a term designating the form of the first movement of a sonata. In the Classical period, it was used in the first movements of many instrumental forms, such as concertos, symphonies, string quartets, as well as in other movements of these same forms.
The term itself may be misleading, since it does not designate the form of the whole sonata. The sonata-form, as practiced by classical composers such as Haydn, Mozart, Beethoven, and some of the Romantic composers after them, is constructed of three
main sections and a coda, according to the following plan.
Exposition:
Introduction of the principal theme in the tonic; a transition or bridge which leads to the dominant (when the first theme is in a major key) or to the relative major (when the first theme is in a minor key); introduction of the second theme in the new key (if the first theme can be based on a major or minor
key, the second one is almost always in a major key); introduction of a closing theme in the new key which almost always ends with a repeat sign.
Development:
This is a working out section, in which the composer selects various musical ideas which were introduced in the Exposition, and elaborates upon them in a kaleidoscopic variety of modulations and textures. This section returns to the main key, and leads back to the first theme.
Recapitulation:
Now the whole Exposition is repeated, but this time with some changes. The bridge does not lead to a new key, but remains in the main key so that the second and closing themes are written in the tonic. There may be some other minor changes, depending on the composers.
Coda: (In Italian, "coda" means "tail").
Composers usually add a short appendage which closes the
movement. Sometimes, the coda is largely expanded, as in many of Beethoven's symphonies, and takes the form of a second Development section. By comparing the Recapitulation with the Exposition, you can almost discern when the Coda begins.
