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Naming the triads built on modes
The scenario is:
G Mixolydian: G-A-B-C-D-E-Fnat
The wrinkle: This mode is written with one sharp in the key sig and a natural sign in front of F. (No choice here. I'm writing a book about theory and fiddle tunes, and this is how they are key sigged.)
So, are the Roman numerals for the chords written like this:
I - ii - iiio - IV - v - vi - >VII< ?
Or this: I - ii - iiio - IV - v - vi - >bVII< ?
(Using the same system, which would the Dorian mode would include: vi o or #vi o ?)
"bVII" is better, IMO, especially in a context where it's being notated with a 1-sharp key sig and naturals for the Fs.
Originally Posted by ceilr
IOW, it's being related back to the G major key, which is actually quite a good way to look at G mixolydian. ("G major with b7")
As for dorian, I'm guessing from what you say that it's being notated in a similar way: like the parallel minor, but with natural or sharp accidentals for the 6th. ("Minor key with major 6th", which is the way most people would hear it.)
Following that priniciple, it makes sense for the vi chord to be labelled "#vio".
However, it's also quite common to spell any scale with reference to the parallel major, and many people will be used to that. In that system, dorian would be:
i - ii - bIII - IV - v - vio - bVII
The important thing with any system, of course, is to be consistent!
IOW, whichever system you decide on, I think you should explain at the beginning how it works, what it relates to.
So if mixoldyian is being shown as "major scale with flattened 7th", then dorian is best shown as "minor scale with raised 6th". And it would make sense for any chords to be indicated the same way. (I don't personally like "#vio", but I can see the logic.)
However (although I don't know if it helps), it would be very rare to actually encounter a chord on the 6th degree in dorian mode. Dorian tends to use only i, ii, IV, v or VII chords, and often only 2 or 3 of those - especially in a folk fiddle tune.
Modal pieces don't really work the way major and minor keys work, with all possible harmonized chords being available.
OK, one more question, based on this discussion: the harmonic minor scale.
C harm. min.: 3 flats, and the 7th degree gets a natural sign.
Based on the principle of bVII, wouldn't the triad of the 7th degree be named #viio, because of the added natural sign? I've never seen it that way, but it somehow makes sense!
Normally, it would be plain viio, because that's the standard 7th degree chord. In conventional minor keys, both the V and vii are derived from harmonic minor. (The others all come from natural minor.)
Originally Posted by ceilr
If Bb major were used, then that would be "bVII".
That leaves the question of whether Ab amd Eb would be "bVI" and "bIII", or just "VI" and "III" seeing as they're the normal chords in the key!
Again it comes down to which system you want to use. In popular music in general (including rock and jazz), I think people are used to seeing the chords labelled in comparison to parallel major.
So the chords in natural minor would be
i - iio - bIII - iv - v - bVI - bVII.
In harmonic minor:
i - iio - bIII+ - iv - V - bVI - viio
In melodic minor (rarely used for derivation of chords):
i - ii - bIII+ - IV - V - vio - viio.
In classical harmony theory, however, it's assumed you know both the degree interval and type of chord in the scale/key you're using.
So the chords in a minor key would simply be: I II III IV V VI VII .
(AFAIK that is. Happy to be corrected here.)
As I understand it, "VII" would signify the dim7 chord on the raised 7th step. If a chord on the flattened 7th degree were used, I suspect it would be regarded as a secondary dominant, belonging to the relative major. Eg, in key of C minor, Bb would be "V/III".
(Again, not totally sure about this, so don't quote me )
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