Building a piece of music around the presentation of a theme (a melodic idea) followed by a series of variations on that theme is not new to the Classical era. However, the frequent use of this structure in movements, often the 2nd movement, of larger Classical works such as symphonies and string quartets merits some additional study as we consider Classical forms.
In music, variation is a formal technique where material is repeated in an altered form. The changes may involve harmony, melody, counterpoint, rhythm, timbre, orchestration or any combination of these.
Variation forms include ground bass, passacaglia, chaconne, and theme and variations. Ground bass, passacaglia and chaconne are typically based on brief ostinato motifs providing a repetitive harmonic basis and are also typically continuous evolving structures. ‘Theme and variation’ forms are however based specifically on melodic variation, in which the fundamental musical idea, or theme, is repeated in altered form or accompanied in a different manner. ‘Theme and variation’ structure generally begins with a theme (which is itself sometimes preceded by an introduction), typically between eight and thirty-two bars in length; each variation, particularly in music of the eighteenth century and earlier, will be of the same length and structure as the theme. This form may in part have derived from the practical inventiveness of musicians; “Court dances were long; the tunes which accompanied them were short. Their repetition became intolerably wearisome, and inevitably led the player to indulge in extempore variation and ornament”; however, the format of the dance required these variations to maintain the same duration and shape of the tune.
Variation forms can be written as ‘free-standing’ pieces for solo instruments or ensembles, or can constitute a movement of a larger piece. Most jazz music is structured on a basic pattern of theme and variations.
Examples include John Bull’s Salvator Mundi, Bach’s Canonic Variations on “Vom Himmel hoch da komm’ ich her, Passacaglia and Fugue in C minor, Violin Chaconne, and (D minor solo violin suite), Corelli’s La Folia Variations, Beethoven’s Diabelli Variations, the Finale of Brahms’s Fourth Symphony, Variations on a Theme of Haydn, Op. 56, Elgar’s Enigma Variations, Franck’s Variations Symphoniques, and Richard Strauss’s Don Quixote. Both Schubert’s Death and the Maiden Quartet and Trout Quintet take their titles from his songs used as variation movements.