Harmonic Sequences
A harmonic sequence repeats one chord-and-voice-leading pattern from a new pitch level. The first unit is the model; each repetition is a copy. Once the model is clear, listeners can predict the motion even while the chord names change.
- model plus copies
- repeated root and voice-leading pattern
- diatonic or exact
What is a harmonic sequence?
A sequence repeats a musical pattern higher or lower. In a harmonic sequence, the root motion and the relationship between chords repeat.
The copies do not need identical chord qualities. A diatonic sequence stays inside the key, so major, minor and diminished chords change according to the scale.
What are model and copy?
Model. The first unit establishes the interval and harmonic motion to imitate.
First copy. The same relationship begins from a new scale degree.
Later copies. Repetition confirms the pattern and creates momentum toward an ending or modulation.
Mark units before labeling every chord. Two-chord or four-chord groups often reveal the repeating design more clearly than a continuous numeral string.
How does the descending-fifths sequence work?
In C major, a complete diatonic circle can run:
C-F-Bdim-Em-Am-Dm-G-C
The roots move by descending fifth or ascending fourth. In Roman numerals: I-IV-vii°-iii-vi-ii-V-I.
The final ii-V-I is familiar because it continues the same root cycle. Earlier chords extend that motion backward through the key.
Why do chord qualities change?
Exact transposition would preserve every interval and chord quality, introducing chromatic notes as the pattern moves.
A diatonic sequence adjusts notes to remain within the scale. In C major, the triad on B is diminished because B-D-F comes from the key.
| Type | Pitch handling | Result |
|---|---|---|
| Diatonic sequence | adjusts copies to the scale | chord qualities vary |
| Exact sequence | transposes every interval exactly | chromatic notes appear |
| Modified sequence | changes part of the model | pattern continues with a tailored destination |
What other sequence patterns are common?
- Descending thirds
Roots descend by third and often connect through intervening chords, creating patterns such as I-vi-IV-ii.
- Ascending fifths
The reverse root direction increases brightness or instability depending on context.
- Parallel 5-6 sequence
One voice alternates fifths and sixths above a stepwise bass, avoiding continuous parallel fifths.
- Pachelbel-type sequence
A descending bass combines root-position and inverted chords in a repeating pattern.
How do sequences create direction?
Repetition makes the next unit predictable, while transposition prevents literal stasis. The listener recognizes the design and hears it travel.
Sequences can prolong a key, drive toward a cadence or cross into another key. An exact chromatic copy may introduce the dominant of a new tonic; a diatonic copy often remains within the original key.
The sequence usually needs an exit. A cadence interrupts the pattern and confirms where the passage has arrived.
How do you analyze one?
- Find repeated melodic or bass intervals.
- Divide the passage into equal units.
- Label the first unit as the model.
- Compare each copy and note diatonic adjustments.
- Identify the chord that breaks the pattern and begins the cadence.
How can you write a sequence?
Choose a two-chord model such as Am-Dm. Move both roots down a scale step to G-C, then F-Bdim, adjusting pitches to C major.
Play the copies separately before joining them. Keep one rhythmic pattern and similar voicing so the repeated relationship remains audible.
Finally, stop the copies and use ii-V-I to close the phrase.