If your song is in a major key, you know that the ii-chord is going to be minor. So if your song is in the key of C major, the chord based on the note D will be Dm (D-F-A). And you’ll be using progressions that might be like the following:
- C F Dm G C
- C Dm G Am
- Am F Dm G7 C
If you’re looking for a way to branch out and come up with chord progressions that are a little more creative rather than randomly throwing in chords that come from other keys (an improvisatory process that can take a long time to give good results), you might try:
- choosing one of the chords from a basic progression, and then…
- keeping the root the same, but changing the quality of the chord (change a major chord to a minor one, let’s say) built on that note.
That’s what’s going on when you substitute the F chord (IV), using Fm (iv) instead. That kind of substitution is called a modal mixture, or a borrowed chord, because the Fm comes from the minor key of C minor. So in that sense, we’re borrowing Fm from the key of C minor.
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There are other chords you can borrow, and one that’s related to that minor iv-chord is the diminished-ii chord. Here’s how it works.
As you hopefully know, take any note that comes from the scale of the major key you’ve chosen, build a 1-3-5 triad on that note, and you’ve got the chord that lives naturally in that key. That means that in C major, the tonic triad — also called the I-chord — is C-E-G. A triad on D is the ii-chord, D-F-A. A triad on E will give us the iii-chord, E-G-B, and so on.
That ii-chord (D-F-A) is minor. It’s minor because minor triads are created by forming a perfect fifth (D to A) and then inserting a minor 3rd above the root (D-F).
But if you change that A to Ab, you get this triad: D-F-Ab. That triad is a diminished triad, because diminished triads are created by forming a diminished fifth (D to Ab) and then inserting a minor 3rd above the root (D-F).
How to Use the Diminished-ii-Chord
You’ll be pleased to know that the diminished-ii chord (iiº) can be used practically anywhere a minor ii-chord might be used. So if you look at those 3 sample progressions near the start of this post and change the Dm chords to Dº, you’ll get these:
- C F Dº G C
- C Dº G Am
- Am F Dº G7 C
Earlier I said that the Dº is closely related to the minor iv-chord. Here’s how: In C major, the minor iv-chord uses the notes F-Ab-C. The iiº uses two of those notes, the F and Ab. In fact, playing the iv-chord but using D as your bass note will give you iiº7: D-F-Ab-C.
So the iiº in those 3 progressions above will also sound great when you use the minor iv-chord instead (C F Fm G C).
It’s not an overly-used chord in pop genres. It was quite popular in slower ballads, like “Afterglow” by Genesis, the intro for which used the progression G Gmaj7 C Aº G… an Aº when we were expecting Am.
The best way to be sure you’re using it in a way that makes tonal sense is to write out some standard major key progressions, and then replace any ii-chord or IV-chord with iiº.