Chord (music)

A chord is the simultaneous sound of two or more musical notes.

This combination of notes creates harmony, which adds depth to a single melody. The term itself comes from the Middle English word "accord," meaning an agreement or a harmonious sound. In the 17th century, the spelling changed to "chord" to avoid confusion with the word "cord." While a single note provides a pitch, chords provide the texture and color that define musical styles. Understanding chords allows musicians to build complex structures that guide a listener through a piece of music.

To understand how a chord works, one must look at its internal structure. The most common chord is a triad, which consists of three specific notes. These notes are called members or factors, and they include the root, the third, and the fifth. The intervals, or the distance between these notes, determine the chord's specific quality. For example, major and minor chords are defined by the quality of their thirds. In contrast, diminished and augmented chords are identified by the quality of their fifths. Musicians can also play these notes one after another rather than all at once. This technique is called an arpeggio, which is essentially a "broken" chord.

Chords can become much more complex than a simple three-note triad. By continuing to stack notes in intervals of thirds, musicians create extended chords. This includes the seventh, ninth, eleventh, and thirteenth chords.

In jazz music, these extended chords are a central characteristic. Some musicians even create polychords, which are large sonorities made by combining two different chords. Other contemporary styles use tone clusters, which are groups of notes played with very small intervals, such as seconds. Some composers even utilize microtonal chords to explore sounds outside of standard tuning.

Music history shows a steady evolution in how chords are used. In the Middle Ages, harmony was simply any combination of two notes. Early church music used a style called organum, where a plainchant was paired with another melody. This often involved doubling the chant in a perfect interval, such as a fourth, fifth, or octave.

During the Renaissance, the definition of harmony shifted toward the simultaneous sound of three notes. By the 16th century, seventh chords began to appear, and by the Baroque era, they began to function in specific ways to enable smooth voice leading.

The Baroque era also introduced new ways to organize and write music. Composers began using melodies accompanied simply by chords rather than complex polyphonic lines. They used a shorthand called figured bass, or thorough bass, to indicate harmony. In this system, numbers were written below a bass melody to tell the player which chords to perform above it. As music progressed, tonality expanded through the use of chromatic notes. This led to the creation of special structures like Neapolitan and augmented sixth chords, which use notes outside the standard scale.

Theory has helped musicians organize these sounds through various systems. Jean-Philippe Rameau developed the nomenclature for chord inversion, which is still used today. A chord is in root position if the root is the lowest note. If the root is not the lowest note, the chord is considered inverted. For instance, if the third is the lowest pitch, it is in first inversion.

Later, Hugo Riemann developed the idea of functional harmony. He analyzed every chord based on its relationship to the tonic, or the home pitch, or the dominant.

In Western music, chords often work together in a series called a chord progression. These progressions move toward a specific destination, such as reinforcing the tonic or modulating to a new pitch center. In classical music, composers often use a homophonic texture. This is a style where the melody and the harmony move in unison or a similar way. A famous example of this is the "Promenade" from Modeste Mussorgsky's "Pictures at an Exhibition."

Whether through simple triads or complex jazz harmonies, chords remain the essential building blocks of musical expression.