Slow Soulful Blues - Harmony Question

[procky1845]

Hi Guys,

I'm just going back over the Slow Soulful Blues lesson to pick up any bits I missed the first time through and I was wondering if somebody could help explain the chord choices in bars 8 and 9 of Franks Blues.

I understand that the chord choices originate from harmonising the descending bass line, but what I don't understand is why the A+7 and G+7 have been used here.

Are the +7 chords simply used as passing chords like the dim7 chords are earlier in the piece?

Could this have been harmonised using dim7 chords instead or is there a specific reason why +7 chords are used?

Thanks,

Lee

[place]

It's a series of extended dominates with, in this case, tritone substitutions. Bb7 - Eb7 - Ab7 - Db7 would be with dominate motion. Eb is replaced with its tri-sub A7 (using + or alt is common in these types of substitutions) and Db is replaced with its tri-sub G7, which leads nicely to the Cm7 in the next bar. As you correctly stated, this makes a nice chromatic descending bass line. Make sense?

[procky1845]

Hi Mark,

Thanks for that. Yes that does make sense. I'm not massively familiar with tritone substitutions however I understand the basic idea (substituting the chord that is a tritone away).

I was trying to relate it to the walk-up/walk-down examples that Willie discusses in the lesson, I remember him saying that the chords used in the examples are basically harmonised from the bass note using mainly I, IV, V chords in varying inversions and the odd diminished chord. I guess this particular one is slightly different though!

Thanks for the explanation. I'll be looking to upgrade my membership soon to gold as I'm currently a member of the blues site and have finished nearly all the lessons in that section. So I'm sure I will come across more of this when I start studying the Jazz lessons!

Thanks again.

Lee