Seventh chord
A chord of root, third, fifth, and seventh.
What it means
A seventh chord consists of four notes stacked in thirds: root, third, fifth, and seventh. It arises by adding a further third to a triad. Because the seventh is dissonant against the root, every seventh chord demands continuation.
Musical use
Depending on the kind of the underlying triad and the seventh, various types result. The most important are: the dominant seventh chord of a major triad and a minor seventh, which stands on the fifth degree and carries the cadence; the minor seventh chord of a minor triad and a minor seventh; the major seventh chord with a major seventh, which sounds soft and floating; the half-diminished seventh chord of a diminished triad and a minor seventh; and the fully diminished one of a diminished triad and a diminished seventh, which consists entirely of minor thirds.
On every degree of the scale a seventh chord can be formed diatonically. In classical harmony the dominant seventh chord has the central position; the others appear as passing sonorities, in sequences, and as substitutes. In jazz, by contrast, seventh chords on every degree belong to the basic stock, and the triad without a seventh is there rather the exception.
The three inversions are named after the intervals above the bass: the six-five chord with the third in the bass, the four-three chord with the fifth in the bass, the Sekundakkord with the seventh in the bass.
In four-part writing the fifth is often omitted and the root doubled, especially with the dominant seventh chord in root position.
Depending on the kind of thirds and the seventh, various seventh chords are distinguished: dominant seventh chord, major seventh chord, minor seventh chord, half-diminished, and diminished seventh chord. In classical harmony the seventh counts as a dissonance resolved downward. In jazz, by contrast, the seventh chord is the normal sonority of every degree.
Performance practice
Lead the seventh downward, unless something else is demanded, and give it weight beforehand. Determine the type for every seventh chord — half-diminished and fully diminished sound distinctly different. And practise seventh chords in all inversions, so that you recognize them quickly in the notation.