Watch the Sixths online guitar lesson by Robben Ford from Chord Revolution: Foundations
We've talked about the use of thirds, the use of fifths, and now we're going to talk about sixths. Each of these refers to an interval. Thirds are the root note (tonic note) and then add the third degree of the major scale. In the key of G - One, two, three. That's a third. When you say thirds, in this case it's referencing harmonizing the major scale. We've talked about its use generally in the pentatonic scale. Generally you're going to hear fifths used in the pentatonic scale, and they're generally referred to as power chords and they're played low. Now if we were literal about that - One, two, three, four, five, six, that would be a G six chord. You add the six to the triad, the G major triad. That's another way of playing it.
It is also used for playing nine chords. You go down a whole step with the G in the root, and you've got G nine - One, two, three, four, five, six, seven, eight, nine. Fifth, seventh. One, two, three, four, five, six, seven. That's your literal G six chord. The sixth interval - you play the root, G, and the sixth above. If you keep that going, these are six intervals. One, two, three, four, five, six. That's the G six chord. That is a sixth interval. Root to the sixth. Harmonize the major scale. That's your basic G triad. Now we're just playing the third and the root on top. Once again, please learn to play these all over the neck of the guitar. How do you use them? That's always the important point. You learn something and then how do you use it?. So these things are very easily used. In any kind of - thirds, fifths, sixths.