Half-diminished seventh chord
For example, the half-diminished seventh chord built on B, commonly written as Bm7(♭5), or Bø7, has pitches B-D-F-A: It can be represented by the integer notation {0, 3, 6, 10}.
[4] The half-diminished seventh chord is frequently used in passages that convey heightened emotion.
For example, the "mournful affect"[5] of the sombre opening Chorus of J. S. Bach's St Matthew Passion (1727) features the chord on the seventh beat of its first bar and on the first beat of its third bar: Similarly in the Et carnatus est section from Michael Haydn's Missa Sancti Nicolai Tolentini (1768): Et incarnatus est on YouTube from Michael Haydn's Missa Sancti Nicolai Tolentini, MH 109 performed by Le Choeur de Filles de la Maîtrise de Bordeaux In contrast, however, one of the most striking and best known examples of a half diminished seventh can be found in a piece that expresses joyful celebration, namely the chord that follows the fanfare at the start of the Wedding March from Mendelssohn's incidental music to A Midsummer Night's Dream (1842).
An instance of the power latent in this "quintessentially dramatic chord"[6] can be found in the "shriek of despair" that launches the "torrent of fury" that is Chopin's Scherzo No.
)[8] However, in his final opera Parsifal (1882), the composer used the half-diminished seventh to colour a leitmotif that conveys how its hero develops as the story progresses.
His leitmotif consists almost entirely of diatonic chords: "As the hero grows in wisdom, so his music develops.
"[9] When Parsifal re-appears in the final act, set many years later, half-diminished chords permeate the leitmotif.
"[11] The low register of the half-diminished chord at the start appropriately conveys a dark, brooding character.
A striking phrase on the tenor horn unfolds the chord as an arpeggio in the second bar.
In his book celebrating popular songs of the first half of the twentieth century, musicologist Allen Forte writes, "The half-diminished seventh chord is in many respects the star of the seventh chord harmonic cast.
[15] Half-diminished seventh chords are often symbolized as a circle with a diagonal line through it, as in Bø7 or simply Bø.
[19] Transposing this gives { A♭ C♭ D F♯ }, a virtual minor version of the French augmented sixth chord.
[20] Like the typical augmented sixth chord, this enharmonic interpretation gives on a resolution irregular for the half-diminished seventh but regular for the augmented sixth chord, where the two voices at the diminished third (enharmonic major second) converge to unison or diverge to octave.
