A chord is a combination of two or more pitches that are sounded simultaneously or understood as a simultaneous harmonic structure. In common Western music theory, the term usually refers to a group of three or more notes organised according to intervals above a fundamental or root, although broader uses can include two note sonorities.
Chords provide harmonic support for melodies, establish or destabilise tonal centres, create musical tension and release, and contribute substantially to the colour and structure of a composition. A basic triad contains three pitch classes and is constructed from stacked thirds. A major triad consists of a root, major third and perfect fifth, while a minor triad contains a root, minor third and perfect fifth. Diminished and augmented triads modify the fifth, producing different intervallic structures. Chords therefore represent organised pitch relationships rather than merely arbitrary collections of simultaneous notes.
Chords can be classified according to their constituent intervals and their root. The four basic triad qualities in common Western theory are major, minor, diminished and augmented. A major seventh chord adds a major seventh above the root to a major triad, while a dominant seventh chord adds a minor seventh above a major triad. Minor seventh, half diminished seventh and fully diminished seventh chords provide additional structures.
Chords can be extended beyond sevenths through ninths, elevenths and thirteenths, although practical voicings often omit some tones. Added tone chords place an additional pitch into a basic structure without necessarily implying a complete tertian extension. Suspended chords replace the third with another scale degree, commonly the second or fourth. These distinctions allow musicians to describe harmonic sonorities precisely and indicate expected relationships between notes.
The root is the pitch from which a chord is theoretically constructed, although the root does not have to be the lowest sounding note. When the root is in the bass, the chord is in root position. When another chord member occupies the bass, the chord is inverted. A first inversion triad has its third in the bass, while a second inversion triad has its fifth in the bass. Seventh chords have additional inversion categories.
Inversions alter the vertical spacing and bass movement without necessarily changing the chord's fundamental identity. This distinction is important because the lowest note strongly affects the perceived harmonic function, while the theoretical root describes the chord's underlying structure. Slash chord notation can also indicate a particular bass note, such as C over G, which specifies a C sonority with G in the bass.
Chords perform different harmonic functions depending on musical context. In tonal harmony, chords are commonly understood through relationships such as tonic, predominant and dominant function. The tonic represents relative stability, predominant harmony commonly prepares dominant harmony, and dominant harmony often creates a strong tendency towards tonic resolution. A major or minor chord therefore does not possess a single universal function simply because of its internal structure. The same chord can serve different functions in different keys and contexts.
For example, a D minor chord can function as a tonic in D minor, a predominant chord in C major, or a chord with another role in a different harmonic environment. Functional harmony consequently depends on relationships between chords, key, scale degrees, voice leading and cadence rather than on isolated chord labels.
Chords can be voiced in many ways, and voicing refers to the specific arrangement of chord tones in register. Close position places notes relatively near one another, while open voicing distributes them over a wider span. Doubling means that one chord tone occurs more than once, which can influence emphasis and resonance. Omitting a chord member can be appropriate when another instrument supplies the missing tone or when the omitted pitch is less structurally important.
In jazz and popular music, voicings may include extensions, alterations and carefully selected omissions to produce particular colours. On a piano, a chord can be distributed across both hands, while an orchestra may distribute its tones among several sections. Consequently, a chord symbol alone often does not specify the exact sound or arrangement of every pitch.
Chords occur in many musical systems, but the concept should not be assumed to have identical meaning across all traditions. Western tonal theory developed sophisticated chord classifications through the growth of polyphonic and harmonic practices, particularly from the seventeenth century onward. Earlier medieval and Renaissance music was often analysed primarily through contrapuntal voice relationships rather than through the later concept of vertically conceived chords.
In other musical traditions, simultaneous pitch combinations may be organised through different principles, and some traditions place less emphasis on chord progression as understood in Western popular and classical harmony. Modern music also includes clusters, quartal and quintal harmonies, polychords and other structures that do not fit neatly into conventional stacked thirds. Chord theory therefore represents one important analytical framework rather than a universal definition of simultaneous pitch.
Chords are used for practical purposes in composition, accompaniment, arranging, improvisation and performance. A guitarist may use chord shapes to accompany a singer, a pianist may realise a lead sheet through chord symbols, and an arranger may distribute chord tones among different instruments. Composers can use chords to establish tonal stability, create transitions, intensify climaxes or provide timbral colour. Chord progressions can also determine the harmonic framework over which melodies and improvisations occur.
In film and game music, chord structures may be used to reinforce changes in mood, narrative emphasis or dramatic tension, although emotional interpretation depends on many musical parameters. Chords can also function as sustained sonorities rather than as rapidly changing harmonic units, making them useful for creating harmonic fields, pedals and static modal textures.
A chord is therefore best understood as a structured harmonic sonority whose identity can involve pitch content, root, quality, inversion, voicing, extensions, alterations and context. Chord symbols provide a compact way of communicating much of this information, but a symbol normally leaves some decisions open, particularly exact voicing, register, doubling and instrumentation. The distinction between chord and note is fundamental because a note identifies an individual pitch, whereas a chord describes a relationship among multiple pitches.
The distinction between chord and chord progression is equally important because a chord is an individual harmonic structure while a progression describes movement among harmonic structures. Understanding chords provides the basis for analysing tonal harmony, reading chord symbols, writing accompaniments, arranging ensembles and understanding how simultaneous pitches contribute to musical form and expression.
