Music Theory - Solving Chord Functions

Music Theory - Solving Chord Functions

If you are viewing a progression for the first time, especially if you have never heard the tune before, it can seem very difficult to figure out what to play over it.  Non-diatonic harmony can appear very complex, but if you have a formula for analyzing and dissecting progressions, it's a piece of cake.  

Here's how it works:

Step 1:  Look for dominant chords to determine key centers.

When you subdivide your progression by dominant chords, you need to determine if they are functioning, non-functioning, or static.  

Dominant chords are the most powerful chords in music because they "push" the harmony.  Therefore, you should immediately see the skeleton of the harmony and the implied tonal centers once you figure out the function of each dominant chord.

Step 2:  If the dominant chord is functioning, determine if it is a primary or secondary dominant. 

To review, primary dominants resolve to the tonic and secondary dominants resolve to something other than the tonic.  

Example:  C   D7   G7   C

In this example, both the D7 and G7 are functioning, but the D7 is the secondary dominant and the G7 is the primary.  

Therefore, this progression is:

I   V7/V   V7   I

Once you determine the primary dominant chord(s), you should have a much clearer idea of the tonal centers - but that won't always get you the whole way - it will usually just give you the “skeleton.”

Step 3:  Look for modal interchange.

Once you have subdivided your progression by dominant chords, take a look at the other chords in the progression.  For each of the non-diatonic chords, determine if they are borrowed from parallel mode. 

If you do determine that the chord(s) in question are borrowed from a parallel mode, then you know that you can play that parallel mode over those chords.  

This should get you most of the way, but what if there are some chords which just do not fit a key-centered approach?

Step 4 : Chord scale approach.

For every chord that doesn't fit the key-centered approaches outlined above, apply a chord-scale approach.  

Look at the chords around the chord in question to determine the already existent scale degrees and make a decision.  The decision is up to you. 

For example, if you encounter an altered chord that has no discernible key-centered function, and you feel its role is to color the progression in the spot, you can choose to color it with the altered scale, but you could also choose the dominant diminished scale.  

The point is that, once you get to chord scale thinking, there are a great deal of options at your disposal.  It comes down to what you want the function and color of that chord to be in that specific context.

The last thing to talk about in this lesson is tri-tone substitution.  

The tri-tone, if you remember, is the #4/b5.  Tri-tone substitution is yet another way to imply a dominant chord's need for resolution, but not as a V7 chord.  

Simply put, dominant chords that are a tri-tone apart perform the same function.  

This is because the 3 and b7 of a dominant chord are the exact same notes as the 3 and b7 of a dominant chord a tri-tone apart, just inverted. 

For example:

The notes of a G7 chord are:

G   B   D   F

The notes of a C#7 are:

C#   F   G#   B

Notice that the 3 and b7 of G7 - B and F - are the same notes as the 3 and b7 of C#7 - F and B.  

This means that we could actually play C#7 instead of G7 in a progression and achieve the same chord function.  

Check out the two progressions below:

Dmi7   G7   C           Dmi7   C#7   C

While the second progression could be written as IImi7   bII7   I,  it's function is really that of a IImi7   V7   I.

Practice messing around with tri-tone substitution and get comfortable identifying it in progressions.  

And of course, if you encounter tri-tone substitution in a progression, you can improvise over it as if it was the V7 chord function it implies.