It is a fact that the majority of popular western music is diatonic. Therefore, it was composed using a fixed bank of available pitches that belong to one major or minor key signature. This system, however, is limiting.
Borrowing Weird Chords
In fact, thought-provoking and interesting harmonies are created by “borrowing” chords that are not diatonic to the key of the song but rather, to a parallel key. Furthermore, they are called modal interchange chords and are evident in baroque, classical, and jazz music as well as in modern compositions from artists like Radiohead, Muse, Moby, Deadmau5 and Thelonious Monk. In addition, incorporating modal interchange chords will expand the “color pallet” of your music and the range of emotions you can evoke.
For example….
If you begin a song in the key of F Major, then the diatonic scale degrees are F, G, A, B♭, C, D, E. Correspondingly, the diatonic triads built upon these scale degrees are as follows…
- F major (F A C)
- G minor (G B♭ D)
- A minor (A C E)
- Bb major (B♭ D F)
- C major (C E G)
- D minor (D F A)
- E diminished (E G B♭)
But you can use more than just these 7 chords…..
Additionally, the parallel minor of F major is F minor. This means the two key signatures share a tonal center or “do”. But, the 3rd, 6th, and 7th degrees in F natural minor are a half-step lower than in F major.
- A becomes A♭
- D becomes D♭
- E becomes E♭
Diatonic Triads
Also, the diatonic triads upon the scale degrees of F natural minor are as follows….
- F minor (F A♭ C)
- G diminished (G B♭ Db)
- Ab major (A♭ C Eb)*
- Bb minor (B♭ D♭ F)
- C minor (C E♭ G)*
- Db major (D♭ F A♭)
- Eb major (E♭ G B♭)*
Minor
* In minor, diatonic triads that include the 7th degree of the scale are typically altered by raising that 7th degree a half-step (E♭ to E in this case). Consequently, the Ab major triad would become an A♭ augmented triad (A♭ C E), the C minor triad would become a C major triad (C E G) and the E♭ major triad would become an E diminished triad (E G B♭). This is an adaptation from classical harmony and the “Harmonic Minor” scale. Moreover, this raised seventh is called a “leading tone”. It enables a sense of resolution because it allows the chord built upon the fifth degree to be major or dominant.
Roman Numeral Analysis
As can be seen below, I have isolated the triads from F natural minor that are most commonly interchanged for diatonic triads in F major, with their respected roman numeral analysis**.
- i: F minor ——-> (interchanges I: F major)
- iv: B♭ minor —-> (interchanges iv: B♭ major)
- v: C minor ——-> (interchanges V: C major)
- ♭VI: D♭ major –> (interchanges vi: D minor)
- ♭III+: Ab augmented—–> (interchanges iii: A minor)
** As shown above, Roman numeral analysis is a representation system used to standardize chord functions. In like manner, modal interchange chords with the same roman numeral analysis add the same “color” to the arrangement no matter what key you’re in.
For example……
- Playing an F minor triad in the key of C major will feel the same as playing a C minor triad in the key of G major because the F minor and C minor chords are both functioning as the modal interchange chord, “iv”, in their respected keys.
- Playing a D minor triad in the key of D major will feel the same as playing a D♭ minor triad in the key of D♭ major because the D minor and D♭ minor chords are both functioning as the modal interchange chord, “i”, in their respected keys.
In addition, you can also use “7th chords” from parallel keys. Some modal interchange chords are more effective as “7th chords” than as triads, such as “♭II maj7”.
Below are some more exotic modal interchange chords from the modes.
Roman Numeral Mode of Origin Example using F major
♭II maj7 (Neapolitan chord) *** Phrygian G♭ major 7 (G♭ B♭ D♭ F)
IV7 Dorian B♭ dominant 7 (B♭ D F A♭)
♭VII maj7 *** Dorian E♭ major 7 (E♭ G B♭ D)
♯iv Ø*** Lydian B half diminished (B D♭ F A)
I7 Mixolydian F dominant 7 (F A C E♭)
*** In contemporary harmony, a flat or a sharp is placed in front of a roman numeral to indicate that its root note has been raised or lowered in reference to the major scale degrees.
