By categorizing chords, you avoid the randomness that leads to chord muddle.
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If it seems like a random occurrence to you when you finally get a chord progression to work, it’s going to help if you categorize them as being in 3 different groups. There are actually more than 3, but those 3 categories will cover most of the chords you’ll ever use in your songs: 1- Diatonic; 2- Modal Mixtures; and 3- Secondary Dominant chords. Chords from outside those three categories need to be used with great care.
Let’s look at each category in some detail. The first category, diatonic chords, are ones that occur naturally in a key by simply creating a scale, and then using each note of that scale as the root of a chord. It’s something I’ve described in several blog postings recently. Creating chords in this way gives you the following chords:
Key of C major:
C Dm Em F G Am Bdim
Key of C minor:
Cm Ddim Eb Fm G Ab Bb
That’s a quick and easy way to create chords that work well together, and you may already be doing that.
The second category of chords, modal mixture chords, are also called “borrowed chords”. Let’s say your song is in C major. You know the 7 diatonic chords that work well in that key. But it’s possible to “borrow” a chord from the minor list, and it can sound very interesting.
Here’s what you do: Take a typical major key chord progression: C F Dm G C, where you play each chord for 2 beats. You’ll notice that the third chord in that progression is Dm. Now, let’s switch that chord for the minor key’s version of a D chord: Ddim. Now your progression is this: C F Ddim G C.
There’s no theoretical reason why you would need to change Dm to Ddim — it simply sounds interesting, and it increases your chord palette. It’s a fun thing to experiment with. Try taking any progression from a major key, and switch certain chords for their minor key counterparts. Some substitutions will work better than others, and sometimes it works nicely to use the diatonic version of a chord, and then follow it with the modal mixture choice, like this: C F Dm Ddim G C.
The 3rd category of chords is a classification called secondary dominant chords. The theory behind secondary dominants can take a while to explain, but in shorthand, you’ve created one when you take a chord that’s normally minor in a certain key, and do two things: 1- change it to major; and 2- follow it with the chord whose root is a 4th higher or 5th lower.
So this: C F Dm G C; becomes this: C F D G C. The Dm chord was changed to become D.
There are many other categories of chords, but the three listed above will cover easily 90% or more of the progressions you’ll hear in today’s popular music genres.
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