Watch the Theoretical online guitar lesson by Brad Carlton from Chord Studies: Evolving Triads Vol. 1
In all of our previous examples we played a I - IV - V progression, and measure two was always the D chord. In this example we are going to change that up by "substituting" an F♯m chord in measure two. All we have to do is move the fifth of the A chord up a whole step and that will give us the vi chord, F♯m. The A chord and the F♯m chord are a third apart and share two tones, F♯ and A.