How to Use Roman Numerals to Represent Chords on the Guitar

In traditional music theory, Roman numerals (I, II, III, IV, and so on) represent both the degrees of the major scale and the chord quality of each chord. Uppercase Roman numerals represent major chords, while lowercase numerals represent minor chords. Here is a list of the Roman numerals that represent chords, along with the major/minor sequence of the major scale and a sample key of G major.

How to visualize numbers on the fretboard

Here is the number pattern made by the G scale on the fretboard. Notice that the chords in this pattern are the same chords shown. Guitarists come to know this pattern very well because songs regularly use chord progressions that move through it in predictable ways.

Credit: Illustration courtesy of Desi Serna

There is a video of how to play the major scale chord patterns at Chapter 6, Video Clip 11: Major Scale Chord Patterns.

This chord pattern needs to be memorized now. While you play through it, call out each chord number as you play it. As you rehearse, try the following different combinations:

• Play chords I through vi forward and backward.

• Play just the majors (I, IV, and V) forward and backward.

• Play just the minors (ii, iii, and vi) forward and backward.

• Alternate between the 6th and 5th strings by playing I-IV, ii-V, and iii-vi.

Most progressions are based on the first six chords of the major scale, so you can disregard the seventh chord, viif5, and leave it out of the patterns. The minor triad with a flattened 5th is also called a diminished triad. The diminished triad is not to be confused with or used in the same way as full diminished and diminished 7th chords.