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Use of Diminished 7th Chords...


(@mcstivi)
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Hello! This is my first question so feel free to guide me if i am doing something wrong.

I was reading the following article, it discusses some of the more popular uses of the diminished chord...
http://www.guitarplayer.com/article/demystifying-diminished-chord/jun-06/21064

I have a question on this line... "For instance, both F#dim7 and Adim7 act like D7 (the V7 of Gm) and resolve to Gm voicings, while Bdim7 acts as G7 (the V7 of Cm) and resolves to Cm, and C#dim functions like A7 (the V7 of D) and resolves to D."

If we focus on the first substitution, the F#dim7 acting as the D7 for Gm, why is it that the D7 is the dominant chord for Gm? Although it IS the fifth of G, in the key of Gm wouldn't the dominant chord be F7? I am thinking of Gm as the relative minor for A#, leaving the F as the Dominant chord.

Thank for anyone's help in advance.


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(@noteboat)
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D7 is the dominant chord for Gm, because chord progressions in minor keys most often use the harmonic minor scale. G harmonic minor is:

G-A-Bb-C-D-Eb-F#-G

So building a chord on the V (D) gets you to D-F#-A-C, or a D7 chord.

Btw, Gm is the relative minor of Bb major. The key of A# doesn't really exist, because its major scale would be:

A#-B#-Cx (C-double sharp) -D#-E#-Fx-Gx

You're right that in the key of Bb, the dominant chord is F. And that means you can use an F7 chord in the key of Gm... but that gets into another little issue. There are dominant chord types (i.e. 7th chords, 9th chords, etc) which build tension, and there are dominant chords... which are any chords built on the "dominant" of the scale - the V. So if you're in the key of C, G is a dominant chord, even if it's not a 7th.

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(@mcstivi)
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Ahhh.

That makes good sense, thank you. So in minor songs does one use the minor scale (aeolian) for solo-ing purposes, but this will be over the chord progression coming from the MELODIC minor? Or does this really free up one to play a 7th and a b7th during a feature?


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(@noteboat)
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Minor keys give you lots of freedom. You can use the 6, #6, 7, or #7. In fact, you can also use the b2 (found in the Phrygian, which is also a minor scale). About the only tones generally avoided are the 3 and the b5 - but you'll even find a few tunes that use those!

Because there are so many different minor scales, we're used to hearing more chromaticism in minor keys. So if you use Aeolian (natural minor) over a chord progression that's built on the harmonic minor, our ears hear both 7 and #7 - and we think it's ok, because we've heard that combination in melodies that use the melodic minor... even if you're not using #6.

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(@mcstivi)
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Thanks again for all your help with this. It solves a lot of puzzles I've had.

I haven't delved deep yet into the minor scales outside of the modes derived from the major. From what you said it sounds like almost anything goes in minor land (for the most part). Is it the harmonic and melodic minor that are the most used?

And just when I thought understanding the major modes was enough...


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(@noteboat)
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Depends on the style.

For the average tune, the harmonic minor is the most common; that's also the most common in metal (even though metal guys stress modes when they talk about their music, not that many actually use them). For jazz, it's the Dorian, harmonic, melodic, and the "jazz minor" - which is just the ascending melodic minor. For classical it's the melodic minor; for flamenco it's the Phrygian, for gypsy jazz it's the gypsy minor....

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(@mcstivi)
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Ahh, thanks for your help with this. It's making more and more sense everyday.


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