Sunni Islam is the most prevalent denomination of Muslims worldwide. Islam, like other major religions, is defined by a set of core beliefs. Groups that maintain those beliefs can properly be called “Islamic,” even if they differ on other details. A sect that denies one or more cornerstone ideas might claim an Islamic title, but it cannot legitimately be considered Islamic. Sunni Islam is by far the most common form of Islamic religion, with Shia Islam a distant second and smaller sects a relatively tiny fraction. Some estimates claim as many as 90 percent of the world’s Muslims are Sunni, though 75—80 percent is more likely.
Because Muslims worldwide are primarily Sunni, this denomination is considered “mainstream” Islam. Beliefs associated with Sunni Islam are most frequently defended or debated in discussions of Muslim beliefs. Denominations such as Shia and Ahmadiyya, and offshoots of Islam such as Sufi and Druze, are most easily defined by their differences with Sunni Islam. Conversely, since Shia Islam is the second most common sect, it is frequently used to highlight Sunni Islam’s contrast with other denominations.
The split between Sunni and Shia Islam resulted from their approach to Muhammad’s son-in-law Ali. Sunni Islam believes the Islamic people are to be led by a caliph. This caliph, per Sunni doctrine, should be based on merit and consensus. For this reason, Sunni Islam views Ali as the fourth successor to Muhammad, preceded by Abu Bakr, Umar ibn Al-Khattab, and Uthman ibn Affan. Shia Islam, in contrast, believes in rule by an imam, a title Shiism ascribes by bloodline, making Ali the first imam of the Islamic people.
Consistent with that perspective, Sunni Islam has virtually no formal requirements for leadership. Those who speak or teach in a Sunni mosque are those their fellow Muslims deem most learned or capable to do so. The Sunni use of the term for a spiritual leader—imam—is informal, especially compared to its use in Shia Islam. Whoever is leading prayer or study, in whatever setting, is acting as an imam, according to the Sunni approach.
As in all forms of Islam, Sunnis consider the Qur’an to be the ultimate, infallible source of divine revelation. Unlike the Bible, however, the Qur’an is not primarily composed as a narration or dialogue. Rather, it is a collection of individual statements supposedly given to Muhammad by Allah. As such, Islamic doctrines and practices are mostly grounded in the use of hadith: oral traditions assembled into collections and used much like a second tier of scripture. The choice of which hadith to accept or reject is a major distinction between sects such as Sunni and Shia Islam.
Unlike other faiths, Islam makes little or no distinction between political, military, judicial, and religious spheres. The concept of “Islamic Law,” or sharia, applies to all aspects of life and culture. As a result, varied applications of oral traditions, a discipline called fiqh, led to the development of differing schools of Islamic law. In Sunni Islam, there are four major schools of law used to interpret sharia. These are Hanafi, Maliki, Shafi’i, and Hanbali. Each of these forms a different balance among the Qur’an, hadith, and the statements of religious scholars when defining day-to-day life.
The varied interpretations of sharia are important when discussing Islam’s relationship to terrorism. As expected, one can find subdivisions within any group, and each of those divisions has branches of its own. Most of what the world defines as “Islamic terrorism” is associated with a particular branch of Islam: Salafi, a subset of Wahhabi, itself a segment of Hanbali. Among Salafis, a minority believe in active pursuit of violence to achieve their goals. ISIS, Al Qaeda, and Boko Haram are all associated with this specific strain of Islamic theology. The overwhelming majority of Sunni Muslims have no close doctrinal connection to such practitioners of overt terrorism.