Johann Sebastian Bach
Bach worked before sonata form existed. His instrumental music is organised by counterpoint and by the ritornello: a full-ensemble passage that opens a movement and returns, in different keys, between episodes for smaller groups. In a concerto movement you follow the ritornello the way you would follow a rondo refrain.
The other organising principle is dance. Suites and many concerto finales are built on dance types (gigue, minuet, bourrée), each with a fixed metre and character and a simple two-part or three-part layout with repeats.
Texture is where Bach's music lives. Two, three or four independent lines run at once, each a real melody. Listening for the lines separately, and then for how they fit, is the whole skill.
What to listen for
- The ritornello: the opening full-group passage. Each return is a landmark; count them.
- In the Brandenburg concertos, the change between the full group and the solo group. The alternation is the form.
- Sequences: a short figure repeated a step higher or lower several times. Bach uses them to travel between keys.
- The bass line. It is never just accompaniment; it is often the clearest melody in the texture.
Source: Johann Sebastian Bach