Suomeksi | In English

Four-note chords

If we add one third above a triad, the result is a four-note chord or a seventh chord; the interval between the bottom and top notes is a seventh. The symbol for four-note chords or seventh chords is 7.

Sometimes four-note chords are classified on the basis of the types of triads and sevenths used. The symbol maj7 (major seventh) stands for a chord with a major chord and the M7 interval counted from the root. Correspondingly, a half-diminished 7th chord, 7/75, has a diminished triad and a m7.

Minor keys are richer in chords of different types than major keys; they also include a minor triad with a major 7th on the I degree and a diminished 7th on the VII degree.

Four-note chords in a major scale

Four-note chords in a minor scale

Less common chords in a minor scale

Below is a table containing chord symbols and absolute chord symbols. Other structures of thirds, for example "augmented major seventh" on the III degree of a minor scale, are possible but rare.

major seventh ds7 Cmaj7
dominant seventh dp7 G7
minor major seventh ms7 Cmmaj7
minor seventh mp7 Am7
half-diminished seventh vp7 Dm75 or D7
diminished seventh vv7 Hdim7 or H 7 (or Bdim7 and B7)

Four-note chord inversions and scale degree symbols

When a seventh interval from the bass is added to a triad, the chord gets the upper index 7 and the resulting four-note chord is named a seventh chord.

The indexes derive from the Baroque figured bass markings, where chords were indicated with a number in connection with a bass note. The numbers showed the intervals included in the harmony from the bass upwards.

It was possible to write homophonic music with several parts quickly when only a few numbers were added to the melody and bass lines. Harpsichordists implemented the numberings, applying their musicianship and improvisational skills.

Four chord notes included three intervals counted from the bass, but in notation they were soon standardized to show only certain intervals.

In the first inversion, the 3rd appears as the lowest tone (five and six from the bass note); in the second inversion, the 5th is the lowest tone; in the third inversion, the 7th is lowest.

As late as the 19th century, composers and musicians thought about harmonies by using the figured bass symbols as the bass line, which was considered to show the most determinative note of the harmony. A later tradition is to discuss chords, which include the same notes, in terms of inversions of a scale degree. In this tradition, notes are stacked as a pile of thirds, and the inversion is determined by the lowest (bass) note of the pile.

The traditional way of writing a four-note chord is complex: first we form a pile of thirds, and then we find out the interval relationship between the bottom note and the real root note of the chord, in other words define the inversion. Even though complex, the method is quite common.

In the animation below we see some ways of forming a pile of thirds.

Two superimposed thirds form a frame of fifths. When the fifths are interposed, the result is a pile of thirds. Thus, it is enough to find the fifth (or fourth) in a chord and place the notes between (thirds) into the frame (bars 14). Correspondingly, thirds and sevenths can be part of a four-note chord (bars 58). One and the same chord can, on two staves, form highly different interval structures (bars 912).

The ground note or the root of a chord is the lowest note of an uninverted chord. In chord inversions, the interval highest in the chord index indicates the actual root of the chord.

The original way of perceiving chords may feel awkward if one is used to thinking of all harmonies as piles of thirds. It is, however, useful in recognizing chords; it is unnecessary to name more than three intervals. It is often possible to recognize the root note (and the scale degree) by just one interval (numbers in bold below):

in a seventh chord intervals 3, 5 and 7
in a first inversion 3, 5 and 6
in a second inversion 3, 4 and 6
in a third inversion 2, 4 and 6

The current concept of harmony has in some ways been shackled by the idea of piles of thirds. It was not until the 20th century that art musicians were able to discuss harmonies in other forms than superimposed thirds.

Added notes in four-note jazz chords

Functional harmony in jazz is usually based on four-note chords. The function is determined by the third and the seventh:

  • minor third and minor seventh: subdominant
  • major third and minor seventh: dominant
  • major seventh: tonic (minor or major).

The fifth has no effect on the function. In a tonic, the fourth note can also be a sixth instead of a major seventh. This is actually a more traditional (and less dissonant) form. It is worth noting that in a minor tonic chord the sixth is always major. This sixth common in popular music is not to be confused with the sixth chord in classical music theory denoting the first inversion of a triad.

A four-note chord can be extended by added notes 9, 11, and 13. While added notes affect the colour or tone quality of the chord, they have no effect on the function. Added notes can also be altered in the same way as the fifth of a chord. The most alterable is the dominant chord with a possibility for both 5 (=#11), #5, 9, and #9. A practical help for remembering the "forbidden" added notes is to avoid a minor ninth (or augmented eighth). The only exception is the 9 common in a minor 7th (resolving into a tonic fifth). Therefore, an m75 chord can include only a major ninth, a major and a dominant chord can include only a #11, and so on.

Examples of four-note chords with added and altered notes:

The following rules usually apply to chord symbols:

  • if an interval larger than a seventh is added, minor seventh is not written (root note + added note, e.g., E9)
  • if the added note is altered, for example C79, minor seventh is written
  • common symbols: Cmaj7=CD, Cm7=C-7, Cdim=C, Cm75=C