The New International Encyclopædia/Rondo
RONDO (It., from Fr. rondeau, roundel). One of the oldest and most generally used of the musical forms, characterised by the constant recurrence of one principal theme. The oldest rondos of the sixteenth century consisted of a plain theme of four bars, which was followed by a few bars of interlude, when the original theme was repeated. Soon the theme itself was lengthened to eight or sixteen bars, and the interlude avoided the principal key. Then the intermediate passage appeared as a fully developed second theme in a related key. The fundamental idea of the rondo as established by Beethoven is (denoting the three themes by A, B, C respectively): A, B (in key of dominant), A, C, A, B (in key of tonic), coda. On its second and third recurrence A appears in different keys. Also, in order to avoid monotony, Beethoven does not repeat literally. When only two themes are employed the following may be given as the fundamental schedule: A, B, A (in key of B), B (in key of A), A. Under later composers (notably Chopin) the rondo form becomes even more elastic.