What is music theory? Most of my favourite musicians and guitar players CAN NOT read music (including Sir Paul McCartney, Angus Young, Dave Grohl, Eric Clapton and even my personal favourite film composer of all time - Danny Elfman). So do they know any music theory? You bet they DO! To be able to write a song, jam with other musicians or play a guitar solo - you MUST know at least some music theory. Having an ability to read traditional music notation IS NOT essential to do these things.