Theogerus of Metz

Theogerus of Metz (c. 1050 – Cluny, 29 April 1120) was a music theorist from south-western Germany and a leading figure in the monastic reform of Hirsau. Probably of noble birth, he was trained in the liberal arts under Manegold of Lautenbach.

In 1073 he was a canon of St Cyriacus in Neuhausen, near Worms. In the late 1070s he entered Hirsau, a monastery observing Cluniac customs, where Abbot Wilhelm commissioned learned works from him, perhaps the Musica, around 1080. He was Abbot of St George from 1088 for thirty years, a charismatic leader who spread the Hirsau reform throughout southern Germany and Alsace. In 1117 he was elected Bishop of Metz, but the political power struggle that the office entailed undermined his health; he died of fever at Cluny, where he was buried. He was venerated as a saint in southern Germany during the twelfth century.

The Musica, despite its conservative content, is notable for its careful construction and for original contributions such as its division of the monochord, its musical proportions and its theory of the modes. Its organisation reflects Platonic epistemology: the first part treats the systems according to the immutable laws of nature, and the second treats the Gregorian repertory by mode, in the form of a tonary, according to the changeable rules of custom.

The work circulated chiefly among the monasteries linked to Hirsau and St George, and its surviving sources outnumber those of Hermannus Contractus and Wilhelm of Hirsau. The Vita Theogeri, written between 1138 and 1146 by Wolfger of Prüfening and based in part on eyewitness testimony, is fragmentary but is one of the most extensive biographies of any medieval theorist. It has been suggested that his musical theory may have inspired the peculiar allegorical interpretation of a dream vision that the Vita places at Amtenhausen between 1107 and 1110.