Mode mixture is a form of chromaticism in music where a chord is “borrowed” from the parallel minor key to use in a progression in major, or vice versa, when a chord is borrowed from the parallel major to use in a progression in minor. The borrowing occurs between the major and minor modes – it is not borrowing from church modes (Dorian, Phrygian, etc.). This technique is also sometimes called modal borrowing. These chords give a nice change of color and add interest to the harmony.
Here is one simple and very common example of mode mixture: in a chord progression in the key of D major, instead of using the usual triad IV (a G major chord), one might “borrow” the iv chord from the parallel minor key of d minor (a G minor chord) to use instead. The regular diatonic progression is on the left, and on the right, the minor iv chord has been substituted for the major iv instead.
There are several key points about borrowed chords that are useful to remember:
1. The chords are always borrowed from the parallel minor or major, not the relative minor or major.
2. There are only three scale degrees that differ between the major and minor scales, 3, 6, and 7, so these are the only steps where accidentals will occur when borrowing. When in a major key and borrowing from the minor, these notes will need to be lowered by one half step. The lowered 6th scale degree is the most commonly used note in mode mixture.
3. Borrowing chords from minor keys occurs more often than borrowing from major, because chords with raised 6th & 7th scale degrees are already used in minor. This means there are fewer options when trying to find new chords in major to borrow, since many of them are already existing diatonic chords in minor.
4. When the root of the borrowed chord is on an altered note, the Roman numeral is usually preceded by a flat sign (such as a bVI chord, called a “flat-six chord”.)
5. Conversely, if borrowing chords from major for use in the parallel minor key, notes will need to be raised. The raised 3rd scale degree is the main note that will be altered during this type of mode mixture, since the 6th and 7th scale degrees already may be raised in minor. The main chord that is borrowed from the parallel major into minor is the major tonic triad (in other words, major I used in place of minor i). This is also known as the “Picardy Third.”
How to use borrowed chords:
1. Borrowed chords are often substituted for the usual chord on that same Roman numeral, such as using a major I chord instead of the minor i chord when ending a piece in a minor key (the Picardy Third). Or a borrowed bVI from the parallel minor might be used in place of the regular vi chord; a borrowed iv can be used in place of IV, etc.
2. Sometimes borrowed chords are inserted into a progression, after the same diatonic Roman numeral is used. For example, we might have a progression such as I – IV6 – V - I, into which we could insert the minor iv chord creating this progression: I – IV6 – iv6 - V - I. When borrowed chords are inserted in addition to their diatonic counterpart, the borrowed chord should be used after the regular chord, so that the chromatic note is approached from above and then resolves downward in the chord following the borrowed chord. Here is that example:
3. Inserting the borrowed chord after the same Roman numeral will only work when the borrowed chord contains only one accidental, otherwise parallels will occur (e.g. you cannot move from vi to bVI without having parallels, since both the root and fifth need to be lowered one half step.)
4. When choosing a chord to precede a borrowed chord, use a chord that will approach the chromatic note smoothly, and which also has good root movement to the borrowed chord. For example, if your borrowed chord contains the lowered 6th scale degree, approaching that note from the regular 6th scale degree or the 5th scale degree would be good choices. Make chromatic movement in the same voice to avoid cross relations.
5. Just as when working in the minor mode, avoid creating an augmented second interval (A2) between the lowered sixth scale degree and the leading tone in your voice leading.
Modulation using borrowed chords:
A borrowed chord can be used as a pivot chord in a common chord modulation. Because these chords are from the parallel major or minor, they enable you to make modulations to more distant keys than diatonic common chords do. Borrowed chords link very easily to keys that are three or four “notches” away on the circle of fifths, to the chromatic mediant keys.
For example, one can modulate from C major to A-flat major by using the borrowed chord bVI in C major (an A-flat major triad, borrowed from c minor) as the pivot chord, which would function as the tonic chord (I) in the key of A-flat major.
Or to modulate from C major to E major, you could use the vi in C major (A minor triad) which would function as the borrowed iv chord in E major as your pivot chord. In other words, the chord function could be borrowed in the first key or the second key, depending on which will work better to link the keys in question. Consult the circle of fifths to see which parallel minor brings you closer to the desired key. We will look at detailed examples of this kind of modulation later after we have learned to use borrowed chords in non-modulating progressions.