Borrowed chord
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A borrowed chord is a chord borrowed from the parallel key. If the root of the borrowed chord is not in the original key, then they are named by the accidental. For instance, in major, a chord borrowed from the parallel minor's sixth degree is a "flat six chord" written bVI. Borrowed chords are an example of mode mixture.
In the Baroque, Classical and Romantic eras, six chords borrowed from the parallel minor key are most commonly found (shown here in C major):
- Diminished Supertonic Triad (ii°): D, F, A flat
- Half-Diminished Supertonic Seventh (ii°7): D, F, A flat, C
- Major Triad on the Lowered Third Scale Degree, or "Flat Three" (bIII): E flat, G, B flat
- Minor Subdominant (iv): F, A flat, C
- Major Triad on the Lowered Sixth Scale Degree, or "Flat Six" (bVI): A flat, C, E flat
- Fully Diminished Leading-Tone Seventh (vii°7°): B, D, F, A flat
The following three chords are also found in Romantic era, albeit rarely:
- Minor Subdominant Seventh (ivb7): F, A flat, C, E flat
- Major-Minor Subdominant Seventh (IVb7): F, A, C, E flat
- Minor Dominant Ninth (Vb9): G, B, D, F, A flat
The Major-Minor Subdominant Seventh, which contains an A natural, is borrowed from the parallel ascending melodic minor scale.
Borrowing from a parallel major key is generally limited in western music to ending a minor piece on a major tonic triad, a chord which is then called a Picardy third.