This literally means 'to lead '; al-imam means 'the leader'. In Islamic terminology al-imamah (Imamate) means 'universal authority in all religious and secular affairs, in succession to the Prophet'
[al-'Allamah al-Hilli: al-Babu 'l-hadi 'ashar, Eng. tr. W. M. Miller, p. 62; Mughniyyah: Falsafat Islamiyyah, p. 392]
al-Imam means 'the man who, in succession to the Prophet, has the right to the absolute command of the Muslims in all religious and secular affairs '.
The word al-khilafah means 'to succeed' and al-khalifah means 'the successor'. In Islamic terminology al-khilafah and al-khalifah practically signify the same meanings as al-ima'mah and al-ima'm repectively.
al-Wisayah means ' the executorship of the will', and al-wasiyy means 'the executor of the will'. Their significance in Muslims' writings is the same as that of al-khilafah (caliphate) and al-khalifah (caliph).
The question of Imamate and caliphate has torn the Muslim community apart and has affected the thinking and philosophy of the different groups so tremendously that even the belief in Allah (at-tawhid) and the prophets (an-nubuwwah) could not escape from this divergence of views.
This is the most debated subject of Islamic theology. Muslims have written thousands upon thousands of books on caliphate. The problem before me is not what to write; it is what not to write. In a small work such as this section - Islamic Unity, one cannot touch on all the various aspects of this subject, let alone go into detail on even those topics which are described therein. This provides only a brief outline of the differences regarding the caliphate.