Ars Nova: Jean de Muris

Treatise on Musical Intervals, by Jean de Muris

Jean de Muris was mentioned in the post on Ars Nova as the author of Ars novæ musicæ [New technique of music]. He did more than that, however: he was also a mathematician and philosopher, an astronomer, a colleague of Philippe de Vitry, a lecturer at the Sorbonne.

Born near Lisieux about 1300 (he died c. 1351), he studied at the University of Paris and spent a lot of his time there as well as at Evreux, Fontevrault and Mezières-en-Brenne. He wrote a few books—perhaps as many as five (we are not sure whether some were written by him, but similar style is a reason for ascribing some works to him).

There are over 150 manuscripts of copies of works attributed to Muris. At one point, a work that criticized the Ars Nova was considered to have been written by him, but later it was determined that someone else wrote it. Muris certainly approved of the new style in his works. One of these, the Quæstiones super partes musicæ ["Questions on the parts of music"], can be read (in Latin) here.

Here's a section in English:

What is music? Music is the mistress art of the arts, containing in herself the beginnings of all methods [...], confirmed in the nature of all things, remarkably internalized proportionally, delightful to the intellect, loved by the ear. Music gladdens the downcast, rewards the eager, thwarts the envious, comforts the weak, keeps awake the vigilant, awakens the sleepers, nourishes love, honors its possessor, if music, which was established at last for the praise of God, has pursued its just goal. [link, p.239]

This embodies the Ars nova, which brought formal music out of the Church and made it complex, expressive, and secular. 

Ars nova

from Italian manuscript J. IV.115,
an example of Ars Nova notation

Beginning in the early 1300s there was a change in musical style, an evolution from monophony (a single melody) to polyphony, in which two or more lines of melody intermingled. The result was to give music a richer, more expressive sound.

The Church didn't like it.

Pope John XXII rejected it (as he tried to reject elections of which he did not approve). The sacred monophonic chant of the Church was being mixed with secular tunes. Music was becoming "fancy" and "frivolous" in ways that did not suit the pope.

The new style caught on, however, and there was no turning back. Two books describing the new technique helped to spread the new ideas. They were Ars novæ musicæ [New technique of music] by Jean de Muris c. 1320, and Ars nova notandi [New technique of musical notation] by Philippe de Vitry in about 1322. Because of these titles, 20th century historians refer to this style and period of time in music (the 14th century) as the Ars Nova. This new style developed at the same time in France and Italy. In France, one of its greatest exemplars was the poet Guillaume de Machaut. A sample of his musical composition is found in this post.

Among the new forms of non-sacred music given to us by the Ars Nova are the Madrigal, usually a song of love for two voices, and the Ballad, a story with a non-religious theme which was meant to be sung in public. The music in the manuscript of the Roman de Fauvel is an example of Ars nova.