Guy of Saint-Denis, Tractatus de tonis

The Tractatus de tonis of Guy of Saint-Denis (written ca. 1300-10) differs from other treatises on plainchant in the depth of its analysis of the various tones into which chant was traditionally classified. The treatise of Guy of Saint-Denis is preserved as the concluding item in an anthology of texts about plainchant that Guy compiled (now London, British Library, MS Harley 281), beginning with some writings of Guido of Arezzo and a Cistercian tonary, but also including the Ars musice of Johannes de Grocheio and the Tractatus de tonis of Petrus de Cruce. Guy's treatise presents itself as a synthetic overview of both the theory and practice of plainchant in a way that combines the very practical reflection of Guido of Arezzo with ideas of more Aristoteleian inspired theorists such as Johannes de Grocheio and Peter of Auvergne.