In
jazz and
blues music,
blue notes are
notes added to the
major scale for expressive quality. They correspond approximately to the flatted third, flatted fifth, and flatted seventh
scale degrees, although they approximate non-chromatic pitches found in
African work songs. Blue notes are the most important notes in the
blues scale.
In its earliest manifestations, the flatted third and seventh were the main blue notes. Emphasis on the flatted fifth was an innovation in bebop in the 1940s.