WholeARTs
Music Conservatory
Courses in Music Theory and Composition
(Certain subsidiary links like this one are comprehensive discussions of rather narrowly defined subjects. They define and amplify on the key terms used in the Dialogues. Do not become bogged down trying to understand each point. You will be returning here again in other contexts. First read this page through, and then click on the links to study related terms.)
The Diminished 7th Chord
The diminished 7th chord may be understood as an intensification of the Dominant harmony in any key. In other words, wherever it appears, it tends toward immediate resolution, either on the Tonic, or on another pitch degree which is being made into a kind of temporary Tonic.
When it appears within the context of music in a major key, it must be viewed as a borrowing from the minor mode, since all of its notes are taken from the harmonic minor scale.
The derivation of its tones, however, has not cleared up the origin and nature of its function within a harmonic progression. Indeed, the fact that even the name, diminished 7th, has been derived in various ways, has itself created a fair amount of confusion.
The origin of the name has been related to the fact that it's notes are the same as the diminished chord that occurs on the seventh degree of the scale, with the addition of one more minor 3rd at the top. From this point of view, it is often labeled a VII7 chord.
It's name has also been explained as a reference to the interval created by the root of the chord and the 7th of the chord, which is a diminished seventh - one semi-tone smaller than a minor 7th.
As an intensification of the Dominant, however, it has been convenient to think of the diminished 7th chord as an incomplete 9th chord whose "real" but absent root is the 5th degree of the scale: namely, the Dominant.
It is, some say, problematical to posit a chord with a missing root, since the idea of silent roots is highly abstract and possibly an oxymoron. It won't help our understanding of progressions in terms of successions of roots, if we indiscriminantly import into their number tones that are not actually present in the music. Nonetheless, when viewed in this way as an incomplete Dominant, the diminished 7th is labeled a V9 chord.
The diminished 7th chord is constructed out of a very special harmonic interval, the Tritone. It consists either of an augmented 4th (or, enharmonically, a diminished 5th), and is considered one of the dissonant intervals.
Moreover, the diminished 7th may be seen to consist of two Tritones superimposed.
And, the two Tritones together significantly intensify the dissonant effect. Clearly the diminished 7th chord is well employed as an intensification of the Dominant harmony, which must always be, by definition, dissonant.
In the resolution of the "Dominant" diminished 7th chord, these two Tritones move according to the traditional rules of counterpoint: when spelled as diminished 5ths, the two pitches resolve toward each other by step (whole- or half-step).
When spelled as augmented 4ths, they resolve away from each other by step (whole- or half-step).
It is worth noting that a tritone is formed between the Leading Tone and the Sub-Dominant Degree of every scale. The use of these two tones together, and their resolution, leaves little doubt as to where the Tonic is. Thus, the use of the Tritone has become one of the most effective ways of establishing a key. The Leading Tone prepares the arrival of the Tonic in the normal way, as its dissonance gives way to a consonance. In the key of C, for example, the Leading Tone, B, invariably is succeeded by a C. The Sub-Dominant, conversely, shows by its presence that we are not moving toward the key of the Dominant, which is the greatest rival to the key of the Tonic, because it negates the Leading Tone of that key. In the key of C, for example, the Sub-Dominant, F, makes it impossible to think in terms of the key of G, which, of course, uses an F-sharp as its Leading Tone instead.
Being constructed entirely out of minor 3rds, the diminished 7th chord creates a self-limiting structure: to add additional minor 3rds only results in doublings of the previous notes in the chord. For the same reason, building successive diminished 7th chords on all of its four notes produces only identical copies of the original chord.
Thus, as may be seen, only three different diminished 7th chords exist; each one consists of four pitches that are not shared by either of the other two diminished 7th chords; and all three together use all twelve notes of the chromatic scale. Every diminished 7th chord in the literature is made out of one of these three combinations of minor 3rds.
It is the peculiar nature of this oddly symmetrical chord that each of its notes may be taken as a Leading Tone, and may be resolved as such. It may be seen that there are two keys that may resolve each Tritone spelled as a diminished 5th, and two keys that may resolve them as augmented 4ths, making a total of four possible resolutions for each of the three diminished 7th chords.
This makes it uniquely suitable as a harmonic pivot. Approached as a Dominant harmony in one key, it makes possible an immediate move toward any one of three other keys.
What it gains in flexibility, however, it loses in vagueness. It has been noted that the ultimate chromaticism in diatonic harmony arises out of a simple succession of diminished 7th chords. Here, it is equalled only by the employment of the chromatic scale itself, (and possibly the whole-tone scale as well, but this is clearly a special case in the diatonic context).
Courses in Theory and Composition
WholeARTs Productions
P.O. Box 2963, Stateline, NV 89449
702-588-1329
WholeARTs and The
WholeARTs Music Conservatory
are Trade Marks of WholeARTs.
Copyright © 1996 by WholeARTs