This argument has raged since the invention of popular music and has reached fever pitch in the rock era. Do guitarists need to know music theory? One side says that theory interferes with feel and emotion. The other side says that you need to understand what’s going on before you can really be creative. I don’t know how the percentages on each side shake out. I do know, though, that the best predictor of a person’s position on this question is whether or not they admit to knowing any theory.
While there are arguments to be made for and against knowing more music theory, the person who truly knows none is not a musician. At least they are not one who gets any gigs. Let me explain. Even a relatively new guitar player knows that if he strums a C chord, he can strum a G chord next and it will sound alright, if fairly common. He may not know the terms ‘Tonic’ and ‘Dominant’ (at least not in a musical context) but he knows that if he starts a song with C he can use G and F and maybe A minor. He knows that after he plays those other chords for a while he should come back to C at the end. He knows this because he’s heard other people play it, he’s played it himself…a lot. After awhile he thinks of it as a rule or, at least, a convention. Then he plays or hears someone play C, D minor and G7 and he says, ‘hey, that sounds okay, too,’ and he adds another convention to his vocabulary. One day, he gets really adventurous and plays C and G# and F#. He’s not sure what he thinks about how that sounds, but he suspects that it’s ‘jazz.’
My point is that music theory is really a set of terms for rules and conventions in music. The terms allow people to communicate their musical ideas quickly. Just because you don’t know the terms doesn’t mean you don’t know the rules, and how to break them. If a person truly knew no theory, every time they stepped up to play a twelve bar blues that would have to ask what the chords are and when do they change.
Just because a musician doesn’t know the terms doesn’t mean that they don’t know the rules and conventions. Just because someone does know the terms doesn’t mean they can’t play with feel and emotion. Call it what you want, we all operate on the same set of rules, using or breaking them as our creative impulse dictates.