In that volume, editor Muqtedar Khan of the University of Delaware will criticize Abou El Fadl as too traditional, because he favors application of Sharia (Islamic law) as interpreted by religious jurists. Though Abou El Fadl has a liberal interpretation of religious law and supports democracy, Khan says, on this point "he says what Islamists are saying."

The moderate cause also is embraced in group pronouncements like one in July from 18 scholars of the Fiqh Council of North America. They declared that "targeting civilians' lives and property through suicide bombings or any other method of attack is haram — or forbidden" under the Quran and Muslim law.

A parallel event occurred the same month in the Muslim heartland. Jordan's King Abdullah assembled 180 teachers from 40 nations representing Islam's eight major schools of legal thought. They declared that only fully qualified authorities have any right to issue fatwas (religious decrees) and carefully restricted the right of Muslims to declare fellow Muslims to be heretics.

If honored, that decree would end any regard for religious edicts from self-appointed amateurs such as al-Qaida leader Osama bin Laden and any claims that it's legitimate for Muslims to murder other Muslims for political reasons, as in Iraq.

The problem, says Abou El Fadl, is modern Islam faces a "crisis of authority" about who speaks for the faith that has deteriorated into "full-fledged chaos."

Islam once recognized the Quran and Hadith — authoritative traditions about the Prophet Muhammad and early followers — interpreted by the consensus among the ulama (religious jurists). Seminaries trained recognized authorities who agreed on major points but allowed flexibility on details.

Abou El Fadl describes modern developments as follows:

European colonialism eroded the old system, as Western-influenced laws and lawyers rivaled traditional Islamic institutions.

After the colonial era, autocrats in Muslim countries who cared little for the faith seized remaining Sharia schools, formerly run by religious endowments independent of the state. Jurists and mosque leaders became state functionaries and lost religious legitimacy.

This impoverished intellectual climate created a dangerous "vacuum in religious authority" that has been filled by popular movements, radical schools and religious edicts from ill-trained propagandists.

The key to the current split is Saudi Arabia's Wahhabi movement. It originated by treating non-Wahhabi Sunnis and Shiites as virtual apostates, which justified repression, torture and killing of fellow Muslims — along with unwavering hostility toward non-Muslims.

This movement disrupted Muslim unity and replaced tolerance with a "very narrow and idiosyncratic view of Islamic law," Abou El Fadl says. Out went music, chess and pets (he defiantly keeps three dogs) and in came required beards, dress codes and severe restrictions on women.