Ash'ari theology (Arabic: al-Ash'ariyya or al-Ash'ariyyun) is a school of Islamic speculative theology (kalam) founded in the early 10th century CE by Abu al-Hasan al-Ash'ari (c. 873-935 CE). It represents one of the principal Sunni theological traditions and developed as a systematic rational defense of classical Sunni doctrine against both the rationalist Mu'tazila school and the strict textualist (athari) approach of the Hanbalis. Ash'ari theology occupies a middle position: accepting the use of rational argument and philosophical method to defend revealed doctrine while subordinating reason to revelation on matters where the two appear to conflict.
Abu al-Hasan al-Ash'ari was himself a student of the Mu'tazila theologian al-Jubbai before publicly renouncing Mu'tazilism and aligning with the Hanbali tradition in doctrine, though not in method. He retained the rational and dialectical tools of kalam while rejecting the Mu'tazila's conclusions on divine attributes, human freedom, and the nature of the Quran. His school attracted major systematizers in subsequent centuries, including al-Baqillani (d. 1013), al-Juwayni (d. 1085), and al-Ghazali (d. 1111), who brought Ash'ari theology to its classical mature form. For a fuller account of its development, see Ash'ari Theology - History.
Ash'ari theology holds that God's attributes (sifat) are real and distinct from His essence, though not separate from it - a position navigating between the Mu'tazila view that attributes are identical with essence and the anthropomorphist readings it opposed. The school holds that God is the sole agent of all acts in the universe, with created beings possessing kasb (acquisition or appropriation) of acts rather than independent causal power - a doctrine with significant implications for discussions of free will and determinism. On scripture, Ash'aris hold that the Quran as the eternal speech of God is uncreated, while its physical expression in letters, ink, and sound is created - a distinction from both the Mu'tazili position (the Quran is created in all respects) and the strict Hanbali position (the Quran is uncreated in every sense). Ash'ari epistemology holds that certain knowledge is possible through sense perception, sound reasoning, and revelation, but that unaided reason has limits that revelation supplies.
Ash'ari theology became and remains the dominant theological school among Sunni Muslims in North Africa, the Levant, Egypt, South and Southeast Asia, and large parts of sub-Saharan Africa. It is closely associated with the Shafi'i and Maliki legal schools, though it has significant adherents among Hanafis as well. The Maturidi school, associated primarily with Central Asian and Turkish Hanafi communities, shares many Ash'ari commitments while differing on several points of epistemology and the scope of rational theology. Together, Ash'arism and Maturidism are often cited as constituting mainstream Sunni kalam.
Several doctrinal questions within and around Ash'ari theology remain subjects of intra-Muslim disagreement. The doctrine of kasb has been criticized by philosophers and theologians from multiple directions as either incoherent or insufficient to ground genuine human moral responsibility; see Kasb and Moral Responsibility - Debate. The relationship between Ash'ari theology and Sufism - particularly the synthesis attempted by al-Ghazali - is debated by scholars of Islamic intellectual history. Salafi and Hanbali critics argue that Ash'ari kalam introduces illicit innovation (bid'a) by applying philosophical categories to revealed doctrine; Ash'ari defenders argue the method is necessary to defend orthodoxy against rationalist challenges. See Permissibility of Kalam - Debate.