The Twelver Shia, or Ithna-'Ashariyya, is the largest of the Shia Muslim sects. They believe that legitimate Islamic leadership is vested in a line of descent starting with Muhammad's cousin and son-in-law, Ali, through Ali's two sons, Hasan and Husayn, and then through Husayn's descendants. These were the first 12 imams, or leaders of the Shia Muslim community. The Shia Muslims believe that Muhammad designated all 12 successors by name and that they inherited a special knowledge of the true meaning of the scripture that was passed from father to son, beginning with the Prophet himself. This family, along with its loyal followers and representatives, has political authority over the Shia Muslims.
In contrast to the Shias, the Sunnis believed that leadership was in the hands of the Muslim community at large. The consensus of historical communities, not the decisions of political authorities, led to the establishment of the four legal schools. In theory a Muslim could choose whichever school of Islamic thought he or she wished to follow and could change this choice at will. The respect and popularity that the religious scholars enjoyed made them the effective brokers of social power and pitched them against the political authorities.
After the first four caliphs, the religious and political authorities in Islam were never again united under one institution. Their usual coexistence was underscored by a mutual recognition of their separate spheres of influence and their respective duties and responsibilities. Often, however, the two powers collided, and invariably any social opposition to the elite political order had religious undertones.
In contrast to the legal-minded approach to Islam, Sufis emphasized spirituality as a way of knowing God. During the 9th century Sufism developed into a mystical doctrine, with direct communion or even ecstatic union with God as its ideal. One of the vehicles for this experience is the ecstatic dance of the Sufi whirling dervishes. Eventually Sufism later developed into a complex popular movement and was institutionalized in the form of collective, hierarchical Sufi orders.
While the Druze are not regarded as Muslims by other Muslims, they regard themselves as Muslims as well as carriers of the core of this religion. The origin of Druze is to a large extent from a group of Shi'is, the Isma'ilis, but they have diverged much, and the Koran does not seem to be a part of their religion.
The Druze call themselves muwahhidun, 'monotheists'.