Dominant Seventh

Complexity : 4/10 (intermediate)

In C scale, this is G-B-D-F.

The V7 chord is unstable and actively seeks resolution. The main motive for this instability is the diminished fifth interval between the 3rd and the 7th, which seeks resolution to a major 3rd or minor 3rd, with the 7th moving down, and the 3rd moving up.
A strong discord also exists between the root and the 7th and the 7th falling a step to its resolution makes the chords of resolution either I or VI.

GENERAL
- In root position, the fifth may be omitted.
- The inversions of the dominant seventh must be complete.

RESOLUTIONS
- Best :: V7-I, Good :: V7-VI, Acceptable :: V7-IVb
- The 3rd of the chord (being the leading tone of the scale) has a strong tendency to move to the tonic center (or root). This combined with the strength of root movement by 5th provides for a strong resolution tendency to I, and makes V7-I a powerful perfect cadence.
- Ornamental resolution is occasionally used. In this, the 7th moves either to the the 5th or the root of the chord before finally resolving. Resolution to IVc is also used as a decoration to the perfect cadence (the progression being V7-IVc-I).
- The inversions will resolve only to the tonic chord.
- The seventh may be transferred from one voice to another, resolving in the latter. In this case, the part which originally had the 7th must fall.

USAGE
- Broadly speaking, any chord which involved some form of V-I can be harmonized by some form of V7-I. In most cases, though, it is more fluent to introduce the seventh as a passing note.
- When the fourth note of a scale is repeated (or tied) weak to strong and falls a step, the strong note is to be harmonized as V7d.
- If a part leaps from the leading note up a diminished fifth and then falls a step, the leap is from the 3rd to 7th of a dominant seventh.
- If a part leaps up a 7th from the dominant and falls a step, the leap is from the root to the 7th of the dominant.
- Do not use V7 as the a substitute for V as the second chord of an imperfect cadence. The cadential effect is destroyed.

CADENCES
- V7-I is a perfect cadence. V7-VI is an interrupted cadence.
- V7b-1, V7c-I and V7d-Ib can be used as inverted perfect cadences. V7d-Ib is the most common, but all are good.
- In harmonizing a cadence involving V7-I, introduce the 7th as late as possible. Otherwise the cadence tends to feel unnaturally drawn out.