Response: This question was answered by one of their Sheikhs, Muhammad bin An-Nu’man, who they nicknamed Al-Mufeed, when he said the Shiites are: “followers of Ali (Allah be pleased with him) by way of allegiance, believing in his imamate after Rasulullah Sallallahu Alayhi Wasallam without severance (1) and repudiating the imamate of those who preceded him on the seat of Khilafah, with the belief of accepting that for them but not in the spirit of followership for anyone of them (2)”. (3)
Whenever the word “Shiite” is mentioned nowadays, it refers solely to the twelver sect (4). This is because they make up the highest population amongst the Shiites in Iran, Iraq, Syria, Lebanon, Gulf countries and many other places today. Also is the fact that their sources of hadith and narrations encompass the views of most of the other Shiite sects that emanated in the epochs of history.
(1) This depicts that an imamate Shiite is one who believes that Ali (Allah be pleased with him) is the Khalifah immediately after the Prophet (PBUH) without interruption. This is based on the belief of the Shiites that repudiates the legitimacy of the Khilafah of Abubakr, Umar and Uthman (Allah be pleased with them all). Thus, in the light of the words of this Sheikh, Al-Mufeed, Shiism is an adjective suitable only for those who believe in the Imamate of Ali (Allah be pleased with him) uninterrupted from the death of the Prophet (PBUH) until his death.
(2) According to him, Ali (Allah be pleased with him) was a follower to the three Khulafah only in the exterior, while in the interior they were actually his followers. In his view, Ali’s followership to them was not on the precept of emulation, rather it was on that of Taqiyyah (i.e. concealment). This means that his followership to the Khulafa was not in the precept of internal belief, but was merely in the form of external conformity.
(3) Awaa’il al-Maqaalaat fee Al-Madhaahib Al-Mukhtaarah p. 35, Chapter: Speech on the Difference between Shiite being attributed to Shiism and Mu’tazilites (the Isolators, who made a certain theological school of thought in Islamic history) being worthy of the name I’tizaal (Isolation) authored by their Sheikh Al-Mufeed (D 413 AH)
(4) This was mentioned by Hussein An-Noori At-Tabrasi (D 1320) in his book “Khaatimat Mustadrik Al-Wasaa’il” Vol. 1 p. 119