jazzblues_essentialchords.pdf |
In a traditional I-IV-V blues, we have the dominant I7 for four bars, IV7 for bars 5-6, then back to the I7 for two bars. Bar 9 would go to the V7, climaxing with the most tension, then moving to the IV7 and finally back to the I7.
In a Jazz Blues, a few things are different. First, the IV jumps up in Bar 2. Second, instead of going directly to the V from the I, we lead into it though a more jazzy I-VI-ii-V cadence starting bar 8. The final two bars repeat the I-VI-ii-V cadence in half the time.
Notice that the VI chord is a dominant, not a minor, as would 'diatonically' fit in the key of Bb major. The IV chord is also a dominant, as is usually the case in a traditional major blues.
Don lists typical extensions of 9, 13 and 11 for the I and IV chord which work well.
Since the VI7 is really a sub for a vi-7, those extensions will sound off. Instead, try using an altered chord -- a chord with the 9 and 5 raised or lowered a semi-tone. The #5, b5, #9 and b9 are 'altered' tones which better lead the cadence to the minor ii chord. The VI7 is really a 'secondary dominant.' For just a couple bars, the harmoy is shifting to the ii, and the VI7 of Bb is *functioning* as the V of the ii. The short of it is that a dominant leading to a ii will sound better with altered tones, which jives with minor scales like the harmonic and melodic minor.
For the V (F7), pretty much any extension, alteration, or combination thereof can work. You can mix nines and thirteens with flat nines and sharp fives and so forth. This is because the V is really the peak of tension from which everything will fall back into place with the I.