Abu Hamid al-Ghazali, also known in west as Algazel, was born at Tus, Iran in the year 1058 CE. His father died while he was very young. He received his early education at Tus and at the age of fourteen he went to Gurgan. Here he studied Fiqh (Islamic Jurisprudence) and after seven years he moved to the city of Nishapur and became the student of famous scholar Abu Maali Juwayni.
He soon acquired a high standard of scholarship in religion, philosophy and fiqh. The vizier of the Seljuk Sultan, impressed by his scholarship, appointed him as a Professor at the Nizamiyah University of Baghdad, which was the most reputed institution of learning at that time.
After a few years, however, he gave up his academic pursuits and worldly interests and became a wandering ascetic.
After spending some time in Jerusalem, Makkah and Medina he came back to Tus and spent several years in seclusion. He finally ended his seclusion, opened a Sufi school khanakah and started teaching and lecturing. He remained in Tus until his death in December of 1111 CE.
Among the Muslim theologians, al- Ghazali was the most influential; in addition he was a philosopher, a Jurist and a Sufi mystic. He was a prolific writer, authoring more than 70 books. Probably his major work, the multi-volume Ihya ul-Uloom ud-Din, (The Revival of Religious Sciences), can be divided into four parts, which cover perhaps all aspects of Islam, including Islamic jurisprudence, theology and Sufism.
In this series he pointed out that the traditional teaching about Islam did not convince him in his adolescence. His conviction came later, through his Sufi mystical experience. In his autobiography; The Deliverance from Error, he recounts how his spiritual crisis was resolved by a light from God, the key to all knowledge. The Sufi mystical experience brought changes in his theological thought.
Al-Ghazali authored two books on Islamic theology, The Middle Path in Theology and The Jerusalem Epistle. In both books the theological position he expressed matches with the Asharite school of thought. He wrote three books on Aristotelian logic, The Standard Measure of Knowledge, The Touchstone of Proof of Logic and The Just Balance.
Al-Ghazali was very much interested in logic and philosophy, and he studied intensively while he was teaching at Baghdad. He composed two books on philosophy; The Intention of the Philosopher, in which he has summarized his own conclusions about philosophy, and set the stage for the second book; The Incoherence of the Philosophers. In this book he has used exhaustive logic against philosophers. He vehemently rejected Aristotle, Plato and all Muslim philosophers starting from eighth century who incorporated the ancient Greek philosophy into Islamic theology. The main among them were al Kindi, al-Farabi and Ibn Sina. Point by point, he refuted their arguments.
For 100 years his arguments were unchallenged. Ibn Rushd, an Andalusian philosopher, made a counter-argument in his book The Incoherence of the Incoherence, but the epistemological course of Islamic thought had already been set by al-Ghazali.
Al-Ghazali divided knowledge into three categories; praiseworthy, permissible and blameworthy–which he has discussed in his book Ihya Ulum-id-Din(Revival of the Religious Sciences). All learning connected to religion is praiseworthy, but when mixed with other than religion sometimes becomes blameworthy. Learning medicine and mathematics he said are permissible and declared it as farze Kefayah, not ferze Ayin. If a man in a town or a locality acquires such knowledge, the whole community get absolved from the sin.
In his book al-Mustasfa which he wrote towards the end of his life, he stated that arithmetic and geometry are pure rational sciences and as such not recommended for study. They fluctuate between false and true knowledge that yield no practical application. He saw no usefulness in the study of physics and said some part of the subject as it was understood in his time contradicted the Shariah and thus were useless or blameworthy.
Al-Ghazali believed in the certainty of God which he experienced by mystic revelation, a phenomena he said was beyond logic or sensory perception. He argued that you can not prove the presence of God by logic or philosophy, and saw philosophy as largely a waste of time and inadequate for discovering the truth. Contingent events, he said, are not subject to natural physical cause, but are direct result of Godâ€™s constant intervention. This concept of God is consistent with the Asharite school of theology.
Al-Ghazali’s work had a widespread influence on western medieval scholars especially Thomas Aquinas. He received wide recognition in the religious institutions of the Ottoman empire, southeast Asia, and Africa. In the Indian subcontinent, he enjoyed wide recognition both among the Deobandi school as well as the arch-rival Barelwi school.