Canon

Imitation of a complete subject by one or more voices at fixed intervals of pitch and time.  If each successive following voice ("comes") follows the leading voice ("dux") in every detail, the canon is strict; if, however, the "comes" modifies the "dux" by minor changes in accidentals, the canon is free.

Canons may be self-contained entities or may occur within larger pieces (canonic imitation).  They may also be combined with independent lines (mixed or accompanied canons) or even with other canons (groups or compound canons).

Canons are usually classified on the basis of the following elements:

The technique of canonic imitation, that is, of canon in the present-day sense, was first used in the 13th century.  Several motets include long passages in canonic imitation.  Also in this category are the caccia and chace of the 14th century.  A number of 14th- and 15th-century motets and Mass compositions open with a section in canonic imitation.  Prominent in late 15th- and early 16th-century music (Josquin and others) is the canonic chanson, in which two voices form a canon.  Palestrina often used canons in the last Agnus Dei of his Masses.  It was chiefly through Bach that the canon won an important position in music, a position it has maintained to the present day.