You don't have to just use the chords in one key.

Use the chords in the keys next to them.

There is a common misunderstanding in music that when a song is written in a specific key, the chords in the song should all fit into that key. This is not always true. Always remember that music is a conglomeration of mathematics, patterns and formulas all brought together to make rhythms and melodies to please the ear. Sometimes you have to think outside the quadrilateral parallelogram to achieve this.

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Nomenclature: M7 = Major 7th, m = minor, m7 = minor 7th, ° = diminished, °7 = diminished 7th, b = flat and # = sharp.

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Adding chords from other keys.

Let's start off where we normally do, in the key of C major: 

Triads:

C, Dm, Em, F, G, Am and B°.

With 7th's:

CM7, Dm7, Em7, FM7, G7, Am7 and B°7.

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Let's go to the fourth chord in the key of C major: (F) and look at the chords in that key:

Triads:

F, Gm, A, Bb, C, Dm and E°.

With 7th's:

FM7, Gm7, Am7, BbM7, C7, Dm7 and E°7.

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Now, let's go to the fifth chord in the key of C major: (G) and look at the chords in that key:

Triads:

G, Am, Bm, C, D, Em and F#°.

With 7th's:

GM7, Am7, Bm7, CM7, D7, Em7 and F#°7.

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How many total common chords do we have in combining all three keys?

C, CM7, C7, D, Dm, D7, Dm7, E°, E°7, Em, Em7, F, FM7, F#°, F#°7, G, GM7, Gm, Gm7, G7, A, Am, Am7, Bb, BbM7, Bm, Bm7, B° and B°7.

Wow! That's a lot of possibilities; and these are just the triads and the 7ths! Now, imagine how much broader your strokes with your paint brush will be when you try to write a song. Imagine the combinations you could come up with, knowing how many more chords you actually have available to use outside of one key, by incorporating the chords in the fourth and fifth of that original key. This is the beauty of learning the circle of fifths, and all that you have available to you when you are writing and learning how to create chord structures and progressions in music.

Of course, not every chord combination is going to sound great. Most of them will sound good enough to create a melody and progression that will sound good. 

I suggest as an exercise, that you take the above list of twenty-nine chords and play them in various combinations of four chords:

1) C, CM7, C7, D

2) C7, D, Dm, D7

3) Dm, D7, Dm7, E°

4) Dm7, E°, E°7, Em

5) E°7, Em, Em7, F

6) Em7, F, FM7, F#°

7) FM7, F#°, F#°7, G

8) F#°7, G, GM7, Gm

9) GM7, Gm, Gm7, G7

10) Gm7, G7, A, Am

11) A, Am, Am7, Bb

12) Am7, Bb, BbM7, Bm

13) BbM7, Bm, Bm7, B°

14) Bm, Bm7, B°, B°7

I highly recommend that you record yourself (on your smartphone), practicing these chord combinations, then listen back to them to hear which combinations sounded the best. It may surprise you at just how many chord combination ideas you can come up with that will sound good together. You might actually hear some combinations that sound like songs you may already know.

I hope this lesson helps you better understand chord combinations and combining keys. Please leave a comment below and share this article. Thanks, Dave.