Outline of sonata formThe basic outline of a sonata-allegro movement

Introduction – This section is optional, or may be reduced to a minimum. If it is extended, it is generally slower than the main section, and focuses on the dominant key . It may or may not contain material which is later stated in the exposition. The introduction increases the weight of the movement, and also permits the composer to begin the exposition with a theme that would be too light to start on its own.

Occasionally the material of introduction reappears in its original tempo later in the movement. Often, this occurs in the coda.

Exposition – the primary thematic material for the movement is presented. This section can be further divided into:

• First subject group – this consists of one or more themes, all of them in the home key.

• Transition – in this section the composer modulates from the key of the first subject to the key of the second.

• Second subject group – one or more themes in a different key to the first group. If the first group is in a major key, the second group will usually be in the dominant, that is to say in a key a perfect fifth higher, so that if the original key is C major, the key of the music of the second group will be G major. If the first group is in a minor key, the second group will generally be in the relative major, so that if the original key is C minor, the second group will be in E flat major. The material of the second subject is often different in rhythm or mood from that of the first subject (frequently, it is more lyrical), but this is not always so; see below under "Monothematic expositions".

• Codetta – the purpose of this section is to bring the exposition section to a close with a perfect cadence in the same key as the second group. Often the codetta contains a sequence of themes, each of which arrives at a perfect cadence. The whole of the exposition may then be repeated.

Development – generally starts in the same key as the exposition ended, and may move through many different keys during its course. It will usually consist of one or more themes from the exposition altered and occasionally juxtaposed and may include new material or themes - though exactly what is acceptable practice is a famous point of contention. The development varies greatly in length from piece to piece, but almost always shows a greater degree of tonal, harmonic and rhythmic instability than the other sections. At the end, the music will turn towards the home key and enter the recapitulation.Recapitulation – this is an altered repeat of the exposition, and consists of:

• First subject group – usually in exactly the same form as it appeared in the exposition.

• Transition – now altered so that it does not change key, but remains in the piece's home key.

• Second subject group and codetta – usually in the same form as in the exposition, but now in the same key as the first group. If the first group was in a minor key, the second group and codetta may be shifted into the minor for the recapitulation. On rare occasions may be in the parallel major key (for example, C minor/C major).

Coda After the final cadence of the recapitulation, the movement may continue into a "tail", which will contain material from the movement proper. Codas, when present, vary considerably in length, but, like introductions, are not part of the "argument" of the work, however it ends with a perfect cadence in the home key. Codas may be quite brief tailpieces, or they may very long and elaborate; a famous example is the finale of Beethoven's Eighth Symphony.