By the early eighteenth century, the time of Antonio Vivaldi, most ‘solo concertos’ consist of a standard plan of 3 different movements – fast, then slow, then fast again. Most commonly these movements were built up using a structure known as RITORNELLO FORM.
Ritornello form: is the principal used to build up a musical structure in a Baroque concerto movement. It comes from the Italian word ritornare , meaning to return. We can therefore expect a plan to the music similar to that which we would find in a “rondo”, where the opening music returns several times within the movement. There are, however, three important differences between the two forms.
1. The Italian word ending (or suffix) ello, meaning “small”, implies that, when the opening music returns, we hear a shortened version of the theme. In a rondo the whole theme is normally heard when it returns.
2. When the opening theme returns in a rondo it is nearly always in the same key as the opening theme. However, each new ritornello in ritornello form may be in any key of the composer’s choice.
3. In the episodes between the various ritornelli, the music features above all the soloist(s). In a rondo there is no clear-cut distinction as to who plays the returning opening theme and who plays the episodes.
As one might expect, ritornello form is only used where the music features a soloist with accompaniment from other instruments. e.g. in the Baroque concerto or in the operatic aria of the Baroque.