Chapter three presents the views of the prominent Zaydī scholar al-Nāṭiq bi-’l-Ḥaqq Abū Ṭālib al-Hārūnī (d. 424/1033) in his Theoretical Underpinning of the Imamate (al-Diʿāma fi tathbīt al-imāma). Al-Nāṭiq draws on key Muʿtazili concepts and technical terms to propound a comprehensive argument in defence of the Zaydi conception of the imamate while refuting the doctrines of his Muʿtazili, Sunni, and Twelver Shiʿi peers. Against the Twelvers, al-Nāṭiq sought to refute three assumptions: the rational necessity of the imamate, the necessity of infallibility, and the necessity of divine designation (naṣṣ). He was intimately familiar with Twelver doctrines because his father and larger family identified as Twelvers. Al-Nāṭiq’s Theoretical Underpinning became as a seminal work on the Zaydi imamate.

Chapter four presents the views of the prominent Twelver Shiʿi scholar Muḥammad b. al-Ḥasan al-Ṭūsī (d. 460/1067). Like other Zaydis and Twelver Shiʿis of his era, al-Ṭūsī incorporated Muʿtazili doctrines into his writings on theology. His seminal work on the imamate is an abridgment of The Curative Book (al-Shāfī) by al-Sharīf al-Murtaḍā (d. 436/1044). Al-Ṭūsī’s work was similarly entitled The Curative Book on the Imamate: A Paraphrastic Rendering (Talkhīṣ al-Shāfī fī al-imāma) and reflected his own understanding of the text. Both al-Murtaḍā and al-Ṭūsī ground the Twelver conception of the imamate in Bahshamī Muʿtazili theology to argue for the rational necessity of the imamate and its necessity according to the Qurʾan and hadith. They accomplish the former by tying the existence of imams to the existence of moral obligations (taklīf) in the sight of God. As long as moral obligations exist, humans need imams who function as a type of divine assistance (luṭf).