Chords began as accidents of singing lines
A chord is two or more notes sounding together—yet until the Middle Ages "harmony" meant any pair, and Renaissance ears only slowly treated three-note stacks as the unit. Between the sixteenth and eighteenth centuries, chords quit being side-effects of polyphony and became music's primary architecture.
The English word traces to Middle English "cord" from "accord," meaning agreement; seventeenth-century spelling shifted to "chord" to dodge confusion with rope. In early church organum, plainchant simply doubled at fourth, fifth, or octave—so vertical sonorities were incidental. Renaissance polyphony thickened; seventh chords appeared in the 1500s; Baroque practice made the dominant seventh a cadence engine and let melody ride chordal accompaniment under figured-bass shorthand.
A common triad stacks root, third, and fifth—intervals named from the root. Major and minor label the third; diminished and augmented the fifth. Stacking further thirds yields sevenths through thirteenths; jazz thrives on such extensions, while tone clusters of seconds and quartal stacks blurred tonality in the twentieth century. Jean-Philippe Rameau named inversions still taught today: root in the bass, then first (third lowest) and once-dissonant second (fifth lowest).
Progressions aim somewhere—reinforcing tonic or modulating—and homophonic melody-plus-harmony remains classical pedagogy's default. Hugo Riemann cast every chord by tonic or dominant function. Notation splinters across Roman numerals, Nashville numbers, and letter symbols, yet theorists insist the ear still decides. Voice leading, cadences, and borrowed chords show how harmony can pull a listener forward even when the melody barely moves at all. From Neapolitan sixths to microtonal stacks, the story of the chord is how simultaneous sound stopped being a by-product and became the destination composers chase.
Source: Chord (music)
