Musical composition characterized by systematic imitation of one or more themes in counterpoint .
Fugues vary greatly in their actual form. The principal theme (subject) is imitated
i.e., repeated successively in similar form at different pitch levels by different parts or voices
in the so-called exposition. The countersubject is the continuation of the subject that accompanies the subject theme's subsequent entries in the other voices. Episodes using modified themes often separate the subject's entries. The fugue emerged gradually from the imitative polyphony of the 13th century. Johann Sebastian Bach 's keyboard fugues are the most famous of all. The works of Bach and George Frideric Handel inspired the later fugues of Wolfgang Amadeus Mozart , Ludwig van Beethoven , and others, many of whom commonly included fugues in the final movements of symphonies, string quartets, and sonatas.