Pro’s refer to chords by Roman numbers, which tell the chords’ place in the key, or its degree. The first chord in the key is called the I chord, the fourth chord in the key is called the IV chord, etc. Since any key contains seven chords you have seven Roman numbers/degrees. Why give the chords number names? It makes it easy to change keys! If a song uses a I,IV,V chord progression in the key of C, you can play the I,IV,V chords in the same sequence in the key of G. That’s how you change keys, it’s just a line by line substitution. Below is a chart of the keys of C and G with their common degree names. (Upper case Roman numbers mean the chord is major, lower case means minor, lower case plus degree sign means diminished).
DEGREE NAME KEY OF C KEY OF G
I C Major > G Major
ii D minor A minor
iii E minor B minor
IV F Major > C Major
V G Major > D Major
vi A minor > E minor
viiº B dim. F# dim.
Changing keys is easy! Say you’re playing a song in the key of C. The chords are; C,G,Am,F. Looking in the chart you notice these chords have the degree names; I,V,vi,IV in the key of C. If you want to change the song to the key of G, just locate the chords that have the same degree numbers in the key of G (I,V,vi,IV chords in G are; G,D,Em,C) and substitute those chords. That’s it! A simple chart of all 12 keys with degree names is in the appendix of my book,”No Fail Guitar” available on Amazon.
