Roman numerals

A shorthand for every key

The page Diatonic chords describes the Roman numerals, in its section on the shared system, as an international shorthand that works independently of the key. A capital letter such as I, IV or V stands for a major triad, a lower-case letter such as ii, iii or vi for a minor triad, a small circle after the numeral, vii°, for a diminished triad.

The great advantage, according to the same page: I – V – vi – IV means the same chord progression in every key, in C major C – G – Am – F, in G major G – D – Em – C. If you think in degrees, you transpose effortlessly and recognise patterns again.

Minor

In minor the qualities change: tonic and subdominant are minor (i, iv), the sixth degree is a major chord (VI), and for an effective close the dominant is raised from v to V, as the page Cadences explains in its FAQ. The minor numerals are described there in detail, for example V – VI as the deceptive cadence in minor.

Numerals and chord symbols

The chord symbols such as C, Cm or C7 above songs, explained on the page Chords, name the chord concretely. The Roman numeral, by contrast, names its role. The two systems complement each other: the symbol says what you have to play, the numeral why the chord is there.