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 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 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:
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:
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:
Not all development takes place in what is commonly known as the "development section" of a work. It can take place at any point in the musical argument. For instance, the "immensely energetic sonata movement" that forms the main body of the overture to Mozart's Opera Don Giovanni announces the following theme during the initial exposition. It consists of two contrasting phrases: "first determined, then soft and conspiratorial."
William Mann says the "the first, insistent phrase [of the above] is very important. At once it is taken up imitatively by various departments of the orchestra, and [starting in] A major, jumps through several related keys." Each repetition of the descending phrase is subtly altered one note at a time, causing the music to pass from the key of A major, through A minor and thence via a chord of G7 to the remote key of C major, and thence back to A major.
The central section of the Overture (the part commonly known as the "development section") utilizes both phrases of the theme, developing it through repetition in a modulating sequence. The steady plod of the bass line against the sequential repetitions of the "soft and conspiratorial" phrase outlines a circle of fifths chord progression:
Simultaneously, Mozart adds to the mix and continues to develop the imitative counterpoint that grew out of the first phrase. In the words of Willam Mann, this development "unites both halves" of the theme. This is how this tightly woven texture pans out: