Theme and Variation

Theme and variation is a compositional procedure in which a melody is stated and then repeated in a series of altered versions — decorated, reharmonised, rescored or transformed in character — while remaining recognisable. It runs from Baroque ground-bass dances through the Classical variation set to some of the largest piano works of the nineteenth and twentieth centuries: *Bach*'s "Goldberg Variations", *Beethoven*'s "Diabelli Variations" and *Rzewski*'s "The People United Will Never Be Defeated!" are its benchmarks. The interest lies in invention under constraint: unity is given, and the composer's task is maximum variety within it.