The Incoherence of the Philosophers
|The Canon of Medicine|
|The Book of Healing|
|Hayy ibn Yaqdhan|
|Criticism of Avicennian philosophy|
The Incoherence of the Philosophers (تهافت الفلاسفة Tahāfut al-Falāsifaʰ in Arabic) is the title of a landmark 11th century work by Al-Ghazali of the Asharite school of Islamic theology criticizing the Avicennian school of early Islamic philosophy. Muslim philosophers such as Ibn Sina (Avicenna) and Al-Farabi (Alpharabius) are denounced in this book. The text was dramatically successful, and marked a milestone in the ascendance of the Asharite school within Islamic philosophy and theological discourse.
This book was preceded by a summary of Muslim philosophical thought titled: Aims of the philosophers Maqasid al-falasifah. This book is the summary of Avicenna's philosophical doctrine. Al-Ghazali stated that one must be well versed in the ideas of the philosophers before setting out to refute their ideas.
Al-Ghazali also stated that he did not find other branches of philosophy including physics, logic, astronomy or mathematics problematic. His only dispute was with metaphysics, in which he claimed that the philosophers did not use the same tools, namely logic, which they used for other sciences.
The tahafut is organized into twenty chapters in which al-Ghazali attempts to refute Avicenna's doctrines.
He states that Avicenna and his followers have erred in seventeen points (each one of which he addresses in detail in a chapter, for a total of 17 chapters) by committing heresy. But in three other chapters, he accuses them of being utterly irreligious. Among the charges that he leveled against the philosophers is their inability to prove the existence of God and inability to prove the impossibility of the existence of two gods.
The twenty points are as follows:
- Refuting the doctrine of the world's pre-eternity.
- Refuting the doctrine of the world's post-eternity.
- Showing their equivocation of the following two statements: God is the creator of the world vs. the world is God's creation.
- The inability of philosophers to prove the existence of the Creator.
- The inability of philosophers to prove the impossibility of the existence of two gods.
- The philosopher's doctrine of denying the existence of God's attributes.
- Refutation of their statement: "the essence of the First is not divisible into genus and species".
- Refutation of their statement: "the First is simple existent without quiddity".
- Their inability to demonstrate that the First is not a body.
- Discussing their materialist doctrine necessitates a denial of the maker.
- Their inability to show that the First knows others.
- Their inability to show that the First knows Himself.
- Refuting that the First does not know the Particulars.
- Refuting their doctrine that states: "the heavens are an animal that moves on its own volition.
- Refuting what they say regarding the reason that the heavens move.
- Refuting their doctrine that the heavens are souls that know the particulars.
- Refuting their doctrine that disruption of causality is impossible.
- Refuting their statement that the human soul is a self-sustaining substance that is neither a body nor an accident.
- Refuting their assertion of the impossibility of the annihilation of the human soul.
- Refuting their denial of bodily resurrection and the accompanying pleasures of Paradise or the pains of Hellfire.
Beyond Heresy 
The three irreligious ideas are as follows:
- The theory of a pre-eternal world. Ghazali wrote that God created the world in time and just like everything in this world time will cease to exist as well but God will continue on existing.
- God only knows the universal characteristics of particulars - namely Platonic forms.
- Bodily resurrection will not take place in the hereafter only human souls are resurrected.
The late 11th century book brings out contradictions in the thoughts of philosophers about God and the universe, favoring faith instead. In some ways, it can be seen as a precursor to Søren Kierkegaard's Either/Or or Immanuel Kant's Critique of Pure Reason, where some even describe it as a "more incisive and decisive critique of metaphysics than that of Kant."
The Incoherence of the Philosophers is famous for proposing and defending the Asharite theory of occasionalism. Al-Ghazali wrote that when fire and cotton are placed in contact, the cotton is burned directly by God rather than by the fire, a claim which he defended using logic.
He explained that because God is usually seen as rational, rather than arbitrary, his behavior in normally causing events in the same sequence (i.e., what appears to us to be efficient causation) can be understood as a natural outworking of that principle of reason, which we then describe as the laws of nature. Properly speaking, however, these are not laws of nature but laws by which God chooses to govern his own behaviour (his autonomy, in the strict sense) - in other words, his rational will.
This is not, however, an essential element of an occasionalist account, and occasionalism can include positions where God's behavior (and thus that of the world) is viewed as ultimately inscrutable, thus maintaining God's essential transcendence. On this understanding, apparent anomalies such as miracles are not really such: they are simply God behaving in a way that appears unusual to us. Given his transcendent freedom, he is not bound even by his own nature. Miracles, as breaks in the rational structure of the universe, cannot occur, since God's relationship with the world is not mediated by rational principles.
Cosmology and Astronomy 
Al-Ghazali expresses his support for a scientific methodology based on demonstration and mathematics, while discussing astronomy. After describing the scientific facts of the solar eclipse resulting from the Moon coming between the Sun and Earth and the lunar eclipse from the Earth coming between the Sun and Moon, he writes:
Whosoever thinks that to engage in a disputation for refuting such a theory is a religious duty harms religion and weakens it. For these matters rest on demonstrations, geometrical and arithmetical, that leave no room for doubt.
In his defense of the Asharite doctrine of a created universe that is temporally finite, against the Aristotelian doctrine of an eternal universe, Al-Ghazali proposed the modal theory of possible worlds, arguing that their actual world is the best of all possible worlds from among all the alternate timelines and world histories that God could have possibly created. His theory parallels that of Duns Scotus in the 14th century. While it is uncertain whether Al-Ghazali had any influence on Scotus, they both may have derived their theory from their readings of Avicenna's Metaphysics.
Critical reception 
Ibn Rushd (Averroes) wrote a refutation of Al-Ghazali's work entitled The Incoherence of the Incoherence (Tahāfut al-Tahāfut) in which he defends the doctrines of the philosophers and criticizes al-Ghazali's own arguments. It is written as a sort of dialogue: Averroes quotes passages by al-Ghazali and then responds to them. This text was not as well received by the wider Islamic audience. In the 15th century, a refutation of Ibn Rushd’s arguments in Tahāfut al-Tahāfut was written by a Turkic scholar Mustafā Ibn Yūsuf al-Bursawī, also known as Khwājah Zādā (d. 1487), who defended al-Ghazali's views. This once again indicated to Islamic scholars the weakness of human understanding and the strength of faith.
Another less critical response to Al-Ghazali's arguments was written by Ibn Rushd's predecessor Ibn Tufail (Abubacer) as part of his Arabic philosophical novel, Hayy ibn Yaqzan (later translated into Latin and English as Philosophus Autodidactus). Ibn Tufail cites al-Ghazali as an influence on his novel, especially his views on Sufism, but was critical of his views against Avicennism. Ibn al-Nafis later wrote another novel, Theologus Autodidactus, as a response to Ibn Tufail's Philosophus Autodidactus, defending some of al-Ghazali's views.
Al-Ghazali's insistence on a radical divine immanence in the natural world has been posited  as one of the reasons that the spirit of scientific inquiry later withered in Islamic lands. If "Allah's hand is not chained", then there was no point in discovering the alleged laws of nature. For example:
...our opponent claims that the agent of the burning is the fire exclusively;’ this is a natural, not a voluntary agent, and cannot abstain from what is in its nature when it is brought into contact with a receptive substratum. This we deny, saying: The agent of the burning is God, through His creating the black in the cotton and the disconnexion of its parts, and it is God who made the cotton burn and made it ashes either through the intermediation of angels or without intermediation. For fire is a dead body which has no action, and what is the proof that it is the agent? Indeed, the philosophers have no other proof than the observation of the occurrence of the burning, when there is contact with fire, but observation proves only a simultaneity, not a causation, and, in reality, there is no other cause but God.
The Ottoman sultan Mehmed II (a.k.a. el-Fatih) once commissioned two of the realm's scholars to write a book summarizing the ideas of the two great philosophers as to who won the debate across time.
- "Avicenna", Encyclopedia Iranica, retrieved 2007-12-30
- Paul Edwards (1973), The Encyclopedia of Philosophy, MacMillan Publishing Company, Volume 3-4, p. 327
- Anwar, Sabieh (October 2008), "Is Ghazālī really the Halagu of Science in Islam?", Monthly Renaissance 18 (10), retrieved 2008-10-14
- Taneli Kukkonen (2000), "Possible Worlds in the Tahâfut al-Falâsifa: Al-Ghazâlî on Creation and Contingency", Journal of the History of Philosophy 38 (4): 479–502, doi:10.1353/hph.2005.0033
- Ahmad, Jamil (September 1994), "Ibn Rushd", Monthly Renaissance 4 (9), retrieved 2008-10-14
- "Myth 4. That Medieval Islamic Culture was Inhospitable to Science" in Ronald L. Numbers (ed.): Galileo Goes to Jail and Other Myths About Science and Religion, Harvard University Press, 2009, esp. pp. 39-40
- Sakir Kocabas (2006). Islam And Scientific Debate: Searching For Legitimacy. India: Global Vision Publicing House. p. 29.
- Aristotelianism in Islamic philosophy
- The Incoherence of the Philosophers Lahore, 1958, 1963 English translation by Sahib Ahmad Kamali. [large pdf file]
- Marmura: Al-Ghazali's The Incoherence of the Philosophers, (2nd ed.). Brigham Young University Press, 2002. A new English translation of tahfut al-falasifa includes the Arabic text. ISBN 0-8425-2466-5.
- The Incoherence of the Incoherence translation by Simon van den Bergh. [N.B.: This also contains a translation of most of the tahafut as the refutations are mostly commentary of al-Ghazali statements that were quoted verbatim.]
- Review of Tahafat al-Falasifa