Plainsong (also plainchant) is a body of traditional songs used in the liturgies of the Roman Catholic Church. The liturgies of the Eastern Orthodox Church, though similar in many ways, are generally not classified as plainsong, though the musical form is nearly as old as Christendom. Plainsong is also commonly used in the Anglican churches.
Plainsong is monophonic; it is in free, rather than measured, rhythm. Plainsong often uses the lengthy reverberations and resonant modes of cathedrals to create harmonies.
Gregorian chant is a variety of plainsong named after Pope Gregory I (6th century A.D.). Though frequently asserted, it is not true that Gregory invented the chant, or that he ordered the suppression of previous chant styles, such as the Ambrosian or Mozarabic, for the chant pre-dated Gregory. He did codify and standardize the use of plainchant throughout Christendom. The chant was so named for his promotion of its use in the Roman liturgy.
For several centuries, different plainchant styles existed concurrently. Standardization on Gregorian chant was not completed, even in Italy, until the 12th century. Plainchant represents the first revival of musical notation after knowledge of the ancient Greek system was lost. Plainsong notation differs from the modern system in having only four lines to the staff and a system of note shapes called neumes.
In the late 9th century, plainsong began to evolve into organum, which led to the development of polyphony.
There was a significant plainsong revival in the 19th century, when much work was done to restore the correct notation and performance-style of the old plainsong collections, notably by the monks of Solesmes Abbey, in Northern France. After the Second Vatican Council and the introduction of the New Rite Mass, use of plainsong in the Roman Catholic Church declined and was mostly confined to the Monastic Orders and to ecclesiastical Societies celebrating the traditional Latin Mass (also called Tridentine Mass). But, since Pope Benedict XVI's motu proprio, Summorum Pontificum, use of the Tridentine rite has increased; this, along with other Papal comments on the use of appropriate liturgical music, is promoting a new plainsong revival.
In the late 1980s, plainchant achieved a certain vogue as music for relaxation, and several recordings of plainchant became "classical-chart hits".
plainsong in Esperanto: Plejnkanto
plainsong in French: Plain-chant
plainsong in Hebrew: קנטוס פלאנוס
plainsong in Portuguese: Cantochão