A chord is a group of notes sounding together (the evocative German term is Zusammenklang). Chords can be implied or actually heard, and they can occupy part or all of the texture. Chords with only two notes are generally called dyads rather than chords.

History and etymology

The term chord is derived from accord for agreement. The idea is that the notes in a chord should agree with each other; they should form a harmonic unit. The sound may be quite bracing, as long as the chord is somehow consistent with others in the piece and the style.

An old account of the history of Western music is that dissonance was progressively emancipated, starting with thirds in the Renaissance and progressing to sevenths through the common-practice period, etc. This story responds to the fact that our ears today are indeed far more capable of analyzing vertical tone relations than they were, say, a millennium ago. But the account is simplistic, because it assumes a linear evolution, when in fact different styles have developed contemporaneously, especially since the turn of the twentieth century, and these styles sometimes have different norms of consonance and dissonance or no notion of consonance and dissonance at all.

Specific chords

Chords can be categorized by their building blocks. A particular interval can be stacked, as with secundal, tertian, and quartal chords, and other notes or entire chords can be added to these stacks.

Secundal chords (tone clusters)

Secundal chords, commonly called tone clusters, are chords built in seconds. Tone clusters can have three or more notes. They can be diatonic, chromatic, whole-tone, or from some other scale:

They can appear in different positions and voicings, but they can easily thereby seem like other kinds of chords:

Example: Kraftwerk, “Megaherz,” from Kraftwerk (1970): Wavering tone clusters with organ and tape loops.

Example: Henry Cowell, “Antinomy,” no. 4 of Five Encores to Dynamic Motion (ca. 1917), conclusion: Best. Clusters. Ever. Despite the raucous sound, these tone clusters require tremendous skill to pull off. Note that the tone clusters marked with a natural sign use all white keys; the rest are chromatic.

Tertian chords

Tertian chords are chords built in thirds. Tertian chords can be triads or seventh chords, or they can be extended chords: ninth, eleventh, or thirteenth chords. The most common tertian chords, which use a diatonic, acoustic, or symmetrical scale, are as follows:

You can label augmented-sixth chords enharmonically as dominant seventh chords in root position, or as dominants with a missing root:

Quartal chords (fourth chords)

Quartal chords, commonly known as fourth chords, are chords built in fourths. Fourth chords can have three or more notes. Normally all the fourths are perfect. Altered fourth chords include augmented or (less commonly) diminished fourths:

Like tone clusters, fourth chords can appear in different voicings and positions, but they can easily thereby seem like other kinds of chords. Even without revoicing, a four-note fourth chord is identical with a minor seventh chord with an added fourth:

Note that a five-note quartal chord makes up a pentatonic collection, a seven-note quartal chord makes up a diatonic collection, and a twelve-note quartal chord makes up the chromatic  collection:

Fourth chords inverted and voiced in fifths are callled quintal chords or fifth chords:

Bernhard Haas has a handy labeling system for fourth chords / fifths chords: “Q” followed by the span of fifths. For example, the chords just shown would be “Q Bb–C” and “Q Eb-C.”

Example: Joni Mitchell, “I Had a King,” from Song to a Seagull (1967): The song uses several quartal chords in different positions. One is accented before the chorus. They contribute to the wistful tone of the song.

Example: Miles Davis, “So What,” from Kind of Blue (1959): Bill Evans plays fourth-chord voicings of tertian chords.

Added-note chords

Added-note chords are chords with extra notes. The most common added-note chords are tertian chords with added ninths (or seconds), fourths, or sixths. Added-sixth chords are commonly called sixth chords. A six-nine chord has an added sixth and ninth. A major six-nine chord completes a pentatonic collection. Added-note chords can often be understood just as tertian chords; for example, C7add13 can be understood as C13, and C7 split third is generally labeled as C7#9:

Example: The Beatles, “She Loves You,” from The Beatles’ Second Album (1964): The chorus ends with a tonic sixth chord.

Example: Sara Bareilles, “Gravity,” from Careful Confessions (2004): The verse and chorus both begin with Dm7add4 (C: II). The chorus continues: Dm7add4–G/B–Cadd9–G/B–Amadd9–Am/G (C: II–V–I–V–VI).

Example: Jimi Hendrix, “Purple Haze,” from Are You Experienced? (1967): The syncopated tonic chords after the introduction are E7 split third (E7#9).

Example: Mahler, Das Lied von der Erde (1908): The work ends with a tonic sixth chord.

Polychords

Polychords are combinations of two or more chords. The chords that make up polychords may share a note but otherwise rarely overlap in register. Polychords may be indistinguishable from extended chords. Often voicing is the only difference. For example, the first and fourth chords below could be C7b9#11 if they were voiced more uniformly. Polychords and extended chords are so similar that polychord symbols are often used for extended chords in jazz to make them easier to play. Polychords are often confused with polytonality; chordal roots can be tonics, but not necessarily. There are no standard symbols for polychords, but they are often symbolized as follows:

Example: Igor Stravinsky, “Dance of the Young Girls,” from Rite of Spring (1913): The movement begins with accented polychords. This is the most famous example of polychords.

Example: Charles Ives, “The Cage” (1906). The accompaniment uses fourth chords with a few accented polychords.

Closely related to polychords are slash chords, chords over a bass note other than the root. All inverted chords are slash chords, but so are chords where the bass is not a member of the upper chord. Slash-chord notation can be used for polychords, as long as the chord symbols are not confused with bass note names.

Example: John Lennon and Paul McCartney, “Tomorrow Never Knows,” from Revolver (1966): There is a repeated slash chord that alternates with the tonic triad:

Further reading

• Vincent Persichetti, Twentieth-Century Harmony, Chapters 4, 6, and 7
• Stefan Kostka, Materials and Techniques of Post-Tonal Music, Chapter 3

External links

The Wikipedia article on chords does not have a unifying principle, and it is difficult to determine what information is important and generally accepted.