Guillaume de Machaut (1300-1377), from Machaut in northern France, was a poet/musician and became a cleric, so some of his work is sacred. But he is best known for his secular music and was very influential on Chaucer. Machaut is known for his use of pan-isorhythm -- isorhythm appearing in all parts -- and his through-composed monophonic lais. He oversaw his own collected works, the six "Machaut Manuscripts," so we're beginning to move out of the generally anonymous medieval period with the "rise of the artist." In his Livre du voir dit (Book of the True Poem), Machaut amassed assorted poems, letters, and songs into a semi-autobiographical scrapbook dedicated to Péronne d'Armentières, a young woman with whom a much older Machaut was infatuated.
Machaut's Messe de Nostre Dame (Mass of Our Lady), composed in the 1350s or '60s is the only 14th-century complete setting of the Mass Ordinary attributable to a known composer -- what later would be called a Mass Cycle. Though the movements are not all unified by any particular theme, each movement is based on the appropriate chant for that part of the Mass, and Machaut uses isorhythm in each. Thus, the Kyrie is based on the plainchant Kyrie Cunctipotens Genitor Deus. This four-voice medieval polyphony is characteristic in its being very horizontally composed, line overlaid by line, rather than displaying the vertical sensitivity and even chord functions of later composition. Double leading-tone cadences are also distinctive.
Machaut works with the 14th-century formes fixes too. Je puis trop bien ma dame comparer is one of his 42 ballades: strophes with a refrain, a bit more melismatic than other forms. His Douce dame jolie is one of 33 virelais: following the pattern AbbaA. And Ma fin est mon commencement (My End Is My Beginning), one of his 22 rondeaux, is a clever composition (ABaAabAB) in which retrograde lines illustrate the text. 24 motets also survive.
Bonds, Mark Evan. A History of Music in Western Culture. Upper Saddle River, NJ: Prentice Hall, 2003.
Crocker, Richard. A History of Musical Style. NY: McGraw-Hill Inc., 1966.