WHENEVER conflict flares between groups of people who are divided by theology (often rather obscure points of theology), commentators will say: "Of course, it's not really about religion—the actual cause has to do with economics, or geopolitics, or just tribal identity..."

And the clever commentators have a point. In Northern Ireland, Protestants and Catholics do not fight because they disagree over the pope or rosary beads; they fight because the former mostly want to remain part of the United Kingdom while the latter yearn (eventually, at least) to join the Irish republic. But that doesn't mean that religion is completely irrelevant. At least in the recent past, if Protestant firebrands wanted to whip up anti-Catholic sentiment, it was convenient to portray their adversaries as practitioners of an exotic and vaguely frightening cult, and their own side as a people mandated by God to maintain the truth in a hostile land. Even if religion is not the main cause of conflict, nothing keeps conflict on the boil like a dose of fiery religious rhetoric.

Something similar goes for the escalating contest across the greater Middle East, and Muslim world generally, between Sunnis and Shias. As my fellow-blogger Pomegranate has noted, the Shia self-flagellation ritual of Ashura, remembering the martyrdom of Hussein in the year 680, was conducted with particular intensity this year, everywhere from south Beirut to Iran. But there has also been a hardening of sectarian sentiment on the Sunni side, as a new report by the European Council on Foreign Relations, a London-based think-tank, makes clear.

Take the influential Qatari-based Sunni preacher Yusuf al-Qaradawi (pictured), who in years past was a supporter of Sunni-Shia rapprochement. He now sees the Syrian civil war in militantly sectarian terms and has urged Sunnis everywhere to support the opposition. He has described Syria's dominant Alawite minority, who practise a variant of Shia Islam, as "worse infidels than the Jews or Christians" and denounced mainstream Shias for their erroneous beliefs, such as the imminent return of the 12th in a line of successors to Muhammad. In 2006, Mr Qaradawi incurred the disapproval of purist Sunnis in Saudi Arabia by praising the war waged by Lebanon's Shia fighters against Israel. The preacher now says he regrets being so soft on the Shias and acknowledges that his Saudi critics had a point.

Here's another little sign, mentioned in the multi-authored report "The Gulf and Sectarianism", of a hardening pan-Sunni front. The Sunni version of early Islamic history was assertively proclaimed this summer in a television series entitled "Omar"—about the second Muslim caliph, who is regarded as a model ruler by Sunnis (accounting for over 80% of Muslims) but held in much less esteem by Shias. The series was endorsed both by Mr Qaradawi and a Saudi scholar of Islam; it was funded by Qatar and broadcast by a Saudi channel. Until recently there was a cleavage within Sunni Islam between the conservative theocracy of Saudi Arabia and the populist Islamism propagated by Mr Qaradawi from his Qatari base to his supporters in the Muslim Brotherhood. But lately, the report suggests, there has been some closing of the ranks within the Sunni world—against the Shias. For the Saudi elite, stoking anti-Shia sentiment may be a way of heading off the challenge from the Sunni populism of the Arab spring. A Shia cleric in Saudi Arabia is on trial for "waging war against God" and a prosecutor has reportedly demanded "death by crucifixion".

Behind all this intra-Muslim animosity, many will argue, is the ongoing geopolitical contest between Saudi Arabia and Iran, respectively guardians of Sunni and Shia orthodoxy, and rivals for control of the Gulf. But to follow the Sunni-Shia dispute, you have to know a little about the founding events of Islam, and understand why the two camps were so split over the succession to Muhammad. (The Shias thought the prophet's kin were his legitimate successors, and therefore backed the claim of Ali, Muhammad's cousin and son-in-law. The Sunnis favoured Muhammad's friend Abu Bakr.)

People of broadly the same religion who disagree over theology are not doomed to fight. But if they do fight, theological difference gives their disputes an extra-sharp edge. At least in a metaphorical sense and sometimes in a physical one, rival interpretations of the same religion are competing for the same space.