Mozart, Rondo alla turca. Audio cover from the Melos sound library.
Of all the names of musical forms, rondo is the one that frightens the fewest people, for a simple reason: anyone who has ever sung a song with a refrain already knows it. The rondo is exactly this: a main theme that keeps coming back, always the same or nearly, separated by different episodes. Refrain, verse, refrain, another verse, refrain. In letters: A-B-A-C-A. Pop music has lived inside it for a century; the eighteenth century lived there entirely.
The name comes from medieval French poetry, the rondeau, which went round in a circle; the success comes from psychology. The return of the theme is a promise kept: the listener recognises it, waits for it, and the composer plays with that expectation, delaying it, disguising it, bringing it back in the wrong key only to correct himself. That is why the rondo is almost always the last movement of a symphony or a concerto: after the reasoning and the song, the farewell wants a theme the audience takes home. Haydn packed it with jokes, Gypsy themes, finales that pretend to end; Mozart raised it to a genre in its own right with the Rondo alla turca and pages where the refrain becomes a character who always re-enters in a good mood; Beethoven crossed it with sonata form, producing the hybrid the textbooks call sonata-rondo and which is the classical finale par excellence.
The listening game we propose is elementary and it works: put on the third movement of any Mozart concerto and raise a finger each time the refrain returns. By the third return you will notice you can already hum it, which is the effect intended by the builder; by the fourth you will notice it is coming back different, and that is where art begins. Then repeat the same exercise with any radio hit: same architecture, same trick, same satisfaction. Between the Rondo K. 331 and a refrain from this summer lie two and a half centuries and no structural difference. The audience does not have to understand, we always say so; but when it discovers it has understood all along, the look on its face is the reason this column exists.