The large body of traditional ritual melody of the Western Christian Church, in its final form called Gregorian chant. Comprises single line of vocal melody, properly (but not always nowadays) unacc. in free rhythm, not divided into bar‐lengths. Has own system of notation, employing stave of 4 lines instead of 5. The word is a trans. of cantus planus—in contra‐distinction to cantus figuratus (florid song, implying a counterpoint added to the traditional melody) or cantus mensuratus (measured song, implying the regularity of rhythm assoc. with harmonic mus.). The Eastern (or ‘Greek’) branch of the Christian Church and the Jewish Synagogue have similar bodies of melodic ritual song, but the term plainsong, as ordinarily used, does not incl. them.
Plainsong rhythm is the free rhythm of speech; it is a prose rhythm, which of course arises from the unmetrical character of the words to be recited—psalms, prayers, and the like.
In character, plainsong falls into two essentially distinct groups—the responsorial (developed from recitation of psalms round a ‘dominant’), and antiphonal (developed as pure melody).
Plainsong developed during the earliest centuries of Christianity, influenced possibly by the mus. of the Jewish synagogue and certainly by the Gr. modal system (see modes). A major reform was instituted in the 6th cent. at, it is said, the request of Pope Gregory.
Further reform was attempted at the end of the 16th cent., but the results were disastrous. Palestrina was charged with the work of revising the plainsong of the Gradual, Antiphonal, and Psalter, but died almost immediately after accepting the commission. Felice Anerio and Soriano undertook the work, and their edn. was pubd. by the Medicean Press in 2 vols., 1614–15. This Medicean Edition, as it is called, with its addition and suppression of melismata, its altered melodies, and its new ones, became the basis for many cheaper performing edns. In the 18th cent. there was a fashion for introducing grace notes and passing notes into the plainsong (called in Fr. machicotage). In the 19th cent. there was another cry for reform and the famous Ratisbon (Regensburg) edns. appeared—unfortunately based on the Medicean Edition. Years of controversy followed, for the Benedictine monks of Solesmes, in Fr., had long been at work in the most scientific spirit, photographing and collating innumerable manuscripts, in all the libraries of Europe. They pubd. their Gradual in 1883 and their Antiphonal in 1891. The Ratisbon edn. had had papal privileges conferred upon it, but in 1903 these expired and in the same year Pius X was chosen Pope and he at once issued his famous Motu Proprio on church mus., laying down, among other things, the importance of plainsong and the necessity of taking it from early and pure sources.
Among the reforms of the Solesmes monks (who, temporarily driven from France by anti‐clerical legislation in 1901, carried on their work for some years in Eng.) was the introduction of a lighter and more rhythmic manner of perf.