Module 11: Harmony II: substitution and reharmonisationLesson 4advanced⏱ 90 min + two weeks of daily practice

Modal interchange and borrowed chords

Borrow chords from the parallel minor (iv, bVImaj7, bVII7, iiø7), play the backdoor progression and the minor plagal cadence, use bIII, bVI and bII major sevenths in turnarounds, and recognise all of it in standards.

Why a major key keeps borrowing from its minor

A tune in C major has seven diatonic chords, but it also has a shadow: C minor, the key with the same tonic and three flattened notes. Composers reach into that shadow all the time. A IV chord that turns minor for two beats before the tonic, a bVII7 that resolves up a step into I, a bVImaj7 in a turnaround, a half-diminished ii before a 7b9: these are the darkest and warmest sounds in the standard repertoire, and all of them are modal interchange, chords borrowed from the parallel minor (or, less often, from another parallel mode). The borrowed chord keeps the tonic, so the key does not change; only the colour does. Once you can hear which notes have been flattened, every one of these chords becomes a predictable, nameable device rather than a surprise.

The parallel minor and what it lends

Here are the diatonic seventh chords of C major and of C natural minor side by side. The minor key is the source of everything in this lesson.

Four chords from the minor column are borrowed constantly, and they are the subject of this lesson:

• iv7 (Fm7), and its close relatives Fm6 and FmMaj7: the subdominant turned minor.
• bVImaj7 (Abmaj7): a major seventh chord a major 3rd below the tonic.
• bVII7 (Bb7): a dominant seventh a whole step below the tonic, which resolves up into I rather than down a 5th.
• iiø7 (Dm7b5): the half-diminished ii, which turns a major ii–V–I into something that sounds like the minor cadence from minor-key harmony but still resolves to a major tonic.

Two more appear mainly in turnarounds and are covered at the end: bIIImaj7 (Ebmaj7) and bIImaj7 (Dbmaj7, borrowed from C Phrygian rather than from C minor). The common thread is a small set of flattened notes: the b3, b6 and b7 of the key (Eb, Ab and Bb in C), with the b2 (Db) for the Phrygian chord. When you solo, these are the notes to play; when you comp, they are the notes to bring to the top of the voicing.

The backdoor progression: iv7–bVII7–I

The most important borrowed progression is the backdoor: Fm7 Bb7 | Cmaj7 in C. It is a ii–V (the ii–V of Eb major) that resolves not to Eb but up a whole step to C. Think of it as entering the tonic through the back door instead of the front door of G7. The reason it works is in the chord notes: Bb7 contains D and F, which are the 9th and 11th of C, plus Ab, which falls a half step to G, the 5th of the tonic, while the root Bb rises a half step to the 7th of Cmaj7. Everything about it is smooth, and because it carries three flattened notes it sounds much darker than V7–I. You will find it in the last four bars of many A sections (ii–V–I followed by iv–bVII7–I), in bars 9–10 of some blues choruses, and at the end of countless bridges.

\tempo 90
.
\ts 4 4
:1 (3.5 5.4 4.3 5.2){ch "Cmaj7"} | :2 (3.5 3.4 1.3 4.2){ch "Fm7"} (1.5 3.4 1.3 3.2){ch "Bb7"} | :1 (2.5 2.4 0.3 1.2){ch "Cmaj7"} |

Compare it carefully with two things it is often confused with. A bVII7 that resolves down a half step (Bb7 to Am7) is the tritone sub of E7 from lesson 2, not a backdoor dominant. And Fm7 Bb7 going to Ebmaj7 is a plain ii–V–I in Eb, which may be a modulation and not interchange at all. The backdoor is specifically bVII7 going up a whole step to the tonic of the key you are in.

For soloing, the backdoor dominant takes a natural 9 and a 13 (C and G, both tonic notes), and the scale that fits is Bb Mixolydian, which is the same notes as the Fm7 before it. The line below is chord tones of Fm7, then the Bb9 arpeggio, then a resolution to the tonic; the flattened notes Ab and Eb are what you should hear leaning into the tonic chord.

\tempo 120
.
\ts 4 4
:8 6.4{ch "Fm7"} 5.3 8.3 6.2 9.2 8.1 9.2 6.2 | 8.4{ch "Bb9"} 7.3 6.2 9.2 10.1 8.1 9.2 6.2 | 8.2{ch "Cmaj7"} 5.2 :4 5.3 :2 4.3 |

The minor plagal cadence: IV–iv–I

The oldest borrowed chord is the minor subdominant. Take the plagal cadence IV–I (the "Amen" of hymns) and darken the IV on its way home: Fmaj7 | Fm6 | Cmaj7. Compare the two chords in the table: the A falls to Ab, and the major 7th E gives way to the 6th, D. The half step from A to Ab is the whole effect; the D is there to keep the chord in the key. The Fm6 is usually preferred to Fm7 here because its D (the 6th) is a tonic-key note and keeps the chord from sounding like a ii–V in Eb. Fm(maj7) and Fm7 both work too; they are darker. Listen for this in the last bars of ballads, in the second half of many AABA A sections (IV going to iv and back to I), and in the intros pianists play on standards.

\tempo 72
.
\ts 4 4
:1 (5.4 5.3 5.2 7.1){ch "Cmaj7"} | (3.4 5.3 5.2 5.1){ch "Fmaj7"} | (3.4 5.3 3.2 4.1){ch "Fm6"} | (2.4 4.3 1.2 3.1){ch "Cmaj7"} |

bVImaj7 and bVII7: the "Ab–Bb–C" cadence

Borrow the VI and VII chords of the parallel minor together and you get bVImaj7–bVII7–I: Abmaj7 Bb7 | Cmaj7. It is the sound of a hundred film scores and of the endings of several standards, and it is just the backdoor with the iv7 replaced by bVImaj7 (which shares three notes with Fm7). The bass rises by whole steps into the tonic, which gives it a triumphant quality the ii–V–I does not have. Used in a turnaround, Cmaj7 | Abmaj7 Bb7 | Cmaj7 is a complete, self-contained alternative to I–vi–ii–V.

\tempo 90
.
\ts 4 4
:1 (3.5 5.4 4.3 5.2){ch "Cmaj7"} | :2 (3.5 5.4 1.3 4.2){ch "Abmaj7"} (1.5 3.4 1.3 3.2){ch "Bb7"} | :1 (2.5 2.4 0.3 1.2){ch "Cmaj7"} |

iiø7: the half-diminished ii in a major key

Borrowing the ii chord from minor gives Dm7b5 G7 | Cmaj7, usually with a b9 on the dominant because the b9 (Ab) is the same flattened note that made the ii half-diminished. The progression sounds like the minor ii–V–i you know from Module 3 until the last chord, which is major, and that reversal is the effect: a dark approach to a bright arrival. It is everywhere in the ballad repertoire and in the last two bars before a return to the top of a tune. Half-diminished and 7b9 shapes were covered in Modules 3 and 8; here they are in context, with the rootless G7b9 from the diminished lesson.

\tempo 90
.
\ts 4 4
:2 (5.5 6.4 5.3 6.2){ch "Dm7b5"} (5.5 6.4 4.3 6.2){ch "G7b9"} | :1 (3.5 5.4 4.3 5.2){ch "Cmaj7"} | :2 (3.5 3.4 1.3 4.2){ch "Fm7"} (1.5 3.4 1.3 3.2){ch "Bb7"} | :1 (2.5 2.4 0.3 1.2){ch "Cmaj7"} |

bIII, bVI and bII major sevenths in turnarounds

The last family is a set of major seventh chords on the flattened degrees. bIIImaj7 (Ebmaj7) and bVImaj7 (Abmaj7) are diatonic to the parallel minor; bIImaj7 (Dbmaj7) comes from the parallel Phrygian mode and is also the major-seventh cousin of the tritone sub bII7. String them together and you get a turnaround made entirely of major sevenths: Cmaj7 Ebmaj7 | Abmaj7 Dbmaj7 | Cmaj7, or I–bIII–bVI–bII–I. This is a constant-structure progression, one chord quality moved around, and it is a favourite of modern players because the ear follows the bass line (C, Eb, Ab, Db, C: down a 5th, then by half steps) while the chord colour never changes. A dominant version of the same bass line was the chromatic turnaround of lesson 2; this is its gentler, more ambiguous relative.

\tempo 100
.
\ts 4 4
:2 (3.5 5.4 4.3 5.2){ch "Cmaj7"} (5.5 5.4 3.3 4.2){ch "Ebmaj7"} | (3.5 5.4 1.3 4.2){ch "Abmaj7"} (3.5 3.4 1.3 2.2){ch "Dbmaj7"} | :1 (2.5 2.4 0.3 1.2){ch "Cmaj7"} |

A simpler and very common use of bIII is as a single substitute chord: in a I–vi–ii–V turnaround, replace the vi with bIIImaj7 (or bIII7, the tritone sub of VI7) and the first two chords become Cmaj7 Ebmaj7, a shift that sounds surprising the first time and inevitable after that.

Hearing borrowed chords in standards

A short field guide, in Roman numerals so that you can check it in any key:

• iv after IV in the second half of an A section (IVmaj7 | iv7 or iv6 | Imaj7): the minor plagal cadence. Extremely common in ballads and in 1930s songs.
• iv7–bVII7 before I at the end of a phrase: the backdoor. Often right after a normal ii–V–I, as a second, darker cadence.
• bVII7 resolving down a half step is a tritone sub (lesson 2), not a borrowed chord. Check the resolution.
• iiø7–V7b9–Imaj7: the borrowed ii. If the tonic is minor, it is simply the minor ii–V–i.
• bVImaj7 followed by bII7 or bVII7 in the last two bars: a borrowed turnaround.
• A major seventh chord on the b3, b6 or b2 anywhere: usually interchange or constant structure, and almost always played with a #11 by modern rhythm sections.

For the soloist, the method is the same for every borrowed chord: find the flattened notes (b3, b6, b7, and b2 for the Phrygian chord), and make sure your line contains them while the chord lasts. A line that stays in C major over Fm7 Bb7 sounds wrong; a line that uses Ab and Eb and then resolves them into the tonic chord sounds like you meant it.

Exercises

1. Parallel-minor table. For each of the twelve keys, say the iv7, bVImaj7, bVII7 and iiø7 out loud and check them against the table. Then play each set as a drop-2 shape on strings 5–4–3–2.
2. Backdoor through the cycle. Play Imaj7 | iv7 bVII7 | Imaj7 in all keys, 90 bpm, with the voice leading from the example. Then the line over iv7 | bVII7 | Imaj7 in five keys.
3. Minor plagal. Play Imaj7 | IVmaj7 | iv6 | Imaj7 in all keys on strings 4–3–2–1, then with iv7 and with ivMaj7 instead of iv6 and decide which you prefer in each register.
4. bVI–bVII–I. Play the turnaround in all keys. Then combine it with the backdoor: Imaj7 | iv7 bVII7 | Imaj7 | bVImaj7 bVII7 | Imaj7.
5. iiø7–V7b9–I. Play it in all keys with the rootless 7b9 shapes from lesson 3. Follow each one with the ordinary ii7–V7–I and listen to the difference.
6. Major-seventh turnaround. Play I–bIIImaj7–bVImaj7–bIImaj7–I in all keys. Then try I–bIIImaj7–ii7–V7, the single-chord substitution.
7. Analysis. Go back to the tunes you have been labelling. Mark every chord that comes from the parallel minor and name it. Note where a bVII7 is a backdoor and where it is a tritone sub.

Quiz