Aristoxenus (flourished 4th century bc) was a Greek Peripatetic philosopher, the first authority for musical theory in the classical world.
Aristoxenus was born at Tarentum (now Taranto) in southern Italy and studied in Athens under Aristotle and Theophrastus. He was interested in ethics as well as in music and wrote much, but most of his work is lost. Apart from his musical treatises, fragments remain of his reconstruction of the old Pythagorean ethics as well as of his biographies of Pythagoras, Archytas, Socrates, and Plato. His theory that the soul is related to the body as harmony is to the parts of a musical instrument seems to follow early Pythagorean doctrine. In musical theory, Aristoxenus held that the notes of the scale should not be judged by mathematical ratio but by the ear. His remaining musical treatises include parts of his Elements of Harmonics (edited by P. Marquard, 1868, and by H. Macran, 1902) and of his Elements of Rhythm (edited by R. Westphal, 1861 and 1893) that are extant. The fragments of his other works were edited by F. Wehrli in Aristoxenos, being part 2 of Wehrli’s Die Schule des Aristoteles; Texte und Kommentar (1945; “The School of Aristotle; Text and Commentary”).