What is the structure of the first movement of a Classical symphony?

The first movement of a Classical symphony is predominantly structured in sonata-allegro form. This form is characterized by three main sections: exposition, development, and recapitulation.

In the exposition, the main themes are introduced. Typically, there are two contrasting themes presented in different keys, establishing a musical dialogue. The development section then takes these themes and explores them, often transforming and modulating them through various keys, which adds drama and tension. Finally, in the recapitulation, the themes return, generally in the original key, bringing a sense of resolution and closure.

Sonata-allegro form became a fundamental structure for not just symphonies but also for other types of instrumental music during the Classical period and beyond, making it a vital concept in understanding the evolution of Western art music. The clarity and balance of this form reflect the ideals of the Classical era, emphasizing structure and thematic development.