Hoping someone can explain this chord progression to me, I'm used to standard progressions such as I > IV > 5 etc.

Cmi9 > Ab9 > Cm11 > C7(#9,b13)

Would this be essentially I > vi > I > I?

Thrown off by the Ab dominant 9th chord, is this chord in the key of C?

Bit of an open question but any insight into how this chord progression would be named would be fantastic.


  • A dominant 9 or Ab dominant 9? And it certainly won't be 'vi'. And - don't get fooled by 'chords must be in a key'.
    – Tim
    Oct 6, 2020 at 16:52
  • Hi Tim, Ab dominant 9 sorry. I suppose the chords don't fit within a key but sound nice together regardless Oct 6, 2020 at 16:59
  • These chords (especially the first 2) sound the same, the bass note changes but the other notes don't change (and change few after). Nothing to do with your question, though
    – gui3
    Oct 6, 2020 at 17:04
  • 1
    @gui3 Ab9 has a Gb in it :s
    – Judy N.
    Oct 6, 2020 at 17:25
  • 1
    what happens after C7? Oct 6, 2020 at 17:40

3 Answers 3


Thrown off by the Ab dominant 9th chord, is this chord in the key of C?

As long as C stays the home note and C minor stays the home chord, you can consider being in the key of C minor. It really doesn't matter what notes or chords are played, if playing them doesn't disturb your sense of home chord.

"This song is in C minor" means three things: (1) home note is C, (2) home chord is C minor, (3) the default basic scale is C natural minor, with three flats in the key signature. If your sense of home doesn't change, then the key doesn't change. You can literally play any notes, and they will cause some temporary pressure and feelings, without necessarily changing the key.

Some people like to think of "key" as being one single scale, but such a definition won't really stand the light of day, when exposed to actual music. It's extremely common to have non-diatonic notes in melodies and harmonies. C - F - D7 - G - C. These are denoted with accidentals in music - and as you know from musical notation, accidentals are temporary. Permanent sharps/flats are written in the key signature. This notational convention just reflects the way music works. Most notes outside the basic scale can be written with temporary accidentals, because the sharpening/flattening of that note is temporary anyway.

If you play the Ab9 chord for a minute, and then play a C#m chord for another minute, then your sense of home chord probably changed. But in a chord progression like the one you posted, that's not the case.

When the only tool you have is a hammer, you want everything to be a nail. The functional harmony model with Roman numerals etc is a simplified educational tool, For Dummies, My First Harmony Thing. Instead of demanding everything to look like the basic structural example from theory classes, look at and experiment with what happens in the harmonic context at every chord change. What happens when that Ab9 chord is played is, the G note is temporarily flattened, and a soloist probably shouldn't try to play a G natural note over that. (YMMV of course) But it doesn't need to cause any more side-effects.

  • This was extremely helpful and a bit of an eye opener! Thanks very much for taking the time to explain this in great detail I really appreciate it. Oct 6, 2020 at 20:58

In fact Ab major lies very much "within" the sound world of C minor and will crop up in many many pieces in C minor. What is unusual is that it is a dominant chord, and so contains a Gb, which is a very "outside" tone in C minor. One illustration of how a plain Ab major would be "within" C minor can be seen towards the end of the progression: the C dominant is setting up a move to F minor, and Ab major is the relative major of F minor. However as I said the Gb is a very strong "colour" tone making this progression sound quite novel/distinctive


Playing/hearing the progression is perhaps the best way to understand the "how" of it.

In addition to key (C minor, as others have explained), it can be helpful to understand the chords in terms of voice-leading; that is, how one chord voicing proceeds to the next and leads the ear through the progression.

For example:

  • Cm9 contains G;
  • Ab9 contains Gb;
  • Cm11 contains F;
  • C7(#9b13) contains E.

A couple points of interest:

  • Aside from the initial G, each of the tones proceeding chromatically downward is unique to its chord within the progression.
  • Note also how Bb and Eb(D#) are maintained across the progression, lending stability to the sound.
T:Cm9 => Ab9 => Cm11 => C7(#9b13)
T:G - Gb - F - E chromatic descent
[V:V1] "_G""^Eb/Bb"[G_B_e] "_Gb""^Eb/Bb"[_G_B_e] "_F""^Eb/Bb"[F_B_e] "_E""^'Eb'/Bb"[E_A_B^d] |
[V:V2 clef=bass] "_Cm9"[C,C] "_Ab9"[_A,,C] "_Cm11"[C,D] "_C7(#9b13)"[C,C]     |

To emphasize the "key of C-ness" of the progression, you could re-voice/reinterpret the chords to produce a C pedal tone. In this case Ab9 becomes Cm7b5b13.

Two more points of interest:

  • Notice here that the upper voices from the previous example are preserved.
  • Also notice the alternating Bb/Ab in the tenor voice.
T:Cm9 => Cm7b5b13 => Cm11 => C7(#9b13)
T:C pedal tone
[V:V1] [G_B_e] [_G_B_e] [F_B_e] [E_B^d] |
[V:V2 clef=bass] "_Cm9""^Bb"[C,_B,] "_Cm7b5b13""^Ab"[C,_A,] "_Cm11""^Bb"[C,_B,] "_C7(#9b13)""^Ab"[C,_A,]     |

There are quite a few voice-leading patterns embedded in this chord sequence, especially when you allow for re-voicing/reinterpreting the chords. Another option emphasizes the alternation between G and Ab. In fact, not just G and Ab, but the G/Bb => Ab/C dyad alternation, again while preserving the voice-leading in the upper part.

T:Cm9 => Ab9 => Cm11 => C7#9/Ab
T:G/Ab bass alternation
[V:V1] [G_B_e] [_G_B_e] [F_B_e] [E_B^d] |
[V:V2 clef=bass] "_Cm9""^Bb"[G,_B,C] "_Ab9""^C"[_A,C] "_Cm11""^Bb"[G,_B,C] "_C7#9/Ab""^C"[_A,C]     |

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