Key Takeaways
- viio7 (fully diminished, minor keys) and viiø7 (half-diminished, major keys) carry dominant function by sharing 3 notes with V7; use viio7 constantly in minor, almost never in major
- Every inversion of viio7 maps 1-to-1 with an inverted V7 sharing the same bass note — swap scale degree 5 for scale degree 6 to convert between them
- Voice leading is uniform across all inversions: ^7↑, ^2↑, ^4↓, ^6↓
Quality by Key ▶ 1:00
- Minor key → viio7 (fully diminished 7th) — extremely common
- Major key → viiø7 (half-diminished 7th) — extremely rare; root position only, ^6 virtually always in melody
- Ignore the subtonic bVII chord in minor — only use chords built on the actual leading tone
Equivalence with Inverted V7s ▶ 6:22
To convert any inverted V7 to its viio7 equivalent: replace ^5 with ^6
| V7 Inversion | Bass Note | viio7 Equivalent |
|---|---|---|
| V6/5 | ^7 | viio7 |
| V4/3 | ^2 | viio6/5 |
| V4/2 | ^4 | viio4/3 → resolves to I6 |
| (none) | ^6 | viio4/2 — not used |
Voice Leading ▶ 9:00
- ^7 (leading tone) → up by step to ^1
- ^4 → down by step to ^3
- ^2 → preferably up to ^3
- ^6 (chordal 7th, new vs. V7) → down by step — same rule as all chordal 7ths