Chord (music)
In Western music theory, a chord is a group of notes played together for their harmonic consonance or dissonance. The most basic type of chord is a triad, so called because it consists of three distinct notes: the root note along with intervals of a third and a fifth above the root note. Chords with more than three notes include added tone chords, extended chords and tone clusters, which are used in contemporary classical music, jazz, and other genres.
Chords are the building blocks of harmony and form the harmonic foundation of a piece of music. They provide the harmonic support and coloration that accompany melodies and contribute to the overall sound and mood of a musical composition. The factors, or component notes, of a chord are often sounded simultaneously but can instead be sounded consecutively, as in an arpeggio.
A succession of chords is called a chord progression. One example of a widely used chord progression in Western traditional music and blues is the 12 bar blues progression. Although any chord may in principle be followed by any other chord, certain patterns of chords are more common in Western music, and some patterns have been accepted as establishing the key in common-practice harmony—notably the resolution of a dominant chord to a tonic chord. To describe this, Western music theory has developed the practice of numbering chords using Roman numerals to represent the number of diatonic steps up from the tonic note of the scale.
Some chords can be microtonal. This means that it has chords outside the normal accidental range of a normal instrument.
Common ways of notating or representing chords in Western music include Roman numerals, the Nashville Number System, figured bass, chord letters, and chord charts.
Definition
The English word chord derives from Middle English cord, a back-formation of accord in the original sense of agreement and later, harmonious sound. A sequence of chords is known as a chord progression or harmonic progression. These are frequently used in Western music. A chord progression "aims for a definite goal" of establishing a tonality founded on a key, root or tonic chord. The study of harmony involves chords and chord progressions and the principles of connection that govern them.Ottó Károlyi writes that, "Two or more notes sounded simultaneously are known as a chord," though, since instances of any given note in different octaves may be taken as the same note, it is more precise for the purposes of analysis to speak of distinct pitch classes. Furthermore, as three notes are needed to define any common chord, three is often taken as the minimum number of notes that form a definite chord. Hence, Andrew Surmani, for example, states, "When three or more notes are sounded together, the combination is called a chord." George T. Jones agrees: "Two tones sounding together are usually termed an interval, while three or more tones are called a chord." According to Monath, "a chord is a combination of three or more tones sounded simultaneously", and the distances between the tones are called intervals. However, sonorities of two pitches, or even single-note melodies, are commonly heard as implying chords. A simple example of two notes being interpreted as a chord is when the root and third are played but the fifth is omitted. In the key of C major, if the music stops on the two notes G and B, most listeners hear this as a G major chord.
Since a chord may be understood as such even when all its notes are not simultaneously audible, there has been some academic discussion regarding the point at which a group of notes may be called a chord. Jean-Jacques Nattiez explains that, "We can encounter 'pure chords' in a musical work", such as in the "Promenade" of Modest Mussorgsky's Pictures at an Exhibition but, "often, we must go from a textual given to a more abstract representation of the chords being used", as in Claude Debussy's Première arabesque.
History
Chords evolved out of the early church organum, which reflected the different vocal ranges. In its earliest written form, found in the treatise Musica enchiriadis, organum consisted of two melodic lines moving simultaneously note against note. Organum was further developed with the staff notation established by monk Guido d'Arezzo.In the medieval era, early Christian hymns featured organum, with chord progressions and harmony - an incidental result of the emphasis on melodic lines during the medieval and then Renaissance.
The Baroque period, the 17th and 18th centuries, began to feature the major and minor scale based tonal system and harmony, including chord progressions and circle progressions. It was in the Baroque period that the accompaniment of melodies with chords was developed, as in figured bass, and the familiar cadences. In the Renaissance, certain dissonant sonorities that suggest the dominant seventh occurred with frequency. In the Baroque period, the dominant seventh proper was introduced and was in constant use in the Classical and Romantic periods. The leading-tone seventh appeared in the Baroque period and remains in use. Composers began to use nondominant seventh chords in the Baroque period. They became frequent in the Classical period, gave way to altered dominants in the Romantic period, and underwent a resurgence in the Post-Romantic and Impressionistic period.
The Romantic period, the 19th century, featured increased chromaticism. Composers began to use secondary dominants in the Baroque, and they became common in the Romantic period. Many contemporary popular Western genres continue to rely on simple diatonic harmony, though far from universally: notable exceptions include the music of film scores, which often use chromatic, atonal or post-tonal harmony, and modern jazz, in which chords may include up to seven notes. When referring to chords that do not function as harmony, such as in atonal music, the term "sonority" is often used specifically to avoid any tonal implications of the word "chord".
Chords are also used for timbre effects. In organ registers, certain chords are activated by a single key, so playing a melody results in parallel voice leading. These voices, losing independence, are fused into one with a new timbre. The same effect is also used in synthesizers and orchestral arrangements; for instance, in Ravel’s Bolero #5 the parallel parts of flutes, horn and celesta, being tuned as a chord, resemble the sound of an electric organ.
Usage and trends
Chord frequency and diversity
A 2025 analysis of 52 million chords across 680,000 songs found that G major and C major were the most commonly used chords, accounting for 24% of all chords. These were followed by D major, A major, and F major. The study also observed a decline in chord diversity over time, with songs containing fewer unique chords and a decreasing ratio of unique chords to total chords. This ratio fell from 13% in the 1930s to 8% in the 2020s, indicating a trend toward more straightforward chord progressions in popular music.Notation
Chords can be represented in various ways. The most common notation systems are:- Plain staff notation, used in classical music.
- Roman numerals, commonly used in harmonic analysis to denote the scale step on which the chord is built.
- Figured bass, much used in the Baroque era, uses numbers added to a bass line written on a staff, to enable keyboard players to improvise chords with the right hand while playing the bass with their left.
- Chord letters, sometimes used in modern musicology, to denote chord root and quality.
- Various chord names and symbols used in popular music lead sheets, fake books, and chord charts, to quickly lay out the harmonic ground plan of a piece so that the musician may improvise, jam, or vamp on it.
Roman numerals
In some conventions upper-case Roman numerals indicate major triads while lower-case Roman numerals indicate minor triads ; other writers use upper case Roman numerals for both major and minor triads. Some writers use upper-case Roman numerals to indicate the chord is diatonic in the major scale, and lower-case Roman numerals to indicate that the chord is diatonic in the minor scale. Diminished triads may be represented by lower-case Roman numerals with a degree symbol.
Roman numerals can also be used in stringed instrument notation to indicate the position or string to play. In some string music, the string on which it is suggested that the performer play the note is indicated with a Roman numeral. In some orchestral parts, chamber music and solo works for string instruments, the composer tells the performer which string to use with the Roman numeral. Alternately, the composer starts the note name with the string to use—e.g., "sul G" means "play on the G string".
Figured bass notation
Figured bass or thoroughbass is a kind of musical notation used in almost all Baroque music, though rarely in music from later than 1750, to indicate harmonies in relation to a conventionally written bass line. Figured bass is closely associated with chord-playing basso continuo accompaniment instruments, which include harpsichord, pipe organ and lute. Added numbers, symbols, and accidentals beneath the staff indicate the intervals above the bass note to play; that is, the numbers stand for the number of scale steps above the written note to play the figured notes.For example, in the figured bass below, the bass note is a C, and the numbers 4 and 6 indicate that notes a fourth and a sixth above should be played, giving the second inversion of the F major triad.
If no numbers are written beneath a bass note, the figure is assumed to be, which calls for a third and a fifth above the bass note.
In the 2010s, some classical musicians who specialize in music from the Baroque era can still perform chords using figured bass notation; in many cases, however, the chord-playing performers read a fully notated accompaniment that has been prepared for the piece by the music publisher. Such a part, with fully written-out chords, is called a "realization" of the figured bass part.