CHAPTER 15 – DIATONIC SEVENTH CHORDS AND SEQUENCES WITH SEVENTH CHORDS

The 7th in chords without a dominant function is quite exceptional in Classical Tonal music, except in the case of the II degree, where we frequently find it, or in the circle-of-fifths sequence including diatonic sevenths. There is another type of sequence involving seventh chords, the "chain of dominants", also described in this topic.

1. CHORDS WITH DIATONIC 7TH. DEFINITION.

- We call diatonic 7th chord a chord with a 7th, but without a dominant function. Hence, a I, II, IV or VI degree with a 7th.

- In these chords the 7th must always be prepared. This means that the note must sound as a chord tone in the preceding chord, and in the same voice. It is very often slurred. This is why these chords are also known as "prolongation 7th chords". This can be seen in the following example:

Im. 15-1

- The 7th must also always be resolved. This can be done in 2 ways:

a - Descending stepwise, just like the one of the dominant 7th.

b - Remaining tied to a chord tone of the following chord.

- The 7th on the I, IV and VI degrees is quite infrequent. But it is widely used on the II degree. In the case of II, the 7th is sometimes used without preparation, but it is always resolved.

2. APPLICATION IN 4-PART WRITING. INVERSIONS AND NOTATION.

- Diatonic 7th chords are used in all their inversions, as shown below:

Im. 15-2

- As with the dominant 7th chord, its use in inversion usually facilitates a good voice leading, especially for the bass.

3. CIRCLE-OF-FIFTHS SEQUENCE WITH DIATONIC SEVENTHS AND CHAIN OF DOMINANTS.

CIRCLE-OF-FIFTHS SEQUENCE

- It is a sequence of 7th chords with the roots of the chord in a 5th relationship, in which the model would be formed by two chords, as shown in the example:

Im. 15-3a

- As you can see:

- The 7th is always prepared in the previous chord.

- And it resolves by descending stepwise in the following chord.

- There is an alternation of complete and incomplete chords (with the 5th omitted and the root doubled).

- In this sequence all seventh chords are non-dominant, except the one in bar 3, which appears by chance.

- It is common for this sequence to contain inversions, which improves the voice leading and allows all the chords to be complete, as shown in the example:

Im. 15-3b

CHAIN OF DOMINANT 7TH CHORDS

- If in the previous example, we make all the chords in the sequence major and use always a minor 7th, i.e. we make them Dominant 7th chords, the sequence would look like this:

Im. 15-3c

- The characteristics of this sequence are as follows:

1 - As you can see in the realisation, the leading tone of a chord, instead of ascending, descends chromatically to the 7th of the following chord.

2 - These series can be "introtonal", like the one in the example, or modulating, if they lead us to a key other than the starting one. In the example, by adding one more repetition, we would end in the key of Eb.

- Finally, we can transform this sequence so that VII degrees also appear (leading-tone 7th chords). In this case, the 5th relation is normally preserved among the roots of the "tonic" chords to which each chord would normally have to resolve. With a slight transformation in the previous series, we obtain the following example:

Im. 15-3d

4. SEQUENCES WITH SEVENTH CHORDS IN THE MUSIC REPERTORY.

- As with other sequences, these ones are often arranged in a thematic way, and it is common for them to contain irregularities. Here is an example:

Im. 15-04

Mozart, Sonata no. 12, KV 332 – 1st movement

5. SUGGESTED EXERCISES.

- Harmonize the soprano lines given below, following the given indications:

  3.  Write a harmonic structure with the following features:

- Key: A Major, Time signature: 4/4.

- Form: 3 phrases, in which:

- 1st Phrase: After fully confirming the key, perform use a chain of dominants whose first dominant is the V/VI, ending in the key of D Major. Make a perfect cadence in this key.

- 2nd Phrase: Make a common-chord modulation to the key of A Major, ending the phrase in a half cadence.

- 3rd Phrase: It stays in A Major. Include a sequence with diatonic 7th chords and end with a cadential 6/4 before the perfect cadence.

- Harmonic rhythm: half notes, with an acceleration before the cadences.

- Include some chords with diatonic 7th, especially in the II degree.

- Add a free melody, which is structured in a motivic way. Make sure that it is similar in the 1st and 3rd phrases.