There are moments in music history, like all history, that stand as dividing lines. Once they happened, nothing could ever be the same.
One such moment was the writing of French theorist, poet, philosopher and composer Philippe de Vitry. In 1322, de Vitry wrote a treatise on music that forever changed the way music was written and expressed. It was entitled Ars Nova notandi, a new technique in writing music. We use this moment as the line to divide two eras of music; everything before we call Ars Antiqua, which means old art, and everything after we call Ars Nova, or new art.
The differences in the music of these writing techniques are subtle to our modern ears, but the innovations of de Vitry’s new system allowed for greater rhythmic freedom and expression to the composer. A good analogy would be the use of perspective in the visual arts; the use of foreground and background. No longer were all of the voices in music on the same rhythmic plane, they now had greater independence from each other.
One of the most prominent composers of the Ars Nova style was Guillaume De Machaut, another French poet and composer who was a little younger than de Vitry.
His work, Messe de Nostre Dame, is earliest complete mass we know of that was written by a single composer. This is significant because it stands as an example of music taking on the personality of an individual. Machaut used the tools of the Ars Nova to create a work that was unified and expressive. He put his stamp on it and made it human. This was not a work written to simply be a tool of worship in a church service; it stands as an object of art by itself, an expression of an individual. That’s what the innovations of de Vitry and Ars Nova allowed.