"Al-Mamun picked up the pro-science torch lit by the second caliph, al-Mansur, and ran with it. He responded to a crisis of legitimacy by attempting to undermine traditionalist religious scholars while actively sponsoring a doctrine called Mu’tazilism that was deeply influenced by Greek rationalism, particularly Aristotelianism. To this end, he imposed an inquisition, under which those who refused to profess their allegiance to Mu’tazilism were punished by flogging, imprisonment, or beheading. But the caliphs who followed al-Mamun upheld the doctrine with less fervor, and within a few decades, adherence to it became a punishable offense. The backlash against Mu’tazilism was tremendously successful: by 885, a half century after al-Mamun’s death, it even became a crime to copy books of philosophy. The beginning of the de-Hellenization of Arabic high culture was underway. By the twelfth or thirteenth century, the influence of Mu’tazilism was nearly completely marginalized.

In its place arose the anti-rationalist Ash’ari school whose increasing dominance is linked to the decline of Arabic science. With the rise of the Ash’arites, the ethos in the Islamic world was increasingly opposed to original scholarship and any scientific inquiry that did not directly aid in religious regulation of private and public life. While the Mu’tazilites had contended that the Koran was created and so God’s purpose for man must be interpreted through reason, the Ash’arites believed the Koran to be coeval with God — and therefore unchallengeable. At the heart of Ash’ari metaphysics is the idea of occasionalism, a doctrine that denies natural causality. Put simply, it suggests natural necessity cannot exist because God’s will is completely free. Ash’arites believed that God is the only cause, so that the world is a series of discrete physical events each willed by God."

More controversially:

"Christianity acknowledges a private-public distinction and (theoretically, at least) allows adherents the liberty to decide much about their social and political lives. Islam, on the other hand, denies any private-public distinction and includes laws regulating the most minute details of private life. Put another way, Islam does not acknowledge any difference between religious and political ends: it is a religion that specifies political rules for the community.

Such differences between the two faiths can be traced to the differences between their prophets. While Christ was an outsider of the state who ruled no one, and while Christianity did not become a state religion until centuries after Christ’s birth, Mohammed was not only a prophet but also a chief magistrate, a political leader who conquered and governed a religious community he founded. Because Islam was born outside of the Roman Empire, it was never subordinate to politics. As Bernard Lewis puts it, Mohammed was his own Constantine.

...

What is needed in Islam is less self-pride and more self-criticism. Today, self-criticism in Islam is valued only insofar as it is made as an appeal to be more pious and less spiritually corrupt. And yet most criticism in the Muslim world is directed outward, at the West. This prejudice — what Fouad Ajami has called (referring to the Arab world) “a political tradition of belligerent self-pity” — is undoubtedly one of Islam’s biggest obstacles. It makes information that contradicts orthodox belief irrelevant, and it closes off debate about the nature and history of Islam."