Dominant
The dominant is the fifth degree of a scale, and the chord built on it (V), whose pull back to the tonic drives most endings in tonal music.
What is the dominant in C major?
In C major the dominant note is G, seven semitones above the tonic C. The dominant chord is V: G–B–D. Add one more third on top and you get the dominant seventh, V7: G–B–D–F.
In a minor key the dominant chord is normally made major by raising the seventh degree. In A minor that turns E–G–B into E–G♯–B, so that the key has a leading tone too.
How does the dominant sound?
Unfinished. The dominant is the one chord in a key that wants to move, and it wants to move to the tonic specifically. The reason is a note: the third of V is the leading tone, one semitone below the tonic. In C major that is B, and it rises into C.
In V7 a second note joins in. F falls a semitone to E while B rises to C, and the two notes B and F form a tritone, the most unstable interval in the key. That is why V7–I is the strongest close there is.
A phrase that stops on V sounds like a comma. That is the half cadence, and it tells you more music is coming.
Is a “dominant seventh” always the V chord?
No, and this is the usual confusion. “Dominant” names two things:
- a function: the chord on degree 5 of the key you are in;
- a chord type: a major triad with a minor seventh on top, written with a plain 7, such as C7 (C–E–G–B♭).
The two meet on V7, but a chord of the dominant-seventh type can appear elsewhere. D7 in C major has that shape, yet it is not the V of C: it is a secondary dominant, borrowing the pull to point at G.
Try it: The Pull of the Dominant plays a progression with its last chord missing and asks where the dominant was heading.