Watch the Triads & Modes online guitar lesson by Robben Ford from Blues Revolution
This lesson illustrates how to derive the triads from a major scale. Triads are numbered by the number of the note in the scale. So in the key of C, C is 1, Dm is 2, Em is 3, F is 4, G is 5, Am is 6 and B dim is 7.
Starting the C major scale on any note other than C gives us the other modes of the key of C. For example, playing the C scale from D to D (D-E-F-G-A-B-C-D) is called the Dorian mode.
The three major chords in a major scale (I, IV and V) can be very versatile played over different bass notes. For example, in the key of C, the triads C, F, and G work well over a constant G bass, or D bass but you can experiment with all the notes of the key. Robben stresses how important it is to learn the triads, over the entire neck of the guitar, to be able to play in any position and to vary what you play to make it more musical and interesting. You can also just take pieces from each of the triads and mix them together. Endless possibilities.