The Ismailis, among whom are the followers of the Aga Khan, rose to prominence during the fourth Islamic/tenth Christian century. They developed a remarkably successful intellectual programme to sustain and support their political activities, promoting demands of Islamic doctrine together with the then newly imported sciences from abroad. The high watermark of this intellectual movement is best illustrated in the writings of the Ismaili theoretician Abu Yaqub al-Sijistani. Using both published and manuscript writings of al-Sijistani that have hitherto been largely hidden, forgotten or...