Fauxbourdon

Du Fay may have been the first composer to use the term "fauxbourdon" for this simpler compositional style, prominent in 15th century liturgical music in general and that of the Burgundian school in particular.

The top line is a paraphrase of the chant; the middle line, designated "fauxbourdon",(not written) follows the top line but exactly a perfect fourth below.