The medieval Bar form can be classed as a sectional binary form in which only the first part is repeated, giving an AAB structure. Even in the early rondeau and other formes fixes, in which a complex system of phrase repetition was required by the verse structures, the music itself was often made up of two periods or phrases. With the disappearance of the formes fixes, and the development of instrumental music whose shaping owed a good deal to the symmetries of phrases required for dancing, binary movements became more and more frequent.
Some of the keyboard settings from a Venetian collection of about 1520 ( I-Vnm Ital.iv.1227) illustrate this. De che le morta la mia signora has two strains closely corresponding in rhythm, the first in G minor, the second beginning in B♭ and moving back to G minor. No repeats are indicated but they would make good sense. Elsewhere in the collection double bars suggest that repeats should be made (...
