CHAPTER 13 – HARMONIC SEQUENCES AND

PARALLEL SIXTH CHORDS

Within Classical Tonal Harmony, Sequences and Parallel Sixth chords are practically the only procedures in which functional logic can cease to operate. Sequences are a very frequent resource used by composers in order to generate dynamism in the musical discourse.

1. DIATONIC SEQUENCE

- The repetition of a pattern starting on a different pitch is called a sequence. Depending on the direction of the repetition, they can be described as ascending or descending. Their characteristics are detailed below:

- The pattern contains 2 or more different harmonies.

- The interval at which the pattern is repeated is usually always the same. The most common is a 2nd or a 3rd.

- Besides the pattern, there are usually between 1 and 3 repetitions.

- It is common that the repetitions do not have harmonic functionality. In other words, they do not agree with the Basic Harmonic System. For this reason, we write their degrees in brackets.

Im.13-01

- The sequence in the above example is called diatonic because the repetitions fall within the starting key. Consequently, the melodic and harmonic intervals do not coincide exactly with those of the model.

- As specified in the features, the harmonic functionality is often cancelled during the repetitions. It is recovered at the moment that the sequence is broken.

- The above example of sequence is very common, and is known as a "circle-of-fifths progression", because the root of all the chords that appear are in a fifth relationship.

2. MODULATING SEQUENCE

- If in the repetitions we preserve the harmonic functions of the model, placing each repetition in a different key, we obtain a modulating sequence. In this case, the repetitions will therefore include accidentals different from those of the model:

Im. 13-02a

- As can be seen in the example above, which would also be a "circle-of-fifths progression", apart from modulating on each repetition, the sequence eventually leads to a different key than the starting key. However, a modulating sequence can also finish in the initial key. These sequences are called "intratonal":

Im. 13-02b

- In short, modulating sequences can be very useful to easily modulate, even to keys that are far away from the starting key. Or simply to create changes of "harmonic colour", in the case of intratonal sequences.

3. SEQUENTIAL PROGRESSIONS IN 4-PART WRITING

- From the above examples we can deduce some indications on how we should write a sequence:

1 - It is essential to come up with a good model. The models that offer the best results are those that contain a 4th or 5th relationship between their chords, such as I - V, V - I or I - IV.

2 - The model must be made in such a way that, when it is connected to the repetition, there is no voice leading mistake (consecutive or similar 5ths, 8ves, etc...). Moreover, the more carefully the link between the pattern and the repetition is made, the more convincing the sequence will sound. This is especially important in modulating sequences.

3 - If the sequence is ascending, you must start from a low register of the voices in order not to go beyond the range. And vice versa!

4 - In modulating sequences, we must establish the key we want to reach, and set up the pattern and repetitions in such a way that the sequence leads us towards it.

4. SEQUENCES IN THE MUSIC LITERATURE

- In the previous sections, sequences have been described from the point of view of their harmonic structure. However, in the music literature, sequences are often thematically developed. This development helps strongly to establish the feeling of sequence. Two examples are presented here:

Diatonic sequence:

Im. 13-04a

J.S. Bach, Prelude no. 21 from The Well-Tempered Clavier, book 1.

Modulating sequence:

Im. 13-04b

Beethoven, Sonata Op. 49, no. 1 - 1st movt

- In addition, it is common for sequences to contain variations. This can make them more interesting, as it can be seen in the example of Beethoven.

5. PARALLEL SIXTH CHORDS

- The use of parallel sixth chords is a procedure with a certain resemblance to a sequence where the model would be a single chord in first inversion. This chord is repeated at different pitches and in a succession in which stepwise motion predominates.

Im. 15-5a

- Like sequences, the intermediate repetitions in a series of parallel sixth chords have no harmonic function.

- When used in 4-part writing, one of the voices is silenced and the upper voices are arranged in such a way that they form an interval of a 4th, as a 5th interval would cause parallel fifths.

- In the music literature, parallel sixth chords are often thematically developed. This can be seen in the following fragment:

Im. 13-5b

Beethoven, Sonata Op. 2, no. 1 – 2nd movt.

6. SUGGESTED EXERCISES

- Harmonise the following soprano lines, realizing the indicated sequences.

- In Exercise 2, perform a tonicization of the relative major key before the first cadence. The modulating sequence leads to B major. Return to E minor after the second cadence, using a common-chord modulation.

- In Exercise 3, complete the sequence, arriving at G minor, and making a cadence in this key. Then, add a descending modulating sequence ending in the original key. Conclude the exercise with a perfect cadence reinforced by a cadential 6/4.

- In this last exercise there is first a modulating sequence that leads to the key of F#m. After the second cadence the music modulates back to A Major and we find another diatonic sequence.