Examining this progression in F:
| F | A7 | Dm7 | Bb, Bbm | | F, E7 | Gm7, C7 | F, D7 | Gm7, C7 |
In the fifth measure I really don't understand what role has the E7 chord because I can't identify as:
- primary dominant - it isn't on the fifth degree of the scale
- secondary dominant - it doesn't resolve to his relative first degree (Am7)
- tritone substitution - it does not resolve to Eb his relative IIb
So what is the role of the chord?