So I thought I'd do a little exercise on arranging and try and demonstrate how we can use theory to expand simple chord progressions without really changing the overall tone of the song.

A friend wrote an arrangement of Amazing Grace that I think encompasses a good number of effective changes. A simple arrangement of Amazing Grace would be:

    G                C        G
Amazing grace how sweet the sound
    G        C        D
That saved a wretch like me
    G    Em        C      G
I once was lost but now am found
     G        D    G
Was blind but now I see.

Let's take a look at this progression:

I - IV - I
I - IV - V
I - vi - IV - I
I - V - I

This progression is pretty basic. The first and third line prolong the phrase and give us some time before we have to reach a dominant chord. The second line contains a half cadence which is appropriate as this divides the first and second halves of the verse. The final line ends the verse and contains a perfect cadence.

Now let's expand.

    G        G7        C        G      
Amazing grace how sweet the sound
    Em        A7        D
That saved a wretch like me
    G    B7        C7      Cm7    F
I once was lost but now am found
     G        D    G
Was blind but now I see.

In our notation this is:

I - I7 - IV - I - vi
I - V of V - V
I - III7 - IV7 - iv7 - bVII
I - V - I

In the first line we see a very effective and common usage of applied dominance. The tonic moves to a dominant seventh chord which creates a tension that is resolved by moving to the subdominant. This is particularly effective here because the tonic is the dominant of the subdominant, i.e. G is the dominant of C and C is the subdominant of G. When we use G7 instead of G we are changing the function of our tonic chord from a tonic chord to a dominant one, the dominant seventh chord in particular has stronger dominant function than just the triad.

The first line functions in the same way as the first line in the original arrangement. It exists to prolong the phrase.

The second line ends on a half cadence and again uses applied dominance.

The third line is the tricky one. For starters, the I-III is a very strong change and complements the melody quite well as the word "lost" is sung as an F#, a note that is voiced in the B7 chord. The next change is a variation on the jazz change called a backdoor. The backdoor progression is a cadence from iv7 to I which we hear here with the Cm7 moving to G with the F as a passing chord. If we wanted to make the F feel more like a passing chord we could walk up from the F to the G by playing either:

    G    B7        C7      Cm7    F F# G
I once was lost but now am found
     G        D    G
Was blind but now I see.

or

    G    B7        C7      Cm7    F F#dim G
I once was lost but now am found
     G        D    G
Was blind but now I see.

The final line is the same as the original and serves to end the verse.

One more thing that we can add to this would be a plagal cadence at the end of the song. These are always fun and are particularly prevalent in church music because adding the cadence would give the chorus an opportunity to say "amen". A quick plagal cadence is almost always effective when a chord progression would otherwise stay on the tonic for another bar. It looks like this:

     G        D    G  C G
Was blind but now I see.

This is an example of a rearrangement that preserves most of the character of the original chord progression. Each line in the new arrangement achieves the same purpose as the line in the old arrangement, it just does so a bit more complexly.

Great work, perhaps when you have compilled all your lessons together, you could get it published??

The problem with chord charges is that they can easily be played without any consideration for voice leading.
For instance, G to G7 to C will still sound awkward unless there is some thought into the concept of a decending bass line.
So, if one thinks in terms of Chord Symbols one needs to remember that they are Shorthand for something much more complex. There are many ways to play a G chord.

Glad you pointed this out. You're absolutely right. Chord changes are lacking without considering voice leading, but looking at things this way allows us to simplify our analysis and to be honest, works pretty well. The reason I say this is that I'm expecting most readers to be guitarists and with the close range of note in chords played on guitar voice leading and choosing inversions is not a huge concern. Moreover, once you start playing with other people, particularly more guitarists, your concerns for voice leading lessen so long as you play different inversions. Musicians, over time, hopefully get used to certain changes and figure out ways of making them flow better and sound more interesting. Thanks for bringing this up, I wanted to do some discussion of voice leading but it's just too hard without a real score.