Ars antiqua

Ars antiqua, also called ars veterum or ars vetus, is a term used by modern scholars to refer to the Medieval music of Europe during the High Middle Ages, between approximately 1170 and 1310. This covers the period of the Notre-Dame school of polyphony (the use of multiple, simultaneous, independent melodic lines), and the subsequent years which saw the early development of the motet, a highly varied choral musical composition. Usually the term "ars antiqua" is restricted to sacred (church) or polyphonic music, excluding the secular (non-religious) monophonic songs of the troubadours, and trouvères. However, sometimes the term "ars antiqua" is used more loosely to mean all European music of the thirteenth century, and from slightly before. The term "ars antiqua" is used in opposition to "ars nova" (meaning "new art", "new technique" or "new style"), which refers to the period of musical activity between approximately 1310 and 1375.
History.
The original Middle Ages uses of the expression, found in the "Speculum Musice" of Jacobus and once by Johannes de Muris (the only one to use the exact term "ars antiqua"), referred specifically to the period of Franco of Cologne, approximately 1250–1310, but this restricted usage is rarely employed in modern scholarship. Almost all composers of the "ars antiqua" are anonymous. Léonin (fl. late 12th century), and Pérotin (fl. c.1180 – c.1220) were the two composers known by name from the Notre Dame school; in the subsequent period, Petrus de Cruce, a composer of motets, is one of the few whose name has been preserved.
In music theory the "ars antiqua" period saw several advances over previous practice, most of them in conception, and notation of rhythm. In the early Medieval music era, notation indicated the pitches of songs without indicating the rhythm that these notes should be sung in. The most famous music theorist of the first half of the 13th century, Johannes de Garlandia, was the author of the "De Mensurabili Musica" (about 1240), the treatise which defined, and most completely elucidated the rhythmic modes. A German theorist of a slightly later period, Franco of Cologne, was the first to describe a system of notation in which differently shaped notes have entirely different rhythmic values (in the "Ars cantus mensurabilis" of approximately 1280), an innovation which had a massive impact on the subsequent history of European music. Most of the surviving notated music of the 13th century uses the rhythmic modes as defined by Garlandia.
The early Gothic includes the French music composed in the Notre-Dame school up until about 1260, and the high Gothic all the music between then, and about 1310 or 1320, the conventional beginning of the "ars nova." The forms of organum and conductus reached their peak development in the early Gothic, and began to decline in the high Gothic, being replaced by the motet.
Though the style of the "ars antiqua" went out of fashion rather suddenly in the first two decades of the fourteenth century, it had a late defender in Jacques of Liège (alternatively known as Jacob of Liège), who wrote a violent attack on the "irreverent, and corrupt" "ars nova" in his "Speculum Musicae" (c.1320) vigorously defending the old style in a manner suggestive of any number of music critics from the Middle Ages to the present day. To Jacques, the "ars antiqua" was the "musica modesta", and the "ars nova" was a "musica lasciva"—a kind of music which he considered to be excessively indulgent, capricious, immodest, and sensual.