Using chords in Parallel and Adjacent Keys.
What are they?
Sharing chords in adjacent keys.
I get asked all the time by my students, "That chord is not in the same key as the song. Where did it come from?" With a simplified explanation, I show the student that chords "borrowed" from other keys, usually come from “adjacent” keys that share common chords.
For example, the key of C major and the key of G major share four common chords in both keys:
C - C, Dm, Em, F, G, Am, B°
G - G, Am, Bm, C, D, Em, F#°
The shared chords are: C, Em, G and Am.
This means not only can you use the seven chords in one key, you can also use other chords in keys with common chords.
So, what are parallel Keys?
The easiest way to understand parallel keys is to understand the circle of 5ths (4ths). Adjacent keys allow common chords in other keys to be used in music. Parallel keys use a different approach.
Here are the basic triad chords the key of C major again:
C, Dm, Em, F, G, Am, B°
The parallel key to C major is C minor:
Cm, D°, Eb, Fm, Gm, Ab, Bb
As you can see, a few things have changed, going from a major key to minor key. Minor key structures are very different from major key structures. The minor key has shifted all of the chords to different positions.
The major key chord structure looks like this:
I, ii, iii, IV, V, vi, vii°
The minor key chord structure looks like this:
i, ii°, III, iv, v, VI, VII
Honestly, I think that the easiest way to understand this is to not necessarily think of the key as C minor. Instead, think of it as the key of Eb major, but starting on the Cm as the first chord in its minor key.
So, the key of C major and the key of Eb minor do not have any common chords to share because they are not adjacent to one another. However, parallel chords are often used in song writing to change a feeling, a mood or a direction of a song.
For example in the song "Daniel" by Elton John, the song is played in the key of C major. A substitution chord is used in the verse:
C, Dm7, G, "E7", Am, F, G, Am, F, G, C.
The "E7" is not in the key of C major. "E7" is used to substitute the Em of that key. I imagine that this was a decision based on the direction of the melody itself.
But wait, there's more! The chords in the chorus of the song are as follows:
F, C, F, C, Am, F, "Ab", C, "A7", Dm7, G.
So, now, we see an example of using the parallel key approach for one of the chords in the chorus. The "Ab" comes from the C minor parallel key. Also, you may have noticed that there is an "A7" used in the chorus. Again this is a substitution chord to replace the Am chord in the key of C major.
Watch this video by David Bennett for more examples of parallel key songs.
I think that the easiest way for you to figure out chords (and notes) between parallel keys is to “shift” the way you look at relative major and minor keys, by moving together (parallel), the "tonic" (or the root) of both major and minor keys with the same note. Or, you can also simply go to the minor third of a major key to find the parallel major key. The minor 3rd of C major is Eb. The 6th of the Eb major key is C minor. This now becomes the parallel key to C major.
Instead of using relative keys:
C major - A minor
G major - E minor
D major - B minor
etc...
Use this for parallel keys:
C major - C minor (Eb major)
G major - G minor (Bb major)
D major - D minor (F major)
…and so on.