Religion

The primary concern of Muslim religious thinking has been the elaboration of the rules for living, including social and political life. The key concept here has been shari'a, the "path" God has laid out for believers to follow, involving the moral evaluation of actions as "obligatory," "recommended," "permitted," "discouraged," and "forbidden." The details of this are worked out in fiqh (literally "understanding") by qualified scholars, or ulema. The authoritative sources are the Koran and the sunna (the words and deeds of Muhammad, usually understood as protected from error; for Shiites the words and deeds of the imams are included), and the ulema engage in effort, ijtihad, to derive from these sources rules for particular situations. The Sunni view has generally been that whenever they come to a consensus on some issue, this is binding on future generations. Among Sunnis several traditions or "schools" of fiqh developed, of which four survive into the twenty-first century, the Hanafi, Maliki, Shafi'i, and Hanbali. Although there have been tensions among them in the past, they are now mutually recognized and in principle a Muslim should follow one of them. Twelver Shiites give less weight to consensus, and the currently dominant form of Twelver fiqh stresses the need to follow a living mujtihid (one qualified to practice ijtihad), or ayatollah. As a result, some ulema acquire a following and have considerable influence. While fiqh in principle covers all areas of life, in practice some areas have been more elaborated than others, and the degree to which fiqh is applied in practice has varied considerably with time and place.

Theology (kalam) in Islam arose, in a considerable measure, out of the challenge of Greek philosophy, which was still very much alive in a Christianized form in the areas the Muslims had conquered. The first major school of kalam was the Mu'tazila, who appear to have been influenced by disputations held with Jewish, Christian, and other scholars. Among their better-known views is the claim that the Koran is created and that humans have free will. Al-Ash'ari (873–935) used their rational methods to uphold the uncreated nature of the Koran and divine determination. Another school, that of al-Maturidi, was similar but somewhat less extreme on the last point. Over against all of these, the Hanbalis largely rejected the venture of kalam as an inappropriate probing into the divine. An attempt to impose Mu'tazilism as orthodoxy in the ninth century backfired and the Mu'tazila lost ground among Sunnis, though their ideas continued to be influential among Shiites.

Kalam sought to use reason to interpret revelation, but the philosophers sought to build on reason alone and saw themselves in the line of Plato and Aristotle. For them reason gave the purest knowledge but was only for an elite; revelation provided the same basic knowledge in symbolic and concrete form for ordinary people. The greatest of the philosophers was Avicenna (Ibn Sina; 980–1037), who developed a system designed to incorporate all experience and knowledge, from the physical to the psychological to the spiritual. For him reason at its highest level is a divine faculty that leads us to the vision of the divine. The more spiritual side of Avicenna was later developed in Iran into a kind of philosophical mysticism known as 'irfan, whose greatest proponent was Mulla Sadra (d. 1641), and which continues very much alive in the early 2000s. Conceptions drawn from philosophy are also central to the teachings of the Ismailis and most of the esoteric groups mentioned below.

More important than kalam or philosophy has been the Sufi movement. From the early centuries individuals such as Rabi'a al-Adawiya (d. 810), Abu Yazid Bistami (d. 874), and al-Hallaj (857/858–922) sought a more direct contact with God and expressed this in sometimes unconventional ways. From about the thirteenth century this developed into large-scale movements, turuq ("orders"), which provided spiritual and moral guidance and distinctive rituals (dhikr) designed to produce ecstasy. Later Sufi theoreticians made considerable use of philosophical concepts to express their views and experiences. The greatest of these was Ibn al-'Arabi (1165–1240), known for his doctrine of the "unity of being" (wahdat al-wujud) in which the Names of God correlate with the visible world in a kind of mutual dependence via a spiritual realm of prototypes.