No area of Islamic jurisprudence is more disputed than the Hadiths. Scholars have been arguing for centuries over which of these oral traditions are authentic and which were invented to suit the needs of the time or the political ambitions of various rulers or upstarts.

Hadiths are the second essential pillar of Islamic law after the Koran and more than 90 per cent of Sharia is based on them. Their number, however, runs into hundreds of thousands, as pious believers over the centuries attempted to embellish the Prophet's reputation and sagacity. Scholars have therefore been at pains to promote only those that can trace their lineage back to a witness and in, deciding which are important, the chain of transmission counts for as much as the content itself. Most of the Muslim world now accepts that only six collections are reliable, especially one collated by Muhammad al-Bukhari, who lived in 810-870, and confirmed as authentic only 2,062 of the 300,000 he recorded over 16 years.

Hadiths are the main source for many of the most controversial practices in Islam, including the killing of apostates, the seclusion of women, the ban on fine arts, the stoning of adulterers and other violent punishments for sinful behaviour. The value put on these sayings varies between Islamic schools and sects, such as the Wahhabis, Hanbalis or the Sufis. That is why there is little agreement on abolishing those now seen as outdated, misogynist or incompatible with scientific knowledge.

Any attempt at “reinterpreting” the Koran itself is fraught with difficulty as Muslims believe the revealed word to be immutable and valid for all time. But, especially in the diaspora, there is now lively discussion of reviving the practice of analogous reasoning — ijtihad — which is the fourth pillar of Islamic jurisprudence. This allows scholars to offer opinions on contemporary issues based on an interpretation of Koranic intentions, rather as the US Supreme Court interprets the spirit of the Constitution in situations not foreseen when it was written.

This practice, halted by a caliph in medieval times on the ground that it would lead to a straying from Koranic practice, is still highly controversial, with fundamentalists denouncing any attempt to “update” the Koran and modernists insisting that only thus can Islam be made compatible with modernity.

Some senior religious figures, such as the Grand Mufti of Egypt, insist that ijtihad is nowadays as essential as it is theologically valid. And other reform-minded muftis, the main exponents of Sharia, are determined to purge Islam from the obscurantism and literalism that they consider eclipse its validity.

A vigorous debate on Islamic jurisprudence and modernity has been central to political life in Iran, with Shia scholars having an important say in political decisions. But this re-evaluation has had little application outside Iran because of the long-standing rift between Shia and Sunni Islam. Scholarly opinion in Turkey, a Sunni country and the former seat of the caliphate, is likely to have greater resonance in the Muslim world, despite mistrust of Turkey's post-1920 secularism, because of the political success of a modern Islamist government.