al- Khalīl ibn Ahmad

Jalil ibn Ahmad, known as al-Jalil, was an Arab philologist born and deceased in Basra, around the years 718 and 790. He is considered the father of Arabic lexicography, and his name is also linked to the disciplines of prosody and musical metric, fields in which his work carried considerable weight.

Among his writings on music are the Kitāb al-nagham (Book on the «notes») and the Kitāb al-īqā‘ (Book on metre and rhythm). Neither has survived, although it is thought that they influenced the musical teaching of Ishāq al-Mawsilī and his school. The sources of his musical theory are not known with certainty: besides the Arab tradition, with Syriac, Byzantine and Persian elements, Indian ideas on musical metre may also have had some influence.

It is believed that he was not acquainted with the classical Greek theorists, nor did he have practical experience of music. His musical treatises were judged less favourably than his philological works by scholars such as al-Nazzam (d. 845) and al-Jahiz (d. 868).

His legacy rests above all on the idea, inherited from Antiquity and central to Arabic teaching, that musical metric is a discipline sister to prosody. This conception reappeared in the West in the Middle Ages, although this does not rule out that the Arabs transmitted it.