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I came across a chord progression called the Mixolydian Vamp denoted as : I bVII IV I, but I don’t recognize bVII. What is its relation to the diminished 7th diatonic triad (vii degree)?

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    I wonder if BTO knew about the Mixolydian vamp when they wrote “Takin Care of Business”. Commented Apr 5, 2022 at 4:13

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I think there are three ways to think of the symbol ♭VII depending on the analysis or musical style.

In a very common style of analysis key is given with Roman numerals and upper case means chord with major third and lower case means chord with minor third, o means diminished triad. Diatonic triads in, for example, C major key are C: I ii iii IV V vi viio. For C minor the symbols are Cm: i iio III iv V VI VII. Notice that no flat signs are given on the Roman numerals. That is because sharps or flats are understood from the key indication - Cm - and all chords are understood to be diatonic.

  • Cm: VII is a B♭ major triad, which is the diatonic triad of the subtonic scale degree in minor.

In that system you can do analysis to show mode mixture or borrowed chords. When you do that sharps and flats are given with the Roman numerals to indicate a change of chord root from whatever is the diatonic root of the given key. So, for example in C major, C: I ♭VII IV I, means the seventh scale degree, which in C major is a B natural, is chromatically altered down a half step to B♭. The Roman numerals are upper case so the chord third is major, the final chord is a B♭ major triad.

  • C: ♭VII is a B♭ major triad, which is the subtonic triad in major borrowed from the parallel minor key.

In pop/rock/jazz a lot of mode mixture is used and it often gets analyzed differently. A basic, diatonic major key tonality is common, but various chromatic tones are added. Tones like the lowered seventh scale degree. In, for example, C major, the lowered seventh scale degree is B♭. In terms of scales that gives us C D E F G A B♭ C, which is the same set of tones for a C mixolydian scale. You could call this "borrowing" from mixolydian, or mixolydian "coloring", etc.

  • The final point is then pop/rock/jazz will often consider ♭VII as some kind of borrowing from mixolydian but the first two methods I describe consider the borrowing to be from the parallel minor key.

You could call the mixolydian view "pop" or "jazz" analysis and the parallel minor "classical" analysis. Personally, I don't like those labels, but they are commonly used. The difference is technical, but if you aren't aware, it can lead to confusion.


...bVII. What is its relation to the diminished 7th diatonic triad (vii degree)?

Comparing the two I would say this. Comparing either major or minor key or common modes like mixolydian and dorian, they all have the same ^2 and ^4 scale degree a major second and perfect fourth above their tonics. Relative to a tonic of C those ^2 and ^4 degrees will be D natural and F natural in major, minor, mixolydian, and dorian modes (basically all the common modes except phrygian and locrian, and locrian has never been used as a common tonality.)

In both chords - ♭VII and the diminished diatonic triad viio - their chordal thirds and fifths are the same. The only thing differing is their roots. How you get one chord or the other is largely a matter of how the seventh scale degree is handled. In tonal music the "default" seventh scale degree is one half step below the tonic and is called the leading tone. When that scale degree is a whole step below the tonic it is called the "lowered seventh" or the subtonic.

So the relationship between the two chords is one of an alteration of the chord root, an alteration of the seventh scale degree.

But I think it's better to think of the relative relationship between the two chords and the tonic. The root of ♭VII is whole step below the tonic, and the root of viio is a half step below the tonic.

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  • Thank you so much Michael for your comprehensive answer, particularly the 2 viewpoints on borrowing. I’ve learned a lot. I’m amazed at how kind you are all at sharing your knowledge. Is C: bVII == Cm: VII ever referred to as C mixolydian: VII ? Commented Apr 9, 2022 at 12:06
  • C mixolydian: VII ...I think would know what you mean, but it seems more conventional to put accidentals on those "modal" chords. You probably want to write C mixolydian: ♭VII. Take a look at music.stackexchange.com/questions/78844/…. That linked list of "modal" chord symbols is like borrowed chords in major. Perhaps that's a bit inconsistent. But that seems to be the convention. Commented Apr 10, 2022 at 23:46
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The diatonic diminished seventh triad contains scale degrees 7 - 2 - 4.

The bVII chord contains b7 - 2 - 4.

So, for example, in the key of C, the viio is B - D - F; whereas, the bVII is Bb - D - F.

The bVII chord is not diatonic to major, but it is diatonic to mixolydian.

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  • Thanks Aaron. So to summarize for my understanding it follows that the b7 - 2 interval being M3 (a major 3rd) means capital numerals are used for bVII, and the 2nd interval D - F is m3, so overall this is a major diatonic triad. What relates this to mixolydian? I thought mixolydian in Cmaj had the same keys as Cmaj but starting from the 4th degree, while here there is a Bb which is not in Cmaj? Commented Apr 5, 2022 at 6:15
  • Ah I think I get it. Bb is the scale degree 4 in Fmaj, making it the tonic of Fmaj mixolydian. Woohoo, i learned something. Thanks again Aaron for putting me on the right track. Hopefully these rules will sink in sometime, it’s a lot to process. Commented Apr 5, 2022 at 6:31
  • @acidtrancejunkie Starting on different scale degrees is just how the modes are derived. When you say C Mixolydian it is simply a C major scale with a Bb, the b7. C is the tonic. If you want to know what major scale it is derived from then you must know the Mixolydian scale comes from the 5th degree of the major scale. That means it comes from and has the same notes as an F major scale, but it is not an F scale or the key of F, it is a C Mixolydian scale with a tonal center of C. Commented Apr 5, 2022 at 6:46
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    @acidtrancejunkie In the long run it it best to think of modes not as an X scale from Y to Y but to know the actual interval construction of the scales, for example a Lydian scale is 1,2,3,#4,5,6,7. A Dorian scale is 1,2,b3,4,5,6,b7. etc. Commented Apr 5, 2022 at 6:53
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    @Tim Thats valid, to each his own! I think of them as a series of scales with the same tonic that have a single note difference between each one from bright to dark. Lydian (#4), Ionian (make the 4 natural), Mixolyidian (b the 7), Dorian (b the 3), Aeolian (b the 6), Phrygian (b the 2), Locrian (b the 5). The interesting thing about this is that using C as an example you end up going through the cycle of 5ths: G (C Lydian) C (C Ionian) F (C Mixolydian) Bb (C Dorian) etc. Commented Apr 5, 2022 at 19:17
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The relationship is two notes identical. But the sound is rather different.

♭VII in key C is B♭ major, whereas vii° is B°.

The first is non-diatonic, the second diatonic.

The diminished triad tends not to stand up on its own, as it's neither major nor minor, thus is often used as a transitionary chord. ♭VII is 'out of key', and often followed by IV, as it could be heard as IV/IV.

♭VII tips its hat towards Rock and Blues, due to its flat 7, but it's rare to find a diminished chord in those genres.

As already stated, in key C, vii° is B (m3>) D F, whereas ♭VII is B♭ (M3>) D F.

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