A chord is a set of three or more distinct musical notes sounded simultaneously, forming the harmonic foundation of most Western music. Chords are built from intervals (typically thirds) and are classified by their quality (major, minor, diminished, augmented) and extension (seventh, ninth, etc.). In the arts, chord theory underpins composition, improvisation, and analysis across genres from classical to jazz and popular music.
1 Definition and Basic Concepts
1.1 What is a Chord?
A chord is defined as the simultaneous sounding of three or more pitches. The simplest chord is a triad, which consists of three notes stacked in thirds. The lowest note is the root, the middle is the third, and the top is the fifth. Chords are named by their root note and quality. For example, a C major chord contains C (root), E (third), and G (fifth). Two-note combinations are called dyads or intervals, not chords. Chords can be built using any set of intervals, but Western harmony predominantly uses tertian (third-based) construction.
1.2 Triads and Seventh Chords
A triad is a three-note chord. There are four basic triad qualities: major (root, major third, perfect fifth), minor (root, minor third, perfect fifth), diminished (root, minor third, diminished fifth), and augmented (root, major third, augmented fifth). A seventh chord adds a fourth note a third above the fifth, creating a seventh interval above the root. Common seventh chords include major seventh (major triad + major seventh), dominant seventh (major triad + minor seventh), minor seventh (minor triad + minor seventh), half‑diminished seventh (diminished triad + minor seventh), and fully diminished seventh (diminished triad + diminished seventh).
1.3 Chord Inversions
Inversions occur when a note other than the root is the lowest pitch. In root position, the root is the bass note. In first inversion, the third is the bass; in second inversion, the fifth; in third inversion (for seventh chords), the seventh is the bass. Inversions change the chord's sound and voice leading but not its fundamental identity. They are denoted by figured bass symbols (e.g., ⁶ for first inversion, ⁶₄ for second inversion).
1.4 Chord Voicings
Voicing refers to the arrangement of a chord's notes in register and order. Close voicings place notes within an octave; open voicings spread them over a wider range. Voicings affect timbre and clarity, especially in dense extended chords. In jazz and pop, specific voicings (such as drop‑2 or drop‑3) are used to create smooth voice leading or to avoid muddiness.
2 Chord Types
2.1 Major and Minor Chords
Major chords have a bright, stable sound, built from a major third and a perfect fifth. Minor chords sound darker or sadder, using a minor third and a perfect fifth. These two qualities are the most common in Western music. A major triad can be found on the first, fourth, and fifth scale degrees of a major key; a minor triad on the second, third, and sixth degrees.
2.2 Diminished and Augmented Chords
Diminished chords consist of two minor thirds stacked (root, minor third, diminished fifth). They are tense and unstable, often functioning as passing chords or leading to a resolution. Augmented chords consist of two major thirds stacked (root, major third, augmented fifth). They are also unstable and often used for color or modulation. Both are less common but essential in harmonic variety.
2.3 Extended Chords
Extended chords add notes beyond the seventh, such as the ninth, eleventh, or thirteenth, each a third above the previous. They are commonly used in jazz and progressive genres to create richer harmonies.
2.3.1 Seventh Chords (Dominant, Major, Minor, Half‑diminished, Diminished)
- Dominant seventh (e.g., G⁷): Major triad plus minor seventh. Strong tendency to resolve up a perfect fourth or down a fifth.
- Major seventh (e.g., Cma⁷): Major triad plus major seventh. Smooth, lush sound.
- Minor seventh (e.g., Dm⁷): Minor triad plus minor seventh. Common in minor keys and jazz.
- Half‑diminished seventh (e.g., Bø⁷): Diminished triad plus minor seventh. Often functions as a ii chord in minor keys.
- Diminished seventh (e.g., B°⁷): Diminished triad plus diminished seventh. Symmetrical (all intervals minor thirds) and used for chromatic modulation.
2.3.2 Ninth, Eleventh, and Thirteenth Chords
Ninth chords add the ninth scale degree (e.g., C⁹ = C–E–G–B♭–D). Eleventh chords add the eleventh (e.g., C¹¹), often omitting the third to avoid clash. Thirteenth chords add the thirteenth (e.g., C¹³), the richest extension. In jazz, players often alter extensions (♯¹¹, ♭¹³) for color.
2.4 Suspended Chords
Sus chords replace the third with either a second (sus²) or a fourth (sus⁴), creating a sense of suspension. For example, Csus⁴ = C–F–G. They lack major/minor quality and often resolve by moving the suspended note to the third. They are common in pop and rock.
2.5 Altered Chords
Altered chords modify one or more of the basic chord tones or extensions, such as ♭⁵, ♯⁵, ♭⁹, ♯⁹. Altered dominant chords (e.g., G⁷alt) are especially common in jazz, where the fifths and ninths are raised or lowered to increase tension before resolution.
3 Chord Progressions
3.1 Functional Harmony
Functional harmony categorizes chords by their role: tonic (T, stability), subdominant (SD, movement away), and dominant (D, strong tension pointing back to tonic). In a major key, I is tonic, IV is subdominant, V is dominant. Minor keys use i, iv, V or v, and VII. This framework explains why certain progressions sound logical and satisfying.
3.2 Common Progressions
3.2.1 I‑IV‑V and I‑V‑vi‑IV
The I‑IV‑V progression is a cornerstone of blues, rock, and folk. For example, in C: C–F–G. The I‑V‑vi‑IV progression (C–G–Am–F) is ubiquitous in pop music from the 1950s onward, often called the "four-chord progression."
3.2.2 ii‑V‑I and Circle Progressions
The ii‑V‑I progression (e.g., Dm⁷–G⁷–Cma⁷) is the most common cadential pattern in jazz. Circle progressions move by descending fifths (e.g., C–F–B♭–E♭), creating smooth harmonic motion.
3.3 Modal Interchange
Modal interchange borrows chords from parallel modes, such as using a ♭III chord from the minor mode in a major key. For example, in C major, borrowing E♭ major (♭III) adds color. This technique enriches progressions without abandoning the tonal center.
3.4 Cadences
Cadences are harmonic punctuation points that end phrases.
3.4.1 Authentic, Plagal, Half, and Deceptive Cadences
- Authentic cadence: V → I (full close). Perfect authentic (both chords in root position, tonic in highest voice) is strongest.
- Plagal cadence: IV → I (the "Amen" cadence).
- Half cadence: ends on V (temporary pause).
- Deceptive cadence: V → vi (or ♭VI), avoiding the expected tonic.
4 Chord Notation and Symbols
4.1 Lead Sheet Symbols
Lead sheet symbols denote chords above the melody. They use the root note, quality, and extension. Examples: C, Dm, G⁷, B♭ma⁷, A⁷(♯⁹). Slash chords like C/E indicate a specific bass note. This system is standard in jazz and pop.
4.2 Roman Numeral Analysis
Roman numerals indicate the chord's scale degree and quality. Upper case (I, IV, V) = major; lower case (ii, iii, vi) = minor; diminished = vii°. Seventh chords add superscripts (V⁷, ii⁷). This system shows harmonic function regardless of key.
4.3 Figured Bass
Figured bass, used in Baroque music, numbers indicate intervals above the bass note. For example, ⁶ on a bass note means a chord in first inversion (the third and sixth above the bass). It is still used in music theory pedagogy.
4.4 Guitar Chord Diagrams and Tablature
Guitar chord diagrams show fret positions on a grid. Dots mark where to press strings; X or O indicates muted or open strings. Tablature (tab) uses numbers on six lines to represent frets, often including chord names. These are practical for guitarists learning songs.
5 Chord in Music Genres
5.1 Classical Harmony
Classical harmony (c. 1600–1900) is governed by functional tonality. Composers use triads, seventh chords, and occasional extended chords within strict voice‑leading rules. Modulations to related keys are common. The cadence and phrase structure are precisely controlled.
5.2 Jazz Chords and Voicings
Jazz harmony extends functional tonality with complex chords: extended, altered, and substitute chords. Voicings often omit the root (played by bassist) and emphasize guide tones (third and seventh). Chord progressions frequently use ii‑V‑I cycles and tritone substitution. Improvisation uses chord‑scale theory.
5.3 Pop and Rock Harmony
Pop and rock harmony is simpler, often based on I‑IV‑V or I‑V‑vi‑IV. Power chords (root and fifth, no third) are common in rock. Modal interchange (borrowing from parallel minor) adds color. Extended chords appear occasionally but less densely than in jazz.
5.4 Folk and Traditional Music
Folk harmony often uses basic major and minor triads in simple progressions like I‑V or I‑IV‑V. Open tunings on guitar and drone notes (e.g., in bagpipe music) create unique chord colors. Harmonization is often parallel or by ear.
6 Advanced Topics
6.1 Polychords
A polychord is the simultaneous sounding of two or more different chords, often notated as a fraction (e.g., D/C). Polychords create complex sonorities used in modern classical and jazz, such as superimposing a major triad over a minor triad.
6.2 Quartal and Quintal Harmony
Quartal harmony builds chords from stacked fourths (e.g., C–F–B♭), while quintal harmony uses stacked fifths. These systems break away from tertian tradition and are favored by composers like Debussy and McCoy Tyner for their open, ambiguous sound.
6.3 Chord‑Scale Theory
Chord‑scale theory pairs each chord with a scale that contains its notes. For example, a Cma⁷ chord corresponds to C major scale; a G⁷ chord to C major (or G mixolydian). This aids jazz improvisers in choosing notes that fit the harmony.
6.4 Voice Leading and Part Writing
Voice leading describes the smooth movement of individual melodic lines within chord changes. Good voice leading moves each voice by the smallest possible interval, avoids parallel fifths and octaves, and resolves dissonances correctly. Part writing rules, taught in harmony classes, ensure logical and singable lines.