Hmm…the blog post title sounds like a mashup of my two favorite musical elements! Well, it is…but leaning more towards the rhythmic aspects of when and where chords move. In other words, harmonic rhythm refers to the rate of chord change or how often one chord progresses to another.
Most songs or compositions are written in a form in which the total number of bars is divisible by two. Hence, we naturally tend to hear and feel music in 2-bar phrases. For example, a standard 32-bar song form can be thought of as a structure of four sections with eight bars each. Refer to the lead sheet of “Autumn Leaves below”:
This torch song has a classic A-A-B-C form, where each letter represents an 8-bar phrase. Within this 8-bar phrase, we can further subdivide it into a 4-bar phrase and then a 2-bar unit. The odd-numbered bars within each 8-bar phrase, i.e. Bars 1, 3, 5 & 7, are considered strong bars while the even-numbered ones, i.e. Bars 2, 4, 6 & 8, are considered weak bars, hence, forming a “Strong-Weak, Strong-Weak, Strong-Weak, Strong-Weak” dichotomy within the 8-bar musical phrase. This means that a chord on a weak bar will always have a natural pull back to a strong bar, or a tendency to move towards or resolve into a chord in the strong bar.
This is why it is common to see II-V-I progressions that fall on a 4-bar “Strong-Weak-Strong-Weak” phrase. Chords I and II are commonly found on odd-numbered or strong bars, while the V7 chord with its natural need to resolve is usually found on the weak bars.
Examples from “Autumn Leaves” are the following progressions: Ami7/// D7/// Gma7/// //// and F#mi7(b5)/// B7/// Emi/// ////. You will also notice the duration of each chord before it changes, i.e. Chords II and V have the exact same number of beats (4 beats each) while Chord I usually has twice as many (8 beats).
This principle also holds true when the phrase breaks down to a basic 2-bar unit. A II-V-I progression within a 2-bar phrase usually sees Chords II and V getting two beats each while Chord I lasts for four beats. Within a 2-bar phrase, Beats 1 and 5 are the strong beats, while Beats 3 and 7 are the weak beats. Refer to the lead sheet of “Blue Moon” above.
Two-bar phrase examples from “Blue Moon” are the following progressions: Fmi7/ Bb7/ Eb/// in Line 5 and Abmi7/Db7/ Gb/// in Line 6. You will also notice the duration of each chord before it changes, i.e. Chords II and V have the exact same number of beats (2 beats each) while Chord I usually has twice as many (4 beats).
This applies to all contemporary music. It is common for chords to change every two beats within a 4/4 bar or measure, or sometimes a chord may last for a whole bar or two. Refer to Daniel Powter’s “Bad Day” below:
The 2-bar phrase with its harmonic rhythm is consistent with the “Strong-Weak” concept that we have been discussing, i.e., Eb5/Absus2/ Bbsus///, the chords on Beats 1 & 3 last for two beats each, while on Beats 5, the chord duration is twice as long, four beats.
For music in 3/4 time, it is very common to see a chord lasting for a whole bar, or if there are two chords, they will always be placed on Beat 1 and Beat 3. Refer to Miles Davis’ version of’ “Someday My Prince Will Come” above:
The whole piece has only chord changes on every first beat of the bar, except for one. Look at the last line: the first chord Cmi7 on F bass lasts for two beats and changes to F7 on Beat 3. Also check out this classic A-B-A-C form in terms of its harmonic rhythm. The “Strong-Weak” principle is strictly adhered to.
Occasionally, you will come across some pieces that break this “Strong-Weak” rule of harmonic rhythm. However, this does not happen consistently and eventually “rights” itself along the way. For example, take a look at the very popular “Fly Me to the Moon” below:
The progressions: Ami7/// Dmi7/// G7/// Cma7/ C7/ and Fma7///Bmi7(5)///E7///Ami7/A7/. The G7 and E7 chords in both these 4-bar phrases are definitely prominently on the strong bars while the resolution chords Cma7 and Ami7, respectively, are on the weak bars. Furthermore, both dominant 7th chords occupy four beats to their counterparts’ two – truly a reverse of what we have learned. These are occasional exceptions to the rule.
You will notice that eventually at the close of the 4-bar phrase, the C7 (on the weak bar and beat) does resolve to the FMa7 on the strong bar, and so does the A7 to the Dmi7. The following next two four-bar phrases “right” themselves by employing the natural harmonic rhythms: Dmi7/// G7/// Cma7/// Emi7/ A7/ and Dmi7/// G7/// Cma7/// Bmi7(b5)/ E7/.
So make the most of this knowledge that you have about harmonic rhythms and ensure that your chord changes fall on the correct places within the bar!
(All music sheets used here are only for educational purposes.)