What are roman numerals chords and how and why are they used in piano chord progressions? Learn more about chords and how to understand these chord markings.
The Roman numerals represent the steps of a music scale, either major or minor.
From each step of the scale, a triad or a basic chord in root position can be built. These triads are also called "Diatonic" ("through the key").
The chord on the first step will then be called I, on the second II, third III, on the fourth IV, and the fifth V, and so on. The I, IV and V chords in any major or minor scale are the most important. They are also the main chords of the scale.
Since there are a lot of other numbers involved when playing chords, for example the "number label" for seventh chords (7); to avoid confusion, roman numerals are used to represent steps on the scale, as well as the chord built on that step.
This also makes it easy to “translate” a piano chord progression to any scale/key you want.
So, you just need to know the scale/key you want to use, then find each chord from the steps in that particular scale. Then follow a (roman numerals) chord progression you like. You can in this way easily change it also to another scale/key.
Well, those tell you to play in a specific tonality- while the roman numerals chords can be used to play chords in any key. Here is a page where you can see how it's used in famous chord progressions, both with chord markings and roman numerals chords.
If we build chords on every step in the scale (called Diatonic Harmony), all the major scales will get the following chords from each step up:
I - ii - iii - IV - V - vi - vii° and back to I (or VIII)
(The little circle ° means that the chord is diminished.)
Translated to for example a C major scale, the chords are:
C – Dm – Em – F – G – Am – B dim, and back to C
Any natural minor scale will get these chords:
i - vii° - III - iv - v - VI - VII - (i)
Translated to for example an A minor scale, the chords are:
Am – B dim. – C – Dm – Em – F – G - Am