Learning to play popular guitar lends itself to playing by ear because of the visual orientation of the fretboard (huh?). When a player finds new discoveries on the fretboard visually; some favorite song that they have listened to a lot has likely inspired it. Even accidental discoveries often trigger recognition of some songs main hook or other audible feature.
That same visual approach is also the reason why so many guitarists are terrible readers (musical nation that is). There is very good reason for that…We don’t have to! Woo Hoo! However, there is this old joke that goes, “How do you get a guitarist to turn down?...Put a sheet of music in front of him.” Being musically illiterate is not a good thing. It isolates you by inhibiting your ability to communicate fully with other musicians. So it'll just be you and your bassist friend.
The word ‘theory’ can actually scare some guitarist into thinking that their world is a better place without it. I’ve lived that fantasy, however in my first year at Mohawk College’s Applied Music Program, I found myself thinking, “Oh, that’s what that’s called” all the time. If you can hear it, musical theory has a name for it. If you can’t hear it yet, musical theory can help light up the path.
To learn your theory will not make you a better player than your technique allows. As you learn your instrument however, theory offers up directions to explore any style of music quickly and confidently, which eventually helps you become a better player. It’s not what you know; it’s how you play it.
Theory is best thought of as the language of music. What makes it scary is the steep learning curve ahead if you try to take it all in all at once. So, pare down the challenge with what I call Guitar Theory. Guitar theory is the same as musical theory but is more directed to playing and understanding your guitar’s neck. It’s the knowledge that allows you to communicate and to jam with musicians other than guitarists and understand what they’re talking about/planning. Eventually you can recognize chord progressions and teach yourself songs with your ears rather than relying on tablatures (which are really someone else’s ears).