In classical music, musical development is a process by which a musical idea is communicated in the course of a composition. It refers to the transformation and restatement of initial material. Development is often contrasted with musical variation, which is a slightly different means to the same end. Development is carried out upon portions of material treated in many different presentations and combinations at a time, while variation depends upon one type of presentation at a time.
In this process, certain central ideas are repeated in different contexts or in altered form so that the mind of the listener consciously or unconsciously compares the various incarnations of these ideas. Listeners may apprehend a "tension between expected and real results" (see irony), which is one "element of surprise" in music. This practice has its roots in counterpoint, where a theme or subject might create an impression of a pleasing or affective sort, but delight the mind further as its contrapuntal capabilities are gradually unveiled.
In sonata form, the middle section (between the exposition and the recapitulation) is called the development. Typically, in this section, material from the exposition section is developed. In some older texts, this section may be referred to as free fantasia.
- The division of a theme into parts, each of which can be developed in any of the above ways or recombined in a new way. Similarly, two or more themes can be developed in combination; in some cases, themes are composed with this possibility in mind.
- Alteration of pitch intervals while retaining the original rhythm.
- Rhythmic displacement, so that the metrical stress occurs at a different point in the otherwise unchanged theme.
- Sequence, either diatonically within a key or through a succession of keys.
The Scherzo movement from Beethoven's Piano Sonata No. 15 in D major, Op 28 (the "Pastoral" Sonata) shows a number of these processes at work on a small scale. Charles Rosen (2002) marvels at the simplicity of the musical material: "The opening theme consists of nothing but four F sharps in descending octaves, followed by a light and simple I/ii/V7/I cadence with a quirky motif repeated four times."  These opening eight bars provide all the material Beethoven needs to furnish his development, which takes place in bars 33-48:
The division of a theme into parts
The falling octave in the first two bars and the repeated staccato chord in the left hand in bars 5-8 are the two fragments that Beethoven later develops:
Alteration of pitch intervals
The somewhat bald falling octave idea in the first four bars is transformed in bars 33-36 into an elegant shape ending with an upward-curving semitone:
In this movement, the repeated left hand chords in bar 5 are displaced so that in bar 33 onwards, they fall on the 2nd and 3rd beats:
Sequence and the development of two or more themes in combination
In bars 33-48, the two fragments combine and the development goes through a modulating sequence that touches on a succession of keys;
The following outline demonstrates Beethoven’s strategic planning, which he applied on a larger scale in the development sections of some of his major works. The bass line traces a decisive progression through a rising chromatic scale:
- Benward & Saker (2009), Music in Theory and Practice: Volume II, p.138-39. Eighth Edition. ISBN 978-0-07-310188-0.
- Wennerstrom, Mary (1975). "Form in Twentieth-Century Music" (chap. 1), Aspects of Twentieth-Century Music. Wittlich, Gary (ed.). Englewood Cliffs, New Jersey: Prentice-Hall. ISBN 0-13-049346-5.
- Temperley, N. (2002, p. 355) “Development” in Oxford Compasnio to Music. Oxford University Press.
- Rosen, C. (2002, p.161), Beethoven's Piano Sonatas, a Short Companion. Yale University Press.
- Rosen, C. (2002, p.162), Beethoven's Piano Sonatas, a Short Companion. Yale University Press.