In the section on 3 Chord Theory we showed how to find the I, IV and V chords built on the 1st, 4th and 5th notes of a harmonized major scale. We now introduce chords built on the 2nd, 3rd and 6th notes of the scale. These are called secondary chords and Roman Numerals are used in the same way to identify which note of the scale each chord is based.
The VI chord is based on the 6th note of the major scale in any key and is called the relative minor. Its natural form is as a minor chord but it can also be played as a major or seventh.
The II chord is the 2nd note of the scale and is called the supertonic. It also is usually played as a minor but can also be a major or seventh chord.
The III chord is based on the 3rd note of the scale and is called the mediant. It is called this because it is half way between the tonic I and the dominant V. It is usually a minor but can also be played as a major.
We will use C as an example again because it has no sharps or flats. As you can see from the chart below the the II chord is a D, the III chord is an E and the VI chord is an A. These chords can be worked out in other keys using the same method.
Below are some common chord progressions using the six scale chords we now have. The progressions shown below represent most of the variations used in simple popular songs. NOTE: The last two progressions key of G do use a B minor chord. See the EZ Guitar Chord Finder to learn this chord.