In the world of harmony, there is a basic rule that two chords with the same function can substitute for each other. I don’t want to elaborate on that too much today but I will say that in my mind, I have three general pools of chords and if a chord belongs to one pool, any of the other chords in the same pool are potential substitutions.
Note that I said “potential substitutions.” Just because I can defend a substitution because it has the same function does not mean I should use it. There are two big factors that have to be considered. First, the chord has to work with the melody note(s) it is played under. That is another can of worms I won’t open now. The second is simple but deadly effective: the chord has to sound good.
While I can show you on paper a bewildering number of chord substitution possibilities, those two factors usually limit your options dramatically. The moral of the story is to listen to your ear. I know brilliant musicians who insist on viewing music intellectually and use harmony that is defensible but not very pleasant. They they wonder why no one wants to listen to them…
So, today I am going to give you a virtual slam dunk in the world of chord substitutions. It almost always works and almost always sounds good: substituting minor IV for IV.
Here are a few recent examples from my last arrangement (“When I Survey the Wondrous Cross”):
The minor IV is in bars 6 and 7. This is the introduction and I am vamping on a I – IV/I progression. To get a different sound, I chose to substitute minor IV for some of the IV’s. (Don’t get confused: the minor IV is in second inversion.)
The melody starts in bar 15 and notice use of the minor IV (second inversion) in bar 16. In your hymnal, you would see a IV there (I think).
Here is the basic rule. Any time you see a IV chord, a minor IV will likely sound great. The big exception? If the melody note is the third of the IV, it will sound horrible. For example, in bar 16 above, what if the melody note had been D natural? Playing that against the Db in the minor IV would not work.
Now, be careful with this one because once you get it in your fingers, you may have a tendency to overuse it. It is simple and sounds great, but if you go overboard, it will become a liability for you quite quickly.
For those of you that are advanced, let’s talk a second about getting more mileage and color out of the minor IV. The first thing to know is that the best extra note to add is the 6th. IVm6 is a huge part of my normal chord palette. In fact, if you go back to that first example, note that I am working the 6th (G) into the melody to take advantage of that sound. That is intentional.
After the 6th, you can get an even more exotic sound by adding the major 7th. I love that sound and use it when I can. Avoid the minor 7th (normally) though. And if you want to go beyond the 6ths/7ths, you can add natural 9 and natural 11.
That is about it. Go use this simple substitution liberally but not too liberally.