The exposition need not be limited to key areas. Schubert composed sonata forms with
three or more key areas. The first movement of his string quartet in D minor D 810
‘Death and the Maiden’ has three separate key and thematic areas, in D minor, F major
and A minor.
First subject group need not be entirely in tonic key
In the more complex sonata expositions there may, in the first subject group, be brief
modulations to remote keys followed by reassertion of the tonic. The first subject group
of the first movement of Mozart’s string quintet in C major K 515 visits C minor, D flat
major and D major before finally moving to the dominant of G major. Many works by
Schubert and later composers use even further harmonic convolutions. In the first subject
group of Schubert’s piano sonata in B flat major D 960, the theme is presented three
times, in B flat major, G flat major and then again in B flat major. The second subject
group is even more wide-ranging as it starts in F sharp minor, moves into A major then
through B flat major to F major.
Recapitulation of first subject may be omitted or truncated
In the first movement of Chopin’s piano sonata in B flat minor the recapitulation of the
first subject is omitted altogether and in his piano sonata in B minor it is truncated.
Sonata form in concertos
The sonata form is varied in the first movement of classical concertos. The orchestra
usually prepares for the entrance of the soloist by playing some of the themes that will be
heard during the main part of the movement. This preparation is a kind of introduction
but is in the main tempo. The solo instrument then enters, sometimes with material of its
own as in a number of Mozart’s piano concertos, and continues with a sonata-form
exposition which is usually, but not always, closely related to the opening orchestral
introduction. Mozart sometimes defers some of the most memorable themes of the
opening orchestral tutti until the development section. In his piano concerto no. 25 a
theme not heard since the introduction becomes the main ‘subject’ treated in the
development. Towards the end of the recapitulation there is usually a cadenza for the
soloist alone. This usually has an improvisatory character although it is usually not
improvised but is written by the composer, by another composer, or by the pianist.
History of sonata form
The term ‘sonata’ is first found in the seventeenth century when instrumental music had
just begun to separate itself from vocal music. The term (derived from the Italian word
‘suonare’, to sound an instrument) meant a piece for playing, in contrast with ‘cantata’
which was a piece for singing. At this time the term implied a binary form, usually
AABB with some aspects of three-part forms.