Table of Contents
Section 6: Bibliography
1. Seventh chords are merely triads (root, third, and fifth) with the note an interval of a seventh above the root added.
2. Any triad may have a seventh added, but the most common seventh chord is the dominant seventh.
3. The common types of seventh chords in tonal music are the ones that fall naturally into the key. They are identified by a variety of names, the most common of which are described below.
4. A seventh chord has at least one dissonant interval in it, and therefore is not a stable sonority; in tonal music, a seventh chord will require a resolution. One notable exception is the major seventh chord (C-E-G-B), which in some musical styles is, by convention, a stable chord.
Types of seventh chords: Some theorists label the types of seventh chords according to the type of triad included in the seventh chord and the type of third above the fifth of the triad. Therefore, the V7 chord (G-B-D-F) is called a major-minor seventh chord, because it has a major triad with a minor third above the fifth. Note also that the seventh above the root is minor.
According to this nomenclature, the seventh chords built on the I and on the IV in a major key (C-E-G-B and F-A-C-E) are major-major seventh chords. The seventh chords built on ii, iii, and vi are minor-minor seventh chords.
Diminished seventh chords: The seventh chord built on vii (B-D-F-A) in a major key is a half diminished seventh. Notice that the intervals from B are minor third, minor third, and major third. Also notice that the half diminished 7th chord has a slash across the degree sign.
A fully diminished seventh chord consists of all minor thirds, and is diatonic in a minor key, built on the raised seventh scale degree, as in the harmonic minor scale. Therefore, in C minor, vii°7 is spelled (B-D-F-A flat) and is fully diminished.
Resolution of Seventh Chords: The dissonance in a seventh chord requires resolution. Notice in the V7 chord, there are two dissonant intervals: the minor seventh between the root and the seventh, and the diminished fifth between the third and the seventh. These dissonant intervals make the chord dynamic, and ordinarily resolve as shown below:
Notice that the augmented fourth (an inverted dim. fifth) between the soprano and alto resolves outward by half step to the consonant minor sixth, and the minor seventh between the bass and alto resolves inward to the major tenth (compound third). This resolution of the V7 chord serves to set up the I chord as tonic.
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