My band plays "Hey Jealousy" by the Gin Blossoms. Pretty much the whole song is D-E-F#m, except for a little part (bridge? pre-chorus?) that goes A-D-F#-E-D. My stupid rock bar-band brain normally says "D is the first chord, probably the key." My slightly more advanced knows a tiny bit of theory brain says "but E major is not diatonic to D." My practical, knows enough to get by, brain, says "hmmm, soloing in D doesn't sound good, but F# minor pentatonic (with added 2d) sounds right." Tiny bit of theory brain says "so that would mean key of A, since F#m is relative minor of A." Then stupid rock bar-band brain says "but A isn't in verse at all and only appears briefly in bridge/pre-chorus thingy, that's odd." Then tiny bit of theory guys says: "yes, but all the chords in the song are diatonic to A." So is it in key of A?