I've been playing guitar for a number of years, and I'm really "into" music, I like jazz, classical, metal, etc, and I'm fascinated by the amount of theory work that goes into many Opeth songs, the key changes, the dissonance that sounds amazing(ie-Bleak), things like that. However, I don't know much about theory myself, other than the very basics. I was curious how any of you musicians out there learned your theory? At this time, lessons is not an option as I don't have the time, but if there are any books/good websites that can fully explain basic-advanced theory, I'd appreciate some reccomendations. Thanks