In part 1, we looked at the most fundamental organization of chord progressions: the cyclic movement (roots going down by intervals of diatonic fifths).

We found that the chords of the diatonic family tend to fall into three categories: tonic chords, predominant chords and dominant chords. Because of the way they are built and the notes they contain, chords have a natural tendency to go to other chords:
– predominant chords have a natural tendency to go towards dominant chords
– dominant chords have a natural tendency to go to tonic chords.
We also found that the iii and vi chords don’t have any predefined function:
– the vi chord can substitute for the tonic chord or it can function as a predominant
– the iii chord can also substitute for the tonic chord or it can substitute for the V chord and function as a dominant chord

But there are other important aspects that will often influence and alter the natural harmonic tendency of the chords. Suppose for example that we have the following melody in G major, harmonized as indicated:

See EXAMPLE 1 (in attachment)

The harmonic analysis of the progression reveals:
I -> V(b) -> vi -> iii(b) -> IV -> I(b) -> V -> I
As you can see, the predominant chords don’t always progress to the dominant (in bar 3, C goes to G/B) and the dominant chords don’t always progress directly to the tonic (in bar 1 and 2, D/F# goes to Em).
Note how the downward root movement by a 5th is restated a 3rd lower each time: G – D, then Em – Bm, then C – G, and a final cadence. Also note the resulting overall bass line and the important role played by chord inversions!

The progression in this example utilizes a sequence, that is, a short melodic and harmonic pattern (in this case: “down a fifth”) that is successively restated on different scale degrees (in this case: a third below each time). In cases like this, the strong linear direction of the melodic pattern (in this example: the melody going down by steps) tends to override the natural chord tendencies.
This shows the fundamental role of the melody in music, an aspect that is often neglected, particularly by guitarists who tend to focus on chords.

When a melodic pattern is repeated in the outer voices (particularly the soprano), and the roots of the chords also move by repeating a specific pattern, we have what is called a harmonic sequence.

An exhaustive study of harmonic sequences is of course completely beyond the scope of this post, but we will briefly look at the most important ones: harmonic sequences where the roots move by (ascending or descending) 2nds, 3rds or 5ths.

1. First case: a melodic passage descends by steps
In that case, the harmony could use first inversion triads, as in the following example:

See EXAMPLE 2

As you can see, we have: IV(b) -> iii(b) -> ii(b) -> I(b) -> vii°(b) -> I, i.e. the roots move by descending 2nds and follow the melody.

Another possibility is chords using a series of descending 3rds between every other chord.
Let’s say the melody (in A minor) goes:

See EXAMPLE 3

The harmony goes: (Am -> Em) > (F -> C) -> Dm
The sequence in this case consists of a series of descending 4th whose starting notes are down a 3rd each time.

2. Second case: a melodic passage ascends by steps
In this case we can also use first inversion triads; for example

See EXAMPLE 4

We have ii(b) -> iii(b) -> IV(b) -> V(b) -> I

Or a series of ascending 3rds in root position on every other note, like so:

See EXAMPLE 5

Dm -> C -> F -> E -> Am -> G -> C
(ii -> I) -> (IV -> III) -> (vi -> V) -> I

3. Third case: a melodic passage consists of thirds alternating with another interval
One possibility is to have the roots descend by fifths:

See EXAMPLE 6

Cm -> Fm/Ab -> Bb -> Eb/G -> Ab -> D°/F -> G -> Cm
i -> iv(b) -> bVII -> bIII(b) -> bVI -> ii°(b) -> V -> i

Another possibility is a series of descending thirds alternating with first inversion triads:

See EXAMPLE 7

i -> V(b) -> vi -> iii(b) -> IV

4. Conclusion
Songs are usually harmonized with a mixture of harmonic cycles (discussed in the previous post) and sequences (discussed here).
This is because melodic sequences like those discussed above override the natural harmonic tendencies of the chords. You probably noticed the critical importance of inversions in this process!