The "Back Door" Chord Progression

The use of IVm and/or bVII dominant chords in an otherwise-major progression is a common harmonic device in "Great American Songbook" tunes and jazz standards. When I was first learning theory, this device was described as "borrowing chords from the parallel minor" or "modal interchange" (i.e., switching briefly from major to minor). Some friends who had gone to Berklee in the early 1970s also used the term "subdominant minor" to describe these chords.

In maybe the last 15 years or so, I've been hearing the term "back door progression" to describe this device, and "back door II V" to describe the combination IVm bVIIdom (leading to the I chord). I've been trying to get some clarity on this term. The first instance of the term in print that I could find is in Jerry Coker's book, Elements of the Jazz Language (1991). Coker briefly describes IVm bVIIdom as a substitute for V7, calling it the "back door progression." A later Coker book, Hearin' the Changes (1997) - a terrific book, by the way - gives a more complete description of the device.

As described in "Hearin' the Changes," the "back door progression" is "a cell made up of IV-7 and bVII7 chords, leading to I." He never actually uses the term "backdoor II V," preferring to call it a "progression."

The book goes into more detail (below, with my comments):

• Historically, this progression began as a simple bVIIdom, substituting for V. "At least as early as the bebop era, the IV-7 was added...providing a quasi II function..." 

Comment: I'm not so sure about this. Certainly bVIIdom was used occasionally in standards as a substitute for V (e.g., "Speak Low," "Georgia"), but IVm or IVm6 was used earlier and more often, not necessarily as a V substitute but rather as a way of importing minor-key color, with jazz players later sometimes adding the bVIIdom to form a quasi II V shape. At least, that's how I see it.

• "The back door progression operates in one of three ways: (1) as a substitute for the II V progression (or just the V); (2) as a means of returning to the original key center after a brief modulation to IV major; and (3) as a free-standing cell, usually sandwiched between two I chords."

Comment: I agree. This is a nice breakdown of the harmonic situations where IVm and/or bVIIdom appear. My only reservation about this explanation is that it disregards the "minorizing" function of these chords, which I think is the basic reason that they are there.

In many, many tunes (e.g., Thad Jones' "A Child is Born," any number of tunes by Cole Porter, etc.), the IVm is obviously there to add minor color. bVIIdom can be used as a substitute for IVm; or the two chords can be used together as IVm bVIIdom. Sometimes IIm7b5 V7b9 can be used in these same spots. All of these variations include the "minorizing" b6 note of the key.

For a good example of early use, check out the original sheet music of "After You've Gone" (1918), bar 2 of the chorus (after the "verse" introduction). It's a IVm chord (not bVIIdom) in the key of C, following a IV. It fits Coker's category (2) above. The lyrics in this bar are "...and left me crying." The composer was clearly supporting the lyrics with evocative minor color. At the same time, the sequence incorporates some voice-leading from the A in the F chord, to Ab in the Fm chord, to the G in the C chord.

It's this sort of use that I think originally was (and still is) the main function of "parallel minor" chords, although it's true that bVIIdom has occasionally been used as a substitute for V.

But beyond the "descriptive" side; there's also the "prescriptive" consideration. That is, how can improvisers work with these harmonic areas?

Coker, who knows his stuff, suggests using IVm and/or bVIIdom as a substitute for V alt (I assume he is talking about both soloing and arranging). I'd add that the reverse can work too - playing V alt over the IVm bVIIdom - as seems to be the case in Clifford Brown's solo in "Joy Spring" (see this post).

As mentioned in that post, another possibility is to simply treat IVm bVIIdom as a II V. That is, if Fm7 Bb7 occurs in a tune in the key of C major, you could play as though it is a II V in Eb major. (Note, though, that I was looking at solos in two jazz tunes, "Lady Bird" and "Joy Spring," where the composer's melody itself was written as a II V lick in those spots.)

I still think that the way I was taught is the approach that is most to-the-point: Treat IVm and/or bVIIdom as borrowing notes from the parallel minor, and use the color brought by the b6 note of the key.

The b6 (Ab, in the key of C) is the important note. The chord progression is not necessarily a complete flip into the parallel minor. E natural, although it is not a note in the key of C minor, can work just fine over Fm6 or Bb7, depending how it is used.

Although it's a convenient shorthand, I'm not sure that "back door progression" is the best term for describing this device. "Chords borrowed from the parallel minor" describes its function a little better, as I see it. I should also mention that the term "back door" has also been used to describe a sequence like F#m7b5 B7 Cmaj7, a rather different concept.

Quibbles aside, I'm a fan of Jerry Coker's educational publications. The book mentioned here, Hearin' the Changes, is a well-written survey of the formulas that comprise most of the harmony in jazz standards. The book is aimed at giving players a means of more easily hearing and memorizing changes. It should be interesting to any fairly experienced jazz player, who enjoys digging into this kind of harmonic thinking.