so my guitarist caught me putting a minor 3rd where it didn't belong, basically saying the mode is mixolydian, the minor 3rd doesn't work. he was right - in that case. BUT - as i worked through our setlist for tonight, i realized i have lot of tunes in mixo (not in minor) where i find myself playing the minor third, especially as i walk back down to the root. mostly in bluesy type numbers. or where the chord is sus-4. is there any rule on this? or a good way to think about it? does it make sense that a minor 3rd would work better than a major third when there's no minor in root chord? also, is it appropriate to think in terms of a hierarchy of notes within a scale? i.e., leaving out the major 3rd sometimes seems correct, but the 3rd and the 5th and the root are supposed to be the most important - so am i doing myself a disservice by sticking with a root, 4th, 7th - for a general groove in a tune?