It is not for no reason that Imam al-Ghazali is named "Hüccetü'l İslam" (The Proof of Islam) for he defeated the philosophers at their own game. "Hüccet" means the strongest evidence to finish a discussion. In the enduring dispute between philosophers and Ghazali, he remains outstanding after a thousand years and despite the words said against him.
This is the best-known characteristic of his from four salient ones, yet not the most important. You can come across many orientalists, including Turkey's agencies of orientalism, blaming Ghazali for disrupting Islamic thought. Never believe them. What Ghazali disrupted was the spread of Greek metaphysics among Muslim scholars.
Against rationalism, for reason
Ghazali has three characteristics beyond being the man who brought philosophers to their knees. He was an Ash'ari theologian, Shafi'i canonist and a Sufi. We need to explain all these three terms in short. Imam al-Ghazali was an important Ash'ari theologian which means he was an important scholar within the theological school founded by Abu'l Khasan al-Ash'ari.
According to Ash'ari theology, human reason alone is inadequate to reach the truth and that what is more important is religious belief and commitment. Imam Ash'ari gave special importance to negate the opinions of the Mutazili sect, which represented a kind of Islamic rationalism.
One of the biggest matters of debate between these two factions was the attributes of God. While the scholars of Mutazilism wanted to develop a rationalist theology, they rejected God's attributes apart from His self. Ash'ari made a distinction between God's self and his attributes and argued that God's attributes were neither His own self nor something apart from Him. Today, people of Sunnah agree and hold beliefs in that way.
Ghazali's novelty in theology was methodological. Even though the first theologians called "Mütekaddimin" (pioneers) tried to avoid Greek logic, Ghazali decided to employ it, which is enough to refute the argument that Ghazali caused Islamic thought to regress.
The Alchemy of Happiness, 1308 Persian copy held in the Bibliotheque Nationale de France.
How could a man making use of logic and philosophy and recommending this method to other people cause retreatment in thought?
Shining star of the Nizamiyyah madrasah
As to Ghazali's other contributions, what we first argue is that belief and law were not separated from each other in Islamic tradition according to him, which means theology (kalam) and law (fiqh) were one. The reason for this is simply the lack of theory-practice dichotomy in Islamic thought. A Muslim cannot engage in abstract ideas away from real life and avoids behaviors, services and practices that are not based on a profound system of thought.
A Muslim is after union, not dichotomies.
Abu Hamid al-Ghazali, born in 1058, studied in the Nishapur Nizamiyyah Madrasah until the age of 28, which was regarded as the best theological education of the era. Madrasah education became technically refined under the rule of the Seljuks. As a boy Abu Hamid, who is better known as Ghazali due to his birthplace (the village of Ghazaleh) or his father's occupation (he was a "ghazzal" meaning thread chooser), came from a poor background, but received the best education he could take in one of the greatest madrasahs under the protection of Nizam al-Mulk.
Having risen quickly due to his ambition and talent, Ghazali was appointed head mudarris (a kind of professor) to the Baghdad Nizamiyyah Madrasah in 1091 when he was 33 years old. It is possible to consider this position as the president of today's greatest university. Before reaching the top, Ghazali had won a lot of debates, while he also read for hours each day. As a product of these studies he wrote a countless number of books.
The most famous works of Ghazali were those written as responses to philosophers. After he examined the ideas of the philosophers with an even-tempered style in "The Purposes of the Philosophers," he revealed the illogicality of philosophers in his best-known and much-debated book called "The Incoherence of Philosophers."
The slanderous claim that Ghazali was the reason Islamic thought had retreated arose from this book. Orientalists who care so much about this book think that peripatetic philosophy would have survived if this book had never existed and they hold Ghazali responsible for the decline of Greek philosophy in Islamic thought. This unscientific delusion and slur has turned into a mindscape in which Turkish orientalists roam.
Let us clarify: Ghazali is the man who halted the Greek metaphysics and the imitations influenced by the Greek tradition in the Islamic world. Yet, if Ghazali had not halted this part of Greek philosophy, it would still have lost its influence on the Islamic world and stopped. The moral foundations of Greek philosophy were not suitable for the Muslim mind, but Ghazali owes his influence to his ideas suitable for a Muslim mind.
Crisis and efforts to revive religious sciences
Ghazali criticized the Batiniyya sect a lot, but somehow they were still able to exist in the Islamic world. Mutazilism and Greek metaphysics would possibly have become insignificant even without Ash'ari and Ghazali. Yet, it would be more reasonable to consider that Ash'ari's attacks on the Mutazila and Ghazali's attacks on philosophy fulfilled the needs of Muslims and thus the thoughts of these two scholars are still alive.
Apart from his refutations, Ghazali is also widely known for his efforts to revive religious sciences. What makes his works (where he criticized philosophy and Batiniyya) multilateral is his voluminous masterpiece called "Ihya Ulum al-Din" (The Revival of the Religious Sciences). Throughout the book, he brings new approaches to law (fiqh) and theology (kalam) along with prioritizing good manners, religious service and caution. To sum up, this book is the effort of a scholar who wants to embrace the whole knowledge of Islam. "Ihya" means revival and awakening and we can argue that Ghazali is the first mujaddid (a scholar who brings religious renewal) of Islam.
When still at the Nizamiyyah, Ghazali fell into a great depression while he was at the top of his fame and career as Baghdad's head mudarris. He could not bear all the debates and his soul appealed for salvation. He desired reclusion, but could not find it due to the tight political atmosphere of the period. He found a way to go to Damascus from Baghdad and then to Hejaz for hajj (pilgrimage). Ultimately, he went back to Tus, his birthplace.
In his autobiographical work "Emancipation from Heresy," which was a product of this 10-year-journey, he both talked about his spiritual journey and gave a final summary of his ideas on kalam, philosophy, Batiniyya and Sufism. He came to decide that the Sufi path was purer than the others. Sufism gave new life to the head mudarris in crisis.