In sonata form, which section returns to the original key and restates the original themes?

In sonata form, the section that returns to the original key and restates the original themes is the recapitulation. During the recapitulation, the composer revisits the primary themes introduced in the exposition, but this time both themes are presented in the tonic key. This is a crucial part of sonata form because it provides a sense of closure and resolution, allowing the listener to experience the themes in a familiar context after they have been explored and transformed during the development section.

The recapitulation is fundamental as it follows the development, where themes are varied and explored in different keys, creating tension and contrast. By returning to the original key and reintroducing the main themes, the recapitulation resolves the harmonic and thematic exploration that occurred earlier in the piece.