Little is known about Muḥammed Raḍī al-Dīn Ibn Ḥasan al-Astarābādhī, the famous Arab grammarian who died about 1289, and even this date depends on whether the colophons of his two major works, the Sharḥ al-Shāfiya and the Sharḥ al-Kāfiya, offer reliable information. Indeed, for long one did not even know his name; he has generally been referred to as the ‘Star of the Imams’ in view of the authority ascribed to his treatises of Arabic. Although al-Astarābād hī followed in many respects the analyses advanced in the Kitāb by Sībawayhi (8th century), his works contain a number of important observations of his own. Thus he was the first to explain the phenomenon of rhotacism in Arabic, and analyzed the function of particular cases and demonstrative pronouns which had hitherto been unsolved in Arabic linguistic scholarship.