Describe ritornello form and give an example of where it is used

Ritornello form was used most predominantly in the Baroque era. The term ‘ritornello’ translates as ‘little return’ and is a passage of music that reoccurs throughout a piece; these passages are separated by episodes. The form is most alike with the Rondo form, however it differs in that the ritornello (or A section) can return in different keys and can be varied by returning, not in its entirety, but as a reduced version, a partial ritornello. An example of Ritornello form can be found in Bach’s Brandenburg Concerto 4 in G: 1^st Movement. Here, Bach utilises the form by making the ritornello sections tutti, whilst the episodes feature solos from the concertino, which includes 2 recorders and a violin. He creates variety within the episodes by changing which instruments have solos and modulating to different keys.