The terms majhūra/mahmūsa denote a phonological correlation, generally held to correspond to the opposition between voiced/voiceless (e.g. Schaade 1911:13), or to that between lenis/fortis phonemes (for a discussion of the difference between these two oppositions, see Ladefoged and Maddieson 1996:95–99). Both terms were first used by Sībawayhi (d. 175/791) in his Kitāb (II, 405). He probably based his observations on earlier research by his predecessors. However, his teacher al-Xalīl ibn ʾAḥmad (d. 175/791) does not mention this classification in the Kitab al-ʿayn, although …