Chord (music)

• 1. Introduction

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  A chord is something you have heard thousands of times without ever stopping to name it. Every time two or more notes ring out at the same moment, a chord is born. The word itself carries history inside it. It comes from the Old French "accord," which traveled through Middle English as "cord," meaning agreement or harmonious sound. In the 17th century, scholars changed the spelling to "chord" specifically to avoid confusion with the rope you tie a knot in.

  But a chord is more than its name. Before the Renaissance, harmony meant any two notes played together. Then musicians began to hear the world differently. Three simultaneous notes became the working definition of harmony, and the triad was born. What drove that shift? How did a simple agreement of pitches grow into the complex vocabulary of jazz and 20th-century classical music? And who decided what any of it means? Those are the questions this documentary sets out to answer.

• 2. Roots in Polyphony

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  Between the 16th and 18th centuries, chords emerged as distinct musical elements. Before that transformation, the earliest form of harmony in the church was called organum. A plainchant melody was paired with a second melody, and those two lines moved together. In organum's simplest version, the chant was doubled at a perfect interval: a fourth, a fifth, or an octave. Chords were not planned. They were side effects.

  As polyphony grew more complex during the Renaissance, something changed. The seventh chord began to appear in the 16th century. By the Baroque era, seventh chords had taken on specific roles. They enabled smooth voice leading and complex cadences. The dominant seventh chord in particular became a fixture of classical music throughout the common practice period.

  Baroque composers also shifted away from requiring counterpoint as the main structural principle. Melodies were now often supported simply by chords. Out of that practice grew a shorthand notation: figured or thorough bass. A bass line was written out, and numbers placed above each note told the performer what harmony to play. That system shaped how European musicians read and taught harmony for generations.

• 3. How Chords Are Built

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  The major chord traces its architecture to the natural overtone series. Overtones 4, 5, and 6 together form the major triad. The next overtone adds a seventh, extending the chord into new harmonic territory.

  Every common triad contains three specific elements: the root, the third, and the fifth. Each note is identified by its distance from that root. Musicians sometimes call these notes the chord's "members" or "factors." The four basic triad qualities are major, minor, diminished, and augmented. Major and minor chords are determined by the quality of the interval of a third above the root. Diminished and augmented chords hinge instead on the quality of the fifth.

  Stack more thirds on top of a triad and the chord continues growing. A seventh appears first, then a ninth, an eleventh, and a thirteenth before the sequence cycles back to the root. Chords large enough to be felt as combinations of two different chords are sometimes called polychords. Extended chords, those built past the seventh, are one of the central characteristics of jazz harmony.

  Jean-Philippe Rameau developed the system of chord inversion that theorists still use today. Root position places the root in the lowest voice, regardless of how the other notes are arranged above it. First inversion puts the third in the bass. Second inversion places the fifth in the lowest sounding pitch, and composers long considered it dissonant even as they used it constantly.

• 4. Harmony and Function

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  Hugo Riemann built on Rameau's framework to create a full theory of functional harmony. In Riemann's view, every chord could be understood by its relationship to either the tonic or the dominant. Other theorists widely adapted his approach.

  The dominant chord acts as a counterweight to the tonic. A simple progression moving from the tonic to the dominant and back again provides the template for countless short pieces. The names assigned to each scale degree carry that logic forward. The dominant fifth scale degree gives the dominant chord its name. Chords inherited these behavioral tendencies from the older traditions of polyphonic part writing.

  That inheritance shows up inside individual chords. A dominant seventh chord contains a tritone, one of the most tense intervals in Western music. In traditional part writing, that tension resolves in a specific way. The seventh steps down to the third, and the leading tone steps up to the tonic. Those two movements are not accidents; they reflect the same stepwise relationships that governed melodic voice leading in polyphony.

  As music grew more chromatic in the 19th and 20th centuries, composers began borrowing chords from other keys without fully modulating. Structures like the Neapolitan chord and the augmented sixth chord introduced notes outside the diatonic scale. Altered chords blurred root relationships to the point where tonality could be asserted simply by emphasis rather than by strict harmonic logic.

• 5. Notation and Naming

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  Roman numerals entered the chord-labeling toolkit in the 18th century, and that system remains in active use today. The Roman numeral identifies which scale degree is the root of the chord. The table of Roman numerals for major keys assigns each scale degree a name: tonic, supertonic, mediant, subdominant, dominant, submediant, and subtonic or leading tone.

  In the 20th century, that Roman numeral approach evolved into the Nashville Number System, a shorthand developed in the professional recording studios of Nashville. Instead of letter names or Roman numerals, the Nashville Number System uses arabic numbers to identify scale degrees, which means a musician can transpose a chart instantly without rewriting anything.

  Musicologists also simply label chords by the letter name of their root, then add symbols to indicate quality and any added tones. That practice is common in popular music, where chord charts use letters and abbreviations rather than classical notation. Figured bass, Roman numerals, the Nashville Number System, and alphabetical chord notation all represent different answers to the same problem: how do you write down something you want someone else to play?

  Apart from notation, theorists began examining chord structure systematically in the 16th century. The discipline of harmony involves not just chords in isolation but the principles that govern how one chord connects to the next.

• 6. Chords Beyond Tonality

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  20th-century composers expanded the chord vocabulary in directions that earlier theorists had not anticipated. Some structured chords in fourths and fifths rather than thirds. These sonorities are more tonally ambiguous, and that ambiguity opened new compositional possibilities.

  Others compressed chords down to tone clusters, groups of pitches separated only by small intervals like seconds. The resulting dense sound mass became a recognizable feature of contemporary classical music. Microtonal chords, built from intervals smaller than the standard half step, are also in use among contemporary composers.

  Jazz developed its own particularly eclectic chord vocabulary, one where extended chords are not exceptions but standard tools. Added tone chords and tone clusters appear throughout jazz and contemporary classical writing alike.

  What connects all of these expansions is the principle that Rameau first articulated through his work on inversion and that Riemann extended through functional harmony: the ear keeps listening for a relationship. Whether the chord is a plain triad or a dense cluster of microtones, the question the listener unconsciously asks is always the same one. Where does this want to go?