Chord (music)
The English word chord derives from Middle English cord, a back-formation of accord in the original sense of agreement and later, harmonious sound. Two or more notes sounded simultaneously are known as a chord, according to Ottó Károlyi. Since instances of any given note in different octaves may be taken as the same note, it is more precise for analysis to speak of distinct pitch classes. Three notes are needed to define any common chord, so three is often taken as the minimum number that form a definite chord. Andrew Surmani states that when three or more notes are sounded together, the combination is called a chord. George T. Jones agrees that two tones sounding together are usually termed an interval, while three or more tones are called a chord. Monath defines a chord as a combination of three or more tones sounded simultaneously, with distances between tones called intervals. Sonorities of two pitches, or even single-note melodies, are commonly heard as implying chords. A simple example occurs when the root and third are played but the fifth is omitted. In the key of C major, if music stops on G and B, most listeners hear this as a G major 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. Often, however, we must go from a textual given to a more abstract representation of chords being used, as in Claude Debussy's Première arabesque.
Chords evolved out of early church organum, which reflected different vocal ranges. In its earliest written form found in Musica enchiriadis around 900, organum consisted of two melodic lines moving simultaneously note against note. Organum was further developed with staff notation established by monk Guido d'Arezzo around 1025. Medieval Christian hymns featured organum using simultaneous perfect intervals of fourths, fifths, and octaves. Chord progressions and harmony emerged as incidental results during medieval times and continued through the Renaissance period spanning the 15th to 17th centuries. The Baroque period covering the 17th and 18th centuries began featuring major and minor scale based tonal systems including circle progressions. During Baroque times accompaniment of melodies with chords developed through figured bass techniques. Familiar cadences like perfect authentic and plagal forms appeared in this era. Dissonant sonorities suggesting dominant sevenths occurred frequently in Renaissance music. The dominant seventh proper entered constant use during Baroque periods and remained standard through Classical and Romantic eras. Leading-tone sevenths appeared in Baroque compositions and persist today. Composers began employing nondominant seventh chords throughout the Baroque period. These became frequent in Classical periods before giving way to altered dominants in Romantic times. A resurgence occurred during Post-Romantic and Impressionistic periods. The 19th century Romantic period featured increased chromaticism alongside secondary dominants that became common practice. Modern jazz often includes up to seven notes per chord occasionally more. Film scores frequently utilize chromatic atonal or post-tonal harmony instead of simple diatonic approaches.
Common ways of representing chords include Roman numerals, Nashville Number System, figured bass, chord letters, and chord charts. Plain staff notation remains used primarily in classical music contexts. Roman numerals commonly denote scale steps on which chords are built within harmonic analysis. Figured bass much used in Baroque era uses numbers added to bass lines enabling keyboard players to improvise chords while playing bass with left hand. Numbers stand for count of scale steps above written note to play figured notes. In 2010s some classical musicians specializing in Baroque era still perform chords using figured bass though many read fully notated accompaniments prepared by publishers. Such parts called realizations contain fully written-out chords replacing original figures. Chord letters use upper-case and lower-case letters indicating roots followed by symbols specifying quality. These appear in modern musicology analyzing songs and pieces. Various chord names and symbols lead sheets fake books quickly lay out harmonic ground plans allowing improvisation jamming or vamping. A big letter indicates root note like C. Symbols indicate chord quality such as minor aug or no symbol means major triad default. Numbers indicate stacked intervals above root including seventh or thirteenth. Additional musical symbols show special alterations like five or add13. Slash characters indicate bass notes other than root creating slash chords. Two chords separated by slashes may indicate polychords playing simultaneously.
Triads consist of three distinct notes: root plus thirds and fifths above root. Chords exceeding three notes include added tone extended chords and tone clusters used in contemporary classical jazz genres. Dyads represent two-note combinations heard as chords containing most important notes of certain chords. In C Major after tonic sections dyads with B and D sound as first inversion G Major to listeners. Perfect fifth dyads lack thirds so do not sound major or minor. Tritone dyads outline resolutions implying D7 resolving to G Major or C diminished resolving to Db Major. Unaccompanied flute duos contain only dyads meaning all progressions must be implied through these pairs plus arpeggios. Tetrads contain four notes while pentads use five and hexads six notes. Pedal point dominant seventh extended chords added tone clusters polychords exceed three notes. Polychords form from superimposed two or more chords analyzed sometimes as extended tertian altered quartal quintal harmony Tristan chord examples. Nonchord tones dissonant unstable outside current chord often resolve to chord tones. Hemitonic chords contain semitones whether minor seconds or major sevenths giving characteristic high tension. Atritonic chords lack semitones entirely. Hemichordic chords feature many tritones but no perfect fifths creating distinctive sounds.
A 2025 analysis examined 52 million chords across 680,000 songs finding G major and C major most commonly used accounting for 24 percent of all chords. These followed by D major A major F major completing top five frequencies. Study observed decline in chord diversity over time with fewer unique chords per song decreasing ratio unique total fell from 13 percent in 1930s to 8 percent in 2020s indicating trend toward straightforward progressions popular music. Songs containing fewer unique chords show declining complexity compared earlier decades. This statistical shift suggests contemporary songwriters favor simpler harmonic structures despite available theoretical options. The data reveals how modern production techniques influence compositional choices across genres. Pop rock jazz film scores demonstrate varying approaches though overall pattern shows reduction variety. Researchers note this represents significant change from mid-20th century practices where composers explored wider harmonic palettes. The findings suggest listeners may prefer familiar patterns even when new possibilities exist theoretically.
Scale degrees indicate function within particular keys using Roman numerals I IV V representing tonic subdominant dominant respectively. In C major first degree called tonic note itself forms one chord notated I same found other scales as III A minor or IV G major. Lower-case numerals indicate minor triads upper-case major triads plus signs diminished augmented qualities. Chords outside scale indicated placing flat sharp sign before numeral example E major key C represented III. Tonic of scale indicated left F: understood from key signature contextual clues. Inversions occur when lowest note not tonic creating different positions root position first second third. Four-note chords invert four ways similarly triadic methods. Guitar terminology uses inversion slightly differently referring stock fingering shapes rather than pitch arrangement. Secundal chords decompose series seconds major minor while tertian chords sequence thirds quartals fourths quintals fifths. Tritones important part dominant sevenths giving characteristic tension likely move stereotypically following chord. Semitones present major seventh chords creating high tension moving stereotypically next chord. Major sevenths without minor seconds less harsh sound containing both intervals together. Dominant seventh flat five many tritones no minor thirds perfect fifths create unique textures. Augmented triads feature many major thirds no minor thirds perfect fifths producing bright sounds.
Common questions
What is the definition of a chord according to Ottó Károlyi and Andrew Surmani?
A chord consists of two or more notes sounded simultaneously. Andrew Surmani states that when three or more notes are sounded together, the combination is called a chord.
When did chords evolve out of early church organum and what was Musica enchiriadis?
Chords evolved out of early church organum which reflected different vocal ranges. In its earliest written form found in Musica enchiriadis around 900, organum consisted of two melodic lines moving simultaneously note against note.
Which years define the Baroque period and how did it influence chord progressions?
The Baroque period covers the 17th and 18th centuries. During this era accompaniment of melodies with chords developed through figured bass techniques and dominant sevenths entered constant use.
How many chords were analyzed in the 2025 study and what percentage did G major and C major account for?
A 2025 analysis examined 52 million chords across 680,000 songs finding G major and C major most commonly used accounting for 24 percent of all chords.
What do Roman numerals indicate in harmonic analysis and how do they distinguish triad qualities?
Roman numerals denote scale steps on which chords are built within harmonic analysis. Lower-case numerals indicate minor triads while upper-case numerals indicate major triads plus signs show diminished or augmented qualities.