The Incoherence of the Philosophers

• 1. Introduction

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  The Incoherence of the Philosophers arrived in the 11th century as a direct challenge to the most admired minds in the Islamic world. Written by al-Ghazali, a Muslim polymath trained in the Asharite school of Islamic theology, the book set out to demolish the philosophical legacy of thinkers such as Ibn Sina and al-Farabi. These men had built their systems on Greek foundations, and al-Ghazali believed that path led them, in at least some crucial places, away from Islam itself.

  The title says it all: incoherence. Not error. Not disagreement. Incoherence. Al-Ghazali was not merely saying the philosophers got things wrong. He was saying their arguments could not hold together on their own terms. That was a sharper accusation, and a more dangerous one to make.

  What drove a celebrated professor of law to write such a work? What exactly did he charge against Ibn Sina? And how did the philosophers fight back? The answers stretch across theology, cosmology, and the nature of cause and effect itself.

• 2. Baghdad and Its Mandate

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  In July 1091, al-Ghazali accepted an invitation from Nizam al-Mulk to take up a professorship at the Nizamiyya of Baghdad. This was one of the most prestigious colleges of its time. The college carried a specific institutional purpose: it was designed in part to train scholars who could counter the religious propaganda of the Fatimid caliphs.

  Al-Ghazali's appointment fit that mission precisely. The Tahafut, as the book is known in short, was actually the second work in a series of four that he produced during his tenure there. He had the foresight to build the series as a structured intellectual campaign rather than a standalone attack.

  He started with Maqasid al-Falsifa, a careful exposition of Avicennian philosophical doctrine. Al-Ghazali was explicit that this first book was intended as preparation for the Tahafut itself. His reasoning was methodical: one must fully understand the philosophers before attempting to refute them. A third work, Miyar al-Ilm fi Fan al-Mantiq, laid out Avicenna's logic as an appendix to the Tahafut. The final work, Al-Iqtisad fi al-itiqad, then supplied the Asharite theological alternative to fill the metaphysical space the Tahafut had cleared away.

• 3. Twenty Charges

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  The Tahafut is organized into twenty chapters, each targeting a specific doctrine that al-Ghazali attributed to Avicenna and his followers. Seventeen of those chapters accuse the philosophers of heresy. Three go further, charging outright disbelief in Islam.

  The three charges he considered most severe share a common thread: they concern the boundaries of the world and the nature of the divine relationship to it. The first is the doctrine that the world is pre-eternal, meaning it always existed rather than having been created in time. Against this, al-Ghazali held that God created the world in time and that time itself would eventually cease, though God would not. The second charge targets the claim that God knows only universal characteristics of particulars, a position associated with Platonic forms, rather than knowing individual things directly. The third concerns bodily resurrection: al-Ghazali insisted the philosophers wrongly denied it, claiming only souls would be raised.

  Among the seventeen heresy charges, al-Ghazali pressed the philosophers on their inability to prove the existence of God, their inability to prove the impossibility of two gods existing simultaneously, their denial of God's attributes, and their claim that the heavens move by their own volition. Point after point, he argued that the philosophical system broke down precisely on the questions that mattered most.

• 4. Causation and Cotton

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  One of the most striking arguments in the Tahafut addresses the nature of cause and effect. Al-Ghazali put forward the Asharite theory of occasionalism, and he did so with a vivid illustration: when fire and cotton are placed in contact, the cotton is not burned by the fire. It is burned directly by God.

  This was not mysticism dressed up as argument. Al-Ghazali used logic to defend the claim within Islamic philosophy. His reasoning turned on the character of God. Because God is rational rather than arbitrary, his behavior in consistently causing events in the same sequence can be understood as the outworking of reason. What we call the laws of nature are, properly understood, laws by which God governs his own conduct. They express his rational will, not an independent causal power residing in the fire itself.

  This doctrine had direct implications for two of the three charges al-Ghazali considered most severe. If God is the immediate cause of every event, then the philosophical notion of an eternal causal chain operating independently of God collapses.

• 5. Worlds and Demonstration

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  Not everything in the Tahafut was polemical attack. When al-Ghazali turned to astronomy, he took a position that surprised readers expecting blanket rejection of natural science. He wrote that engaging in religious disputation to refute solar and lunar eclipses harms religion and weakens it, because those matters rest on geometrical and arithmetical demonstrations that leave no room for doubt. He was clear that physics, logic, astronomy, and mathematics were not his targets. His dispute was confined to metaphysics.

  On cosmology, al-Ghazali defended the Asharite position that the universe was created and is temporally finite, against the Aristotelian claim of an eternal universe. To support this, he proposed what can be described as a modal theory of possible worlds, arguing that the actual world is the best among all alternate timelines and world histories that God could have created. A parallel theory appeared in the work of the Catholic theologian Duns Scotus in the 14th century. Whether al-Ghazali influenced Scotus directly is uncertain; both may have drawn from their readings of Avicenna's Metaphysics.

• 6. Responses and Echoes

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  Ibn Rushd, known in the West as Averroes, wrote the most direct counterattack, a work called The Incoherence of the Incoherence. Its format was a dialogue: Averroes quoted passages from al-Ghazali and then responded to them, defending the philosophers and criticizing al-Ghazali's arguments. The wider Islamic audience did not receive it warmly.

  In the 15th century, an Ottoman Turkish scholar named Mustafa Ibn Yusuf al-Bursawi, also known as Khwajahzada, produced his own book about the Tahafut at the request of Sultan Mehmed the Conqueror. Al-Bursawi died in 1487. His treatment of al-Ghazali was so severe that the scholar Ibn Kemal raised a public doubt about whether al-Bursawi's true target was the philosophers or al-Ghazali himself.

  A less hostile engagement came from Ibn Tufail, a predecessor of Averroes who wove a response into his Arabic philosophical novel Hayy ibn Yaqzan, later translated into Latin and English as Philosophus Autodidactus. Ibn Tufail named al-Ghazali as an influence, particularly on his views about Sufism, while still criticizing his stance against Avicennism. That novel in turn prompted Ibn al-Nafis to write Theologus Autodidactus as a response defending some of al-Ghazali's positions. The Tahafut had, by this point, generated a chain of books answering books that stretched across centuries and continents.