I am trying to get better understanding of what scales to be playing throughout a song. Generally, if a song is a certain key, say D mixolydian, playing those 7 notes will sound fine throughout the song. Over the chords, say D, C and G. I have been playing a song which I believe is in E mixolydian (Brown Eyed Women - Grateful Dead). Not positive about this, but it sounds right. During the chorus, which starts out on B and leads into A, I have an issue. If I ascend to the A from the B and play within the E mixolydian, the flat 7th of E sounds wrong (minor 3rd of B). The D# (major 7th or E, major 3rd of B) sounds much better, or "right". This got me curious as to whats going on in the song. Is this music not technically modal because it is leaving the mode? Does a new key arise during the chorus? So I wonder, when you are soloing in a song do you usually solo within the scale of the chord at that time or stick with the key of the song and that scale? This is the first time I've ran into this so I am not sure how to approach it. As far as I understand the chords which comprise a mode are all made up of the same notes as the mode (im not sure if this is true). So for E mixolydian the notes are... E F# G# A B C# D octave. The chords "should" be E7 F#m7 G#m7(b5) Amaj7 Bm7 C#m7 Dmaj7 Sorry for it being confusing, there are multiple questions or things that I am confused about with not only the songs but scales, modes etc. Thanks in advance.