Seventh (interval)

What it means

The seventh is the interval spanning seven scale degrees. It appears in three forms: the minor with ten semitones, the major with eleven, and the diminished with nine, which occurs in the diminished seventh chord. All three count as dissonant and demand continuation.

Musical use

The seventh is the interval that expands the triad into the seventh chord and thereby sets functional harmony in motion. Decisive here is which form is present. The minor seventh over a major triad yields the dominant seventh chord (D7), whose tension lives from the tritone between the third and the seventh and whose resolution carries the cadence: the seventh falls to the third of the tonic, the leading tone rises to the root. The minor seventh over a diminished triad yields the half-diminished seventh chord, the diminished seventh over the same the fully diminished one — a sonority without an unambiguous root, well suited to enharmonic reinterpretation. The major seventh over a major triad, finally, sounds soft and floating and is common above all in jazz.

In classical part-writing the seventh is prepared and resolved downward; this rule loosened over time, until the dominant seventh chord could be used freely.

Upon inversion, the seventh becomes the second; both present the same tension relation, the seventh, however, in a wider and thereby more open position.

A distinction is made between minor, major, and diminished sevenths. The minor seventh is the hallmark of the dominant seventh chord, the major of the major seventh chord in jazz, the diminished of the diminished seventh chord. Melodically the seventh is a large, hard-to-sing leap, often used expressively, for instance to depict pain or a cry. Inverted, it yields the second, which explains its dissonant character.

Performance practice

Lead sevenths downward, unless something else is demanded, and give them weight beforehand. Do not intonate the minor seventh too high — it wants to fall. And when singing, derive the interval from a familiar seventh chord, instead of hitting it in isolation.