I'm trying to get an idea what folks do with the thumb of their left hand i.e. is it slightly curved, straight, behind the second finger, up against the back of the neck, etc, etc, etc... The person I study with places no particular emphasis on where the thumb should be though is a stickler about the shape of the hand and the angle of the arm on the other hand I've encountered another teacher that recommends keeping the thumb curved i.e. the tip of the thumb against the neck and positioned behind the second finger. My personal experience with the latter method is that I don't get adequate force on the string with my thumb bent resulting in a buzzy sound for low notes. What are you folks doing, what have you heard, inquiring minds want to know.