If I want to play G/A... I find the Note 'A' and think in 'Mixolydian Scale intervals. (i.e.) as if the, 'A' is the, 'G'. G,A,B,C,D,E,( flat the,7th ).IF:I think the 'Tonal Centre' is the key of 'A, however, the 'A' becomes the 'Ionian Mode Major', the '3rd, is Phrygian, and the '5th, becomes 'Mixolydian. the Question is... Is this an acceptable theoretical Solution?
I think you're over complicating the modes. This is how I remember them: Take C Major, the easiest of all. If you've learnt scales properly, with all notes following the circle of fifth, you've be been practising the Ionian mode. C major start on C and finishes on C and the notes are C,D,E,F,G,A,B and C to make the octave. However, you can start the C major scale on the next note which is D. When you start the scale on the second note of the Ionian scale, it becomes the Dorian scale. It's no longer C Ionian, it is D Dorian using all the notes of the C major Ionian from D to D, creating a different sound. You can apply this on all "basic" scales you learn as a beginner. The Ionian mode is the base for all scales and what we learn first. Hopefully it's clear so far. If you continue the line of thought, and start your C major(Ionian..remember) but start it it on the 3rd note, E in this instance, you are now using the Phrygian mode, E Phrygian and so on. This is true for all Scales. If you know your Ionian scale in all keys, you can follow the rule. If you have trouble remembering the names of the modes, they are: Ionian Dorian Phrygian Lydian Myxolidian Aeolian Locrian The mnemonic is: I Don't Play Lousy Music Any Longer ..... If you understand the above, you'll find that that the aeolian mode is also the relative minor if that major... Good luck!