I am trying to get a handle on functional harmony and I am noticing that the rock band I play with write songs without regard for theory or scales. I have written down the changes to most of the songs for analysis and cannot find key centers on several of them (maybe I just do not have a clue and need a teacher). In cases such as this what scales or modes should/could be played? I find myself relying on major, minor, pentatonics, the blues scale, and mixolydian alot, and I pick these 1st by knowing what chord I am playing under, and 2nd by what sounds best to my ears for the song. I also used arpreggios and chord tones when I deem them useful. One example of a song we play has 3 main parts. E, C, A, D F, A, C A, C, G, D The absence of any minor chords and dominant 7th chords indicate to be that there is no real key center in this song and any part of the song. If this is correct (and please correct me if I am not), what would you guys who know more about theory try to do in these songs? I know this may be tough to answer without hearing how we play this, but I am just trying to figure out if I am thinking about things the way I should be, or if I just need to bite the bullet and find a good teacher.