I've seen those two chords
iv7 used interchangeably for what seems like the same context following
I -> IV chord movements in B sections (sometimes continuing to the dominant, sometimes not), for example in the Beatles' song "I Saw Her Standing There" in the bar before the final A section where they "wooo!" I'm wondering what context rules affect which chord to write.
With progressions like that where there's a descending bass walking
I-bVII-VI-bVI it's typically over the chords
I / I7 / IV / iv7, which makes the most sense to me as it's part of the typical 1-4-5 idiom. I usually hear that minor sixth as the
IV shifting minor, as is typically done in B sections when you're descending from root to dominant, where the
I7 after the
I doesn't change roots to a
bVII. But for that song in particular, I've seen more versions with it notated as a flat 6 chord.
Is it all about the gut feeling for which note is emphasized the most to serve as a root, or does some rule related to modes or song structure apply here?