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.