Of all the institutions of Islam the caliphate is the oldest, the most fundamental, and in essence the most enduring. For its history see CALIPHATE; the present subject is its origin and nature. Mahomet enjoyed absolute rule over his people as a divinely inspired and guided prophet. He led the public prayers; he acted as judge; he ruled. If he consulted with others or paid attention to public feeling or local usage, it was as a matter of policy; the ultimate decision lay with himself. He was the state. On his death a leader was put in his place of similar authority, though without the divine prophetic guidance. He was called the "successor" (_khalifa_, caliph) of the Prophet, later also the _amir-al-mu'minin_, commander of the faithful, and was elected by the Moslems, just as the Arab tribes had always elected their chiefs. He was thus an absolute ruler, but was democratically elected; and such is the essence of the caliphate among Sunnite Moslems to this day. For them it has been a matter of agreement (see MAHOMMEDAN LAW) from the earliest times that the Moslem community must appoint such a leader (see IMAM). The Shi`ites, on the other hand, hold that the appointment lies with God, and that God always has appointed, though his appointment may not always have been known and accepted. Their position may be called a legitimist one. Some few heretical sects have held that the necessity of a leader was based on reason, not on the agreement of the community. But, for all, the rule of the leader thus appointed is absolute, and all authority is delegated from him and, in theory, can be resumed by him at any time. Just as God can require unreasoning obedience from his creatures (his "slaves" in Arabic), so can the caliph, his representative on earth. But Abu Bekr, the first caliph, nominated his successor, Omar, and that nomination was accepted and confirmed by the people. So a second precedent was fixed, which was again carried a step farther, when Moawiya I., the first Omayyad caliph, nominated his son, Yazid I., as his successor, and caused an oath of allegiance to be taken to him. The hereditary principle was thus introduced, though some relics of the form of election persisted and still persist. The true election possible in the early days of the small community at Medina became first a formal acceptance by the populace of the capital; then an assertion, by the palace guard, of their power; and now, in the investiture of the sultans of the Ottoman Turks, who claim the caliphate, a formal ceremony by the `ulema (q.v.) of Constantinople. The Ottoman claim is based on an asserted nomination by the last Abbasid, who died in exile in Egypt in 1538, of the Ottoman sultan, Suleiman the Great, as his successor. Such a nomination in itself was a perfectly legal act, but in this case had a fatal flaw. It is an absolute condition, laid down in tradition, that the caliph must be of the tribe of Koreish (Quraish), that of the Prophet.