The fact that Classical Arabic uses vowel changes to indicate grammatical information such as aspect, voice, and number was observed very early by the Arabic scholars of the ‘Classical’ tradition (10th–15th centuries); it is discussed in the so-called taṣrīf (ṣarf) part of Arabic grammars (Ibn Jinnī, Munṣif, Ibn al-Hājib, Ibn as-Sarrāj, Ibn ʿUṣfūr, Mumtiʿ, Ibn Yaʿīš, Šarḥ al-Mulūkī). The word ‘apophony’ (or Ablaut) was first used by Grimm (1819) to refer to context-free, morphologically meaningful vowel alt…