In music, an instrumental composition in cyclical form, originally any instrumental work as opposed to a cantata or vocal work. At first the sonata was almost identical with the suite, but it soon abandoned the pure dance forms which the suite embodied. The violin sonata attained a somewhat perfected form before that of any of the keyed instruments. Its slow introductory first movement generally shows traces of ecclesiastical influence; the second movement, an allegro, which corresponds to the first movement of a modern sonata, was derived from vocal madrigals or part music; the third movement, which is characteristically slow, was evolved from solo vocal music, while the last movement showed elements of dance music, and was therefore a pure suite movement. Of the popular dance forms, the minuet survived the longest but was ultimately supplanted by the scherzo, while the gigue and chaconne, of which Bach left so many examples, were succeeded by the finale or rondo. The first noteworthy advance is in a set of seven sonatas for the clavier. Frische Klavierfruchte (1703), by Johann Kuhnau, in which he shows a partial recognition of the relation and balance of keys. Johann Mattheson chose the gigue for the concluding movement of his sonatas, and both he and Alessandro Scarlatti did much to define and unify the sonata form.

In the works of Domenico Scarlatti are found the first traces of a distinct secondary subject in the first allegro. The domain of the sonata was long monopolized by writers for the violin, and through the advances made by Locatelli, Geminiani, and Tartini the sonata finally reached the four movement type. Johann Sebastian Bach wrote many sonatas for various instruments and for combinations of instruments, but he did not aid in the direct development of the form. His son, Philipp Emanuel Bach, established the number of movements as three. Haydn is important principally for having clearly indicated the outlines and for having made the use of the minuet and the rondo imperative. Mozart adds to Haydn's unemotional forms symmetry, grace, and more mature and elaborate themes and harmonies. Beethoven brought the sonata to its greatest perfection. In the Kreutzer sonata, for violin and pianoforte, and in the pianoforte sonatas, in D minor (Op. 31), C Major (Op. 53), F minor (Op. 57), B flat (Op. 106), and C minor (Op. 111), he attains to such a command of technical resource and emotional expression that the form seems incapable of further development.

SONATA FORM is a term applied to the form of the first movement of a sonata, symphony, or chamber-music composition. The first movement of a sonata or kindred cyclical form consists of three sections: (1) the exposition. (2) the development. (3) the repetition. The first section begins with the principal subject in the tonic key. An episode consisting of some development of the principal subject leads into the secondary subject. This appears in the key of the dominant, if the movement is in major. If the movement is in minor the secondary subject is announced in the key of the relative major. Then follows some slight development of the secondary subject. After this the entire exposition section is repeated literally. The second or development section is devoted to a full thematic working out of either one or both the themes announced in the previous section. In the development section episodes built upon new themes may also be introduced. The third or repetition (also recapitulation) section is a repetition of the exposition section, though composers generally vary the instrumentation. In this section the secondary subject appears in the key of the tonic. A more or less extended coda, constructed either upon the material already introduced or upon new material, closes the movement. Frequently the movement is preceded by a shorter or longer introduction in slow tempo. The essential features of this form have not been changed since Beethoven's time. Consult Shedlock, The pianoforte Sonata (London, 1895).