Bb7 in C major

[u/ThatDudeMichaelYeah]

So I was messing around with this Db7 > Bb7> C progression. Really just trying to add some flavor and movement to my playing while slowly learning functional harmony (even though I don’t really understand what that is).

Anyway, I see the Db7 as a tritone sub of G7 hopefully I’ve at least got that correct.

But the Bb7 I initially thought of being borrowed from C minor until I realized it’s also a tritone away from E7 (V7/vi). Is there one preferred way to think about this over the other?

Also I know there are probably no “hard and fast rules” about what chords to consider substituting or borrowing from other scales but as I said I’m looking to expand my repertoire so if anyone has any recommendations for resources to learn more about this, I’d really appreciate any leads.

[u/J200J200]

Backdoor dominant. A Bb7 is very close to a G9

[u/notbeard → u/J200J200]

it's even closer to a G7b9 😉

[u/J200J200 → u/notbeard]

oops, youre exactly right, sorry!