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'backdoor progression'. This name derives from an assumption that the normal progression to the tonic (V7 to I, or the authentic cadence) is, by inference, the front door. It can be found in popular jazz standards in such places as measures 9 and 11 of “My Romance” or measures 10 and 28 of “There Will Never Be Another You”, as well as Beatles songs like In My Life and “If I Fell”. It can be considered a minor plagal cadence in traditional theory.
The flat-VII7 chord, a pivot chord borrowed from the parallel minor of the current key, is a dominant seventh. Therefore it can resolve to I; it is commonly preceded by IV going to iv, then flat-VII7, then I.