Backdoor progression
パターン
IVm7 → bVII7 → I
In C
Fm7 → Bb7 → C
解説
IIm7とIIm7-5は置き換えることができる。Dm7をDm7-5に置き換えて根音のDを省略するとFmになる。7th（Dにとっては9th）を追加するとFm7になる In jazz and jazz harmony, the chord progression from iv7 to ♭VII7 to I (the tonic chord or "home" key) 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 (2-5-1（IIm→V7→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 7th chord. Therefore, it can resolve to I; it is commonly preceded by IV going to iv, then ♭VII7, then I. In C major the dominant chord 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 (Dominant motion) Cadence.