Backdoor progression

In jazz and jazz harmony, the chord progression from iv⁷ to ♭VII⁷ to I (the tonic or "home" chord) has been nicknamed the backdoor progression or the backdoor ii-V, as described by jazz theorist and author Jerry Coker. This name derives from an assumption that the normal progression to the tonic, the ii-V-I turnaround (ii-V⁷ to I, see also authentic cadence) is, by inference, the "front door", a metaphor suggesting that this is the main route to the tonic.

The ♭VII⁷ chord, a pivot chord borrowed from the parallel minor of the current tonic major key, is a dominant seventh. Therefore, it can resolve to I; it is commonly preceded by IV going to iv, then ♭VII⁷, then I. In C major the dominant would be G⁷: (the notes GBDF), sharing two common tones with B♭⁷: (the notes B♭DFA♭). The notes A♭ and F serve as upper leading-tones back to G and E (when the chord moves to the tonic, C major), respectively, rather than B♮ and F serving as the lower and upper leading-tones to C and E in a conventional G7-C major (V7-I) cadence.

A backdoor IV-V is also possible, moving from ♭VI^M7 to ♭VII⁷ to I. This is also commonly known as "Mario Cadence".