In the Western church four main dialects of plainsong developed—Ambrosian, Roman, Mozarabic and Gallican—that seem to have been derived from similar sources. Gregorian chant is named for Pope Gregory I, whose credited role in compiling liturgical books during his papacy (590-604) is now considered questionable.
The origins of the chant go back to early Christian times, and it seems to have derived from musical practice in the Jewish synagogue and Greek musical theory. During the late Middle Ages and the Renaissance, and also in later times, the chant melodies were used as the basis for polyphonic composition. In the 19th cent. the Benedictine monks of Solesmes sought to restore the Gregorian chant to its original form and their published editions from 1889 onward became the official music of the Catholic Church. The texts of plainsong are the words of the Mass, the Psalms, canticles, and certain verse hymns.
The tonality of Gregorian chant is based on the system of eight modes (see mode). The notation of the chant evolved into systems of neumes (see musical notation) that were still used in the 20th cent. in preference to modern mensural notation for plainsong. Little is known of the rhythm with which the chants were performed in the Middle Ages. The chants were contained in two principal books: those for the Mass in the "Gradual," those for the Office in the "Antiphoner." The modern Liber usualis is a compilation of most frequently used chants from the two.
See W. Apel, Gregorian Chant (1958); J. R. Bryden and D. G. Hughes, ed., An Index of Gregorian Chant (2 vol., 1969).
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.
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. The tradition linking Gregory to the development of the chant seems to rest on a mistaken identification of a certain "Gregorius", probably Pope Gregory II, with his more famous predecessor.
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.
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".
Since 2000, the Belgian singer and researcher Hendrik Vanden Abeele, together with his ensemble Psallentes ("the singing"), is doing research on the performance practice of fifteenth-century plainsong, focusing on thorny and controversial problem of rhythm, memory as the major requisite for a good singer of chant, and the voice as a research tool.