Volume II · Chapter 15
Harmonic Sequences
MUSIC 20B · C-ID MUS 130Chapter quiz →
In the musicianship bookChapter 18: Descending Chromaticism
Introduction: Patterns That Travel
Play a short idea, then play it again a step lower, then a step lower again. Your ear instantly grasps the pattern and starts predicting where it will go. That's a sequence: a musical idea (the model) repeated at successively higher or lower pitch levels (the copies).
Sequences are everywhere. Vivaldi and Bach build whole episodes out of them. Pachelbel's Canon is one long sequence. Jazz standards like "Autumn Leaves" and "Fly Me to the Moon" ride the circle of fifths, and so do countless pop songs. Sequences are how composers create forward motion and cover harmonic ground without losing the listener.
Click any example to hear it. The model is shown in red; copies alternate black and blue.
Melodic and Harmonic Sequences
- A melodic sequence repeats a melodic idea at a new pitch level.
- A harmonic sequence repeats a pattern of root motion: the chord progression of the model is transposed for each copy, usually with the same voice leading.
- Most sequences in tonal music are diatonic (or tonal): the copies stay in the key, so chord qualities change (a major triad's copy may be minor or diminished). A real (chromatic) sequence copies the exact intervals, adding accidentals; you'll meet those in Chapter 16.
- A sequence needs at least two copies (model plus one repetition is just a repetition) and it usually breaks off with a cadence.
Sequences are named by their root motion. Four types cover almost everything you'll see:
| Sequence | Root motion | Overall direction | Typical chords (major) |
|---|---|---|---|
| Descending fifths | down a 5th, up a 4th (or every root down a 5th) | descends by step every two chords | I IV vii° iii vi ii V I |
| Ascending 5–6 | down a 3rd, up a 4th | ascends by step | I vi6 ii vii°6 iii I6 IV |
| Descending thirds (descending 5–6) | down a 4th, up a 2nd | descends by step every two chords (bass descends by step) | I V6 vi iii6 IV I6 |
| Parallel 6/3 chords | down (or up) a 2nd | stepwise | a string of first-inversion triads |
The Descending-Fifths Sequence
The most common sequence of all moves every root down a fifth (or up a fourth): the strongest root motion in tonal music, chained around the circle of fifths. In a major key it visits every diatonic chord: I–IV–vii°–iii–vi–ii–V–I. In minor: i–iv–VII–III–VI–ii°–V–i.
The upper voices are easy: in each pair, one voice holds the common tone and the other two move by step. Because the bass alternates up a 4th, down a 5th, the outer voices form a chain of parallel 10ths.
With seventh chords. Add a seventh to every other chord (or every chord) and you get a chain of sevenths, each one prepared by a common tone and resolving down by step into the next chord. This is the sound of countless Baroque episodes and of jazz ii–V chains.
The Ascending 5–6 Sequence
Over a bass that holds a note and then rises a step, an upper voice alternates a 5th and a 6th above the bass: 5–6, 5–6. The 5th gives a root-position chord and the 6th turns it into a first-inversion chord a third lower. The result climbs by step: I–vi6–ii–vii°6–iii–I6–IV. It's the classic way to build energy and climb toward a climax.
The Descending-Thirds Sequence (Pachelbel)
Here the bass walks down by step while the roots fall a 4th and rise a 2nd, so each pair of chords is a third lower than the last: I–V6–vi–iii6–IV–I6. With root-position chords instead (I–V–vi–iii–IV–I–IV–V) it's the famous progression of Pachelbel's Canon, and of a long list of pop songs.
Parallel 6/3 Chords
A string of first-inversion triads moving in parallel is called fauxbourdon (an old technique from the 1400s). The outer voices move in parallel 6ths, and the inner voice moves in parallel 4ths with the top voice, which is fine because neither interval involves the bass. In three voices it's effortless; in four voices, vary the doubling from chord to chord to avoid parallel octaves.
Voice Leading in Sequences
The rule of thumb: voice the model carefully, then copy it exactly. Each voice repeats its own melodic pattern at the new pitch level. Your ear accepts this so readily that a few normal rules are relaxed inside a sequence:
- Diminished triads (vii°, ii°) may appear in root position.
- The leading tone may be doubled, and need not resolve to tonic (it's not acting as a leading tone).
- In minor, the bass may move by an augmented 4th (VI to ii°).
But some rules never relax: no parallel fifths or octaves, and chordal sevenths still resolve down by step. Once the sequence ends, all the usual rules return, especially at the cadence.
Try It: Sequence Explorer
Sequence Explorer
Choose a sequence type and a key. The model is red, and copies alternate black and blue. Play it, then try singing the soprano or bass along.
Summary
- A sequence repeats a model at new pitch levels; it needs at least two copies and usually ends with a cadence.
- Harmonic sequences are named by root motion: descending fifths, ascending 5–6, descending thirds, and parallel 6/3 chords.
- Voice the model well and copy it exactly; inside a sequence, diminished triads may stand in root position and the leading tone may be doubled.
- Never relax the ban on parallel fifths and octaves, and always resolve chordal sevenths.