Al-Ghazali

Al-Ghazali (c. 1058-1111), known in the Latin West as Algazel and honoured in Islam as Hujjat al-Islam, "the Proof of Islam," is among the most consequential thinkers in the history of the faith. His most famous philosophical work, the Tahafut al-falasifa ("The Incoherence of the Philosophers"), is a searching critique of the Islamic Aristotelians, above all al-Farabi and Avicenna (Ibn Sina), whose Neoplatonised philosophy he judged to have overstepped the bounds of reason and religion. He argued that on twenty points the philosophers had failed to demonstrate their claims, and that on three they had fallen into outright unbelief: holding the world to be eternal rather than created, denying God's knowledge of particulars, and denying the bodily resurrection.

Notably, Ghazali attacked not by rejecting logic but by using it, and his discussion of causality, questioning whether the "necessary connection" between cause and effect is anything more than God's habitual ordering, is one of the classic statements of theological occasionalism and drew a celebrated reply from Averroes (the Incoherence of the Incoherence).

At the height of his fame as a jurist and theologian in Baghdad, Ghazali underwent a personal and intellectual crisis around 1095: seized by doubt about the foundations of certain knowledge and by the conviction that his learning had become worldly ambition, he abandoned his prestigious teaching post, left the city, and spent years in withdrawal and Sufi practice.

Out of this came his masterwork, the Ihya ulum al-din ("The Revival of the Religious Sciences"), a vast synthesis that sought to breathe inner, spiritual life back into the outward observances of Islamic law, reconciling the jurist's and the theologian's learning with the heart-knowledge of the mystics, and giving Sufism a securely orthodox place at the centre of Sunni piety. His autobiography, al-Munqidh min al-dalal ("Deliverance from Error"), narrates the whole journey through the claims of theology, philosophy, Ismaili authority and Sufism.

A later and much-repeated thesis, that Ghazali's critique dealt a lasting blow to science and philosophy in the Muslim world, is contested among historians, who note that philosophical and scientific work continued vigorously after him; the claim should be treated as a debated interpretation rather than a settled fact.