When learning guitar?
I am from the old school. You NEVER EVER use your thumb for making chords…you use your thumb under the neck of the instrument to support your other four fingers which do all the work. If you want to do full chords, that is what the index finger is for. Not only that, but you will eventualy give yourself carpal tunnel syndrom from stressing your wrist because it is un natural to try to hold down the base strings like that while trying to extend your other fingers. I would suggest you consult a classical guitar method book and observe how to form chords without the use of your thumb.
