Music from the classical era is characterized by relatively short phrases of around four bars each and an overall sense of balance. Texture, harmony and melody are a great deal more simplistic than in the preceding baroque period. Classical texture is predominantly homophonic--a single melody line with accompaniment--as opposed to the multi-textured polyphonic texture of many baroque compositions.
Sonata form originated in the classical period and was strictly adhered to by the majority of composers from this era. It consists of three clearly defined sections: the exposition (and introduction), the development section (a contrasting section in a different but related key) and the recapitulation (a return to the introductory material, returning to the original key). It was applied to the first movements of sonatas, symphonies and concertos, and was also used for opera overtures, which were always instrumental compositions.
The classical era saw a great deal more emphasis on instrumental genres than any previous period in music history. Two prominent new genres which emerged during this time were the symphony and the string quartet. Both genres are typically four movements long and follow the same form, with a fast first movement in sonata form, a slow second movement, a third movement in minuet form and a fast final movement in sonata rondo form. Joseph Haydn is often referred to as the father of both of these genres.
The harpsichord, which dominated the baroque era as the keyboard instrument of choice, was overshadowed by the more robust and dynamically diverse fortepiano. An enormous repertoire exists for the fortepiano, especially in the form of sonatas and concertos composed by all three of the great classical composers. The modern pianoforte took over from the fortepiano towards the last quarter of the classical era. It benefited from a larger range and pedals for sustaining and dampening the sound. Woodwind instruments also became more refined during this time, particularly the clarinet. This new instrument was brought into prominence by Mozart who wrote a famous clarinet concerto and frequently used the instrument in his orchestration.