In the context of sonata form, what does the Exposition section primarily do?

The Exposition section of sonata form is fundamental as it establishes the main thematic material for the piece. It typically introduces two contrasting themes: the first theme is usually presented in the tonic key, while the second theme is presented in a different key, often the dominant for major works or the relative major for minor works. This contrasting presentation sets the stage for the development of the themes in later sections of the sonata. The clear delineation of these themes helps to create tension and contrast, which is crucial for the overall structure of the sonata form. Thus, the primary function of the Exposition is to lay the groundwork by presenting the thematic ideas that will be explored and transformed in the subsequent sections.