Editing Sonata form (section)

===Monothematic expositions===
<!-- This section is linked from [[Joseph Haydn]] -->

It is not necessarily the case that the move to the dominant key in the exposition is marked by a new theme. Haydn in particular was fond of using the opening theme, often in a truncated or otherwise altered form, to announce the move to the dominant, as in the first movement of his [[Piano Sonata Hob. XVI/49|Sonata Hob. XVI/49]] in E{{music|b}} major. Mozart also occasionally wrote such expositions: for instance in the [[Piano Sonata No. 17 (Mozart)|Piano Sonata K. 570]] or the [[String Quintet No. 5 (Mozart)|String Quintet K. 593]]. Such expositions are often called ''monothematic'', meaning that one theme serves to establish the opposition between tonic and dominant keys. This term is misleading, since most "monothematic" works have multiple themes: most works so labeled have additional themes in the second subject group. Rarely, as in the fourth movement of Haydn's [[List of string quartets by Joseph Haydn#Opus 50|String Quartet in B{{music|b}} major, Op. 50, No. 1]], did composers perform the ''tour de force'' of writing a complete sonata exposition with just one theme. A more recent example is [[Edmund Rubbra]]'s Symphony No. 2.

The fact that so-called monothematic expositions usually have additional themes is used by Charles Rosen to illustrate his theory that the Classical sonata form's crucial element is some sort of ''dramatization'' of the arrival of the dominant.<ref>See his book ''The Classical Style'' (New York: Norton)</ref> Using a new theme was a very common way to achieve this, but other resources such as changes in texture, salient cadences and so on were also accepted practice.