rondo

Italian rondo — from French rondeau, from rond (round) — describes a musical form defined by the return of a main theme (the refrain) after each contrasting section. The structure is circular: A-B-A-C-A-D-A, where A is the main theme and B, C, D are episodes. The music keeps coming back to where it started, like a wheel returning to the same point.

The rondeau was a medieval French poetic form — a poem that returned to its opening lines at fixed intervals. The word round, rondeau, rondeaus, rondo all share the Latin rotundus (round). The musical form borrowed the structural principle from the poetic form: the literary refrain became the musical refrain.

Mozart made the rondo one of the most popular final movements of classical-era compositions. The finale of his Piano Concerto No. 20 in D minor, the finale of his Piano Sonata K. 331 (the 'Alla Turca'), and dozens of other works use rondo form because it provides satisfying variety while maintaining coherence. The theme's return is reassuring; the episodes provide adventure; the final return resolves everything.

Beethoven stretched the rondo to its limits in his late piano sonatas, where the return of the theme is delayed, disguised, or transformed so radically that it barely functions as a refrain. The circle loses its round quality; the return is a surprise. The form that was defined by its circularity became, in Beethoven's late work, a form about the anxiety of return.