Roman numerals describe relationships rather than fixed chord names. A I–V–vi–IV progression has the same structure in every key. This system helps musicians transpose songs, understand common progressions and communicate without rewriting every chord name.
Roman numerals label chords by their scale degree inside a key. They describe relationships that can be moved to another key without changing the harmonic pattern.
Uppercase and lowercase often show quality
In a major key, I, IV and V are major; ii, iii and vi are minor; vii is diminished. Notation conventions vary, but uppercase usually indicates major and lowercase minor.
Scale degree
Each numeral matches a note position in the scale.
Numbers reveal transposition
A I-V-vi-IV progression in C is C-G-Am-F. In G it becomes G-D-Em-C. The chord names change, while the functions and overall pattern remain the same.
Function
I feels like home, V creates strong tension toward I, and IV often provides movement away from home.
Numerals can include inversion and extension information
Symbols such as V7, ii6 or I64 add detail about chord quality and bass position. You do not need all of that notation immediately, but the basic numeral remains the scale-degree identity of the chord.
Borrowed chords stand outside the basic pattern
A progression may include a chord that is not built from the home scale. It can still be labelled relative to the key, often with accidentals such as flat VII or sharp iv, which shows how it differs from the normal scale degree.
Put the idea on the fretboard
- Write the major scale notes.
- Build one chord on each degree.
- Label them with numerals.
- Play a common four-chord pattern.
- Move a familiar four-chord progression to another key using the same numeral sequence.
- Write the seven chords of one major key and label each with a Roman numeral.
When the idea still feels confusing
You use uppercase for every chord
Use lowercase for minor chords so quality is visible.
You confuse scale degrees with fret numbers
Roman numerals refer to positions in the key, not locations on the guitar. The same numeral can be played in many fretboard positions and voicings.