I'm writing a solo over a progression in F Major. However, the progression uses a major mediant instead of the usual minor. Therefore, my progression in F major is IV-III-vi-ii-I (Bbmaj-Amaj-Dmin-Gmin-Fmaj). Currently, I'm only soloing using the F Major scale and would like to expand upon that. I'm looking for scale suggestions and further musical theory information about what I'm doing where I am making the mediant chord of a major scale major instead of minor.
You can write that with secondary dominants as...
...the meaning of that is to say
Amaj is the dominant of
Dmin. Temporarily that moment is like being in
D minor. Actually, you can extend it and say all of the chords are from
D minor! But, probably in practical terms you have a shift back and forth from
F major to
You can try switching between
F major and
D minor for the solo.
D harmonic minor scale will technically fit all the chords. It's the same collection of notes as
F major with one change: the
C#. (Of course the scale tonic changes from
D.) Make that one change to use
C# around the
Amaj-Dmin part and it should make the scale fit the chords.
If you aren't familiar with minor key harmony, keep in mind there is a big difference between the 'natural minor' scale and proper minor key harmony. You use of the
Amaj chord makes the difference and gives this progression the flavor of minor key harmony.
The III (a iii Major) is the V of the relative minor, in this case Dmin. Though if such a modulation were present (i.e. strong) you might use the III7 chord. But the point is that the major third of the III chord is the leading tone to the vi. You could play D harmonic or melodic minor. Don't worry it won't sound too Yngwie-ish, jazz players do this. Really it all depends on what feel you are going for.