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I IV V Blues Key?
  • A student posed this question and I found I couldn't give a definitive answer. Since any given key has only one dominant 7 chord, what key would one say a 12 bar blues is in with the I IV and V chords all being dominant 7's? I mean the obvious answer would be A if the chords are A7, D7 and E7, but from a theory standpoint I don't know.
    Thanks,
    Mark
  • Mark,

    I think that the word "dominant" is used in two separate (but related ways). Any chord can be made into a dominant 7th (as you well know), but that doesn't mean that it must function as the dominant of a particular key. In your example, I think the only way to view that progression is as a dominant blues in A.
  • Thanks for your thoughtful reply!
  • Ted Greene has a nice explanation that with blues and rock music that "dominant 7" sound has become its own thing in that type situation.

    I forget where I read it... he explains it really well.
  • Thanks,
    I'm a big Ted fan and I'd be surprised if I haven't read what he said about that and just forgot. I'll see what I can find out.
    Mark
  • Good question... really good question. Hmmmm...

    Sure, A7 shares the same key signature as D ... But where does the IV chord D7 come from? It's not the IV chord of A Major and the C# is "wrong" since D7 has a C natural. D7 shares more with the key of G than A, or A7.

    D7 and E7 would make more sense if the A7 was an A minor, but this isn't the case.

    Then we proceed to show a young student a Pentatonic scale that has a C natural and have them play over the A7 that has a C#. It's basically a #9 dominant 7 scale -that is over A7 -but what about the C natural over E7? It's an E augmented 7 partial scale?

    Again - all this would make more sense if the A7 was an A minor.

    To me, the three chords don't come from one harmonic progression or one key signature - but of course in the "real" world we say it's a blues in A, of which it is... kind of! And the E7 is the V chord.. and it all sounds perfectly fine.

    So ... I tell students - Blues is a rule breaker and a genre that often defies Western harmony explanation. And our modern ears have acclimated to the dissonance. And it comes from the harmonic place of a minor key, though we play the A Major chord. Then their eyes glaze over...

    And I quickly move on to getting their fingers and hearts aligned - by playing.






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  • Hey Jim,
    I was hoping you'd chime in. Thanks for your eloquent explanation!
    Best wishes,
    Mark
  • The way I see it, for hundreds of years western music was all about harmonic progression. Tension followed by resolution. A dominant 7 chord would eventually resolve to the tonic. That was its purpose!

    Other musical cultures of the world aren't as concerned with this kind of "progress". Sometimes you can just hang out on a dominant 7. It doesn't lead to anything. This still creates a kind of tension, but no resolution is required. The rhythm and the flavor of the moment are enough. The 7th chord has lost its sense of purpose and so has western civilization.

  • Thank you Yreva - It was a tough question and I felt my answer was little inadequate- your gracious comment was appreciated.

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