Harmony
Roman numeral analysis
Roman numeral analysis labels each chord in a progression by its scale degree in the key (I, ii, V7...), with upper case for major chords and lower case for minor.
What is Roman numeral analysis?
Instead of writing C, Am, F, G, you write I, vi, IV, V: each chord is named after the scale degree it is built on. The progression no longer depends on the key.
The conventions:
- upper case = major chord (I, IV, V);
- lower case = minor chord (ii, iii, vi);
- ° = diminished (vii°), ø = half-diminished (viiø7), + = augmented;
- added numbers specify the chord: V7, ii7, Imaj7.
In C major the seven diatonic chords are written like this:
| I | ii | iii | IV | V | vi | vii° |
|---|---|---|---|---|---|---|
| C | Dm | Em | F | G | Am | Bdim |
Roman numerals in a minor key
In natural minor the series becomes i, ii°, III, iv, v, VI, VII. In A minor: Am, Bdim, C, Dm, Em, F, G.
In practice the v is very often replaced by a major V borrowed from harmonic minor: in A minor, E or E7 (with G#) instead of Em. So Am, Dm, E7, Am analyses as i, iv, V7, i. The habit to build: always write the quality of the chord you actually hear, not the one the scale 'should' give.
How do you analyse a progression step by step?
- Find the key: resting chord, key signature, dominant.
- Number each chord's root relative to the tonic.
- Pick the case from the quality (major or minor).
- Add extensions: 7, maj7, m7b5.
- Spot outside chords and label their role.
Example in C major: C, A7, Dm, G7, C. A7 is not in C major, but it leads to Dm the way a V7 leads to its I. You write it V7/ii (the dominant of ii). Full analysis: I, V7/ii, ii, V7, I. Likewise, a Bb in C major is written bVII (borrowed from Mixolydian or the parallel minor).
Why guitarists use Roman numerals
The pop progression I-V-vi-IV works in every key with nothing new to learn:
| Key | I | V | vi | IV |
|---|---|---|---|---|
| C | C | G | Am | F |
| G | G | D | Em | C |
| D | D | A | Bm | G |
| E | E | B | C#m | A |
Singer wants the song in E instead of C? Keep the C shapes and put a capo on the 4th fret. Same logic for the jazz ii-V-I (Dm7, G7, Cmaj7 in C) or the blues I7, IV7, V7. Thinking in numerals lets you recognise a chord progression by ear from one song to the next.
To practise, the chord progressions library sorts progressions by style with their Roman numerals, and the AI progression analysis suggests the key and a Roman numeral reading of your own progression.
Key takeaways
- Upper case = major, lower case = minor, ° = diminished.
- Major: I ii iii IV V vi vii°. Minor: i ii° III iv v (often V) VI VII.
- Outside chords: V7/ii, bVII, borrowed iv.
- A Roman numeral analysis transposes to any key, capo included.
Frequently asked questions
What does I-V-vi-IV mean?
The chord on the 1st degree, then the 5th, the 6th (minor) and the 4th. In C major: C, G, Am, F; in G major: G, D, Em, C. It is the backbone of countless pop hits.
Why are some Roman numerals lower case?
To show a minor chord. In a major key, ii, iii and vi are minor (Dm, Em, Am in C). Lower case followed by ° shows a diminished chord, such as vii° (Bdim).
How do you write a chord that is not in the key?
By its degree with an accidental (bVII, bVI) if it is borrowed, or by its function if it sets up another chord: V7/V for D7 in C major, which leads to G.
Related terms
Practise in the workshop
Take it from theory to the fretboard
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