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.