Editing Sonata form (section)

===Development===
{{Main article|Development (music)}}
In general, the development 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 on occasion juxtaposed and may include new material or themes—though exactly what is acceptable practice is a point of contention. Alterations include taking material through distant keys, breaking down of themes and sequencing of motifs, and so forth.

The development varies greatly in length from piece to piece and from time period to time period, sometimes being relatively short compared to the exposition (e.g., the first movement of ''[[Eine kleine Nachtmusik]]'') and in other cases quite long and detailed (e.g., the first movement of the [[Symphony No. 3 (Beethoven)|"Eroica" Symphony]]). Developments in the Classical era are typically shorter due to how much composers of that era valued symmetry, unlike the more expressive Romantic era in which development sections gain a much greater importance. However, it almost always shows a greater degree of tonal, harmonic, and [[rhythm]]ic instability than the other sections. In a few cases, usually in late Classical and early Romantic concertos, the development section consists of or ends with another exposition, often in the relative minor of the tonic key.<ref>{{Cite journal|last=Wingfield|first=Paul|date=2008|editor1-last=Hepokoski|editor1-first=James|editor1-link=James Hepokoski|editor2-last=Darcy|editor2-first=Warren|title=Beyond 'Norms and Deformations': Towards a Theory of Sonata Form as Reception History|journal=Music Analysis|volume=27|issue=1|pages=137–177|doi=10.1111/j.1468-2249.2008.00283.x|jstor=25171408|issn=0262-5245|doi-access=free}}</ref>

At the end, the music will usually return to the tonic key in preparation of the recapitulation. (On occasion, it will actually return to the sub-dominant key and then proceed with the same transition as in the exposition.) The transition from the development to the recapitulation is a crucial moment in the work. The last part of the development section is called the ''{{Visible anchor|retransition}}'': It prepares for the return of the first subject group in the tonic.

Exceptions include the first movement of [[Johannes Brahms|Brahms]]'s [[Piano Sonata No. 1 (Brahms)|Piano Sonata No. 1]]. The general key of the movement is C major, and it would then follow that the retransition should stress the [[Seventh chord#The dominant seventh|dominant seventh chord]] on G. Instead, it builds in strength over the dominant seventh chord on C, as if the music were proceeding to F major, only to take up immediately the first theme in C major. Another exception is the fourth movement of [[Franz Schubert|Schubert]]'s Symphony No. 9. The home key of the movement is C major. The retransition prolongates over the dominant chord on G, but suddenly takes up the first theme in the flattened mediant [[E-flat major|E{{music|b}} major]].

A particularly common exception is for the dominant to be substituted with the dominant of the relative minor key: one example is the first movement of Haydn's String Quartet in E major, Op. 54 No. 3.

Occasionally, the retransition can begin with a false recapitulation, in which the opening material of the first theme group is presented before the development has completed. The surprise that ensues when the music continues to modulate toward the tonic can be used for either comic or dramatic effect. An example occurs in the first movement of Haydn's String Quartet in G major, Op. 76 No. 1.