When you use Roman numerals to label harmonies, you are identifying three things:
- The scale degree of the root of the chord
- The type and quality of the chord (triad, seventh chord, major, minor, etc.)
- The bass or inversion of the chord
If the root of the chord contains the “borrowed” scale degree, then there is an accidental that goes before the Roman numeral (usually a flat sign). If the root has not been altered, then there is no accidental with the Roman numeral.
Be very careful distinguishing between fully diminished seventh chords, and half diminished seventh chords. Also make sure that you label diminished triads properly.
Writing Modal Exchange Chords:
Make sure that you are thorough and complete when adding accidentals to modal exchange chords. For instance, if the root is altered, make sure that you alter any doublings of the root.
Major triads on flat-3 and flat-6 include altered tones in addition to the root (the fifth of the chord, flat-7 and flat-3, respectively).
Doublings in borrowed chords follow usual part-writing guidelines.
- Double the root of major and minor triads in root position.
- Double the third of diminished triads. (which is usually the bass)
- Double the soprano of first inversion triads. (Gauldin likes this one in particular. Remembering this guideline helps when filling in blanks in his exercises.)
- Seventh chords are usually complete (nothing doubled), except for the possibility of doubled roots in incomplete V7 chords.
- Don’t double tendency tones. (This includes flat-^6, EXCEPT for bVI chords in root position. For bVI in root position, it is ok to double the root unless the bVI has followed a V or V7 chord in a deceptive progression.)