Tonal and modulating sequences: harmonic sequences that stay in or change key · Harmony lessons

Definition

A sequence (or harmonic “march”) repeats a model of two or more chords at different pitch levels, shifting it each time by the same interval. There are two large families:

the tonal (or diatonic) sequence, which stays in the key and adapts the model to the notes of the scale: some intervals change quality (a major third becomes minor);
the real (or modulating) sequence, which repeats the model exactly, with all the necessary accidentals: each repetition is in a different key.

Tonal sequence

Example in C: C – F | B° – E min | A min – D min | G – C (diatonic descending fifths): each pair repeats the rising-fourth movement, but the chord qualities follow the scale.
In the tonal sequence by fifths the IV–vii° is accepted (a diminished fifth in the bass, F–B): it is the only point where the fifth is not perfect.
The result is a continuous drive without a change of key.

Real and modulating sequence

Example: the model C – G7 – C (I–V7–I in C) repeated a whole step higher becomes D – A7 – D (in D major), then E – B7 – E (in E major).
A chain of secondary dominants is a sequence that tonicizes each chord: E7 – A7 – D7 – G7 – C.
In 18th-century Italy the repetition of a phrase a step higher was called the rosalia, from the name of a folk song that used this pattern; the term also passed into German theory.

Two short, widely used patterns

Monte (ascending): V7/IV – IV – V7/V – V. In C: C7 – F – D7 – G. A small climb by step, with tonicizations of IV and V.
Fonte (descending): V7/ii – ii – V7 – I. In C: A7 – D min – G7 – C. One step in minor, then the same a whole step lower in major.

Practical rules

Two or three repetitions are enough: by the fourth the sequence becomes mechanical.
The voice leading must be identical in every repetition; for this reason unusual doublings are tolerated in sequences (even of the leading tone, when the model requires it).
Break off the sequence with a cadence or a change of model so as not to lose the sense of form.
In a modulating sequence, the last repetition must confirm the new key with a cadence, otherwise you remain in an unstable area.

Typical mistakes

Changing the voicing between repetitions: the sequence is no longer perceived as one.
Pushing a real sequence too far without a plan: you end up in remote keys without knowing how to return.
Confusing tonal and real in analysis: check whether the chord qualities stay the same.

Examples

“Fly Me to the Moon”: A min7 – D min7 – G7 – Cmaj7 – Fmaj7 – B m7(b5) – E7 – A min, a tonal sequence by fifths.
“Sweet Georgia Brown”: a chain of dominants (VI7 – II7 – V7 – I) that tonicizes each chord.
Bridge of the Rhythm changes: III7 – VI7 – II7 – V7, a progression of dominants by fifths.
Vivaldi and Bach: the episodes of concertos and fugues are built on sequences by fifths, often modulating.
Mozart, Symphony No. 40, development of the first movement: the main theme travels in sequence through several keys.

How to use it in composition

Use a tonal sequence to build tension in a bridge without changing key.
Use a modulating sequence to reach a distant key logically: the ear accepts the destination because it has understood the model.
In pop, repeating a phrase a whole step higher (rosalia) before the last chorus is an elegant way to raise the energy.

Exercise

Write a two-chord model (I–IV) and carry out a descending tonal sequence by step in G major.
Write an ascending real sequence by whole steps with the model I–V7–I starting from F major, and close in A major with a cadence.
Write a monte and a fonte in D major in four voices.

Harmonic sequences and progression by fifths; Galant schemata 2: sequences and cadences; Secondary dominants; Modulation techniques; Chromatic, direct and “truck driver” modulation.

Sources

en.wikipedia.org