In July 1091, a man who would become the most influential theologian in Islamic history walked into the Nizamiyya college in Baghdad not as a rebel, but as a celebrated professor of law. Al-Ghazali had been invited by the powerful vizier Nizam al-Mulk to teach at one of the most prestigious institutions of the era, a school designed to counter the religious propaganda of the Fatimid caliphs. He was the star of the institution, a man whose intellect was so formidable that he was expected to train the next generation of scholars to defend the Sunni orthodoxy. Yet, within four years of his appointment, this same man would write a book that would systematically dismantle the very philosophical foundations upon which his own intellectual identity was built. He did not merely disagree with the philosophers; he declared their core metaphysical doctrines to be heresy and their understanding of the divine to be a form of disbelief. This was not a quiet academic debate but a public execution of the Avicennian school of thought, a move that would permanently alter the trajectory of Islamic theology and philosophy.
The Four-Part Theological Siege
The Incoherence of the Philosophers was not an isolated pamphlet but the second volume of a massive four-part theological siege that al-Ghazali launched during his tenure at the Nizamiyya. Before he could attack the philosophers, he first had to master their language, a strategy he laid out in his first work, Aims of the Philosophers, which served as a summary of Avicenna's doctrines. He explicitly stated that one must be well versed in the ideas of the philosophers before setting out to refute their ideas, ensuring that his attack was not born of ignorance but of deep understanding. The third volume, Criterion of Knowledge in the Art of Logic, was an exposition of Avicenna's logic that he presented as an appendix to his main attack, while the final work, The Moderation in Belief, provided the Asharite theological framework to fill the metaphysical void he had created. This series demonstrated that al-Ghazali did not reject all philosophical science; he found physics, logic, astronomy, and mathematics unproblematic. His war was strictly limited to metaphysics, where he claimed the philosophers had abandoned the very logic they used to prove other sciences, leaving them vulnerable to his counter-arguments.Seventeen Heresies and Three Blasphemies
The text is organized into twenty chapters, each a surgical strike against the doctrines of Avicenna and his followers, but the severity of the charges varied dramatically. Al-Ghazali identified seventeen points where the philosophers had erred, committing what he termed heresy, and in three specific chapters, he escalated the accusation to outright disbelief in Islam. The charges ranged from the philosophers' inability to prove the existence of God to their failure to demonstrate the impossibility of two gods existing simultaneously. He attacked their denial of God's attributes, their claim that the First is a simple existent without quiddity, and their assertion that the heavens are animals that move on their own volition. The most damning accusations, however, were reserved for the three points of disbelief: the theory of a pre-eternal world, the idea that God knows only universal characteristics rather than particulars, and the denial of bodily resurrection. Al-Ghazali argued that God created the world in time and that time itself would cease to exist, whereas God would continue to exist eternally, directly contradicting the philosophers' view of an eternal universe.