I spent a lot of time teaching myself theory and harmony so I could be free to express myself on the instrument. I learned what relatives and substitutes could be played against a root of a chord, like E minor related to G, and so forth. I've also gathered all this knowledge because for ten years all I've done is play jazz, every day.

Denyer, Ralph (2002). The Guitar Handbook. p. 115. ISBN 0-679-74275-1.