Seventh chord: Wikis

  

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A seventh chord is a chord consisting of a triad plus a note forming an interval of a seventh above the chord's root. When not otherwise specified, a "seventh chord" usually means a major triad with a flat seventh (a "dominant seventh chord"). However, a variety of sevenths may be added to a variety of triads, resulting in many different types of seventh chords, as described below.

In its earliest usage, the seventh was introduced solely as an embellishing or nonchord tone. The seventh destabilized the triad, and allowed the composer to emphasize movement in a given direction. As time progressed and the collective ears of the western world became more accustomed to dissonance, the seventh was allowed to become a part of the chord itself, and in some modern music, and jazz in particular, nearly every chord is a seventh chord. Additionally, the general acceptance of equal temperament during the 1800s reduced the dissonance of some earlier forms of sevenths.

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Types of seventh chords

Most textbooks name these chords formally by the type of triad and type of seventh; hence, a chord consisting of a major triad and a minor seventh above the root is referred to as a "major/minor seventh chord." When the triad type and seventh type are identical (IE both notes are major or minor), the name is shortened; a major/major seventh is generally referred to as a "major seventh." Additionally, when letters are used to indicate triads, a "bare" letter is understood as a major triad (a "C" chord is a "C major triad") while a "bare" 7 is understood as a dominant seventh (a "C7" chord is a "C major/minor seventh chord"). Diminished seventh chords do not follow this system however (a "Bdim7" chord is a "diminished/diminished seventh chord" instead of a "diminished/minor seventh chord").

Of the eight possible constructions of seventh chords using major and minor thirds, seven are commonly found in western music (in addition to the synthetic "altered" seventh). They are built as indicated below:

  • Major Seventh (formally "major/major seventh", also maj7, M7, Δ, ⑦): root, major third, perfect fifth, major seventh
  • Minor Seventh (formally "minor/minor seventh", also m7,-7): root, minor third, perfect fifth, minor seventh
  • Dominant Seventh (formally "major/minor seventh", commonly shortened to just "7", such as G7 ): root, major third, perfect fifth, minor seventh
  • Half Diminished (formally "diminished/minor seventh", also "minor seventh, flat five" among jazz musicians, m7♭5, -7♭5, ø): root, minor third, diminished fifth, minor seventh
  • Diminished Seventh (formally "diminished/diminished seventh", also °7): root, minor third, diminished fifth (tritone), diminished seventh (enharmonic major sixth)
  • Minor Major Seventh (also mM7, mmaj7, mΔ7, -Δ7,m⑦): root, minor third, perfect fifth, major seventh
  • Augmented Major Seventh (also maj7(5), maj+7, Δ+7): root, major third, augmented fifth, major seventh

The following seventh chord is not built using only major and minor thirds:

In tuning systems other than equal temperament there are further possible seventh chords than major and minor. In just intonation, for example, there is the "harmonic seventh" (the 7:4 pitch ratio: slightly below minor seventh). Sometimes called a "blue note", the harmonic seventh is used by singers, through note bending on guitars, and on other instruments not restricted to equal temperament. An often heard example of the harmonic seventh chord is the last word of the modern addition to the song "Happy Birthday to You", with the lyrics, "and many more!" The harmony on the word "more" is typically sung as a harmonic seventh chord.[1]

Dominant seventh chord

Harmonic seventh chord

The harmonic seventh chord is a major triad plus the above-mentioned harmonic seventh interval. Frequent use of this chord is one of the defining characteristics of blues and barbershop harmony; barbershoppers refer to it as "the barbershop seventh." Since barbershop music tends to be sung in just intonation, the barbershop seventh chord may be accurately termed a harmonic seventh chord. The harmonic seventh chord is also widely used in "blues flavored" music. As guitars, pianos, and other equal-temperament instruments cannot play this chord, it is frequently approximated by a dominant seventh. As a result it is often called a dominant seventh chord and written with the same symbols (such as the blues progression I7 - V7 - IV7).

Major and minor seventh chords

While the dominant seventh chord is typically built on the fifth (or dominant) degree of a major scale, the minor seventh chord is built on the second, third, or sixth degree. A minor seventh chord contains the same notes as an added sixth chord (see below under "Sixth chords") - for example, C-E♭-G-B♭ can function as both a C minor seventh and an E flat added sixth (Id chord).

Major seventh chords are usually constructed on the first or fourth degree of a scale, (in C or G major: C-E-G-B). Due to the major seventh interval between the root and seventh (C-B, an inverted minor second), this chord can sometimes sound dissonant, depending on the voicing used. For example, Bacharach and David's Raindrops Keep Fallin' on My Head opens with a major chord followed by a major seventh in the next measure.

The major seventh is sometimes notated as Δ 7 (a delta chord) or just a Δ (which has the same meaning).

Half-diminished seventh chords

A half-diminished seventh chord is a seventh chord built from the seventh degree of a major scale. It's considered "half-diminished" because a fully diminished seventh has a double-flatted seventh, making it enharmonically the same as a major sixth. The half-diminished seventh chord uses a minor seventh over a diminished triad.

Diminished seventh chord

A comparison of the Diminished 7th and Dominant 7th (b9) Chords

A diminished 7th chord is made of three superimposed minor 3rds (e.g. B-D-F-A), which is two tritones a minor third apart (e.g. C-F, E-A). The Diminished 7th Chord has been used by composers and musicians for a variety of reasons over time. Some reasons include: as a symbol of Sturm und Drang; modulation; and for characterisation. The diminished 7th chord is seen more frequently in late classical and romantic period works but is also found in Baroque and Renaissance period works, though not as frequently.

All of the elements of the Diminished 7th chord can be found in the Dominant 7th (b9) chord as seen in a comparison of the two chords.

See also

References

  1. ^ Mathieu, W.A. Harmonic Experience. Inner Traditions International; Rochester, Vermont; 1997. ISBN 0-89281-560-4, pg. 126

External links








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