OK just when i think i'm getting the hang of a bit of theory!
I'm sitting here trying to work out they key for a song - it end's on G, so i figure the key of G is a good place to start.
It also has a Bm (a iii chord) ok, ok, looking good, a C(IV) and a D(V) an Am (ii). Great, must be in G then....hmm what's this, an F!
So where does F come from? Can you just chuck in a random chord from another key?
I've another simple song with a G, D, C, G progression, but then there'll be a D7 inserted after the D sometimes? Hows does this work?
Is it still the same key? And are there some rules to this adding of out of key chords?