Introduction[edit]
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 key. It may or may not contain material that is later stated in the exposition. The introduction increases the weight of the movement, 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 ("The Drumroll") and Beethoven's Quintet for Piano and Winds Op. 16. The introduction usually is not included in the exposition repeat.
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 in D major K. 593, Haydn's "Drumroll" Symphony, or Beethoven's Piano Sonata No. 8 ("Pathétique").