We recommend knowing first
The problem it solves
When you analyse a song by the chords' absolute names (C, F, G…), the information changes in every key and you cannot see what they have in common. You need a label that states a chord's role regardless of the key.
Detailed theory
Key idea
The number gives the scale degree (I = first degree, V = fifth…) and the upper/lowercase tells the quality: uppercase major, lowercase minor, ° diminished.
They are key-independent: I–IV–V–I names the same functional progression in any key, so you can analyse and transpose abstractly.
Understand it
A Roman numeral is a double label. The number says which scale degree the chord is built on (I on the first degree, IV on the fourth, V on the fifth), and the case of the letter says the quality of the chord: uppercase for major (I, IV, V), lowercase for minor (ii, iii, vi) and a small circle beside it for diminished (vii°). A + sign would mark an augmented chord.
In C major, the seven diatonic chords come out like this: I = C major, ii = D minor, iii = E minor, IV = F major, V = G major, vi = A minor and vii° = B diminished. Notice the quality is already set by the major scale, which is why degrees 1, 4 and 5 are major and 2, 3 and 6 are minor.
What makes Roman numerals powerful is that they describe function, not specific notes. The progression I–IV–V–I is the same musical idea both in C (C–F–G–C) and in G (G–C–D–G). That is why you can analyse a song, transpose it to another key and compare different pieces with one shared language.
When a chord carries a seventh, a 7 is added beside the number: V7 is the dominant with a seventh. So the same system covers triads and seventh chords without changing notation.
An analogy: Roman numerals are like a team's jersey numbers. The number tells you the player's role (goalkeeper, striker) whatever the team; the Roman numeral tells you the chord's role (tonic, subdominant, dominant) whatever the key.
Chord progression
Loading audio…
The three major pillars of the key in Roman numerals: I–IV–V (all uppercase = major) in C major.
How to recognise it
How it's written
Read the number first (which degree) and then the form: uppercase = major chord, lowercase = minor chord, a circle ° = diminished. A 7 beside it (V7) means the chord carries a seventh. The analysis is written under the staff, aligned with each chord.
How it feels
You hear roles, not loose notes: the I sounds like home, the IV like a departure, the V like tension asking to return. If you transpose the same progression to another key, the roles (and the feeling) stay even though the notes change.
Common mistake
Confusing the number with the chord's absolute name: V is not "always G", it is only G in C major; in G major the V is D.
Forgetting that uppercase and lowercase encode the quality: writing "ii" as "II" swaps a minor chord for a major one and falsifies the analysis.
Try it
Take C–F–G–C and label it: in C major it is I–IV–V–I. Then transpose it to G major (G–C–D–G) and check that the Roman numerals do not change.
Write the seven diatonic chords of C major with their Roman numeral and say each one's quality aloud (I major, ii minor, vii° diminished…).
On the instrument
Chord progression
Loading audio…
The seven diatonic chords of C major with their Roman numeral: I ii iii IV V vi vii°. Uppercase are major, lowercase minor and vii° is diminished.
Where it's used
- Analysing a song
- Labelling chords by their degree to see their function whatever the key.
- Transposing progressions
- Moving a progression to another key while keeping the same Roman numerals.
- Comparing pieces
- Recognising that songs in different keys share the same functional progression.
Examples
Chord progression
Loading audio…
The same progression I–IV–V–I in C major: C–F–G–C.
Chord progression
Loading audio…
The same I–IV–V–I, now in G major: G–C–D–G. The Roman numerals do not change: that is the proof they are key-independent.
Exercises
Read the roman numerals you hear
Listen to a progression and pick the matching roman-numeral sequence.
Complete 6 attempts · 70% accuracy to pass
Mini test
Check that you've got it.
0/9 answeredQuestion 1/9
What does a Roman numeral tell you about a chord?