Watch the Thumb Thang online guitar lesson by Jeff McErlain from 50 Blues Rock Guitar Licks You MUST Know
I first discovered using the thumb on my fret hand as a kid when I realized that I could make a D/F# chord much easier by using my thumb for the F#. Eureka! To bump it up I then watched Hendrix make full use of his thumb on barre chords. It wasn't until I saw the classic Eric Johnson performance on Austin City Limits did I know you could use the thumb as a pedal point for some very cool licks. I highly recommend the DVD of the Johnson performance from 1988, the clothes and haircuts may be 80's but the playing is timeless.