What innovation is attributed to Machaut in music composition?

The innovation attributed to Machaut in music composition is primarily the combination of sacred and secular texts. Machaut was a pivotal figure in the transition from the Medieval to the early Renaissance period in music, and his work exemplified the blending of genres that was characteristic of this time. He was known for setting both religious texts, such as mass settings, and secular poetry, particularly in his chansons. This dual focus not only enriched the musical landscape of his time but also influenced future composers in how they approached text setting and thematic portrayal in music.

By merging the sacred with the secular, Machaut expanded the expressive possibilities of music, allowing for a greater emotional range and depth in his compositions. This blending can be seen in his use of musical forms that were appropriate for both types of texts, showcasing his versatility and creativity as a composer.

In relation to the other choices, while he did contribute to the development of polyphony, this was established well before his time. Instrumental solos became more prominent after Machaut's era, and his rhythmic innovations did not strictly adhere to traditional rhythms but rather explored more complex and varied rhythmic patterns. Thus, the combination of sacred and secular texts stands out as Machaut’s significant innovation in music composition.