Chapter 5 provides an overview of the history and development of Muslim schools of thought, the Murjiʿa and Muʿtazilites, so called because they reach their intellectual “maturity” in the ʿAbbāsid era where the material conditions of the period allow for a flourishing of intellectual activity (and a cessation of the revolutionary fervor that animated the sectarian movements of the Umayyad period). It stresses how the image of the Murjiʾa changes dramatically as the movement developed, and those who wrote about it found it convenient for their own purposes. The chapter then investigates the Muʿtazilite movement, beginning with their murky origins among the Umayyad-era Qadariyya up to their flourishing in the ʿAbbāsid period. Abū al-Hudhayl’s “five principles” are employed to give an overview of some of the main topics that engaged the Muʿtazilites.