muslim scholars to speak out independently.
There's also a confusion between the faith and those who claim to speak in its name, said Aasma Khan, an American-born Muslim and one of the founders of Muslims Against Terrorism USA. Khan, a New York-based lawyer, said she and others formed the group after the 9-11 attacks. It's important, she said, to draw a distinction between terrorists who use the language of her faith and the practice followed by many more Muslims.
"The fact that the terrorists throw in ishallah (Arabic for "if it is God's will"), that doesn't make it religion. That's like saying that because we put In God We Trust on our coins, it says we only support one kind of Christianity in this country," she said. .