- James Webster
The most important principle of musical form, or formal type, from the Classical period well into the 20th century. This form is that of a single movement, not a ‘sonata’ as a whole; such a movement is most often part of a multi-movement instrumental cycle such as a sonata, piano trio or quartet, string quartet or quintet, symphony etc., or an independent movement like an overture or tone poem. Sonata form as such is less common in fantasies and the like, small movements, concertos and vocal music, but its principles may influence other features of form in such works. Though most characteristic of first movements in fast tempo, it often appears in middle movements and finales, and in moderate and slow tempo; hence the synonyms ‘sonata-allegro form’ and ‘first-movement form’ are best avoided.
A typical sonata-form movement consists of three main sections, embedded in a two-part tonal structure. The first part of the structure coincides with the first section and is called the ‘exposition’. The second part of the structure comprises the remaining two sections, the ‘development’ and the ‘recapitulation’. The exposition divides into a ‘first group’ in the tonic and a ‘second group’ in another key, most often the dominant. Both first and second group may include numerous different ideas; the first or most prominent theme may be called the ‘main theme’, ‘first subject’, ‘primary material’ etc., while the most prominent theme in the second group is often called the ‘second theme’ (or ‘subject’), whether or not it actually is the second important musical idea. The development (the misleading term ‘free fantasia’ is now obsolete) usually develops material from the exposition, as it modulates among one or more new keys. The last part of the development prepares the recapitulation. The recapitulation (or ‘reprise’; but see §3 (iii)) begins with a simultaneous ‘double return’, to the main theme and to the tonic. It then restates most or all of the significant material from the exposition, whereby the second group is transposed to the tonic. The movement concludes either with a cadence in the tonic paralleling the end of the exposition, or with a coda following the recapitulation....