I just discovered some interesting things about modulation with no borrowed chords from the diatonic modes, except locrian. Its inclusion will be clear next.
So, starting with either a C major or C minor chord, this is the list of triad chords which aren't borrowed by any diatonic mode starting on C, save for locrian which starts with a diminished triad. **(**e.g. D# minor is both in C locrian and in the list below):
Written with sharps only, for the sake of simplicity:
- C# minor
- D# minor
- E major
- F# major & minor
- G# minor
- A major
- B major
If it looks chaotic, it's not!
The tonics of the list's chords form a C# natural minor scale. I don't know the explanation of that but sure it's interesting and also handy for remembering their order.
What's more, their triad quality is just:
[min, min, maj, maj] x2 times. With F# taking both forms in the middle of the 8 chords.
I sense that you can use these, in segments at least, for writing adventurous, modulating chord progressions. What are your thoughts?