A rondo, for the sake of my readers who do not know the term, is a musical form used in songs, but usually instrumental compositions. The rondo form is: ABACADA….
Imagine a catchy, pithy theme–we’ll call it the RONDO THEME– that section we’ll call A. It’s sticky, memorable, something we want to hear again.
Now, we do something compositionally DIFFERENT. We’ll call that B. If the A section was chordal, let’s do something melodic. If the A section was loud, let’s do something SOFT. Something DIFFERENT.
Now, let’s have a musical transition from where we just were in the B section, and go back to the A section. The listener thinks: hurrah! I know where I am. Aren’t I smart, and, gee, I like this theme.
Then we move to a contrasting C section. Something even more different than the A or the B sections. It’s whatever those musics were not. Something different.
Then we go back to the A section: tra la, tra la. The mind tucks this music away into the background as we ponder what we’ll be doing later in the day. We’ve already heard this music twice before: I’ve got it, I’ve got it.
Sometimes a composer gives you one more music chunk: the D section. And like before, it has music that is different (to an extent) than the other three sections. In this section, the composer may embed the climax of the movement and build and build and build until we finally get one last return of the A section. We all stand, sing the theme one last time, and clink our beer steins together in brotherly harmony.
As I was throwing the ball for the dogs today, I realized that we rarely have an E section in rondos. One loves the concept of a piece that goes: ABACADAEAFAGAHAIAJA… und so weiter. But in reality, people really can only stand four reiterations of the nifty rondo theme. We seem to be able to effectively perceive four chunks/sections of music in a single movement–especially at the end of a multi-movement composition, which is where the rondo usually occurs.
This is not a scientific study, only a casual observation and recommendation for a future dissertation, but it seems composers have a ceiling of four sections in rondos (ABCD) and no more than four statements of the rondo theme (ABACADA and it’s easier-to-digest little sister ABACA)