I've seen those two chords bVI6
and 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?