This chapter discusses a treatise written by the Zaydī Imam al-Mutawakkil Bi-llāh Aḥmad b. Sulaymān (r. 532-566/1137-1170) or his judge Jaʿfar b. Aḥmad b. Abī Yaḥyā b. ʿAbd al-Salām (d. 573/1177-8) defending the Imam’s conduct on a range of issues which had attracted the vocal criticism of his opponents, particular the group known as the Muṭarrifiyya. Firstly, the treatise seeks to justify hiring ‘immoral’ military forces in a just war; in this case, non-Zaydī, nominally Ismāʿīlī or Sunnī, tribal forces, against fellow Zaydīs. Secondly, the treatise seeks to justify the use of violence as means to collect the maʿūna, a type of religiously justifiable war contribution tax. Relying on non-Zaydī mercenaries against his own Zaydī subjects, and seizing the war tax by force, engendered profound disagreement, sparking off criticism that required a comprehensive response.

One of the most enduring sources of conflict among Muslims is the question of who or what represents legitimate power and authority after the Prophet Muhammad. This introduction briefly examines the diverse answers that key representatives of the classical Islamic tradition offered to this controversial question. A concise overview of early Islamic political history is followed by a survey of Islamic thought on the subject of authority in the formative (seventh-ninth centuries) and classical periods (ninth-thirteenth centuries). This introduction presents the views of six major theological schools of the classical period: Ashʿarism (representative of Sunnism), Muʿtazilism, Ibadism, Twelver Shiʿism, Ismaʿilism, and Zaydism. Finally, this chapter discusses the classical Arabic texts that appear in English translation in this anthology as well as their respective themes, authors, and historical contexts.