The Harmonic Sequence
Four Essential Patterns
This chapter looks at four essential patterns of harmonic sequence. While not related exclusively to the Bach Chorales, this chapter seems an appropriate place to discuss this concept, since Bach's music relies so heavily on the forward-generating compositional technique of the sequence. This technique is sometimes referred to by the German term Fortspinnung or "spinning out." Often, this spinning out of a motivic idea involves a particular approach to a chord progression.
Harmonic sequences can be grouped into four essential categories. (This infomation is borrowed from the text Harmony and Voice Leading by Aldwell and Schacter, who present this concept with admirable clarity.) These are related to the Three Essential Chord Progressions presented at the end of the previous book. Here, however, they specifically refer to the harmonic sequence:
- sequences with descending 5ths
- sequences with ascending 5ths
- sequences using ascending 5-6 technique (alteration of thirds and fifths)
- sequences falling in thirds (descending 5-6 technique).
The first sequence is familiar to you, which is the descending cycle of fifths.
One clear example is the fugue from the Bach Toccata in C minor, where the fugue subject itself is a harmonic sequence of descending fifths.
This technique is extremely common in Jazz standards as well. The tune "All the things you are" is a sequence of descending fifth progresions, with the added technique of shifting the pattern by a half step to create unexpected modulations.
The second sequence, movement up a fifth, is less common but nevertheless musically expressive. This tends to serve as musical elongation, lacking the strong forward motion of the descending fifth.
The third sequence could be thought of as an alteration of root movements by third and then by fifth, except that most often the bass note remains static when the root moves down by a third (resulting in alternating root position and first inversion chords), creating a satisfying ascending bassline.
The manner in which the upper voice moves from a fifth above the bass note to a sixth above the bass note gives this its characteristic sound.
The final sequence as a root movement that begins down a fourth, up a step, down a fourth, up a step and so on, except again every other chord is in first inversion, creating a satisfying descending bassline.
Harmonic sequences abound throughout musical history—they are a logical and satisfying method for spinning out a musical idea. After observing these examples from Bach, you will have many opportunities to discover them in the music of later periods.
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