Musical Canons: How to Distinguish the Basic Types

A canon is a contrapuntal device consisting of an extended melody that is started in one part and strictly imitated in its entirety at a specified time interval by one or more other parts. It functions as either a compositional technique within a piece or as an entire musical form.

The English word canon goes back through Latin canon ("rule, model") to Greek kanon ("rule, model"). The use of the word in music arose in European languages during the Renaissance period, when some early types of canon were indicated by a kind of shorthand, that is, by any inscription ("rule") explaining how to complete the reading of a passage deliberately notated incompletely.

The leading part of a canon is called the dux (Latin, "leader"). The following part, or each of the following parts, is the comes (Latin, "companion, follower").

Canons have accumulated many descriptive labels, which can be condensed into two broad groups: labels of distance and labels of special device.

Canons Named by Distance
Temporal distance. A temporal label indicates the time lapse between the entries of the parts, such as canon of one measure and canon of two measures.

Intervallic distance. An intervallic label indicates the interval of imitation between the first part and the second part, such as canon in unison and canon at the fifth.

Canons Named by Special Device
(1) Circle canon. The melody leads back to its own beginning so that it may be endlessly repeated. Also known as circular canon and perpetual canon.

Simple folk-music circle canons are called rounds (because the voices follow each other round and round), such as Frère Jacques; Row, Row, Row Your Boat; and Three Blind Mice.

The catch (so named because each voice has to "catch" the melody at the right time) is an English round that emerged in the late 16th century. It is marked by texts that are humorous and often ribald.

The term circular canon has also been applied to a canon in which the repetitions modulate through a succession (circle) of fifths.

(2) Canon in augmentation, canon in diminution. The comes has the melody in larger (augmented) or shorter (diminished) note values. Most often, augmentation involves doubled values, and diminution involves halved values.

(3) Canon by inversion. The comes has the melodic inversion of the dux, so that each ascending interval of the dux is changed into the corresponding descending interval and vice versa.

Also called a mirror canon because the comes looks like the dux being read from a mirror held below the notation. (For another mirror canon, see retrograde canon.)

(4) Retrograde canon. The comes imitates the dux in retrograde motion, that is, by repeating the melody backward note for note from the last note to the first. The word retrograde goes back to the Latin verb retrogradi, from retro- ("backward") and gradi ("to go").

Also known as cancrizans canon, canon cancrizans, and crab canon. The word cancrizans comes from the present participle of Medieval Latin cancrizare ("to go backward"), from cancr- (a combining form of cancer, "crab") and -izare ("-ize").

Also called a mirror canon because the comes looks like the dux being read from a mirror held at the end of the notation. (For another mirror canon, see canon by inversion.)

(5) Canon by retrograde inversion. The comes is the retrograde of the inversion of the dux.

(6) Group canon. The dux consists of two or more simultaneous parts; the comes, as usual, follows suit. In effect, this procedure results in two or more canons being played at the same time.

The single-melody canon is sometimes termed a two in one canon, meaning two voices perform one canon. Likewise, group canons are termed four in two (four voices in two simultaneous canons), six in three (six voices in three simultaneous canons), and so on. An example of an eight in four canon is the motet Diliges Dominum by William Byrd (1543-1623).

(7) Spiral canon. The melody ends one tone higher than it started. Therefore, it must be performed six more times to return to the original key, as in C, D, E, F-sharp, A-flat (= G-sharp), B-flat, and C. An example is a canon titled "May the glory of the king rise as the modulation ascends" in The Musical Offering by Johann Sebastian Bach (1685-1750).

Also known in Latin as canon per tonos ("canon for each tone").

(8) Mixed canon. Added parts, usually in the bass, do not participate in the imitation. Examples are the canons in Bach's famed Goldberg Variations.
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Randel, Don Michael, ed. The Harvard Dictionary of Music. 4th ed. Cambridge, Mass.: Belknap Press-Harvard University Press, 2003.

Sadie, Stanley, ed. The New Grove Dictionary of Music and Musicians. 2nd ed. London: Macmillan, 2001.