Ars cantus mensurabilis

Ars cantus mensurabilis (Latin for the art of the measurable song) is a musical treatise from the mid-13th century, c. 1260–1280 (Medieval Period) written by German music theorist Franco of Cologne The treatise was written shortly after De Mensurabili Musica, another musical treatise of the 13th century by Johannes de Garlandia, which summarised a set of 6 rhythmic modes in use at the time. Ars cantus mensurabilis was the first treatise to suggest that individual notes could have their own rhythmic durations. This new rhythmic system was the foundation for mensural notation system and the ars nova style.