Abu Hamid Ibn Muhammad Ibn Muhammad al-Tusi al-Shafi’i al-Ghazali, by virtue of his singular background in various different aspects of Muslim thought, is known to some as the greatest, and most complete, Muslim thinker of his era. Al-Ghazali was conversant with all three major disciplines of eleventh century Muslim thought--islam, iman, and ihsan. Translated roughly as practice, doctrine, and realization, these three components made al-Ghazali's breadth of expertise impressive, as well as invaluable for the modern student attempting to grasp the history and discourse of this philisophical era. He wrote specialized doctrines examining each aspect, as well as broader explications of their relationship and interdependancy.
In addition to his personal history, al-Ghazali was greatly influenced by the Aristotelian methodology and conclusions of a group of his contemporaries, specifically as embodied in the work of al-Farabi (Alfarabi) and Ibn Sina (Avicenna). His reaction to the works of these two individuals, specifically, was overtly negative. He believed that Islam (and religious belief in general)could neither be proven or disproven, and that the effort to do so resulted in little more than incoherent pseudo-justification for belief. He divided philisophical thought into a few sub-categories: Mathematics, logic, physics, politics, ethics, and mataphysics. While he had no major problem with the first five, he was disturbed by al-Farabi and Ibn Sina's conviction that they could investigate, and reach logical conclusions, about issues dealing with metaphysical concerns. Initially, al-Ghazali had chosen to reject philisophical methodology as a whole, but he later tempered this extreme view, attempting to utilize a framework which would make use of his own personal faith and conviction, as well as the tools of the philosopher.
When one understands al-Ghazali's concerns, it is easy to see why he was so enamored with Sufism. If, that is, one understand (at least roughly, as I do) what Sufism is. The Sufi believed that it was not enough to "obey the words" of God, but rather to work towards the experience of Him. To, as he put it strive towards "looking on the face of God." As David Buchman states, in his introduction to The Niche of Lights: "only a person with a pure and beautiful heart-the soul's center-can become aware of God's presence and obtain direct knowledge from him."(Buchman, xxv) Through a sincere personal experience of Islam, the Sufi attains a different kind of knowledge than it is even possible to attain by use of the philisophical method. When, however, this kind of experience is combined with more rational exploration of the physical and logical world, as al-Ghazali ultimately believed that it should, a more total kind of understanding of both the temporal world around us, and the spiritual world within, could be attained.