Canon

Canon, form or procedure of contrapuntal musical composition in which one voice or instrument starts to sing or play a theme and other voices or instruments follow at a specified interval of time, all singing or playing the same theme according to the same rule (canon). The composer might specify that later voices enter at different pitches, or even execute the theme upside down or backwards (cancrizans, crabwise). In the best-known form of canon, the round, the theme is sung (played) identically by all voices, which enter at regular intervals. This very old musical form originated in the church music of the Middle Ages.