Modal rhythm

In medieval music, the rhythmic modes were set patterns of long and short durations (or rhythms). The value of each note is not determined by the form of the written note (as is the case with more recent European musical notation), but rather by its position within a group of notes written as a single figure called a "ligature", and by the position of the ligature relative to other ligatures. Modal notation was developed by the composers of the Notre Dame school from 1170 to 1250, replacing the even and unmeasured rhythm of early polyphony and plainchant with patterns based on the metric feet of classical poetry, and was the first step towards the development of modern mensural notation (Hoppin 1978, 221). The rhythmic modes of Notre Dame Polyphony were the first coherent system of rhythmic notation developed in Western music since antiquity.

Though the use of the rhythmic modes is the most characteristic feature of the music of the late Notre Dame school, especially the compositions of Pérotin, they are also predominant in much of the rest of the music of the ars antiqua until about the middle of the 13th century. Composition types which were permeated by the modal rhythm include Notre Dame organum (most famously, the organum triplum and organum quadruplum of Pérotin), conductus, and discant clausulae. Later in the century, the motets by Petrus de Cruce and the many anonymous composers, which were descended from discant clausulae, also used modal rhythm, often with much greater complexity than was found earlier in the century: for example each voice sometimes sang in a different mode, as well as a different language.

In most sources there were six rhythmic modes, as first explained in the anonymous treatise of about 1260, De mensurabili musica (formerly attributed to Johannes de Garlandia, who is now believed merely to have edited it in the late 13th century for Jerome of Moravia, who incorporated it into his own compilation) (Baltzer 2001). Each mode consisted of a short pattern of long and short note values ("longa" and "brevis") corresponding to a metrical foot, as follows (Reese 1940, 207–209):

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