Muhammad al-Ghazali,

Following al-Biruni and Avicenna in Persia was the philosopher Muhammad al-Ghazali, born in 1058, twenty-one years after Avicenna died. In his late twenties, Ghazali was invited to the court of Nizamul Mulk Tusi, a scholar and vizier of the Seljuq sultans. At 33, the vizier appointed him chief professor in the Nizamiyya of Baghdad, an institution of higher education. Ghazali lectured to more than 300 students. And in pushing his ideas in debates and discussions, it is said he made a name for himself among intellectuals in various Muslim cities.

At the age of 37 he passed through an ideological crisis. As he described it, he was "caught up in a veritable thicket of attachments" and "I was dealing with sciences that were unimportant and contributed nothing of the attainment of eternal life." He disposed of his wealth and adopted the life of a poor Sufi.

Sufism had been around for more than three centuries, and Ghazali would be recognized as giving it a new life. He had not abandoned the world; in his opinion he had abandoned false goals. After ten years he returned to a professorship and to writing. He fused Sufism with philosophy and his view of the role of science. He did not accept Avicenna's metaphysics. He did not concoct an argument for God -- the same road that some Christians would take, including Kierkegaard. He did not want to mix faith and philosophy. He was happy with his belief that God was the ultimate cause of everything -- not an initiator but continuously intervening and moving events.

As some scientists would in the West, Ghazali separated his faith and his science. He described two kinds of diseases: physical and spiritual. Spiritual disease he saw as a result of ignorance and deviation from God, self-centeredness, the pursuit of wealth and social status, cowardice, cruelty and lust.

A statement attributed to al-Ghazali reads:

In God, there is no sorrow or suffering or affliction. If you want to be free of all affliction and suffering, hold fast to God, and turn wholly to Him, and to no one else. Indeed, all your suffering comes from this: that you do not turn toward God and no one else.

Through Ghazali's efforts, Sufism grew and attracted not only orthodox Muslims but many Christians, especially in Egypt and Syria. There, Sufism met the spiritual needs of some Christians, and where Sufism grew Christianity faded.

A 21st-century writer, Matt Ridley, offers one man's opinion on Ghazali, as follows:

Al-Ghazali almost single-handedly destroyed the tradition of rational enquiry in the Arab world and led a return to mysticism intolerant of new thinking. (Ridley, The Rational Optimist, p. 357)