When two or more melodic sequences are combined, they create a harmonic sequence that can supplant standard harmonic function and conventions. As mentioned in the introduction, sequences work because they establish a pattern for the listener and then fulfill this new goal. Look at the following example of a two voice pattern. The first bar establishes tonic, and then a sequence begins in the second measure. After listening to it, discuss with your classmates whether it sounds functional. If you were going to describe this to another person, how would you describe it? Once you finish your discussion, propose a harmonic progression that fits the melody.
While there are some variations on how you could harmonize this sequence, it is possible to make a chord progression that has diatonic chords with roots separated by a P5. I have suggested a version of this below. Using my progression, try adding a third voice as an alto line. As you do this, remember that the sequential pattern will not start until the second measure, so the first measure can just fill out missing chord tones. Your line does not have to have all stepwise motion like the outer two voices do, but it should follow some sort of repeating pattern.
The next example uses my suggested alto voice. It provides the required missing chord tones for each chord in this progression.
In your classification of the two-voice progression above, you likely described each line individually (e.g. descending diatonic 2nds that last one whole note), or you may have described the intervals between the two lines for each measure (e.g. a diatonic 7th resolving to diatonic 6th, then repeating after transposing down a diatonic 2nd). Neither of these is sufficient, however, once we add a third voice.
Instead, we classify harmonic sequences by describing the movement of the roots of each chord. We do not label harmonic sequences by inversions or the bass line. If we were to identify sequences by bass lines, all sequences that created a particular style of bass line (e.g. descending by stepwise motion) would be grouped together, even if they shared no harmonic similarities. (You can see this concept in the next two examples below.) Taking this into account, the description of the sequence in the example above would be:
The above sequence has only one interval and direction in its root movement pattern, a descending P5. Similar to the final example of the melodic sequences above, though, it is also possible for harmonic sequences to have two or more parts within each repetition. Look at the example below, and classify it using our terms from above:
Hopefully you were able to identify that the sequence only covers the first three measures, the final measure is simply a way to allow the pattern to repeat smoothly. For the sequence, there are two possibilities to describe it. You could consider each measure a pattern in which case you would say that this is a diatonic sequence that descends by 3rd. If you consider the pattern to be a half note, though, it has multiple parts. It is a diatonic sequence of triads that moves down by 4th and then up by 2nd. Either is correct, but they have different uses. The larger iteration makes for a cleaner, simpler analysis, but the smaller iteration communicates a more detailed explanation of the pattern. Choose the method that best suits your needs.
How does your description of the sequence change if we change some of the voices to alter the chords’ inversions as in the example below?
While any sequence that establishes a pattern and has clear voice-leading can function, there are common sequences that many composers have relied upon. We discussed the first of these in Unit 7a when exploring the voice-leading that creates the strong pull of the standard circle-of-fifths progression. Now that we understand the nature of sequences, look at each voice here as a melodic sequence. Does this change your view of standard voice-leading practices? Can you come up with a sequence description for this progression?
Sequences can also be used to explain how non-diatonic progressions function in a diatonic context. One common sequence occurs when first-inversion chords are used in succession to create a stepwise bass line. A parallel 6 sequence is any sequence with repeated first-inversion triads, most commonly moving downward by step. Notice that this does not create objectional parallel voices as long as the root of the chord stays above the chordal fifth. If these two voices are inverted, the result will contain parallel perfect fifths. To label a sequence of parallel six chords, label each chord with its Roman numeral and inversion figure and then place a bracket under the entire sequence with a label of “parallel six sequence.”
Another of the most commonly used sequences is known as the Pachelbel sequence.
This sequence takes its name from the German Baroque composer, Johann Pachelbel, who composed a canon using this sequence as its foundation. Since then, the harmonic progression has become a common structure on which to build multiple styles of music. The comedian Rob Paravonian satired many of these takes in his now famous “Pachelbel Rant”. (Caution: contains language not suitable for all ages)
Further to our discussion of the importance of patterns in music, please view the following TED Talk by Dr. Scott Rickard. He used mathematics to try to create music without any repetition, and the results are…interesting.