Mode Mixture
Mode Mixture refers to chords borrowed from the parallel minor key and used in a major key (or vice versa). These chords are also commonly called borrowed chords.
The diatonic chords in a minor key (natural minor*):
1m, 2°, b3, 4m, 5m, b6, b7
Simply put, it sounds great and unexpected to substitute a 4 for a 4m, or to insert a b3 into a normal diatonic progression. The most common of the above chords to show up in a major key include the b3, 4m, 5m, b6, and b7.
b7 (Flat 7)- The What
A b7 chord (flat 7), for example, is built not off the normal 7th degree of the scale, but a half step lower. In C: a b7 chord is a Bb major. This chord is borrowed from C Minor (music theory calls this the parallel key to C major). The b7 chord can always be found a whole step under the 1 chord.
The b7 chord is extremely popular in rock, country, blues, jazz, and pop music. It is a good candidate for most popular non-diatonic chord used in popular music.
Free Bird, Lynyrd Skynyrd (G):
V: (1, 5/7), 6m, (b7, 4), 5
Don’t Do Me Like That, Tom Petty And The Heartbreakers (G):
Intro/V: 1, b7, 4, 1 / 1, b7, 4, 1
The b7 chord in the above two examples would be an F.
Don’t Stop, Fleetwood Mac (E):
V: (1, b7), 4, (1, b7), 4 / (1, b7), 4, 5, 5
The b7 chord in Don’t Stop would be a D.
You’ve Got A Friend (A): (cued up at Bridge)
Bridge: b7, 4, 1, 1maj7 / 4, b7, 6m, 2, 5, 5
The b7 chord in You’ve Got a Friend would be a G.
b7 (Flat 7)- The Why
You might notice that in almost all the above instances, a 4 chord follows the b7. This is because the b7 chord is the 4 chord in the key of the actual 4 chord. In other words, an F is a b7 in G, but temporarily functions as a 4 chord in C (even though C is the 4 chord of the original key). The music is essentially briefly pretending to be in another key by treating a chord besides 1 like the 1 chord. When it comes to non-diatonic chords, if something sounds good and is commonly used outside of the key, there is often a hidden secondary function or structure accompanying the chord.
In the 2nd half of the Bridge on You’ve Got a Friend, the b7 chord acts as a leading tone to the 6m.
b6 and b3- The What
Similar chords that are much more rarely used include a b6 chord (In C, an Ab), and a b3 chord (In C, an Eb). Both chords are found in similar ways, and are also borrowed from the parallel minor key.
Head (in 6/8): 1 1 4 4 / 1 1 4 4 / 2m 2m 5 5 / b3maj7 b6maj7 5 5
Toes, Norah Jones, G: (cued up already at the Bridge)
Bridge (4/4): b6maj7 5m 4 1 / b3maj7 (2m, 4) 1
In both the above examples, the b3 would be a Bb, and the b6 would be an Eb. The minor 5 in the 2nd example is another non-diatonic chord about to be covered.
b6 and b3- The Why
In both examples the artists added natural extensions, (the 7th of the chord). It’s common to add these to give a chord more character and autonomy (especially with b6 and b3 chords). In the natural minor scale, from which we’re borrowing, the diatonic 7th chord forms of b3 and b6 degrees are major 7th chords (displayed as M7 chords in the linked resource page).
These chords are most commonly used in a leading-tone style function in popular music. In Gravity, the b6 leads strongly and smoothly the 5 chord. In the Norah Jones tune, both outside chords lead down to their diatonic neighbors.
Unlike b7 chords, which sound amazing but don’t confuse the ear, b6 and b3 chords can sound cool but also disorienting and confusing. They have a bigger chance of starting to tonicize another chord besides 1, making them harder to follow. For example, with both the b3 and b6 chord present in a progression, a 1, 4 relationship can be heard in reference to the b3, or 5, 1 relationship in reference to the b6- it all depends on context.
In C: Introducing Eb and/or Ab into a progression-
1 5 b7 4 / * b6 b3 ???
The progression up to the asterisk is a dime a dozen. It sounds great, there is some cool symmetry to it (the progression goes up a 5th twice: (1, 5) and (b7, 4). After the asterisk however, another leap up a 5th with two non-diatonic chords and we start to not feel in Kansas anymore. This might be the desired effect, but should be considered when writing songs.
These chords are sometimes up to interpretation. A fair amount of songs with b6 and b3 chords heavily featured in a certain section could be notated as temporarily changing key. It’s always about context. Ask yourself frequently: ‘What sounds like 1?’ Sometimes the answer is purposefully ambiguous.
Because these chords can be a bit harder to grasp when ear-training, old-fashioned interval training to find those root notes can be a lifesaver. There is absolutely no shame in relying on singing up the scale to double check the identity of a chord and its root note.
4m- The What
The 4m chord is a beautiful and heavily-used non-diatonic harmony (though they all have countless moments of beauty).
Some of the most common uses of these chords:
Whole Tune: 1 1 3 3 / 4 4 4m 4m
I Will Follow You Into the Dark, Death Cab For Cutie (F):
Intro/Chorus: (6m, 1), (4, 1) (6m, 1), 5 / (6m, 1), (3, 6m), (4, 4m), 1
Bohemian Rhapsody, Queen (Mixed Keys): (Example is cued up to V2)
Passing chords removed for ease of reading:
V2 (Eb): 1, (6m), 2m, (2m, 5) / (1, 5/7) (6m, 4m on “nothing”), 1….
Lori McKenna - Love Can Put It Back Together (D):
V: 1, (5m, 4), 1, (5m, 4) / 4m, 1/3, 2m, 5
Green Day - Wake Me Up When September Ends (G):
C: 1, 5/7, 6m, 1/5 / 4, 4m, 1, 1
This chord often has a melancholy, romantic sound. It often proceeds a 4 chord and increases the sense of finality at the end of a progression. It can also simply replace a major 4 chord (assuming the minor 3rd doesn’t clash with the melody). It almost always followed by a 1 chord.
4m- The Why
The reason why the 4m chord resolves so nicely to the 1 is due to the leading tone from the b6 scale degree wanting to resolve down to the 5th. In addition to the b6, the 4th scale degree (root) of the chord resolves down to the 3rd.
5m- The What
Coming Soon!
5m- The Why
Coming Soon!