The Ikhwān al-Ṣafāʾ (Brethren of Purity), the anonymous adepts of a tenth-century esoteric fraternity based in Basra and Baghdad, hold an eminent position in the history of science and philosophy in Islam due to the wide reception and assimilation of their monumental encyclopaedia, the Rasāʾil Ikhwān al-Ṣafāʾ (Epistles of the Brethren of Purity). This compendium contains fifty-two epistles offering synoptic accounts of the classical sciences and philosophies of the age; divided into four classificatory parts, it treats themes in mathematics, logic, natural philosophy, psychology, metaphysics, and theology, in addition to didactic fables.

The present volume is the third of this definitive series consisting of the very first critical edition of the Rasāʾil in its original Arabic, complete with the first fully annotated English translation. Prepared by Professor Owen Wright, Epistle 5: ‘On Music’ presents technical concepts such as rhythm, tone, and metre, alongside more subtle aspects such as the psychological applications drawn from the fourfold theory of humours and the correspondence of numeric proportions, which emphasize the Ikhwān’s view of music as ultimately spiritual in nature.