Watch the Thirds online guitar lesson by Robben Ford from Chord Revolution: Foundations
I'm going to play for you a vamp that we've created based on the four chords that are used in the solo section of a song of mine called "Freedom". It is a series of four chords. C major 6, E minor 7, A minor 7, and B minor 7. We just play those over and over again. Now this is the four chord in the key of G. This is the six chord, minor six chord. Key of G. The two chord in the key of G, the three chord in the key of G. It's the G major scale. That is our harmonic information.
Now we're going to be playing in thirds. Basically, I'll just use thirds throughout in a comping manner, a supportive role. Not soloing, and I'm not going to play bigger chords. They're being covered by the acoustic guitar. So I'm just going to be doing nice little thirds throughout and so you have the basic scale. Play it in thirds. You want to be able to play these thirds all over the guitar. So you'll see me moving around the guitar a lot playing thirds in different positions. Nonetheless, I'll slip every now and then and play something else, but all the thirds of the G major scale. Even though there's four different chords here. C major, E minor, A minor, B minor. I can play straight through all of those chords with the G major scale and I'll do that in thirds.