Editing Sonata form (section)

===Introduction===
{{Main article|Introduction (music)}}
The ''introduction'' section is optional, or may be reduced to a minimum. If it is extended, it is, in general, slower than the main section and frequently focuses on the [[Dominant (music)|dominant key]]. It may or may not contain material that is later stated in the exposition. The introduction increases the weight of the movement (such as the famous dissonant introduction to Mozart's [[String Quartet No. 19 (Mozart)|"Dissonance" Quartet]], K. 465), and also permits the composer to begin the exposition with a theme that would be too light to start on its own, as in Haydn's [[Symphony No. 103 (Haydn)|Symphony No. 103 ("The Drumroll")]] and Beethoven's [[Quintet for Piano and Winds (Beethoven)|Quintet for Piano and Winds Op. 16]]. The introduction usually is not included in the exposition repeat: the ''Pathétique'' is a possible counterexample. Much later, Chopin's [[Piano Sonata No. 2 (Chopin)|Piano Sonata No. 2]] (Op. 35) is a clear example where the introduction is also included.

On occasion, the material of introduction reappears in its original tempo later in the movement. Often, this occurs as late as the coda, as in Mozart's [[String Quintet No. 5 (Mozart)|String Quintet in D major, K. 593]], Haydn's "Drumroll" Symphony, Beethoven's [[Piano Sonata No. 8 (Beethoven)|Piano Sonata No. 8 ("Pathétique")]], or Schubert's [[Symphony No. 9 (Schubert)|Symphony No. 9 ("Great")]]. Sometimes it can appear earlier: it occurs at the beginning of the development in the ''Pathétique'' Sonata, and at the beginning of the recapitulation of Schubert's [[Symphony No. 1 (Schubert)|Symphony No. 1]].