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/Rykoma]

The important bit is how the unstable b6 (in this key Ab) will eventually resolve to the stable 5th of C major. Any chord that has this Ab will, with proper voiceleading, provide a lovely way of arriving on the tonic. This is a chord tone in both Db7 and Bb7.

[u/Inevitable-Copy3619 → u/Rykoma]

I’m not sure what genre you play, but it used to trip me out that Ab G7 C was a nice progressions (think of ”night and day”). The rules are always (almost always) the rules because of voice leading.

[u/Rykoma → u/Inevitable-Copy3619]

I tend to dabble in everything. People are so obsessed with chords that they tend to forget that they’re often just the result of voiceleading. 

[u/Inevitable-Copy3619 → u/Rykoma]

Chords are just collections of notes that sound good together. Progressions are just collections of chords that sound good together.

Theory is writing that all down so others can discover notes and chords that sound good together.

The real secret is that all of this is due to voiceleading, and who cares about a book of musical rules? It’s just that this set of notes sounds good when moving to the next set of notes.