Harmonic Rhythm

Harmonic Rhythm and Cadences

Harmonic rhythm is how often chords change in a passage of music, and is measured in note values. For example, if chords change every half-note, we say “the harmonic rhythm is a half-note.” Or, if the harmony changes every quarter note, we say “the harmonic rhythm is a quarter-note.” Sometimes the harmonic rhythm is a combination of note values that change at a regular rhythm, such as a half-note followed by a quarter-note:

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Introduction to Cadences

We have described tonal harmony as a hierarchy of pitches and chords where one pitch or chord has prominence over all the others. This tone or chord, as we learned in this music theory lesson, is the tonic scale degree. We might say that the tonic is the goal in a piece of tonal music. In order to reach that goal, the music progresses towards it (hence, the term harmonic progression).

Harmonic progressions set up expectations in our ears, expectations that are fulfilled only when the tonic chord is reached. Some of the greatest music ever written plays on this idea by setting up expectations, then denying them, creating tension in the music. This tension gives way to relaxation when the tonic chord is finally reached. When music comes to a point of relaxation or repose, it is called a cadence.

All of the elements of music (melody, harmony, rhythm, dynamics, timbre) contribute to cadence, but traditionally, we classify cadences according to their harmonic content. Most of the time, cadences are easy to identify because of the sense of culmination they create in the music. For example, cadences are often accompanied by longer note values, a slowing of the tempo, and a change in the harmonic rhythm.

But not all cadences end with the tonic chord. There are many cadences of varying degrees of strength. Some cadences sound complete, that is, the music comes to a rest, and we don’t hear a need for the music to continue. These types of cadences are called conclusive cadences. Then there are cadences that do not sound complete, that is, the music sounds like it needs to continue. We call these types of cadences inconclusive cadences.

For the remainder of this lesson we’ll show you how to identify and label the various cadence types. In future lessons, we’ll see how these cadences work in actual music. Use this lesson as a reference and to help you memorize the cadences.

Conclusive Cadences

Authentic Cadence

The authentic cadence is the most fundamental and final sounding of all cadences. It consists of a dominant triad or dominant seventh chord followed by the tonic triad (V-I, V7-I). There are two types of authentic cadences: the Perfect Authentic Cadence (PAC), and the Imperfect Authentic Cadence (IAC).

Perfect Authentic Cadence (PAC)

The perfect authentic cadence has specific requirments:

It is a V-I or V7-I progression.
Both chords, V and I, must be in root position.
Scale degree one () must be in the soprano of the I chord.

Here are two examples of a perfect authentic cadence.

Imperfect Authentic Cadence (IAC)

Any authentic cadence (V-I or V7-I) that does not meet the requirements above, is an imperfect authentic cadence. In the first example, scale degree one () is not in the soprano. In the second example, the V chord is not in root position:

Plagal Cadence (PC)

The Plagal Cadence, a IV moving to a I, often is called the “Amen” cadence because of its frequent occurrence at the end of hymns:

Inconclusive Cadences

Half Cadence (HC)

Any cadence that ends with a V chord is a half cadence:

Phrygian Half Cadence (PHC)

A Phrygian half cadence is a iv6-V progression and occurs only in a minor mode. It is characterized by a descending half-step in the bass. The soprano usually contains scale degree 4 moving to 5, but this is not a requirement.

Deceptive Cadence (DC)

When we hear a dominant chord near the end of a musical phrase, we are expecting a resolution to the tonic chord. The deceptive cadence denies this expectation. The most common deceptive cadence is the dominant chord moving to a vi. A variant of the V-vi, and a favorite of Handel, is the V moving to a IV6:

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How to Write Longer Chord Progressions

In the last music theory lesson we learned about chord substitution and chord classes. Here’s a quick review:

Chord Substitution

There are three primary triads: Tonic (I), Subdominant (IV), and Dominant (V).

You can use the rest of the chords of a key (ii, iii, vi, vii) instead of one of the primary triads:

vi is a good substitute for I
ii is a good substitute for IV
iii and vii° are good substitutes for V, but you have to be careful with those or your progression won’t sound right.

Chord Class Review

Because vi can be used instead of I, we say both chords (I and vi) belong to the Tonic Chord Class.
Because ii can be used instead of IV, we say both chords (IV and ii) belong to the Subdominant Chord Class.
Because iii and vii° can be used instead of V, we say all three chords (V, vii, iii) belong to the Dominant Chord Class.

Remember that the primary triads and their secondary counterparts are a third apart and have two notes in common.
We’ll use the abbreviations T, S and D to refer to the chord classes.
See the previous music theory lesson for progression examples using substitutions.

Making Chord Progressions Longer (Chord Prolongation)

Tonic Prolongation

A good way to make a chord progression longer, and to ensure that it sounds good, is to use both chords from the tonic and subdominant chord class, one after the other. For the best progression always start with the primary triad, then move to the secondary triad. In other words, descending thirds (e.g., I-vi) usually sound better than ascending thirds (e.g., vi-I):

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The chord progression above is the basic I-IV-V-I progression, but the first tonic chord moves to the vi before going to the IV, thus prolonging the tonic chord class. We call this tonic prolongation. This progression is very common in classical and popular music, especially popular music from the 1950s. A classic example is Those Magic Changes from the musical Grease.

Subdominant Prolongation

We can make the I-IV-V-I progression even longer by moving to the ii chord after the IV chord:

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You can download a pdf version of this progression written out in every major and minor key on the Harmonic Progressions page.

Harmonic Rhythm

Of course any chord progression can be made longer by holding the chord for a longer period of time. Harmonic Rhythm refers to how fast the harmony changes. For example, if chords change every quarter note, we say the harmonic rhythm is the quarter note.

As you learn to play and write chord progressions, it is important to be aware of the rhythmic tendencies of certain chords. In reality, it is impossible to separate rhythm and harmony. You may have noticed that the last progression above changes the rhythm of the last two chords (V – I).

The resolution to the tonic chord at the end of a progression usually sounds best if it ends on a strong beat.

If the V chord of the progression above were a quarter note, the tonic chord would fall on beat two, a weak beat. Again, don’t think of this as a rule, as much as a tendency. If your progression doesn’t sound right, and you’re not sure why, it may be a rhythm problem.

The TSDT Principle

The TSDT principle is a way of understanding harmonic tendencies. This principle, in one form or another, usually is introduced in formal harmony lessons as rules. From one music theory textbook to the next, the terminology and teaching methods vary, but the essential principle is the same:

Tonic Class Chords (I, vi) are free to move anywhere, that is, they may move to a subdominant class chord or a dominant class chord.

Subdominant Class Chords (IV, ii)
- A IV chord is free to move to a dominant class chord, or back to a tonic class chord.
- A ii chord tends to sound best when it moves to a dominant class chord, but not a tonic class chord.
Dominant Class Chords (V, vii°, iii) usually sound best when moving to a tonic class chord, not a subdominant class chord.

The following diagram summarizes the TSDT principle:

When we follow the TSDT principle all chord progressions (other than harmonic sequences) will follow one of these three patterns:

T-D-T
T-S-T (I-IV-I only)
T-S-D-T

Retrogressions

We’ve already discussed the dominant chord’s strong tendency to move to the tonic. That’s why we call a V-IV a retrogression. It’s not wrong to have a retrogression. Music is art, not science. You can find retrogressions all over the place, whether it be Bach, Mozart, or the 12-bar blues! But it is important for you, as a music student, to understand harmonic tendencies, as stated in the TSDT principle.

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