In music, a canon is a contrapuntal composition that employs a melody with one or more imitations of the melody played after a given duration (e.g. quarter rest, one measure, etc.). The initial melody is called the leader, while the imitative melody is called the follower which is played in a different voice. The follower must be created from the leader by being either an exact replication of the rhythms and intervals of the leader, or a transformation such as those listed in "types of canons" (below). The simplest and most familiar examples are rounds such as "Row, Row, Row Your Boat".
The canon has its origins in Italy and France and was originally called caccia. The Old French canon, which meant 'learned', was taken from the Greek kanon for a rule or law, which eventually came to mean 'an accepted rule' in English. The most rigid and ingenious forms of canon are not strictly concerned with pattern but also with content. During the period of the Netherland School (1430-1550), canon as a contrapuntal art form received its greatest development, while the Roman School gave it its most complete application.
Types of canons
Canons are classified by various traits: the number of voices, the interval at which each successive voice is transposed in relation to the preceding voice, whether voices are inverse, retrograde, or retrograde-inverse; the temporal distance between each voice, whether the intervals of the second voice are exactly those of the original or if they are adjusted to fit the diatonic scale, and the tempo of successive voices. However, canons may use more than one of the above methods.
How voices in a canon are named
Although, for clarity, this article uses leader and follower(s) to denote the leading voice in a canon and those that imitate it, musicological literature also uses the traditional Latin terms Dux and Comes for "leader" and "follower", respectively.
Number of voices
A canon of two voices may be called a canon in two, similarly a canon of x voices would be called a canon in x. This terminology may be used in combination with a similar terminology for the interval between each voice, different from the terminology in the following paragraph.
Another standard designation is "Canon: Two in One", which means two voices in one canon. "Canon: Four in Two" means four voices with two simultaneous canons. "Canon: Six in Three" means six voices with three simultaneous canons, and so on.
An interval canon imitates the leader at any interval other than the octave or unison (e.g. canon at the second, fifth, seventh, etc.). If the follower imitates the precise interval quality of the leader, then it is called an exact canon; if the follower imitates the interval number (but not the quality), it is called a diatonic canon.
The follower may be a contrapuntal derivation of the leader.
An inverted canon (also called canon in contrary motion) moves the follower in contrary motion to the leader. Where the leader would go down a fifth, the follower goes up, and vice versa. A sub-order of canon in contrary motion, "mirror," maintains the precise quality of each interval.
In a crab canon, also known as cancrizans, the follower accompanies the leader backward (in retrograde).
Mensuration and tempo canons
In a mensuration canon (also known as a prolation canon, or a proportional canon), the follower imitates the leader by some rhythmic proportion. The follower may double the rhythmic values of the leader (augmentation or sloth canon) or it may cut the rhythmic proportions in half (diminution canon). Phasing involves the application of modulating rhythmic proportions according to a sliding scale. The cancrizans, and often the mensuration canon, take exception to the rule that the follower must start later than the leader.
Technically, mensuration canons are among the most difficult to write. Many such canons were composed during the Renaissance, particularly in the late 15th and early 16th centuries; Johannes Ockeghem wrote an entire mass (the Missa Prolationum) in which each section is a mensuration canon, and all at different speeds and entry intervals. In the 20th century, Conlon Nancarrow composed complex tempo or mensural canons, mostly for the player piano as they are extremely difficult to play; they have also influenced many younger composers. Larry Polansky has an album of mensuration canons, Four-Voice Canons.
- Other types of canons
The most familiar of the canons might be the perpetual/infinite canon (in latin: canon perpetuus). As (each voice of) the canon arrives at its end it can begin again, in a Perpetuum mobile fashion; e.g. "Three Blind Mice". Such a canon is often called a round or rota. Sumer is icumen in is one example of a piece designated rota.
Additional types include the spiral canon, accompanied canon, and double or triple canon.
The most popular canons heard today are from the Baroque period, such as Johann Pachelbel's Canon in D (Pachelbel's Canon) or every third variation in Bach's Goldberg Variations. What may be George Rochberg's best known work, his String Quartet No. 6, includes a set of variations on the Pachelbel Canon in D. Henryk Górecki's Third Symphony begins with an extensive eight voice canon in the strings. Steve Reich uses a process he calls phasing which is a canon with variable distance between the voices. Many popular recording artists have found success by sampling portions of famous canons in their compositions. (Courtesy of Wikipedia)