Hi, yeah I think Kirk's explanation is a good one - it's basically about chord progressions.
IMHO the distinction was clearer in classical music than in modern music, but (without going into stuff about cadences) if the chord progression resolves to G major, then that's the key; if it resolves to Em, then that's the key. It's more or less about which chord feels like home base - which chord you would want to end the chord song on.
In order to make minor keys feel more resolved, composers often change the v chord (Bm in the key of Em) to a V7 chord (B7 in the key of Em). You may have come across this before (e.g. E7-Am in House of the Rising Sun), and if you're interested, I can go into more detail about why it works...
James
|