Perpetual canon

A round (also called a perpetual canon [canon perpetuus] or infinite canon) is a musical composition, a limited type of canon, in which a minimum of three voices sing exactly the same melody at the unison (and may continue repeating it indefinitely), but with each voice beginning at different times so that different parts of the melody coincide in the different voices, but nevertheless fit harmoniously together (Johnson 2001). It is one of the easiest forms of part singing, as only one line of melody need be learned by all parts, and is part of a popular musical tradition. They were particularly favoured in glee clubs, which combined amateur singing with regular drinking (Aldrich 1989, introductory essay, 8–22, especially at 21: "Catch-singing is unthinkable without a supply of liquor to hand..."). The earliest known rounds date from the 12th century.

Though not all rounds are nursery rhymes, "Row, Row, Row Your Boat" is a well-known children's round for four voices. Other well-known examples are "Frère Jacques" and "Three Blind Mice" (Hoffman 1997, 40).

A catch is a round in which a phrase that is not apparent in a single line of lyrics emerges when the lyrics are split between the different voices. "Perpetual canon" refers to the end of the melody leading back to the beginning, allowing easy and immediate repetition. Often, "the final cadence is the same as the first measure" (Walton 1974, 141).

The term "round" first appears in English in the early 16th century, though the form was found much earlier. In medieval England, they were called rota or rondellus. Later, an alternative term was "roundel" (e.g., David Melvill's manuscript Ane Buik off Roundells, Aberdeen, 1612). Special types of rounds are the "catch" (a comic English form found from about 1580 to 1800), and a specialized use of the word "canon", in 17th- and 18th-century England designating rounds with religious texts (Johnson 2001). The oldest surviving round in English is "Sumer Is Icumen In" (Hoffman 1997, 40)  Play , which is for four voices, plus two bass voices singing a ground (that is, a never-changing repeating part), also in canon. However, the earliest known rounds are two works with Latin texts found in the eleventh fascicle of the Notre Dame manuscript Pluteo 29.1. They are Leto leta concio (a two-voice round) and O quanto consilio (a four-voice round). The former dates from before 1180 and may be of German origin (Falck 1972, 43–45, 57). The first published rounds in English were printed by Thomas Ravenscroft in 1609... "Three Blind Mice"  Play  appears in this collection, although in a somewhat different form from today's children's round:

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