Borrowed Chords

 

The technical term for "borrowed" chords is "modal interchange", meaning the universe of chords can be expanded from the seven chords available in the primary key through a reciprocal interchanging process.

Using the metaphor of the solar system, with Earth as a starting point, the orbit of Mars is the first source of additional chords. If you are in a major key you can go there to obtain more chords from the parallel key (not relative key). In C, the parallel key is C minor, and vice-versa. Using the circle of fifths, the next "planet" is Jupiter, and would be G Major, or its relative minor, E minor. Since it has one sharp, it will give you all the chords that have F# in them, such as B Minor, D Major and D7. Using the circle of fourths, ascending from C, the next destination is F Major and F Minor, one flat and four flats respectively. This could give you access to Bb major and Bb minor triads, C7, Db Major, Eb and Eb7, G minor and G half-diminished and Ab major.

The key to borrowing is to find a way back to the original key, otherwise it is a modulation, and never returns to the original key. Typically, it's through a subdominant-dominant relationship, as a "turnaround". A very common illustration of this in action is Penny Lane by the Beatles.

After watching the short video, perhaps you want to test your knowledge of borrowing.

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