Mixture is the term used for borrowing notes from a minor key in a major piece, or vice versa. Most commonly, a major piece may include elements from its parallel minor.
For instance, in A major, we have these notes:
A B C# D E F# G#
A major’s parallel minor is the natural minor scale that also begins on A. Which has this notes:
A B C D E F G
So there are some differences. C, F and G are all different in the minor, and can be borrowed or “mixed” into the major key area.
For our purposes here, we’re going to refer to mixture with scale degrees. We just discovered that scale degrees 3, 6 and 7 are all different from major to minor. 3, 6 and 7 are all lowered by one half step.
To indicate this, we’re going to use a flat sign (b). So we have three new tones that become available in major due to mixture: b3, b6 and b7.
There’s a couple ways these tones can function. The first is that they can function as passing tones within a bigger structure. That is, you could have a melodic line, in scale degrees, that looks like this: 6 – b6 – 5. Or in A major:
However, mixture can offer some great ways go add in some colorful harmonies. IV which is usually a major chord in a major key can become iv, a minor chord, by altering the third of the chord which happens to be scale degree 6.
In addition, we can use b6 and b3 together to get another interesting chord: bVI.1
We can also use b3 and b7 to create the chord bIII.1
Normally the chords in a major are A major, B minor, C# minor, D major, E major, F# minor and G# diminished. But with mixture we can add in the following harmonies: C major (bIII), D minor (iv) and F major (bVI)
1 Remember that the case of a roman numeral indicates whether is major or minor. Upper case Roman numeral is major, lower case is minor. An accidental before the Roman numeral refers to its root. bIII means a major chord built of the third scale degree that has been lowered a half step. In the case of A major, that means a major chord built on C (b3): C major.