Miles Davis All Blues Harmonic Concept

In Module 2, Lesson 21 of Beginner to Boss, we play what the trumpet and sax play on the Miles Davis song All Blues.

A student named Regina asked an astute question:
Hi Luke, I also wondered about the key, so it is G.
Wouldn’t the I chord be GBDF and the IV chord CEGB, if you include the 7ths?
But we are playing BD CE DF CE (no G) for the I and DF EG FA EG (no C) for the IV, right?
Can you explain why that is? I love your lessons and song selections. Thanks!

I thought I’d repost her question and my response here for anyone who’s interested, and for possible continued dialogue on the subject.

Hey Regina - you are correct in the spelling of the I chord GBDF
And the IV chord, almost: CEGBb
On the I chord the DOWNBEATS are what define the harmony, and the other are what we call PASSING TONES. So you see the DOWNBEATS are BD (3rd and 5th of chord) and DF (5th and b7th of chord.)

But what the heck is going on over the IV chord? The quick answer is this is JAZZ.

Bill Evans is playing very interesting harmony here and what he’s doing could be simplified to say he’s playing a IVsus4 with a 9th and 13th on top (but what I think the way he’s actually approaching it is playing quartal voicings which means chords constructed of 4ths instead of 3rds, in the G Dorian mode, lol.)

Sus4 is called a SUSPENSION and it means you play the 4th interval instead of the 3rd interval. It has a open, more ambiguous, modern sound.

9th and 13th are called TENSIONS, which is an abbreviation of EXTENSIONS. (Most comment TENSIONS are 9th, 13th, #11, and the more dissonant alterations b9, #9, and b13.)

To find the interval used in a tension, subtract 7 from the number.

So a 9th is the the 2nd interval (D over a C chord)
And the 13th is the 6th interval (A over a C chord)

So on the DOWNBEATS we have DF (9th and 4th of Csus4,9,13) and FA (4th and 13th of Csus4,9,13.) And on the upbeats it’s the 3rd and 5th of the chord.

I’m glad you’re enjoying the lessons!