Imāmiyya holds that the theory of imāmate must rely on scriptural evidence and designation and that the Imām, the successor to Muḥammad, is in charge of all political and religious issues. The authority of the Imām includes some religious and social duties such as executing the legal punishments, collecting almsgiving, sustaining social order and declaring holy war. The fulfillment of these duties requires actual leadership of the Imām or his deputy. With the beginning of the great occultation in 329/941, there was an uncertainty among the Imāmiyya followers about who would uphold these responsibilities. In this period, Shīʿī ʿulamā began to undertake the duties of the Imām in order to overcome this uncertainty and to avoid the possible schism. In the beginning, this delegation of authority was limited to the religious sphere; but, later, its scope gradually became wider. This process of delegation of power, which covers a long process, needs to be examined in its various periods. In this study, this subject will be considered with special reference to the scholars of the fifth century of hijra (hijrī). An effort is made in this article to reveal how the issues of the Imām’s powers are discussed in the context of the problem of expanding or narrowing the authority of the scholars who played significant roles in systemization of Uṣūlī (rationalist) thought in the period after Shaykh al-Mufīd.