Roman Numeral Chord Notation

In musical notation, it's common to indicate chords by using roman numerals, where the number refers to the degree of the scale the chord is built on. This type of chord notation will appear often on this blog. For those unfamiliar with the system, here's an explanation of how it works.

• Major chords: are written as upper-case: I, II, III, etc.

• Minor chords: are written in lower-case: i, ii, iii, etc.

• Augmented chords: (major chords with a raised 5th) are written using a plus sign: I+, II+, III+, etc.

• Diminished chords: (minor chords with a lowered 5th) are written using the ° symbol: vi°, vii°, etc.

• Extended chords: extensions (notes added to the basic chord) are written in regular numeric form after the roman numeral: ii7, V9, V13, etc.

• Altered chords: raising or lowering an extended note in a chord is indicated with a sharp or flat symbol before the extension: V6b9 = V chord with an added 6th and a flatted 9th

• Non-diatonic roots: chords with roots that are "outside" of the key are indicated with a sharp or flat symbol before the roman numeral: bIII = a major chord built on the flatted 3rd of the major scale (this would be an Eb major chord in the key of C, for example).

Here's an example. The following progression, notated in roman numerals:

     I - ii7 - V - iii - bIII - bVII - IV - V7 - I 

would be played in the key of C as:

     C - Dm7 - G - Em - Eb - Bb - F - G7 - C 

and in the key of G as:

     G - Am7 - D - Bm - Bb - F - C - D7 - G

Questions? Leave them in the comments section below, and I'll answer them as best I can.