Despite the common elements which hold it together, Islam is not and never has been an absolutely monolithic or homogeneous religion. Over the course of its history, it has given rise to many schools of thought and sectarian divisions as well as esoteric and mystical movements like Sufi sm. Very real and signifi cant divisions exist among Muslims today, just as they do among Jews, Christians, or Buddhists. Of these, the two most important branches of contemporary Islam are usually referred to in English as Sunnism and Shiism (and their adherents as Sunnites and Shi‘ites). A common misconception, based on these names, is that the difference between these two sects has to do with acceptance of the Sunna. Although Sunnites and Shi‘ites do disagree on numerous technical points of doctrine, ritual, and law, they both emphatically believe they are following the Sunna, and in general they do not have major disagreement about the basic principles and rituals of Islam. They use the same text of the Koran, believe in the same notion of God, venerate the same prophet, perform the same number of daily prayers (albeit with minor differences in the ritual), pray in the same direction and to the same God, fast the same number of days, etc. The fundamental divergence with Sunnism developed not over following the Sunna, but over questions of legitimate authority and leadership in Islam. Shi‘ism is itself a rather generic label applied to a number of related but distinct movements within Islam. At the heart of all of them, however, one fi nds the principle of “partisanship” in the sense of (1) veneration of the ahl-ol-bayt, the “People of the House” (i.e., the family of the Prophet), and (2) allegiance to certain members of the ahl-ol-bayt as Imam ( emâm ), the Shi‘ite term for the supreme leader of the Muslim community.

Sunnite Muslims also have great respect for the person of Mohammad, his family, and his descendants (known as sharif s or sayyids), and in earlier historical periods they also recognized a series of caliphs as actual or at least nominal leaders in Muslim affairs. The Shi‘ite conceptions of the ahl-ol-bayt and the Imamate are nonetheless unique in several respects. First of all, the Shi‘ites have a very restrictive view of how membership in the ahl-ol-bayt is constituted. Sunnites, for example, have generally understood the ahl-ol-bayt to include all of Mohammad’s wives (he had about fi fteen and as many as nine at one time); Shi‘ites reject this and in fact regard one of those wives, ‘Âesheh, as an inveterate enemy of the true ahl-ol-bayt. They believe that Mohammad himself defi ned the ahl-ol-bayt on an occasion when he spread his cloak around himself; his daughter, Fâtemeh; his cousin and son-in-law, ‘Ali b. Abi Tâleb; and his grandchildren, Hasan and Hosayn, while reciting a verse from the Koran: “God wishes to remove defi lement from you, People of the House, and to purify you completely.” 3 Mohammad, as a young orphan, had been cared for by ‘Ali’s father Abu Tâleb. Mohammad later reciprocated by virtually adopting ‘Ali, and ‘Ali had married Mohammad’s daughter Fâtemeh. Fâtemeh was the only one of Mohammad’s offspring to survive long enough to have children; thus, Mohammad’s bloodline lived on exclusively through the children of ‘Ali and Fâtemeh. Membership in the ahl-ol-bayt is limited to these fi ve people, the ahl-ol-kesâ (“People of the Cloak”), and their descendants. Their special charisma is attested by the Koranic verse speaking of their “purifi cation,” and the obligation of other Muslims to bless them, to show affection for them, and to confer certain material benefi ts upon them is confi rmed by other verses that emphasize the importance and sanctity of the “close of kin.” On the issue of leadership of the Muslim community, most Sunnites essentially accepted as legitimate the various individuals and dynasties that held the offi ce of caliph, while attributing a special aura of sanctity to the first four caliphs, known as the Râshedun (“Rightly Guided”). In accordance with the historical precedents, they eventually adopted the theory that membership in the Prophet’s tribe, Qoraysh, was one of the criteria of eligibility for the offi ce, which could be obtained through election or designation. Other Muslims took a more restrictive view and questioned the legitimacy of some of those who acted as caliphs. Some early groups associated with the Shi‘ites were apparently willing to extend the right to rule to members of the Prophet’s clan, the Banu Hâshim (which would have included the Abbasid caliphs as descendants of the Prophet’s uncle ‘Abbâs), or to the Tâlebid branch of that clan (i.e., ‘Ali’s brothers or his children by wives other than Fâtemeh).

For the Shi‘ites proper, however, eligibility for the Imamate was the exclusive prerogative of the ahl-ol-bayt and usually conferred through express designation by a previous Imam. The term Shi‘ism is derived from the Arabic word shi ’ a, meaning sect, faction, or party, and the earliest Shi‘ites were the “partisans” or “devotees” of ‘Ali. After Mohammad died, they expected ‘Ali to become the head of the Muslim community. In their view, ‘Ali was distinguished as the first male convert to Islam, a brave warrior, and an exemplary Muslim; moreover, he had been explicitly designated by Mohammad to be his successor in an oration delivered at a place called Ghadir Khomm. Instead, the Prophet’s clear and express will had been frustrated by the machinations of a faction which repeatedly conspired to exclude ‘Ali from power and give the caliphate to others, none of whom had any tie of blood kinship with Mohammad. ‘Ali was passed over for the offi ce three times, but he did eventually become caliph in the wake of a rebellion that had led to the murder of the third caliph, ‘Osmân, in 656. His authority was immediately contested by ‘Osmân’s relatives (especially Mo’âvieh, the governor of Syria and leader of the Umayyad clan) as well as others. A conspiracy among members of a dissident faction resulted in ‘Ali’s assassination in 661. ‘Ali’s son Hasan yielded his claim to rule to Mo’âvieh, first of the Umayyad caliphs, in a negotiated settlement. Hasan then withdrew to Medina, where he lived quietly until around 670, when, according to the Shi‘ites, he was treacherously murdered at the instigation of Mo’âvieh. After Mo’âvieh’s death in 680, the Shi‘ites of Kufa in Iraq invited Hasan’s younger brother Hosayn to lead a revolt against the umayyads. Despite the improbability of success and premonitions of his death, Hosayn set out for Iraq with his family and a small band of supporters. During the first days of the Islamic month of Moharram, they were surrounded by an umayyad army at a place called Karbalâ. Abandoned by the Kufans and cut off from water, Hosayn and his followers suffered terribly. They made their last stand on the tenth day of the month of Moharram, called ‘Âshurâ, and were annihilated. Hosayn was the last to fall, after being repeatedly wounded; he was then beheaded and his corpse trampled by horses. The 72 martyrs included not only Hosayn but his son, ‘Ali-Akbar; his nephew, Qâsem, a handsome young man killed mere hours after his wedding; and his brother, ‘Abbâs, the epitome of bravery and chivalry. Only one male member of Hosayn’s family survived the bloodbath, his young son ‘Ali-Asghar Zayn-ol-’Âbedin (d. ca. 712), who was lying sick in his tent. For Sunnites, these were essentially historical incidents—more tragic evidence of the evil and oppression spawned by confl ict and competition within the Muslim community. They represent much more than that in Shi‘ism. Psychologically, morally, and spiritually, as well as historically, the events culminating at Karbalâ were decisive in the formation of Shi‘ite thought and culture. After Karbalâ, the Shi‘ite movement continued to be pulled back and forth between the contrasting models of the apolitical passivity of Hasan, who was willing to yield his rights to avoid bloodshed and harm to the community, and the militant activism of Hosayn, who was willing to face certain death to stand up against injustice. This was refl ected in the most immediate problem, the question of leadership given the loss of so many members of the ahl-ol-bayt. The Shi‘ites began to split into subsects over questions related to which individual had been designated or should be accepted as Imam, how actively that individual should seek the political power that was rightfully his, and the nature and extent of his religious authority. One group broke away to recognize the Imamate of Zayd, son of ‘Ali Zayn-ol-’Âbedin, who led a revolt against the Umayyad caliphs in 740. The Zaydis had no dynastic principle or concept of designation in their theory of the Imamate; they held that any male descendant of Hasan or Hosayn could be Imam as long as he had the highest degree of religious knowledge and, like Hosayn, he declared and actively pursued his claim to the offi ce against oppressive and unqualifi ed rulers. Despite this emphasis on political activism, the Zaydis were quite moderate in other respects and barely distinguishable from Sunnites. More radical Shi‘ites, known as gholât (“extremists”), recognized various other individuals as Imam, often as leaders of very militant chiliastic movements. They were noted for their tendency to attribute almost divine qualities to the Imam, for dispensing with the need to conform to the usual ritual and legal requirements of Islam, and for their belief in unusual doctrines such as reincarnation.

The mainstream of the Shi‘ites, however, recognized as the fi fth and sixth Imams Mohammad Bâqer (d. 731) and Ja’far Sâdeq (d. 765). Neither of them advocated any violence or made any attempt to seize political power, and both concentrated on the development of a distinctly Shi‘ite school of religious law. Ja’far Sâdeq was particularly important as an architect of Shi‘ite jurisprudence, and many Shi‘ites consequently describe themselves as “Ja’fari” in their legal orientation. Another major division among the Shi‘ites developed when they disagreed over the succession to Ja’far Sâdeq. One group recognized his oldest son, Esmâ’il, as the seventh Imam (even though Esmâ’il had apparently predeceased Ja’far). These Isma’ili or Sabi’a (“Sevener”) Shi‘ites developed their own highly esoteric doctrinal system and eventually established the Fatimid caliphate in North Africa and Egypt (909–1171). Other Shi‘ites recognized the Imamate of Ja’far’s youngest son, Musâ Kâzem (d. 799). He was succeeded by the eighth Imam, Ali Rezâ, whom the Abbasid caliph Ma’mun proposed to make his heir but who died in 818 (poisoned, according to the usual view of the Shi‘ites) before this could come to pass. He was buried near the grave of Ma’mun’s father, the caliph Hârun-or-Rashid, and the religious shrine which grew up around his tomb formed the nucleus of the city of Mashhad and is today the most important religious monument in Iran. Imam Rezâ was succeeded by Mohammad Javâd (d. 835), ‘Ali Hâdi (d. 868), and Hasan ‘Askari (d. 874). The Shi‘ites continued to splinter into different factions during this period, and some claimed that Hasan ‘Askari had died childless, thus leaving no successor. One important group, however, insisted that Hasan had a young son, Mohammad, whom he had concealed in order to protect him from his enemies. This Twelfth Imam remained in “occultation” ( ghaybat ) and communicated with his followers only through a few “emissaries” until 941, the year of the “greater occultation,” when he cut off all contact with the world. The Shi‘ites who recognize his Imamate are thus often called the Twelvers ( Esnâ-ash ’ ariyeh ). In their belief, the Twelfth or Hidden Imam, the Imam of the Age ( Emâm-e Zamân ), did not die; he remains alive but in concealment even now and will ultimately emerge again as the Qâ’em (“the One who Arises”) and the Mahdi (Messiah), who is destined to spread Islam throughout the world and usher in the utopian era that precedes that end of the world. Consequently, the Imami Shi‘ites fervently pray for the imminent return of Mohammad Montazar (“the Expected One”): “Manifest to us, O God, Thy Representative, the descendant of the daughter of Thy Prophet, the namesake of Thy Apostle, that he may overthrow all that is vain and worthless and establish the truth for those who are worthy…O God, be merciful to the helpless, and take away grief and sorrow from this people by granting his presence, and hasten his appearance.” 4 Most Sunnites emphasize that Mohammad, while a prophet and an exemplary moral fi gure, was ultimately a human being without the kind of supernatural or godlike qualities Christians attribute to Jesus. Similarly, individual Muslims like ‘Ali or Hosayn might be regarded as exceptional, but only in terms of their piety and virtue. Sunnis also recognized the need for a successor to Mohammad, as exemplifi ed in the institution of the caliphate, but they generally limited the scope of this offi ce to political, economic, military, and legal affairs; religious authority came to be vested in the community and its religious scholars.

Shi‘ite groups went well beyond this, as the concept of the Hidden Imam makes quite evident. The Shi‘ites not only accorded a special political, moral, and legal status to certain members of the ahl-ol-bayt, they also often gave them a spiritual quality unlike that of any ordinary mortal. In the case of the Imami Shi‘ites, for example, Mohammad, Fâtemeh, and the Twelve Imams constitute the “Fourteen Infallibles” (known in Persian as the Châhârdah Ma ’ sum ), and both Imami religious scholars and popular religion ascribe the most extraordinary characteristics to them. They were created before the world itself out of a pure substance, either light or a heavenly clay, and are superior to all other created beings. They were born without physical blemish, and their births were accompanied by miraculous happenings and portents, as were their deaths. They themselves could work miracles; some spoke the language of animals, revivifi ed dead trees, raised the dead, turned stones into gold, and so forth. They were all absolutely sinless and fundamentally incapable of sinning or making a mistake. The historical record of them is but a pale indication of their spiritual and cosmic signifi – cance; in particular, the willing death of Hosayn in his struggle against evil was a sacrifi cial and redemptive act of the utmost importance. The Imamate was neither a temporal offi ce nor an elective one like the caliphate: God was required by His benevolence to place a supreme guide in the world for the benefi t of mankind, and the world could not exist for a moment without the presence of such an Imam. The Imams are the “proofs” or “lights” of God, the guardians of creation, and God’s direct representatives on earth. They, and they alone, have the special and secret knowledge (‘ elm ) necessary to understand the Koran, and indeed any aspect of religion, completely and perfectly. That, along with their intrinsic inability to sin make them infallible guides in all religious matters, and the faithful are thus absolutely obliged to recognize and obey the Imam in order to attain salvation.