I’ve been revisiting the first four bars of Triste by AC Jobim. What is going on there?
The original (on the album Wave, 1967) is in A, and not Bb as it is usually played by the people I play with. Fair enough, A is an atrocious key for sax players.
The New Real Book gives the first line as:
A△ | % | F△♭5/A | %
For the first two bars on the original the strings are playing A△ and the guitar is playing A△9. So that’s close enough. But I’ve wondered for a long time what this F△♭5/A is all about? Why not notate it as some kind of A chord? Well, between the strings and the guitar and the bass, the notes are ABEF. You’d have to write it as A9♭6 omit 3 omit 7, or something. I mean like no-one will ever sightread that. So the purpose of this notation is to indicate a voicing for the guitar and piano.
But what is the function of this chord? What are we supposed to play on it? Let’s think of it as an A chord. What kind of A chord is it?
1/ It’s got a ♭6 (F), because the ♮5 (E) is present.
2/ It can’t have a ♮7 (G♯). Try it. It sounds wrong. So it’s got to be a ♭7 (G). Similarly it has to have C# because C sounds wrong.
3/ Finally, the missing note in the scale has to be D because of the rule that well-behaved 7-note scales cannot have chromatic sections. I invented this rule for myself but I’d be surprised if it isn’t formally recognised somewhere.
So F△♭5/A is derived from A△♭6♭7, which is the 5th mode of D melodic minor.
Does this information help? Well, yes, in two ways.
We could instead look at this as G7♯11/A, the fourth mode of D melodic minor, which resolves to A△ as a backdoor (yardbird) cadence (♭VII7 | I) familiar from a million tunes. So I should already have a bunch of ideas of what to do with this.
Secondly, expressing the change as I♭6♭7 | I highlights the notes that change. Which is a lot more obvious than if you were to write ♭VII7♯11 | I. Note that the melody of Yardbird in C has B♭ and A♭ over the backdoor, which reinforces the idea that the front line can treat the backdoor as I♭6♭7.
This is called the parallel approach to the modes. Instead of thinking of a chord as derived from a parent scale (eg D Dorian = notes of C major) you can also ask yourself what do I have to do to a major scale to make it Dorian (flatten the third and seventh), or make it Lydian (sharpen the fourth), and so on.
This is useful for motivic playing and for voice leading. Take the notes of the first phrase or chord, alter the highlighted notes and leave the rest the same.
It’s also useful for more general soloing: the highlighted notes are the ones that matter, everything else is less interesting.
And it gets a little step away from the chord/scale relationships that have been so much derided in blogs and on youTube recently.