The majority of the Shi'ites, from whom the previously mentioned groups have branched out, are Twelve-Imam Shi'ites, also called the Imamites. As has already been mentioned, the Shi'ites came into being because of criticism and protest concerning two basic problems of Islam, without having any objections to the religious ways which through the instructions of the Prophet had become prevalent among their contemporary Muslims. These two problems concerned Islamic government and authority in the religious sciences, both of which the Shi'ites considered to be the particular right of the Household of the Prophet.
The Shi'ites asserted that the Islamic caliphate, of which esoteric guidance and spiritual leadership are inseparable elements, belongs to Ali and his descendants. They also believed that according to the specification of the Prophet the Imams of the Household of the Prophet are twelve in number. Shi'ism held, moreover, that the external teachings of the Quran, which are the injunctions and regulations of the Shari'ah and include the principles of a complete spiritual life, are valid and applicable for everyone at all times, and are not to be abrogated until the Day of Judgment. These injunctions and regulations must be learned through the guidance of the Household of the Prophet.
From a consideration of these points it becomes clear that the difference between Twelve-Imam Shi'ism and Zaydism is that the Zaydis usually do not consider the imamate to belong solely to the Household of the Prophet and do not limit the number of Imams to twelve. Also they do not follow the jurisprudence of the Household of the Prophet as do the Twelve-Imam Shi'ites.
The difference between the Twelve-Imam Shi'ism and Isma'ilism lies in that for the latter the imamate revolves around the number seven and prophecy does not terminate with the Holy Prophet Muhammad. Also for them, change and transformation in the injunctions of the Shari'ah are admissible, as is even rejection of the duty of following Shari'ah, especially among the Batinis. In contrast, the Twelve-Imam Shi'ites consider the Prophet to be the "seal of prophecy" and believe him to have twelve successors and executors of his will. They hold the external aspect of the Shari'ah to be valid and impossible to abrogate. They affirm that the Quran has both an exoteric and an esoteric aspect.