What differs between the rondo and its Baroque counterpart, the ritornello?

Question

So, ever since I heard the term ritornello, I have wondered what makes it different from the rondo. So I’ve listened to several pieces in ritornello form to try to find the difference, but I couldn’t. These are the things I checked for:

• Does the main theme come back more than once?
• Does any development occur, main theme or otherwise?
• Does it modulate from the main theme to the episode?
• Is the episode significantly different from the main theme?

And both the rondo and the ritornello checked those boxes. So here is an example of a ritornello:

And here is an example of a rondo:

They both involve development, variation upon repetition, modulation, main theme and episodes. So what’s the difference between them?

Answer 1

I'd say the main difference between rondo and ritornello is one of emphasis. In a typical rondo, the 'refrain' carries the main musical interest or idea, with the 'couplets' providing relief and variety between its repetitions.

In a baroque concerto allegro, on the other hand, the ritornello tends to serve as a brief 'appetizer' or 'motto' for the more interesting musical content played by the soloist(s). Its principal function is to establish the tonality and overall mood of the piece. (Which is why Vivaldi's ritornelli often forcefully emphasize the tones of the tonic triad.)

This is of course somewhat of a simplification; for example, Bach's concerti often feature pretty substantial and fascinating ritornelli. But the above is the typical case, as I understand it.

Answer 2

There are some semi-strict definitions. From my favorite go-to ,

the ripresa, ritornello, and passacaglia are based on the 16th-century Italian dance form. The ripresa or ritornello (often appearing as V-I or IV-V-I) is a unit of music that precedes, follows, or alternates with a dance. The internal ripresa could be used as a portion within a dance or as a conclusion. While the number of internal riprese varies according to the time elapsing between sections of a piece, its harmonic design (i.e., the basic V-I pattern) is fixed. The concluding ripresa, on the other hand, occurs at the end of a piece and shows a greater harmonic variety through the insertion or substitution of alternate chords. In the concluding ripresa, the basic V-I pattern could be varied through the insertion, reshuffling, and mixing of chords, resulting in unpredictable chains of chord progressions such as IV-V-I-I, V-V-I-IV, V-V-I-II, or V-V-I-I. During the 17th-century, these concluding riprese became independent sets and took the name of the passacaglia or ciaccona. The technique of the passacaglia or ciaccona then, is simply an ostinato of derived formulas of the ripresa. Thus, the ripresa, ritornello, and passacaglia evolved from the same harmonic pattern which originally functioned as a unit of the Italian dance form

And for 'rondo,'

an instrumental form in which the first or main section (sometimes called the 'refrain) is repeated between subsidiary sections (called 'episodes', 'couplets', 'digressions' or 'subordinate themes') and to conclude the piece - usually in a lively tempo

Basically, a rondo is a more general form, but the ritornello could be pretty much a subset.