In the Classical period (roughly 1750-1810) 'sonata' came to mean a work in several movements. It was usually three, with the first movement in a special sonata form. Sonatas were a popular and important form, and many were composed for amateur performers to play at home.
During the Classical period the harpsichord had been largely replaced by the piano. Many piano sonatas were written and many composers wrote sonatas for a solo instrument and piano. Violin, cello and flute sonatas were all popular.
Mozart, Haydn and Beethoven all wrote piano sonatas, violin sonatas and cello sonatas.
The standard Classical form is:
The first movement of sonata form has three main sections: exposition, development and recapitulation.
Most of the musical ideas come from two main themes known as the first and second subject.
In the exposition the material is 'exposed' which means that it is presented for the first time.
There are two main melodies known as the first and second subject: