An innovation in rhytmic notation that first appeared in Europe during the 13th century. It allowed for subdivision of longer notes into groups of two or three shorter notes. The ability to notate music using the mensural system led composers in the 14th and 15th centuries to develop higher degrees of polyphony in their music (Busse-Berger 2002, p. 628).
John of Garland set out one of the earliest mensural systems in De mensurabilis musica. His system consisted of six modes (Busse-Berger 2002, p. 629-30). Later developments by Jehan das Murs would lead to the use of mensuration signs placed at the beginning of sections of a piece to specify the subdivisions within that section (Busse-Berger 2002, p. 637). However, by the early 16th century, confusion over a multitude of mensuration systems would cause all of them to be abandoned in favor of fixed binary subdivisions of note values (Busse-Berger 2002, p. 655).