A total of about 70 works can be attributed to al-Ghazali. He is also known to have written a
fatwa against the
Taifa kings of
al-Andalus, declaring them to be unprincipled, not fit to rule and that they should be removed from power. This fatwa was used by
Yusuf ibn Tashfin to justify his conquest of al-Andalus.
Incoherence of the Philosophers Al-Ghazali's 11th-century book titled
Tahāfut al-Falāsifa ("Incoherence of the Philosophers") marked a major turn in Islamic
epistemology. The encounter with
skepticism led al-Ghazali to investigate a form of theological
occasionalism, or the belief that all causal events and interactions are not the product of material conjunctions but rather the immediate and present will of God. In the next century,
Ibn Rushd (or
Averroes) drafted a lengthy rebuttal of al-Ghazali's
Incoherence entitled
The Incoherence of the Incoherence; however, the epistemological course of Islamic thought had already been set. Al-Ghazali gave as an example of the illusion of independent laws of cause the fact that cotton burns when coming into contact with fire. While it might seem as though a natural law was at work, it happened each and every time only because God willed it to happen—the event was "a direct product of divine intervention as any more attention grabbing miracle".
Averroes, by contrast insisted while God created the natural law, humans "could more usefully say that fire caused cotton to burn—because creation had a pattern that they could discern." The
Incoherence also marked a turning point in Islamic philosophy in its vehement rejections of
Aristotle and
Plato. The book took aim at the
Falāsifa, a loosely defined group of Islamic philosophers from the 8th through the 11th centuries (most notable among them
Avicenna and
al-Farabi) who drew intellectually upon the
Ancient Greeks. The influence of Al-Ghazali's book is still debated. Professor of Arabic and Islamic Science
George Saliba in 2007 argued that the decline of science in the 11th century has been overstated, pointing to continuing advances, particularly in astronomy, as late as the 14th century. Professor of Mathematics Nuh Aydin wrote in 2012 that "it is a widespread belief among orientalists that one of the major factors, if not the single most important reason, for the decline of science in the Islamic world after its golden age is al-Ghazali's attack on
philosophers". The attack peaked in his book
Incoherence, whose central idea of theological
occasionalism implies that
philosophers cannot give rational explanations to either metaphysical or physical questions. The idea caught on and nullified the critical thinking in the Islamic world. On the other hand, author and journalist
Hassan Hassan in 2012 argued that while indeed scientific thought in Islam was stifled in the 11th century, the person mostly to blame is not al-Ghazali but
Nizam al-Mulk.
The Revival of Religious Sciences (Iḥyāʾ ʿUlūm al-Dīn) Another of al-Ghazali's major works is
Iḥyāʾ ʿUlūm al-Dīn (
The Revival of Religious Sciences). It covers almost all fields of Islamic sciences:
fiqh (Islamic
jurisprudence),
kalam (
theology) and
sufism. It contains four major sections:
Acts of Worship (),
Norms of Daily Life (),
The Ways to Perdition () and
The Ways to Salvation (). The became the most frequently recited Islamic text after the Qur'an and the hadith. Its great achievement was to bring orthodox Sunni theology and Sufi mysticism together in a useful, comprehensive guide to every aspect of Muslim life and death. The book was well received by Islamic scholars such as
Nawawi who stated that: "Were the books of Islam all to be lost, excepting only the Ihya', it would suffice to replace them all." This reception, however, was not universal as the book was burned in Almoravid Spain in 1109 and 1143 as al-Ghazali criticised the
fuqaha for meddling in politics and due to al-Ghazali's
syncretism and support of Sufism. Allegedly, being outraged upon hearing of the burning of his book, al-Ghazali foretold the rise of the Almohad dynasty and invested its founder
Ibn Tumart with the duty to overthrow the Almoravid rule.
The Alchemy of Happiness The Alchemy of Happiness is a rewritten version of
The Revival of the Religious Sciences. After the existential crisis that caused him to completely re-examine his way of living and his approach to religion, al-Ghazali put together
The Alchemy of Happiness. The first chapter primarily focuses on how one can develop himself into a person with positive attributes and good personal characteristics . The second chapter has a more specific focus: sexual satisfaction and
gluttony. In it, al-Ghazali recounts how, once a crisis of
epistemological skepticism had been resolved by "a light which God Most High cast into my breast ... the key to most knowledge," he studied and mastered the arguments of
kalam,
Islamic philosophy, and
Ismailism. Though appreciating what was valid in the first two of these, at least, he determined that all three approaches were inadequate and found ultimate value only in the mystical experience and insight he attained as a result of following
Sufi practices.
William James, in
Varieties of Religious Experience, considered the autobiography an important document for "the purely literary student who would like to become acquainted with the inwardness of religions other than the Christian" because of the scarcity of recorded personal religious confessions and autobiographical literature from this period outside the Christian tradition.
Works in Persian Al-Ghazali wrote most of his works in
Persian and in
Arabic. His most important Persian work is ''
Kimiya-yi sa'adat'' (The Alchemy of Happiness). It is al-Ghazali's own Persian version of ''Ihya' 'ulum al-din'' (The Revival of Religious Sciences) in Arabic, but a shorter work. It is one of the outstanding works of 11th-century-Persian literature. The book was published several times in
Tehran by the edition of Hussain Khadev-jam, a renowned Iranian scholar. It is translated to
English,
Arabic,
Turkish,
Urdu,
Azerbaijani and other languages. Another authentic work of al-Ghazali is the so-called "first part" of the Nasihat al-muluk (Counsel for kings), addressed to the Saljuqid ruler of Khurasan Ahmad b. Malik-shah Sanjar (r. 490-552/1097-1157). The text was written after an official reception at his court in 503/1109 and upon his request. Al-Ghazali was summoned to Sanjar because of the intrigues of his opponents and their criticism of his student's compilation in Arabic, al-Mankhul min taʿliqat al-usul (The sifted notes on the fundamentals), in addition to his refusal to continue teaching at the Nizamiyya of Nishapur. After the reception, al-Ghazali had, apparently, a private audience with Sanjar, during which he quoted a verse from the Quran 14:24: "Have you not seen how Allah sets forth a parable of a beautiful phrase (being) like a beautiful tree, whose roots are firm and whose branches are in Heaven." The genuine text of the Nasihat al-muluk, which is actually an official epistle with a short explanatory note on al-Manḵul added on its frontispiece. The majority of other Persian texts, ascribed to him with the use of his fame and authority, especially in the genre of Mirrors for Princes, are either deliberate forgeries fabricated with different purposes or compilations falsely attributed to him. The most famous among them is Ay farzand (O Child!). This is undoubtedly a literary forgery fabricated in Persian one or two generations after al-Ghazali's death. The sources used for the forgery consist of two genuine letters by al-Ghazali's (number 4, in part, and number 33, totally); both appear in the
Fazaʾil al-anam. Another source is a letter known as
ʿAyniya and written by Muhammad's younger brother Majd al-Din Ahmad al-Ghazali (d. 520/1126) to his famous disciple ʿAyn al-Quzat Hamadani (492-526/1098-1131); the letter was published in the
Majmuʿa-yi athar-i farsi-yi Ahmad-i Ghazali (Collection of the Persian writings of Ahmad Ghazali). The other is ʿAyn al-Quzat's own letter, published in the
Namaha-yi ʿAyn al-Quzat Hamadani (Letters by ʿAyn al-Quzat Hamadani). Later,
Ay farzand was translated into Arabic and became famous as
Ayyuha al-walad, the Arabic equivalent of the Persian title. The earliest manuscripts with the Arabic translation date from the second half of the 16th and most of the others from the 17th century. The earliest known secondary translation from Arabic into Ottoman Turkish was done in 983/1575. In modern times, the text was translated from Arabic into many European languages and published innumerable times in Turkey as Eyyühe'l-Veled or Ey Oğul. A less famous Pand-nama (Book of counsel) also written in the genre of advice literature is a very late compilatory letter of an unknown author formally addressed to some ruler and falsely attributed to al-Ghazali, obviously because it consists of many fragments borrowed mostly from various parts of the Kimiya-yi saʿadat. == Influence ==