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  • rbedwell3

What is the function of the b5 in a Blues scale?

Thinking about this recently, I came to this conclusion. In an A minor blues, the A blues scale is A C D Eb E G (1 b3 4 b5 5 b7). Looking at it from a different perspective, the Eb is the enharmonic equivalent of D#. Now D# is the third of B7, and B7 is V of the Dominant in A minor E7. So the D# is implying a V - V in A minor. Ok, that makes sense.

Now, focusing on the scale that the B7 comes from. If the 7 note scale used over the A minor is Aeolian, A B C D E F G, then the D# would make the scale E Neapolitan minor. The root of B in the B7 chord would mean it is mode V of the Neapolitan minor being played, B Locrian natural 3 ( 1 b2 3 4 b5 b6 b7).

Some of you may then say to yourself, well so what, it sounds good and that is why I play it. Yes, I get that but to develop the idea, a bit of theory helps. So now we have B Locrian natural 3 to the scale played over the dominant of A minor, E7 in the V - V. Over the E7, the mode often used is E Phrygian Major E F G# A B C D from the Harmonic minor scale. So put them together and you get E Neapolitan minor to A Harmonic minor, or focusing on one note, E Neapolitan minor to E Phrygian Major. This can now be expanded upon and the arpeggios from both scales can be played in succession to create the V - V.

For example: B7b5 (B D# F A) - Bdim7 (B D F Ab) - A minor

See example below in score:

Here the V of E Neapolitan minor is followed by chord ii of A Harmonic minor before resolving to the i chord of A minor.

Listening to the change, it sounds reminiscent of the gypsy jazz changes over the V - i in a minor blues progression. So, next time the b5 is played in your blues scale, a Neapolitan minor is only one step away. Perhaps the b5 in a minor blues could lead to more scales than just the Neapolitan minor?

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