Borrowed Chords

The concept of borrowing a note from the parallel major or minor key is very simple.  In a minor key there are three pitches that are lowered a half-step from the same scale degree in a major key.  These are the 3^rd, 6^th, and 7^th.  When one or two of these scale degrees are borrowed from the parallel minor into the major key, a new chord quality appears.  When a m3, m6, or m7 is imported from a minor key into its parallel major, a borrowed chord is formed. 

The most commonly borrowed pitch is the m6^th.  Using this pitch to replace the 3^rd of a subdominant triad (IV) in a major key yields a subdominant minor chord (iv).  In the key of C, a diatonic IV chord is spelled F-A-C.  A minor iv chord, created by borrowing the m6^th, is spelled F-Ab-C.  This can add interest and unexpected color to the music. 

It is much less common to see a major scale degree borrowed into the parallel minor.  However, a major 3^rd borrowed for the tonic chord at the final cadence is frequently encountered.  It is referred to as a Picardy third.

The following chart shows the quality of diatonic triads and 7^th chords commonly used in both major and minor keys.  Any of the minor chords might be borrowed into the parallel major.  In addition to those in the chart below, a major triad built on the lowered 7th scale degree, or subtonic, is available to borrow.  It’s root appears in the descending form of the melodic minor.