Allāh. Arab. for God: if from earlier Semitic languages (e.g. Aram., alāhā), perhaps the God (Arab. al = ‘the’). Before the birth of Muḥammad, Allah was known as a supreme, but not the sole, God. Muḥammad became aware, early in his life, of conflict between religions and of contest, therefore, between ‘gods’. From his experience in the cave on Mount Ḥirāʾ (with possible influence from ḥanīfs), Muḥammad saw that if God is God, it is God that God must be: there cannot be division of God into separate or competing beings. From this absolute realization of tawḥīd (oneness of God), the whole of Islam is derived—as indeed is the whole of the created order. Hence the fundamental mark of islām (allegiance to God) is the shahāda, lā ilāha illā Allāh… This involves Islam in necessary conflict with polytheism, idolatry, and what was taken to be the Christian understanding of the Trinity.

In the Qurʾān, Allah is described by many epithets, contributing eventually to the ninety-nine beautiful names of God. Controlling all are the two descriptions (occurring in the basmala) rahmān (merciful) and rahīm (compassionate). In later Islam, fierce arguments developed: about the status of the attributes of God (too much status would confer ontological, or truly existent, reality on them, thus converting them into something like independent parts of God); about anthropomorphic statements (e.g. the Qurʾān says that God sits on a throne: to take this literally would limit God in space. This particular issue was resolved agnostically by saying that he does so, bilā kaifa wa lā tashbīh, without knowing how and without comparison, SC. with our way of sitting; and also by tanzīh); and about the power of God to determine all things. This last issue is focused on the term qadar. The Qurʾān emphasizes the absolute power of God to determine all things, which suggests strong predestination (as held e.g. by the Jabriya); in that case, how can humans be held accountable for their deeds and be judged accordingly (the question raised e.g. by the Muʿtazilites)? The eventual solution (at least for the Ashʿarites (acquisition) was formulated in the doctrine of iktisāb, see AL-ASHʿARI).

Theological and rational reflection on God is complemented, in Islam, by the direct and immediate relation of the believer with God, above all in salāt: to everyone, God is closer than the vein in the neck (50. 16). This close and direct relation to God led into the cultivation of the experiential awareness of God, which culminated in Sūfism.

For the controlling and all-important Sūra of Unity (112), which, if a Muslim says it with conviction, leads to the shedding of sins as a tree sheds its leaves in autumn, see TAWḤĪD.