Ninth

What it means

The ninth is the interval spanning nine scale degrees — a second plus an octave. Like the second, it occurs in major and minor forms; the major ninth comprises fourteen semitones, the minor thirteen. It belongs to the compound intervals, which reach beyond the octave.

Musical use

Tonally the ninth relates to the second as every compound interval relates to its basic interval: it seems more open and less sharp, because the notes lie farther apart. A major second in close position rubs; the same notes at a ninth's distance sound wide and transparent.

In a chord it appears as an added note above the seventh chord and thus forms the ninth chord, a sonority of particular fullness that is common above all in the music of the late nineteenth century and in jazz. There the designation belongs to the stock of chord symbols. In classical part-writing the ninth usually appears as a suspension that resolves downward into the octave.

Bear in mind that in practice a distinction is made between the second and the ninth, although both contain the same notes: a chord with an added second sounds different from one with a ninth, because the position decides the effect. In figured-bass notation, by contrast, compound intervals are often reduced to their simple form.

In the chord symbol it appears as 9, for instance in C9 or Cadd9. Major and minor ninths are distinguished. In classical harmony it is dissonant and is resolved, often as a suspension before the octave, being led stepwise downward. In jazz it is a frequent optional tone that colours major and minor chords without a resolution being expected.

Performance practice

Set ninths wide, not narrow — the appeal lies in the spacing; in close position it becomes a harsh second-clash. With ninth chords, watch the distribution of the voices, so that the sonority stays transparent; the ninth belongs on top. And resolve ninth suspensions distinctly downward.