Polyphony

             Polyphony originated in the halls of the Catholic Church as plainchant, or Gregorian chant. Plainchant involved simple unaccompanied chanting without any established rhythm in either medieval major or minor mode. Around 900 CE, the earliest type of polyphony started appearing as organum, in which the chant melody was sung along with an accompanying voice, usually below the original in an interval of either a fourth or fifth. In the eleventh century, the organum started becoming more complicated and flexible, sometimes rising to cross the chant or sound briefly above it. In the 12th century, the trope form of organum began appearing, in which additional texts and melismas were added between notes, elaborating the simple melodies. Later on, the chant melody shifted from the upper to the lower voice; the accompaniment, now on top, gained importance and independence. Next, came the copula form of organum, pioneered by Leoninus, Notre Dame. The top voice gained rhythm in the form of certain repeated rhythmic modes. Discant furthered this trend by giving both the top and bottom voices rhythm. .
             The next big step forward in the development of polyphony was the invention of clausulae, or sections of the piece that were taken out and replaced with new rhythms and new melismas. Perotinus composed a great number of clausulae, using advanced discant. He also composed for three and sometimes four voices instead of just two, giving the chants even more depth and richness. Also during the 13th century, text started to be added to the upper line. At first, the text was religious and had liturgical relevance. Such a form of chant was known as the motet. Later on, the top text started to be written in French and took on secular subjects unrelated to the religious chant. Around 1300, these revolutionary trends culminated in the Ars Nova movement, pioneered by composers like Vitry and Machaut who gave the voices complex superimposed rhythms.