Musical form and compositional technique.
Canons are characterized by having a melody that is imitated at a specified time interval by one or more parts, either at the same pitch or at some other pitch. Imitation may occur in the same note values, in augmentation (longer notes), or in diminution (shorter notes); in retrograde order (beginning at its end), mirror inversion (each ascending melodic interval becoming a descending interval, and vice versa), or retrograde mirror inversion; and so on. Canons range from folk rounds such as "Three Blind Mice" and "Frère Jacques" to the massively complex canons of Johann Sebastian Bach .