I wanted to bring up a topic of the Blues, at its quintessential level anyway, that is not really mentioned much anywhere at all. It has intrigued me now for a little while, and I suspect
it is somewhat strangely ‘hidden’ from many.
That is, that the basic Blues, in its purest I-IV-V dominant chord format, is a non-diatonic chord progression.
Of course, the base triads are diatonic, but the 7th chords are not.
So a “Blues in A” ( A7- D7- E7) is not technically in A at all. There are 3 keys involved in building these 7th chords. Same with any other key signature of this form.
So in A, only the V chord, the E7, is diatonic to the key of A Major.
The I chord, A7, belongs to D Major. It is the V chord of that key.
The IV chord, D7, belongs to G Major. It is the V chord of that key.
So, all built of the V chord of the respective key.
So technically, the 3 chords in a Blues in A ( or any key) actually come from 3 different keys; in the case of “A”, its actually D, G, and A major. There are no keys that contain 3 diatonic dominant 7 chords; melodic minor contains 2 dom7’s I think, but can’t think of any other scales that contain more than one.
Now, I had been studying the Blues methodically for about 9 months at the time, and music theory for over 2 years, when I read this in a coursebook some time ago; I was absolutely flabbergasted that I hadn’t noticed this, and no-one seemed to mention it either. It was like a ‘twilight zone’ moment that was hard to believe. Such a basic and core aspect of musical form and structure, hidden in plain sight.
In fact, I would suspect that the vast majority of guitarists would not realise this on a conscious level. It is an odd situation indeed. And I think its a product also of how the Blues is taught.
Now, the Blues is about the sound, not the theory, but I find it a most interesting topic nonetheless, with I think, real world implications.
What are the implications of this? Well, for me, it probably hasn’t altered anything greatly in the first 18 months or so of my Blues learning, as I’m still building the foundations.
But more recently, as I begin to explore a bit further, at least at a rudimentary level, it has opened up enormous possibilities regarding things like arpeggios etc, that belong to these 3 keys. And in particular, ‘jazzy’ cadences like the II-V-I etc, which can be incorporated into the Blues form; in some instances like a “melody within a melody”, and various others that can create a seemingly infinite array of possibilities.
I am curious if there are any others out there, who’ve been at this a little while, who have in any way explored the Blues in this way; or who may provide some additional clarity on the subject.
It has certainly provided some clarity for me in some more modern blues I’ve come across recently, and where some of these ‘outside’ sounds may originate from.
Cheers, Shane