If you ever took guitar lessons, your teacher probably told you not to hook your fret-hand thumb over the fretboard. Even if you didn’t take lessons, you’ve probably heard the point debated or wondered if you’re doing something “wrong” by using your thumb to fret the low notes or assist your grip when bending strings.
Paul Gilbert has an opinion on the subject, and it’s one worth hearing. As far as Mr. Big’s guitar virtuoso is concerned, if your music has “any kind of rock or blues energy, you’ve gotta have your thumb over the top” of the fretboard.
Gilbert says that as far as he’s concerned, proper thumb usage is more important than stretching. “Because the stretch is just a wide interval, and you can get a wide interval with no stretching at all,” he says while playing the open A string and the high E fretted at the fifth fret.
Of course you can’t use the thumb for everything. “If you play a barre chord,” Gilbert says, “I can't do it for that. So a really good exercise is to go between a barre chord and [bending].”
In the video below, Gilbert demonstrates the benefits of using your thumb and proper placement, and shows an easy exercise to help you quickly switch from behind-the-neck thumb placement to over the fretboard positioning. Take a look.