On page 115 you allude to a concept that I hadn't considered before which is that in a major blues when the I-IV-V are all Dom7s, that we are really using three different keys.
In the case of a blues in C, C7 would be the V of G, F7 is the V of Bb, and G7 is the V of C.
You use this to allude to the fact that a blues solo can be complex by changing major scales to match the chord changes.
My question is why will a single Pentatonic scale in one key work. I have played it that way for years, but now that you have opened my eyes to the fact that the key is actually changing I am questioning what I know. I understand why it works over all of the chords in a single key, but why does it still work when the keys are changing?
This is a great question about applying guitar pentatonic and major scale patterns to songs in a blues music style. Playing the minor pentatonic scale over a chord with a major third interval in it, is actually breaking the rules. As a result, some of the scale and chord tones clash. This dissonance gives blues and blues-based rock music an edgy sound that most guitar players find pleasing to the ear (your grandparents, not so much).
Although this is more music theory information than most guitarists want or need to know, here's how the scale works over what appears to be a typical I IV V (1 4 5) blues chord progression in the key of G. Remember, as I explain in my book Fretboard Theory, each dominant seven chord is actually the V chord of another key.
G7 (V chord C) with G minor pentatonic scale
You get a root, flat third, fourth, fifth, and flat seventh. All the notes relate perfectly to the chord, and the parent C major scale, except for the Bb which is a minor third. This interval contributes to the sour but cool "blues" sound.
C7 (V chord F) with G minor pentatonic scale
You get a root, second, fourth, fifth and flat seventh. All the notes relate perfectly to the chord, and the parent F major scale.
D7 (V chord G) with G minor pentatonic scale
You get a root, flat third, fourth, augmented (or sharp) fifth and flat seventh. You already know that a flat third, or minor third, interval contributes to the bluesy sound. The sharp fifth interval creates an augmented chord which increases the tension and leads to and resolves back to the tonic, G7. D7 augmented, which can be heard at the beginning of "Stormy Monday" by The Allman Brothers Band, can be played like this:
Root D - string 5, fret 5, ring finger
Major 3rd - string 4, fret 4, middle finger
Sharp 5th - string 3, fret 3, index finger
Root D - string 2, fret 3, barre with index finger
Isn't it amazing that a concept that is so easy to play on the guitar fretboard ends up being based on rather complicated guitar theory? I guess some things are easier done than said. This certainly applies to using minor pentatonic scale patterns in blues guitar music.
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