I am trying to find which scale this chord progression (Cmin - G\B - B♭ - Fmin\A♭ - A♭ - E♭\B♭ - Bdim) is borrowed from.

I think it doesn’t fit on any scale because this progression uses modal interchange. I don’t know any better. Do you have any idea ?

  • Not an answer about this particular progression, but you should try to think that there's a "default scale" that's related to the key, e.g. key C minor and scale C natural minor, but during each point in the progression, there can be one or more different plausible in-between harmonies and scales. In sheet music, the default scale is specified with a key signature, and deviations from it are denoted with temporary accidentals. If there's a G major chord when the song is "in C minor", then at least during that chord, you'll be thinking about and using some other scale, not C natural minor. – piiperi Reinstate Monica Sep 7 '20 at 19:25

This chord progression fits comfortably in C minor, sometimes including the ♭VII (B♭), and sometimes the leading tone (B♮).

Cmin    = C E♭ G  
G/B     = B♮ D G  
Bb      = B♭ D F  
Fmin/Ab = A♭ C F  
Ab      = A♭ C E♭  
Eb/Bb   = B♭ E♭ G  
Bdim    = B♮ D F  

Extracting the unique pitches, we get

C D E♭ F G A♭ B♭ B♮ C

which is exactly C natural minor, plus the leading tone.

  • This shows that the bass walks down to Ab then back to B chromatically. It's a very smooth bass line and if the voice-leading is good, different chords could be used. – ttw Sep 6 '20 at 17:38
  • Actually, this is a typical use of minor scale in classical music, where aeolian scale is used, and 7th is raised on the dominant chords (G, Bdim), right? So Bb and B don't really coexist in the scale, but we switch between aeolian and harmonic minor. – user1079505 Sep 7 '20 at 3:55
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    @user1079505 - or, we could just say use the melodic minor scale... – Tim Sep 7 '20 at 9:17

This looks a lot like a descending bass progression. These progressions don't really fit some descriptions as the driving force is the descending bass line which holds things together. Your description has a bass of C-B-B♭-A♭-A♭-E♭-B. It looks similar to the "lament" bass (been around for centuries from pre-tonality to post-rock). An example would be taking C-B-B♭-A-A♭-G as a bass line and using Cm-G/B-B♭-F/A-A♭-E♭/G for example for chords. Other possibilities with the same bass line are Cm-G/B-C7/B♭-F/A-A♭7-C/G-G. or the like.

Certain patterns involving strong bass lines or patterns involving harmonic sequences seem not to follow some "rules of progression" but they create their own regularity (which is what rules are anyway.)

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    +1 for the last seven words at very least! – Tim Sep 6 '20 at 15:36

These chords all belong to melodic c-minor:

B♭ is the VII (♭) of Cm melodic downward (identical with natural minor and the aeolian scale). The VII isn’t augmented.

C, B♭, A♭, G ... is the upper tetrachord downwards. G/B is the 1st inversion of the dominant chord containing the leading tone B.

The Roman numbers are:

i - V6 - VII - iv6 - VI - III64 - vii dim

The melodic minor scale has a “flat” seventh (vii natural) ... relative to E♭ major! and a sharp seventh “borrowed” from the major dominant G in respect to the leading tone B.


You can call it 'modal interchange' if you like. But that sort of assumes that a progression SHOULD stick to one mode or scale, or that it's normal for it to do so, which just ain't so!

This comes pretty close to being in one scale though, if we lump the Natural and Harmonic variants of the C minor scale together.

As @ttw mentions, it implies a strong scalic bass line, always a good alternative to more functional reasons for what chord comes next.

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