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 era of music, developed further through the works of the Mannheim school, and gained prominence in the works of Joseph Haydn, Wolfgang Amadeus Mozart, and Ludwig van Beethoven.
The word sonata is also used to refer to a stand-alone instrumental work on a relatively large scale.
A work in sonata form can be divided into three sections: the exposition, development, and recapitulation.
Outline of form
The sonata form as it developed in late-18th-century central Europe is based on a large-scale plan involving a modulation, or change of key, away from the main key of the work. At the end of the exposition, the music modulates to a second key and finishes off with a decisive cadence. However, in the classic period composers considered it unacceptable to end a work in a different key than which it had begun, so the second half of the movement would represent a dramatic attempt to modulate back to the original key.
While the terms "exposition," "development," and "recapitulation" are useful for defining the typical structure of a sonata movement, the composers themselves did not think in these terms.
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.
The exposition begins with a distinctive theme in the tonic key. As soon as this theme is introduced, it is often repeated and varied, or gives way to new material which sounds transitional. This culminates in a cadence in a new key, usually in the dominant or relative major key (in the case of a sonata in a minor key). New material of a contrasting character is introduced in this second key area. A small codetta brings the exposition to a close with an authentic cadence in the key of the second subject.
Being the very heart of the sonata form's drama, there are as many variations on this basic principle as there are variations on a plot in classical literature. In the sonata forms of Beethoven, for example, the second key area was often not in the dominant; his "Waldstein" Sonata (Op. 53) is one famous example. Also, in many of Haydn's sonata forms, such as the Piano Sonata in Eb (Hob. XVI:62), the second key area contains exactly the same theme as at the sonata's beginning, but presented in a different guise.
Some words of caution are thus in order with the terminology. While textbooks often use the terms "first subject (or theme)" and "second subject (or theme)," they can be misleading and even unhelpful when analyzing real sonatas, and incidentally was not the way that composers conceived of the form. Many sonatas contain many more than two distinct themes, and several contain no recognizeable "second theme," rather musical material of an aphoristic or fragmentary character. Also prevalent in older texbooks is the description of the second theme as being more lyrical, or feminine, in character. This also does not hold true in most real-life examples.
Therefore, what is essential about the exposition is the modulation to a second key, a strong cadence in that key, and a contrast in character between the music of the two key areas achieved by any variety of means. This essential contrast between key and materials is to the sonata form what a conflict is to literature
The development tends to be the most unstable section of the work. Harmonically, the music proceeds through many different keys, some quite far-removed. Thematically, this section also tends to be unstable: breaking down the material presented in the exposition, splintering it into its constituent motives, essentially presenting familiar material in novel ways.
At the end of the development, the harmonic and thematic instability begins to normalize as the return of the main theme in the tonic key is prepared. This can lead up to a dramatic arrival (as is typical in Beethoven), or simply relax the tension and segue gently (characteristic of Mozart), or end in a humorous pause (quite often in Haydn).
This section follows practically the same outline as the exposition, with the crucial difference that all of the exposition's material is presented in the main key. This requires the transitional material to be rewritten in a way that keeps it from modulating, and this is usually the main source of interest in a section which would otherwise become anticlimactic.
Composers will often add a coda to a work in sonata-allegro form, often to the last movement (which was often written in sonata form as well). This could be for many reasons, sometimes to provide an exciting conclusion, and sometimes to resolve a harmonic tension presented earlier in the work. In a minor-key work, a coda often was written in the parallel major (i. e. C Minor/C Major) as a way of banishing the darkness of the minor mode.
The coda varies in length, with some taking up a hefty percentage of the movement. Notably lengthly codas including the finale of the first movement of Beethoven's Piano Sonata Op. 57 ("Appassionata"), and in the finale of his Eighth symphony -- which is almost half the length of the movement!
A coda in a sonata movement corresponds roughly to the denoument of a literary plot.
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:
- linked keys in different themes
- inverting the theme
- use of a pedal note for connection
- the same melody line put into a different but related key
- 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
- a striking feature of one movement could be woven into another movement. This is called "transformation of themes"
Variety is achieved by:
- changing the order of movements
- composing the theme in the style of a Canon whereas when it was introduced it was a single line theme
- using variations by changing the rhythms and time signature, but with the theme still recognisable
- using various modulations and different harmonies
- using ornaments, shakes or trills
- changing the accent and using the devices of counterpoint to introduce new ideas