Why Ab??? (theory question)

[fiebru1119]

Why is it that in jazz, you can use modes of Ab in the key of C (for example). I don't see where this comes from at all. I was asking our pianist and he wasnt very good explaining it. I've been looking for the answer to this for a while and here is the progression in question:

l Fmaj l Bb-/F l Fmaj l Bb-/F l

This is what the piano player does (the quality of the chord is not a simple "maj" chord.. I think he plays maj9 or F6/9.. I just put that down for the basic referrence) He's playing Bb- (natural) which would be the 6th of Db (the aug5 of Fmaj).

My question is, why is it you can use the modes off based off of the major scale of the #5 of the original key?? Thanks TB

* please note this particular song is more of a ballad (not jazz) and the chord progression above is the intro/"flow" that starts the song.. so I guess this comes over into different musical settings *

 

[geoffkhan]

l Fmaj l Bb-/F l Fmaj l Bb-/F l

Well, you could use a Bb melodic minor over both chords.

My question is, why is it you can use the modes off based off of the major scale of the #5 of the original key??

Maybe it's a little modulation or something (although most people wouldn't exactly call it a modulation)? Like use a major 6 on the Fmaj chord, and then flat it to a minor 6th for the Bb-/F chord?

 

[Richard Lindsey]

By Bb- natural I assume you mean Bb-C-Db-Eb-F-Gb-Ab-Bb?

I think this illustrates the problem with learning the modes as the Xth mode of major key Y. I don't think this example has much if anything to do with Ab, and you don't need to appeal to Ab.

You have to remember that the basic reason for playing anything is that it sounds the way you want it to sound. Theory is just a tool for explaining how some things work, not for telling you what sounds good.

But all that aside, I can think of a couple possible theoretical reasons for what he played. One is simply to create a certain kind of strong pull back down to the F. When you have a minor iv chord, you have two tones (Db and Bb) that are half steps above the nearest notes in the tonic chord. In certain contexts, those tones will often sound like they want to resolve downward (to C and A). That's a fairly strong movement. Also, the Gb (in the Bb natural minor scale) may feel like it wants to go down to the F. Using a minor iv in a major key yields a different effect from using the expected major IV.

The guy may also have been intending to suggest a couple of the tones you hear in altered scales--such as the flat 9 (Gb) and the sharp 9 (Ab/G#)--though the other notes don't quite fit with that.

You could also imagine that the overall "blanket" tonality is going from F ionian to F phrygian and back to F ionian. Several ways to skin this cat. But the basic reason he's playing this is that he likes how it sounds.

 

[Daniel Baskin]

You could also imagine that the overall "blanket" tonality is going from F ionian to F phrygian and back to F ionian. Several ways to skin this cat. But the basic reason he's playing this is that he likes how it sounds.

I concur with the last statement. So much of music in the popular genres (correct plural?) is as plain as it can get in a music theory except for closer offshoots of jazz--jazz is pretty undefinable by name--and certain types classical compositions. What your friend is trying to do is invert the chord not by a predictable interval such as the 3rd or 5th, but as a minor 6th (not that the the name of the interval really matters). He makes it appropriate because he makes most of the notes fit and some that don't fit, even if they fit for extra color. Then what he does is just inverts that chord.

That's way the best I can explain it. I think.

 

[Sean S]

"My question is, why is it you can use the modes off based off of the major scale of the #5 of the original key??"

Ab is technically the b6 of C
but I guess I'm just arguing semantics