The grammar of a sonata — the basic harmonic and thematic story that anchors the formal style — is accomplished largely in the exposition, development, and especially the recapitulation. Of course, sonata-form movements typically have other narratives to tell musically, and the bigger the story, the more care composers take to hold it all together.
Larger sonata movements tend to have one or more framing modules: either an introduction, a coda, or both. These help to “frame” the big picture, and to create a coherent musical narrative — often an arc that builds in tension to a climax and resolves to a point of relative rest by the end of the movement.
Some common characteristics of these modules are provided below, many of which are shared with introductions and codas in pop/rock music.
An introduction is any material that precedes the primary theme zone (P). It stands outside the exposition. If the exposition is repeated, the introduction is not repeated with it. Thus, a composer’s open repeat sign ||: in the score can be an important visual clue in identifying the end of an introduction and the beginning of an exposition. Because the introduction is not part of the exposition, it is not repeated in the recapitulation. Thus, even without repeats in a score or a performance, once the thematic cycle of the exposition, development, and recapitulation has been identified, the introduction can be identified as music that precedes the first occurrence of that cycle. Finally, though introductory material may be referenced later in the sonata, the introductory module only occurs once in a standard sonata movement (unlike a pop/rock introduction).
Introductions can be very brief, including simply one, two, or three forte chords from the orchestra as a simple “call to attention.” The opening two chords of Beethoven’s “Eroica” symphony are an example of this brief introduction.
Longer introductions often provide a slow contrast to a lively P theme. These slow introductions sometimes emphasize the parallel minor mode to prepare a major-key P theme. They typically end with a half cadence or other strong dominant arrival to generate anticipation of the tonic-emphasizing P theme that follows. The composer may stand on the dominant for some time to increase that anticipation. An example that does all of these things would be the introduction to Beethoven’s fourth symphony (0:00–2:36 in the following recording).
Haydn’s Symphony 96 (“Miracle”) exemplifies the same traits (0:00–1:30 in the recording below).
A coda is a new module that follows the end of the recapitulation’s thematic cycle. In other words, once the harmonic work of the recapitulation has been accomplished (the arrival of the I:PAC ESC) and the basic themes of the exposition have been presented (such as P TR S C), new material tends to fall into the coda module.
Like the introduction, the coda sits outside the recapitulation. Thus, if the development and recapitulation are repeated (more often in the score than in modern performances), the coda will come after the final repeat. Without a clear repeat mark in the score, codas are primarily identified by their coming after the end of the thematic material being recapitulated.
There is one common exception: often a codetta from the exposition will be expanded in the recapitulation to make a stronger ending punctuation to close the movement. What distinguishes a coda from a codetta is that a codetta is a post-cadential extension of the final cadence of the exposition/recapitulation. A coda does something more — harmonically, such as visiting a new key; or melodically, such as introducing a new theme or revisiting earlier material such as P or the development.
One can compare the codetta–coda relationship to the postchorus–coda relationship in pop/rock music. A codetta or postchorus simply rounds out the ending of a cycle, making its finality clear. A coda makes a notable melodic or harmonic move in order to do something more novel and significant.
An example coda would be at the end of Beethoven’s Piano Sonata in C Major, Op. 2, No. 3, first movement (beginning at 8:29 in the recording below). The recapitulation completes its P TR? S? TR S C cycle. After a shortened version of C, though, a deceptive resolution of the dominant chord leads to an excursion in A-flat major (flat-VI) involving new melodic material. After a harmonic sequence, Beethoven brings back the opening of the P theme in C major, followed by a bombastic, definitive end to the movement. The new melody, the new key area, and the use of a substantial portion of P, all contribute to its coda-ness — and make a codetta interpretation difficult to sustain.
While the coda sits outside the definitive sonata structure, it often plays an important role rhetorically in the movement. For example, since flat-VI is a closely related key in minor, the flat-VI emphasis in Op. 2/3 could be seen as rounding out a bigger tonal story. Beethoven visits minor-V in the exposition and minor-I in the recapitulation as part of the double-MC form. The coda in flat-VI (closely related to minor-I) could be interpreted as rounding off that story — one that comes alongside the normal sonata-form story, but is not part of it. Other times codas may simply allow a composer to extend the resolution of tension built up in a long movement, or complete work begun but not finished during a development section.
Whatever the case, it is important to remember that while what happens in the exposition and recapitulation “makes a sonata a sonata,” what happens in these framing modules (and the development) often defines what is special about one sonata in particular. A complete analysis engages both the normative and the deviant, the grammatical and the rhetorical.