Sonata form

The Sonata form, also known as sonata-allegro form, is a musical form typically used in the first movement of classical works. It is derived from the "binary form" of the Baroque and Rococo eras of music, and gained prominence in the works of Joseph Haydn and Wolfgang Amadeus Mozart.

The word sonata is also used to refer to a stand-alone instrumental work usually in three movements, when first movement is in the sonata form.

A work in sonata form can be divided into three sections: the exposition, development, and recapitulation.

Outline of form

Introduction

Many works in sonata form are preceded by a slow introduction usually excluded from the exposition repeat. The introduction is often used to increase the dramatic weight of a movement, as in Beethoven's Piano Sonata Op. 13 ("Pathetique"), or Haydn's "Drumroll" Symphony No. 103.

Exposition

The exposition begins with the introduction of the first subject in the tonic key. After some transition material, the second subject is introduced, usually in the dominant or relative major key (in the case of a sonata in a minor key); however, this is not always the case, a notable exception being Beethoven's Piano Sonata Op. 53 ("Waldstein"). The second subject tends to be more lyrical than the first subject. A small codetta brings the exposition to a close with an authentic cadence in the key of the second subject.

Development

The development often begins in the same key as the end of the exposition, but modulates through many different keys until the recapitulation. In this section, the themes laid out in the exposition are modified through key changes, breaking down parts of keys and motifs, variations in rhythm and harmony, and other ways.

The end of the development is the retransition, in which the original key of the sonata is increasingly stressed as the recapitulation is approached.

Recapitulation

This section echoes the exposition, except that the second subject is now played in the tonic key, providing a sense of balance to the work.

Coda

Composers will often add a coda to the finale of a work in Sonata-allegro form. The coda varies in length, with notably lengthly codas including the finale of the first movement of Beethoven's Piano Sonata Op. 57 ("Appassionata"), and the first and fourth movements of his Fifth Symphony.

Unity and variety

As in most kinds of music, the sonata relies on a sense of unity and variety to reinforce the work's meaning. Unity may be obtained by:

1. linked keys in different themes
2. inverting the theme
3. use of a pedal note for connection
4. the same melody line put into a different but related key
5. the whole sonata may be working out of one basic idea and perhaps one theme is heard throughout all four movements - for example, one whole movement could be found in a small fragment of the preceding movement
6. a striking feature of one movement could be woven into another movement. This is called "transformation of themes"

Variety is achieved by:

1. changing the order of movements
2. composing the theme in the style of a Canon whereas when it was introduced it was a single line theme
3. using variations by changing the rhythms and time signature, but with the theme still recognisable
4. using various modulations and different harmonies
5. using ornaments, shakes or trills
6. changing the accent and using the devices of counterpoint to introduce new ideas