What is the structural significance of the recapitulation in classical sonata form?

The recapitulation provides the double return of both the tonic key and the primary subject. It is the combination of these two factors that identifies the recapitulation as the concluding section of sonata form. While the exposition and development – as the first two sections of classical sonata form – develop the tonal journey from the tonic through a secondary key (usually the dominant or tonic minor) and then through various (often distant) keys, the recapitulation provides the final return of the tonic. Combined with the return of the primary space, this is then a mirror image of the exposition. However, the main significant difference to the exposition is that the secondary subject remains in the tonic key rather than modulating, which again reinforces the tonic and the conclusion of sonata form.