In Sonata Allegro form, what is the function of the Exposition section?

The function of the Exposition section in Sonata Allegro form is primarily to present the themes of the piece. During this section, the main musical ideas or themes are introduced, usually consisting of two contrasting themes. This is crucial, as it sets the thematic material that will be explored and manipulated later in the piece. The Exposition typically establishes the primary key area and then transitions to a contrasting key for the second theme, allowing the composer to create tension that will be addressed in subsequent sections.

The clarity and establishment of themes during this section is essential for the structure of Sonata Allegro form, as it lays the groundwork for the development and recapitulation that follow. Understanding this function helps in grasping how musical ideas evolve and interact throughout the composition.