In jazz, a constant structure is a chord progression consisting of three or more chords of the same type or quality.Rawlins, Robert (2005). Jazzology: The Encyclopedia of Jazz Theory for All Musicians, p.131. . Popularized by pianists Bill Evans and Herbie Hancock, the combination of functional and nonfunctional chords provides cohesiveness while producing a free and shifting tonal center.
For example, the progression Fmaj7–Amaj7–Dmaj7–Gmaj7–C13sus4 contains four major seventh chords (and one thirteenth chord), none of which are diatonic to the key of F major except the first.
In contrast, the vi–ii–V–I or circle progression from classical theory contains four chords of two or three different qualities: major, minor, and possibly a dominant seventh chord; all of which, however, are diatonic to the key. Thus diversity is achieved within a stable and fixed tonal center.
See also Parallel harmony Side-slipping
References