Abu Hamid Muhammad ibn Muhammad al-Ghazali (1058-1111 CE) was a Persian Muslim theologian, jurist, philosopher, and mystic widely regarded as one of the most influential thinkers in Islamic intellectual history. Born in Tus (in present-day Iran), he wrote extensively in Arabic and Persian across disciplines including Islamic jurisprudence (fiqh), philosophy (falsafa), theology (kalam), and Sufi spirituality. His work stands at a pivotal juncture in medieval Islamic thought, engaging critically with Greek-derived philosophy while defending what he understood as orthodox Sunni theology.
Al-Ghazali studied under the prominent Ash'ari theologian al-Juwayni and rose to become head of the Nizamiyya madrasa in Baghdad - then the most prestigious academic institution in the Islamic world - at approximately age 33 (c. 1091 CE). In 1095 CE, he underwent a spiritual crisis that led him to abandon his position, withdraw from public life, and spend years as a wandering Sufi. He later returned to teaching before his death in Tus in 1111 CE. A fuller account of his life and intellectual development can be found on the Al-Ghazali History page.
His most celebrated work, Ihya' 'Ulum al-Din (The Revival of the Religious Sciences), is a comprehensive guide to Islamic ethics, worship, and spiritual development. His philosophical treatise Maqasid al-Falasifa (The Aims of the Philosophers) summarized the views of Islamic Aristotelians such as al-Farabi and Ibn Sina, followed by Tahafut al-Falasifa (The Incoherence of the Philosophers), which systematically critiqued their metaphysical claims. His autobiography, Deliverance from Error (al-Munqidh min al-Dalal), remains a primary source for understanding his intellectual and spiritual trajectory.
Al-Ghazali's Tahafut al-Falasifa argued that the Islamic Aristotelians had made claims - including the eternity of the world, God's ignorance of particulars, and the non-physical nature of resurrection - that were not only philosophically unsupported but constituted heresy under Islamic law. He identified twenty points of error, three of which he regarded as serious enough to warrant a charge of unbelief (kufr). This work prompted a famous rebuttal by the Andalusian philosopher Ibn Rushd (Averroes), who wrote Tahafut al-Tahafut (The Incoherence of the Incoherence) in response. Whether al-Ghazali succeeded in refuting Aristotelian cosmology or merely raised epistemological objections remains a subject of scholarly debate; see Al-Ghazali and Philosophy - Debate.
In theology, al-Ghazali worked within the Ash'ari school, which held that God's will is the direct and immediate cause of all events, with no necessary causal connection between created things - a position known as occasionalism. His articulation of this view influenced subsequent Islamic theology substantially.
Al-Ghazali's critique of Aristotelian natural philosophy has been linked by some historians to a broader cooling of speculative natural science in the medieval Islamic world, though this claim is contested. Others argue that Islamic scientific activity continued robustly after his death and that the causes of any later decline were institutional, political, and economic rather than theological. His relationship to Islamic astronomy is examined on the Heliocentrism - Islamic Astronomy Viewpoint page.
Al-Ghazali is credited with giving Sufi spirituality a firmer grounding in orthodox Sunni theology and law, integrating mystical practice with the formal requirements of Islamic jurisprudence. Some scholars view him as having legitimized Sufism within mainstream Islam; others argue he reshaped it into a form more compatible with Ash'ari theological constraints. His influence on later Sufi orders was substantial.
There is broad scholarly consensus that al-Ghazali was a major figure in medieval Islamic intellectual history and that his work significantly shaped the subsequent development of Sunni theology and ethics. The extent and character of his influence on Islamic philosophy and natural science remain actively debated among historians. See Al-Ghazali - Historiography Consensus.