Diatonic Chords & Roman Numerals
The chords that belong to a key — the triad and seventh built on each scale degree, its Roman numeral, and its harmonic function. Shown for a major key (C) and a natural-minor key (A minor).
| Degree | Triad | Seventh | In C / Am | Function |
|---|---|---|---|---|
| I | major | Imaj7 | C | Tonic |
| ii | minor | ii7 | Dm | Subdominant |
| iii | minor | iii7 | Em | Tonic |
| IV | major | IVmaj7 | F | Subdominant |
| V | major | V7 | G | Dominant |
| vi | minor | vi7 | Am | Tonic |
| vii° | diminished | viiø7 | B° | Dominant |
Natural minor key
| Degree | Triad | Seventh | In C / Am | Function |
|---|---|---|---|---|
| i | minor | i7 | Am | Tonic |
| ii° | diminished | iiø7 | B° | Subdominant |
| III | major | IIImaj7 | C | Tonic |
| iv | minor | iv7 | Dm | Subdominant |
| v | minor | v7 | Em | Dominant |
| VI | major | VImaj7 | F | Subdominant |
| VII | major | VII7 | G | Dominant |
Build these in any key with the progression generator, and see how they connect on the circle of fifths.
How to read this
Harmonising a scale means building a chord on each degree using only notes from that scale. The qualities that result are fixed:
major key: I ii iii IV V vi vii°
minor key: i ii° III iv v VI VIIUppercase is major, lowercase minor, ° diminished. The pattern is identical in every key.
Notes & gotchas
- Learn the pattern, not the chords. I ii iii IV V vi vii° transposes to all twelve keys for free.
- The minor v is usually raised to V in practice, borrowing the leading tone from harmonic minor to make the cadence pull.
- vii° rarely appears in root position — it most often functions as a rootless dominant seventh.
- I, IV and V are all major; ii, iii and vi all minor. That single fact explains most popular progressions.
- Borrowing from the parallel minor (♭VI, ♭VII, iv) is the cheapest way to add weight without leaving the key.