I have been learning a song by John Frusciante that looks like it's in D minor (or maybe F Major, you tell me). The main changes go something like this:
Amin -- Bb -- Dmin
F -- C -- Gmin -- Dmin
C -- Gmin -- Dmin
But toward the end, he throws in a G-Major:
Dmin -- Gmaj -- Dmin -- F -- Dmin
I have seen this a few times recently, now that I am beginning to analyze songs harmonically, where they will have the same chord be both major and minor at different points of the song, and from what I can tell without really changing key. This is the only example I could find at the moment, but I was wondering what were the rules for this sort of thing. It sounds great in context, in fact these chords combined with the melody he sings is a favorite of mine. Is he borrowing the GMaj from another key, and how would one usually construct a melody involving this type of chord from outside the key? I'm guessing you would avoid the B (major 3rd from the GMaj), but like I said I don't know what the conventions are.