Introduction
Songs (generally) have a given beat, and the melody takes on a specific rhythm on top of the beat. The harmony (that is, the chords) also takes on a specific rhythm on top of the beat and this is called the Harmonic Rhythm.
Harmonic Rhythm
The Harmonic Rhythm is the rate at which the chords change. This influences the strength of a chord progression and even the function of a chord. For example, if we play the following two chord progressions, you’ll notice that the bottom one (Chord Progression #2) sounds ‘stronger’, even though they both use the same chords in the same order. This is because of the Harmonic Rhythm.
| Chord Progression #1 | A7 - Dm7 | G7 - CMaj7 | CMaj7 |
| Chord Progression #2 | CMaj7 - A7 | Dm7 - G7 | CMaj7 |
In 4/4 time, the Harmonic Rhythm occurs in multiples of 2 beats. That is, the chords generally change every:
- ½ bar; or
- Full bar; or
- 2 bars; or
- Even longer for modal and fusion jazz songs where the there are no chord changes at all – you sit on the same chord for the whole song.
In 3/4 time, it occurs in multiples of 3 beats. That is, the chords generally change every:
- full bar; or
- 2 bars.
In Odd Meters, the Harmonic Rhythm can be asymmetrical.
- 5/4 time = 3 + 2 (see the song Take 5)
- 7/4 time = 4 + 3
Now, we hear chords in Groups of 4. And we can allocate a relative strength to each of the chords in that Group of 4.
- The first chord is Very Strong (S)
- The second chord is Weak (W)
- The third chord is Strong (s)
- The fourth chord is Very Weak (w)
where S > s > W > w
This looks as follows:
| Harmonic Rhythm | S - W | s - w | S - W | s - w |
Strength of a Chord Progression
As I mentioned before, the Harmonic Rhythm affects how strong a chord progression sounds; or more specifically how strong a cadence sounds. And the most common cadence is a V-I Perfect Cadence.
A V-I cadence sounds stronger if the V7 chord is on a relatively weaker beat compared to the I chord. This is why Chord Progressions #2 above sounds stronger than Chord Progressions #1.
- In Chord Progressions #2, the V7 resolves to a relatively stronger I beat
- In Chord Progressions #1, the V7 resolves to a relatively weaker I beat
Below are a number of chord progressions that all use a vi-ii-V-I pattern but shift the timing around.
- Chord Progressions #2 sound weak because the V7 is on a relatively stronger beat than the I chord; while
- Chord Progressions #1, 3, & 4 all sound strong because the V7 is on a relatively weaker beat than to the I chord.
| Chord Progression #1 | CMaj7 - A7 | Dm7 - G7 | CMaj7 |
| Harmonic Rhythm | S ------ W | s ------ w | S ------ (W) |
| Chord Progression #2 | A7 - Dm7 | G7 - CMaj7 | CMaj7 |
| Harmonic Rhythm | S ------ W | s ------ w | S ------ (W) |
| Chord Progression #3 | Dm7 - G7 | CMaj7 | CMaj7 |
| Harmonic Rhythm | S ------ W | s ------ (w) | S ------ (W) |
| Chord Progression #4 | Am7 - Dm7 | G7 | CMaj7 |
| Harmonic Rhythm | S ------ W | s ------ (w) | S ------ (W) |
Functionality
And in fact, the location of the V7 chord in relation to the Harmonic Rhythm can even affect the ‘function‘ of the V7 chord. We have not discuss functionality yet (we will in a future lesson). But very quickly: the usual ‘function’ of a V7 chord is to resolve down a 5th to the I chord (like a G7 resolving to a C). The function of the G7 (it’s whole purposes or point in life) is to move to the C (the Tonic Chord). Being on a weak harmonic rhythm beat facilitates this function.
Now, the first chord of a Blues is usually a V7 chord, but it doesn’t have a dominant ‘function’. That is, the first chord of a Blues does NOT feel like it needs to resolve down a 5th. A Blues in C (starting on C7) doesn’t feel like it needs to move to an FMaj7 chord. This is partially because the V7 chord is played on beat 1, which is the strongest harmonic rhythm beat there is – so it doesn’t sound like a cadence (it doesn’t sound cadential).
For a V7 to sound like it is in a Cadence (i.e. like it wants to move to a I chord) it generally needs to be on a weak harmonic rhythm beat.
We will discuss functionality in much greater detail in future lessons.
II-V-I’s
So to extend this further, the most common chord progression in Jazz is a II-V-I. So if the V7 has to be on a weak Harmonic Rhythm beat, the II is usually (though not always) found on a strong Harmonic Rhythm beat. Have a look at Chord Progression #1 & 3 above.
Missing & Extra Chords
When you are analysing a song’s harmonic rhythm, look for the general/overall harmonic rhythm of the song – and ignore the outliers. A chord progression can miss a chord or insert an extra chord without destroying the harmonic rhythm.
- Chord progression #5 (below) has a Harmonic Rhythm of 1 bar (despite the extra chord in bar 2):
- Chord progression #6 (below) has a Harmonic Rhythm of 1/2 a bar (despite the missing chord in bar 3):
Also note that different sections of a song (AABA) can have different harmonic rhythms.
- Section A can have a Harmonic Rhythm of 1 bar; while
- Section B can have a Harmonic Rhythm of 2 bars.
| Chord Progression #5 | DMaj7 | Gm7 - (C7) | FMaj7 | Am7 |
| Harmonic Rhythm | S | W | s | w |
| Chord Progression #6 | Em7 - A7 | Dm7 - G7 | CMaj7 | Dm7 - G7 |
| Harmonic Rhythm | S -------- W | s -------- w | S -------- (W) | s -------- w |
In Practice
You’ll find that in 95% of Jazz Standards, the V7 is on a relatively weaker harmonic rhythm beat than the I chord. So if you’re composing, or reharmonising a jazz song, the harmonic rhythm is something you should keep in mind.