In jazz, a constant structure is a chord progression consisting of three or more chords of the same type or quality.^[1] 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.^[1][2]

For example, the progression F^maj7–A♭^maj7–D♭^maj7–G♭^maj7–C^13sus4[1] contains four major seventh chords (and one thirteenth chord), none of which are diatonic to the key of F major except the first.

A vi–ii–V–I chord progression in C^[3]

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.