Roman numeral analysis

The chord progression vi–ii–V–I in the key of C major. Using lead sheet chord names, these chords could be referred to as A minor, D minor, G major and C major.^[1]

In music theory, Roman numeral analysis is a type of harmonic analysis in which chords are represented by Roman numerals, which encode the chord's degree and harmonic function within a given musical key.

Specific notation conventions vary: some theorists use uppercase numerals (e.g. I, IV, V) to represent major chords, and lowercase numerals (e.g. ii, iii, vi) to represent minor chords. Others use uppercase numerals for all chords regardless of their quality.^[2] (As the II, III, and VI chords always are minor chords and the VII always diminished, a further distinguishment is thought unneeded, see table for Major Diatonic scale below)

Roman numerals can be used to notate and analyze the harmonic progression of a composition independent of its specific key. For example, the ubiquitous twelve-bar blues progression uses the tonic (I), subdominant (IV), and dominant (V) chords built upon the first, fourth and fifth scale degrees respectively.