As part of an exercise I’m doing in a study group at improviseforreal.com I’ve been looking at the idea of dominant chords (a major triad with a minor third on top, so a flat 7). We’ve been working with a loop that is just chords 1 dominant & 4 dominant
Considered in scale degree numbers, that’s
1D = 1, 3, 5, b7
4D = 4, 6, 1, b3
Maybe it’s an obvious thing I’ve been missing, but I feel that something about this has given me a real lightbulb moment about why Blues are usually played on harmonica in ‘2nd Position’.
I know some theory and I’m aware 2nd position could be though of as as Mixolydian mode of the main key & that’s how I’d been thinking of it, The ‘light bulb’ involves how looking at the harmonica literally as being in the key of the 2nd position makes achieving those two flat (blue notes), the b3 & b7 much more practical.
I want to try to describe what I think I’m seeing in case someone wiser than me can see errors in my thinking & if so maybe say what they are? I’d rather write & be shown a to be a fool, than assume & be one without knowing it. LOL!
I’ll start my explanation by taking a step back from 2nd position to 1st.
Looking at a 10 hole diatonic tuning, in the usual tuning in 1st postiton, the notes (as scale degree numbers ) are.
Blow 1 3 5 1 3 5 1 3 5 1 Hole 1 2 3 4 5 6 7 8 9 10 Draw 2 5 7 2 4 6 7 2 4 6
I can’t yet bend (I’m working on trying), but if I could…
To get a b7 from 1st position the only options are a single draw bend on hole 3 (seems like quite a convenient place), or a single blow bend on blow 10 (so probably very high & shrill in most circumstances?)
To get a b3 the only option is a single blow bend on hole 8 (so upper octave & heading for shrill).
However, if 2nd position is literally seen as “the 1 is now at the 5th of the ‘main’ key’” the tuning becomes
Blow 4 6 1 4 6 1 4 6 1 4 Hole 1 2 3 4 5 6 7 8 9 10 Draw 5 1 3 5 b7 2 3 5 b7 2
So in 2nd position we get a couple of b7’s for free, i.e. without any need for bending.
There’s also scope for a b7 from the hole 2 double draw bend.
The b3 becomes available in the same places that were b7 in 1st position, i.e. a single draw bend on hole 3 (still quite a good place), or a single blow bend on blow 10 (still probably very high & shrill).
Of course we no longer have a 7 available (e.g. if we want the 3rd of a 5 chord), but it can be had via two different bends (hole 2 single draw, or hole 9 single blow).
For me that was a useful revelation. I’d much rather understand why something has become the ‘usual way’ rather than just accepting it. Sometimes a bit of study can reveal that ‘usual way’ doesn’t necessarily make sense… LOL!
In this case I think it does make sense. Well, it does to me. 
Have I made sense to you?
