Even in the blues, dominant chords tend to function like five chords. For example, this C chord is about to become a C7. That’s going to bring us to F.
And I’ll concede that F7 is a little hard to quantify, but the Eb lends a certain modality. It creates an ambiguity between the C major and the C minor tonality that’s evident in the blues scale. I’m sure we can all agree that G7 is just a straight up five chord.
But let’s revisit that F with both a diminished tonality and as a five of Bb. Meanwhile, let’s convert that C chord to a 2-5-1 to F. And just for fun, let’s make that F the dominant of Bb.
This A7 is going to be the five of D7, which is going to be the five of G7, which of chorus is the dominant of C. Here’s F reimagined as a diminished chord, an F-sharp diminished chord. And ultimately, it’s the use of all of these dominant chords that creates this amazing major minor ambiguity that peppers the blues with what we know as the blues scale and is just basically awesome.
