Great post, thank you. i am trying to get this all straight in my head too. So is it correct that E Mixo is the same as A Maj scale? And if so, why do we refer to it differently?
E is the 5th step of the A Major scale.
So instead of saying "Start on the 5th step of the Major Scale (A, in this case) and use that as your root", "they" ('not sure who) gave it a name based on some Greek or Latin prefix/suffix, "Mixolyidian", E-Mixolyidian in this case.
"Ionian" is the same as the Major Scale (Root to Root, ie. Do Re Me... etc). Think, Eyes of the World.
"Dorian" starts/ends on the second step of the major scale. Most GD songs in a minor key.
"Mixolyidian" starts/ends on the 5th step of the major scale. Foolish Heart, Music Never Stops jam in B, etc.
JG gets alot of milage out of these three scales.
Mississipi Halfstep solo between verses is Dorian, Mississipi Halfstep jam at the end (A>D) is Mixolyidian.
Stuff like that.
You'll get used to it.
I am at best an advanced intermediate at this theory stuff, but for the GD it is really mostly 100 and 200 level Music Theory.
I won't be playing any Steely Dan songs any time soon... based on my music theory knowledge.