Dominant Seventh, Diminished, and Augmented Chords
Dominant seventh chords are used in many styles of music. This chord type features a major triad plus a minor seventh. Technically speaking, this seventh is categorized as a harmonic extension (as defined later in the chapter). When you write the chord symbol for a dominant seventh, the chord will contain a letter name and the number seven. For example, you will see C7, G7, or B7 etc. Once you add the seventh, you will have a four-note chord, and therefore, three possible inversions can be created. Regarding usage, the dominant seventh chord is used to add color to an otherwise plain V chord. Figure 6-5 shows a C7 chord and its three inversions.
FIGURE 6-5: C7 Chord and its inversions
Diminished chords naturally occur on the leading tone (subtonic) of a major scale. For example, in the key of C major, a diminished chord is rooted on B, the seventh scale degree or leading tone. The diminished chord contains a double minor third interval. In other words, two minor thirds are stacked on top of one another creating a diminished chord quality.
A B diminished chord contains the intervals B to D (minor third) and D to F (minor third). The diminished chord gets its name from the interval created between the root and the flatted fifth (a diminished fifth). A B diminished chord is shown in Figure 6-6. The degree symbol is used to indicate the chord quality.
FIGURE6-6: B diminished chord
Diminished Seventh Chords
Diminished seventh chords are often used as a substitute for V chords. (Again, since a seventh scale degree is used, this chord contains a harmonic extension.) As an unstable chord, they naturally lean in the direction of the tonic. An unstable chord is a transitional chord. It cannot function as a resting place in the music. Instead, unstable chords gravitate toward stable chords such as I, i, or V. A diminished seventh stacks three minor third intervals on top of the root, making the interval between the root and seventh enharmonically the same as a major sixth. For example, a B dim7 chord contains an A-flat on top. If written as a G#, the interval will be a major sixth. However, don't be confused by enharmonic naming. Just remember that a diminished seventh chord contains three stacked minor third intervals. The diminished seventh chord is shown in Figure 6-7.
FIGURE 6-7: Diminished seventh chord
Half Diminished Chord
The half diminished chord is a rather beautiful, impressionistic chord that can be used in a variety of ways. Often spelled out as a minor seven five, the half diminished chord contains most of the same notes as a full-diminished seventh chord. The exception lies in the seventh (extension) itself. Instead of stacked minor thirds, the half diminished contains a major third on top. For example, a B half diminished contains the notes B, D, F, and A. The relationship between F and A is a major third. However, don't confuse this with the intervallic relationship between the root and the seventh, as this is a minor seventh. For example, B and A are minor sevenths. The half diminished chord is notated in Figure 6-8. The symbol for a half diminished chord is a degree symbol with a line or slash through it.
FIGURE 6-8: Half diminished chord
The augmented chord is a major triad with a sharp five. For example, a C augmented chord contains the notes C, E, and G# Enharmonically, this G# is also an A flat. As an A flat, this interval would be called a flatted thirteenth. Like the half diminished chord, the augmented chord was used primarily in music composed during the Romantic period and beyond. Figure 6-9 shows a C augmented chord and a C augmented seventh chord. A C augmented chord is usually written as C7#5 or C+7. The “+” symbol indicates the presence of a sharp five. Usually, augmented seventh chords are used to spice up V chords.
FIGURE 6-9: C augmented and C augmented seventh chords
Italian Sixth, French Sixth, and German Sixth Chords
From the baroque to the romantic periods, augmented sixth chords were commonly used as predominant chords (Predominant means any chord that precedes a V). Three common variants arose: the Italian sixth, the French sixth, and the German sixth. These are chromatically altered chords rooted on the – C – F.
However, unlike its parent chord, the Italian sixth chord contains a , C (usually doubled because of its stability), and F#.
French sixth (Fr +6) and German sixth (Gr +6) chords are both derived from the Italian sixth chord. The French sixth simply adds a fourth pitch: the second scale degree of the key (e.g., D in the key of C major). This means that, in C major, the notes for a French sixth would be: A, and F#.