According to al-Mufid, there is an absolute necessity for prophets, since in order to know God and moral principles man needs revelation, and he noted that "every apostle (rasul) is a prophet but every prophet (nabi) is not an apostle".
On a number of occasions al-Mufid was a critical of his teacher, Al-Shaykh al-Saduq, and his Tashih al-Itiqadat was a correction of al-Saduq's Risalat al-Itaqadat.