Roman numerals in practice
Why thinking in numerals (not chord names) is the secret of every working musician — and how to read, write, and transpose them.
The big idea
Roman numerals describe chords by their function in a key, not by their letter name. The chord built on the 1st scale degree is 'I'. The chord built on the 5th is 'V'. Numerals are key-independent: 'I–V–vi–IV' describes how a song moves, not which chords it uses.
Once you internalize this, transposing becomes trivial: same numerals, different key, same shape relationships. A working session musician thinks in numerals constantly — the singer says 'we're in B♭ now' and the band keeps playing the same I–V–vi–IV.
The notation conventions
- Uppercase Roman = major-quality chord. Lowercase = minor.
- ° after a numeral = diminished (e.g. vii°).
- ⌀ (or sometimes m7b5) = half-diminished, used for 7th chords (e.g. vii⌀7).
- Superscript 7 = 7th chord (V7, ii7, IVmaj7).
- Slash chord like V/V means 'the V of the V' — a secondary dominant. In C, V/V = D7 (which resolves to G, the actual V).
Major-key numerals
Every major key has the same pattern: I (major), ii (minor), iii (minor), IV (major), V (major), vi (minor), vii° (diminished). The qualities never change between major keys — only the letter names do.
Diatonic chords in C major
C major's numerals and chords. Same pattern in every major key.
Minor-key numerals
Natural minor uses: i (minor), ii° (diminished), III (major), iv (minor), v (minor), VI (major), VII (major). When the v gets sharpened to V (the harmonic-minor move that creates a strong cadence), composers usually still write V — context tells you it's been altered.
Diatonic chords in A minor
A natural-minor numerals. Note: the V chord shown is the diatonic minor v; raise its third to make a true V cadence.
Transposing — the practical superpower
Take the most-used pop progression: I–V–vi–IV. In C that's C–G–Am–F. Now move it to G: G–D–Em–C. Now D: D–A–Bm–G. Now A: A–E–F♯m–D. Same numerals, same emotional shape, four different keys — and once you can hear the numerals, you can play the same song in whatever key the singer needs.
Diatonic chords in G major
I–V–vi–IV in G is G–D–Em–C. The roles are identical to C; only the letters change.
Common patterns to recognize by their numerals
- I–V–vi–IV — the four-chord pop progression. Endless examples.
- I–IV–V — 12-bar blues, country, rock & roll.
- ii–V–I — jazz cadence. Foundation of standards.
- vi–IV–I–V — a 'sad' inversion of the pop progression. Used in Adele's 'Someone Like You'.
- I–vi–IV–V — '50s doo-wop. 'Stand By Me', 'Earth Angel'.
- i–VII–VI–VII — the minor-key rock progression. 'Stairway to Heaven' verse, 'House of the Rising Sun'.
Inversions in numeral notation
When a chord isn't in root position (root in the bass), you can write a slash chord: C/E means a C chord with E in the bass. In Roman-numeral analysis: I6 is first inversion (3rd in the bass), I64 is second inversion (5th in the bass). You'll meet this in classical writing more than in pop.
The shortcut for ear training: hum the bass note of each chord in a song and try to name its scale degree (1, 4, 5, etc.). That sequence of degrees IS the Roman numeral analysis.
Practice this week
- Pick three songs you can play. Re-write each chord chart in Roman numerals.
- Take I–V–vi–IV and play it in five keys: C, G, D, A, E. Same fingers wherever the shapes line up; new shapes when they don't.
- Pick a key you don't usually play in (say, B♭). Find the I, IV, V, and vi. Now play a song you know — but in B♭.