The growing views of the intellectual movements, contemporary and rival to Sheikh Mofid (d. 413), regarding the superiority of Imam Ali are among the reasons for the writing of al-Irshad by that prominent imami theologian. In that time, despite a belief in Imam Ali's superiority, some of the discourses emphasized the legitimacy of the caliphate of the earlier figures by issuing the permission for the imamate of the subordinate person. Some others, despite their sympathy with imamiya on the necessity of the imam's superiority, believed that the superiority of the caliphs coincided with their historical order of caliphate; thus, they maintained that Imam Ali lacked superiority. In such an atmosphere, Sheikh Mofid composed al-Irshad by relying on his own theological opinions regarding imamate, proving the necessity of Imam Ali's superiority, making use of historical evidences and – sometimes – the opinions in the rival discourse in order to preserve the identity of the imami discourse. Therefore, identifying the parameters dependent on the Imam's superiority, mentioned by Sheikh Mofid in his book for proving Imam Ali's priority and rejecting the legitimacy of the previous caliphs, is the main concern in the present study. The findings of this descriptive-analytical study show that Sheikh Mofid deals with this important goal by making use of parameters such as highlighting Imam's status and practices, rejecting the status and practices of the previous caliphs (especially the two Sheikhs), and rejecting the companions' choice of the superior or the most virtuous leader.