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A discant (occasionally, particularly later, written descant) is a form of medieval music in which one singer sang a fixed melody, and others accompanied with improvisations. The word in this sense comes from the term discantus supra librum (descant "above the book"), and is a form of Gregorian chant in which only the melody is notated but an improvised polyphony is understood. The discantus supra librum had specific rules governing the improvisation of the additional voices.
Later on, the term came to mean the treble or soprano singer in any group of voices, or the higher pitched line in a song.
Descant can also refer to the highest pitched of a group of instruments, particularly the descant viol or recorder. Similarly, it can also be applied to the soprano clef. Descant can also refer to a high, florid melody sung by a few sopranos as a decoration for a hymn.
Descants in hymns 
Although the English Hymnal of 1906 did not include descants, this influential hymnal, whose music editor was Ralph Vaughan Williams, served as a source of tunes for which the earliest known hymn tune descants were published. These were in collections compiled by Athelstan Riley, who wrote "The effect is thrilling; it gives the curious impression of an ethereal choir joining in the worship below; and those who hear it for the first time often turn and look up at the roof!"
Among composers of descants during 1915-1934 were Alan Gray, Geoffrey Shaw, and Ralph Vaughan Williams. Several of their descants appear in what is possibly the earliest hymnal to include descants, Songs of Praise (London: Oxford University Press, 1925, enlarged, 1931, reprinted 1971).
During the last quarter of the twentieth century, new editions of hymnals increased the number of included descants. For example, the influential Hymnal 1940 (Episcopal) contains no descants, whereas its successor, Hymnal 1982, contains 32. Among other currently used hymnals, The Worshiping Church contains 29 descants; The Presbyterian Hymnal, 19; The New Century Hymnal, 10; Chalice Hymnal, 21. The Vocal Descant Edition for Worship, Third Edition (GIA Publications, 1994) offers 254 descants by such composers as Donald Busarow, John Ferguson, Richard Hillert, Robert Hobby, Hal Hopson, David Hurd, Austin Lovelace, Ronald Nelson, Sam Batt Owens, Robert Powell, Richard Proulx, William P. Rowan, Carl Schalk, Randall Sensmeier, Scott Withrow, and Michael Young.
Further reading 
- Clark Kimberling, "Hymn Tune Descants, Part 1: 1915-1934", The Hymn 54 (no. 3) July 2003, pages 20–27. (Reprinted in Journal of the Ralph Vaughan Williams Society 29 (February 2004) 17-20.)
- Clark Kimberling, "Hymn Tune Descants, Part 2: 1935-2001", The Hymn 55 (no. 1) January 2004, pages 17–22.