What is a sonata form?

A sonata form is a musical structure that originated from a ternary form (a three part form); coming into recognition in the early Classical era. Despite variations in the form, the general form consists of three main sections. Although the term sonata also refers to a larger musical form, e.g. piano sonata, the structure refers to the inner organisation of a smaller form. The first section of the form is the exposition. The exposition is in the tonic key (the "home" key) and generally modulates to the dominant. It generally consists of two constrasting subjects (or themes) the first subject and the second subject. The development includes further modulatory exploration and develops the themes of the exposition but generally they are less recognisable than the first statements. The development acts as a preparation for the return of the tonic ("home" key) in the form of the recapitulation, the third part of the form. In most sonata forms the recapitualtion contains a restatement of the first two subjects followed by an extended ending; generally termed a coda. The primary purpose of the recapitulation is to bring the piece firmly back to the tonic key; giving a strong ending to the movement.