Dominant seventh chord
The dominant with an added minor seventh.
What it means
The dominant seventh chord is the major triad on the fifth degree with an added minor seventh; in functional theory it is called V7 (German D7). In C major it consists of G, B, D, and F. It is the sonority that aims most unambiguously at a tonic and thus the engine of functional harmony.
Musical use
Its directing force rests on the tritone between third and seventh — in C major between B and F. The third is the leading tone and rises to the root of the tonic; the seventh falls a semitone to the third of the tonic. Both semitones of the major scale are gathered in this one sonority and resolve at the same time; the root leaps in the bass a fifth down or a fourth up. From this arises the authentic cadence V7–I, the strongest closing turn of tonal music.
In the study of composition the seventh counts as a dissonance that is resolved downward; originally it was also prepared, but free use prevailed early on. In four-part writing the fifth is often omitted so that the root can be doubled; the leading tone, by contrast, is never doubled.
The three inversions bear names of their own: the six-five chord with the third in the bass, the four-three chord with the fifth in the bass, the second-inversion chord (four-two) with the seventh in the bass, which then leads downward into the first-inversion chord of the tonic. In minor, the seventh degree is raised for the V7 so that the leading tone arises.
The dominant seventh chord is to be distinguished from the identically built sonority in Mixolydian music, where it does not act as a dominant but remains a tonic.
In blues and jazz the dominant seventh chord is a basic sonority that is not always resolved: in the twelve-bar blues, all three principal chords often stand as seventh chords.
Performance practice
Lead leading tone and seventh consistently into their resolution — upward and downward. Take the leading tone close and the seventh not too high. And give the V7 weight before the tonic; the resolution works only if the tension was audible.