Nondominant Seventh Chords
Nondominant seventh chords are frequently used in tonal music to increase tension and provide interest within a harmonic progression. The part-writing procedures for nondominant seventh chords, regardless of inversion, are as follows:
- The seventh of the chord resolves down by step.
- Any common tones are kept.
- Incomplete chords feature a doubled root and may omit the fifth or less commonly the third.
The Supertonic Seventh Chord
The most common of the nondominant seventh chords is the supertonic ii7 (iiØ7). It is a minor seventh chord in major keys and a half-diminished seventh chord in minor keys. When melodic minor is used, the possibility of a minor seventh chord exists in the minor mode, but this is quite rare. The ii7 (iiØ7) chord is freely used in place of the supertonic triad in both major and minor keys and most commonly occurs in first inversion. It can progress directly to the V chord, a viio6, or may first resolve to a cadential six-four chord.
The Subdominant Seventh Chord
The subdominant seventh chord is the second most common of the nondominant seventh chords. It is a major seventh chord (IVM7) in major keys and a minor seventh chord (iv7) in minor keys. When melodic minor is employed, the major-minor seventh IV7 can infrequently be found. The subdominant seventh chord is typically used prior to the ii7 (iiØ7), V, viio6, or I64 (i64) chords. When the IVM7 or iv7moves immediately to the V chord, the third of the subdominant seventh chord should be placed above the seventh to avoid parallel fifths.
The Submediant Seventh Chord
The submediant seventh chord is a minor seventh chord (vi7) in the major mode and a major seventh chord (VIM7) in minor mode. Submediant seventh chords progress to supertonic and subdominant triads and seventh chords. When melodic minor is used, the half-diminished seventh (viØ7) can sometimes be found, and these chords typically progress to viio or viio7 chords.
The Mediant Seventh Chord
The mediant seventh chord is a minor seventh (iii7) in major mode and a major seventh (IIIM7) in minor mode. Like the mediant triad, it usually progresses to the submediant or subdominant chords. Notice how bass lines that move up by step should be balanced by contrary motion in the upper parts. When the iii7 (IIIM7) progresses to a vi7 (VIM7) in root position, complete chords will alternate with incomplete chords, as discussed below.
The Tonic Seventh Chord
The tonic seventh chord is a major seventh (IM7) in major mode and a minor seventh (i7) in minor mode. The addition of a seventh to the tonic triad causes a change in the function of the chord. Tonic seventh chords share three tones in common with the mediant triad, and like the mediant triad usually progress to submediant vi (VI) or subdominant IV (iv) chords. Unlike the mediant chord, tonic sevenths sometimes progress to supertonic triads and supertonic seventh chords. The tonic seventh or the chords to which it progresses may be inverted and may also have sevenths.
The Subtonic Seventh Chord
The minor mode has the addition of the subtonic major-minor seventh chord (VII7). This subtonic triad and seventh chord are the least frequently encountered chords in the circle-of-fifths progression in minor. Both progress to the mediant chord, and for this reason they are referred to by some theorists as a V(7)/III.
Seventh Chords in Circle-of-Fifths Progressions
Seventh chords can be used in the circle-of-fifths progression, for example iii7 – vi7 – ii7 – V7 – I. The part-writing rules for a circle of fifths progression using seventh chords in an SATB texture for both major and minor modes are as follows:
- Complete root position seventh chords will alternate with incomplete root position seventh chords with the fifth omitted.
- First inversion seventh chords will alternate with third inversion chords, for example iii65 – vi42 – ii65 – V42 – I6. All seventh chords are complete.
- Root position seventh chords will alternate with second inversion seventh chords, for example iii7 – vi43 – ii7– V43 – I. All seventh chords are complete.