Seventh chord

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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 and a minor 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 chord, 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.

1 Types of seventh chords
2 The dominant seventh
3 Major and Minor Seventh Chords
4 Half-Diminished Seventh Chords
5 Diminished 7th Chord
6 External links
7 References

[edit] 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, 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 minor 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, five are most commonly found in western music. They are built as indicated below:

Major Seventh (formally "major/major seventh", also maj7, M7, ^Δ7, ⑦): root, major third, perfect fifth, major seventh
Minor Seventh (formally "minor/minor seventh", also m7,-7): root, minor third, perfect fifth, minor seventh
Major/Minor Seventh (commonly called dominant 7th even when not used in that context) (7): 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 (sixth)
Minor Major Seventh (also mM7, m^Δ7, -Δ7,m⑦): root, minor third, perfect fifth, major seventh
Altered Chord (7^alt): root, flat ninth, sharp ninth, third, diminished fifth, augmented fifth, flat seventh

The other two possible seventh chords – the augmented/major seventh and the augmented/minor seventh – are rarely seen in western music.

In tuning systems other than equal temperament there are further possible seventh chords. In just intonation, for example, there are more sevenths than just major and minor. For example, the "harmonic seventh" (the 7:4 pitch ratio), sometimes called a "blue note", used by singers, through note bending on guitars, and on other instruments not restricted to equal temperament. A well-known example of the harmonic seventh chord is the ending of the modern addition to the song "Happy Birthday to You", with the words "and many more!" The harmony on the word "more" is typically sung as a harmonic seventh chord (Mathieu, pg. 126).

[edit] The dominant seventh

Of all the seventh chords, perhaps the most important to understand is the major triad with a minor seventh, also called the dominant seventh chord. Called the Dominant Seventh because its intervallic relationships occur naturally in the seventh chord built on the dominant scale degree of a given key (e.g., G7 in the key of C major), the dominant seventh chord was the first to begin to appear regularly in Western music.

The dominant seventh chord is useful to composers because it is a major chord with a very strong sound, that also includes a tritone between the third and seventh of the chord. In a diatonic context, the third of the chord is the leading-tone of the scale, which has a strong tendency to pull towards the tonal center, or root note, of the key. This, in combination with the strength of root movement by fifth, and the natural resolution of the dominant triad to the tonic triad, creates an incredibly satisfying resolution with which to end a piece or a section of a piece. Because of this original usage, it also quickly became an easy way to trick the listener's ear with a deceptive cadence.

The most important usage, though, is the way that the introduction of a non-diatonic dominant seventh chord (sometimes called a chromatic seventh) which is borrowed from another key, can allow the composer to modulate to that other key.

This technique is extremely common, particularly since the classical period, and has led to further innovative uses of the dominant seventh chord such as secondary dominant, extended dominant, and substitute dominant chords.

Frequent use of the dominant seventh is one of the defining characteristics of barbershop harmony; barbershoppers refer to it as "the barbershop seventh." However, since barbershop music tends to be sung in just intonation, the barbershop seventh chord may be more accurately termed a harmonic seventh chord.

The harmonic seventh chord is also widely used in "blues flavored" music, although it is usually called a dominant seventh chord and written with the same symbols (such as the blues progression I7 - V7 - IV7). The harmonic seventh note is about a quarter-tone flatter than an equal tempered minor seventh. When this flatter seventh is used, the dominant seventh chord's "need to resolve" down a fifth is weak or non-existent. This chord is often used on the tonic (written as I7) and functions as a "fully resolved" final chord (Mathieu, pp. 318-319).

[edit] 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.

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 Δ7 (a delta chord).

[edit] 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.

[edit] Diminished 7th Chord

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

The Diminished 7th Chord has been used by composers and musicians for a variety of reasons over time. Some reaons include: as a symbol of Sturm und Drang, Modulation and for characterisation. A diminished 7th chord is made of three superimposed minor 3rds (e.g. B-D-F-Ab) or two tritones (e.g. C-F#, Eb-A). 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.

[edit] External links

Chords


By Type	Triads	Major · Minor · Augmented · Diminished

	Sevenths	Major · Minor · Dominant · Diminished · Half-diminished · Minor-Major · Augmented major · Augmented minor

	Extended	Ninth · Eleventh · Thirteenth

	Other	Sixth · Augmented sixth · Altered · Added tone · Polychord · Quartal and quintal · Tone cluster

By Function	Diatonic	Tonic · Dominant · Subdominant · Submediant

	Altered	Borrowed · Neapolitan chord · Secondary dominant · Secondary subdominant