For me I have had several "Eurekas!" over the years on the guitar. One of the cool ones was the day I realized the power of the min7b5 (or diminished) chord, when combined with tritone substitutions. I know I know - jazz terminology. But stay with me. When you are trying to grip this, get your guitar and play the chords I am referring to in the examples. It is the best way to make something that sounds very complicated much simpler.
Getting back to our concept. Let me explain how this pretty simple concept can open the fretboard right up for you. Some basics you need to understand:
- A min7b5 chord (said minor seven flat five chord - sounds fancy ... easily played) can very commonly substitute for a Dom7 chord - starting of the chord's 3rd. So instead of A7 you could play Dbmin7b5. (Min7b5 chords are essentially diminished chords. Or commonly referred to as half-diminished. A slightly different chord - but follows similar rules)
- Diminished chord repeat, or invert, every 4 frets (a minor 3rd apart) so the above Dbmin7b5 chord can be slid all around the neck in minor 3rd intervals. As the Mall Cop would say "Fun fact for ya" - A diminished chord can be named by any of the notes of the chord. Any of the notes in the chord can act as the root.
A very common substitution for a dominant chord is it's tritone - so for our A7 example you can sub Eb7. Very quickly, using all of this, you have 3 different chords possibilities - A7, Eb7 and Dbmin7b5 (plus all the sliding inversions of the diminished chord) next time you are playing a blues in A.
Feeling good? Got it? Let me throw a wrench in it!
NOW, what if you do the same diminished chord swap for A7's tritone sub (Eb7) - with ITS min7b5 substitution? Remember - that THIS diminished chord is also found every minor 3rd (4 frets). We are moving away a hair from consonance here but still very much in.
All of a sudden on a simple Blues vamp where all chords are dominant (which is 90% of the blues) you now, armed with this knowledge, have a HUGE amount of available chord options for creating melody or vamping for EACH dominant chord. The same principal applies to any occurrence of a dominant chord. All of which sound pretty damn cool. All of which are still pretty 'inside' sounds.
Now if this works with chords ... could it work with their scales?
The rabbit hole is truly deep folks!!!!