A chord is the simultaneous sound of two or more musical notes. The most common chord has three notes and is known as a triad. Added tone chords, extended chords, and tone clusters can have more than three notes and are common in contemporary classical music and jazz.
An arpeggio is a chord where notes are sounded separately. A series of chords is sometimes called a chord progression. There are several ways to notate chords including figured bass, Roman numerals, the Nashville Number System, and alphabetical chord notation.
Definition
A chord is the sound of two or more notes being played at the same time."Chord." Grove Music Online. Oxford University Press, 2001.Karolyi, Otto. Introducing Music. Penguin Books, 1965. 63–78. The term derives from "accord", which became "cord" in Middle English. The original meaning was an agreement or harmonious sound. In the 17th century, the spelling was changed to "chord" to prevent confusion with "cord"."Chord, N. (2), Etymology." Oxford English Dictionary, Oxford University Press, March 2025."Chord." Merriam-Webster Dictionary. Accessed 20 Feb. 2026.
Until the Middle Ages, harmony was any combination of two notes. In the Renaissance, the simultaneous sound of three notes began to be understood as the working definition of harmony.Jones, George T. HarperCollins College Outline Music Theory. Wildside Press, LLC, 1994. 43.Surmani, Andrew. Essentials of Music Theory: A Complete Self-Study Course for All Musicians. Alfred Music, 2004. 72. An arpeggio is a broken chord where each note is sounded successively instead of simultaneously.Mason, William. A System of Technical Exercises for the Pianoforte. Oliver Ditson & Company, 1878. 73. Chords can also be implied by melodies.Nattiez, Jean-Jacques. Music and Discourse: Toward a Semiology of Music. Translated by Carolyn Abbate. Princeton University Press, 1990. 218.Trainor, Laurel J. and S.E. Trehub. "Key membership and implied harmony in Western tonal music: developmental perspectives", Perception and Psychophysics, 56(2). 1994. 127f.
A chord progression is a collection of harmonies with a specific destination or purpose, such as reinforcing the tonic or modulation to a new pitch center.Schoenberg, Arnold. Structural Functions of Harmony. Norton, 1954. Chord progressions are common in Western music.Malm, William P. Music Cultures of the Pacific, the Near East, and Asia (3rd ed.). Prentice Hall, 1996. 15. Homophonic textures where the melody and harmony generally move in unison are considered the standard practice in classical music and remain central to music instruction.Hyer, Brian. "Homophony." Grove Music Online. Oxford University Press, 2001. The study of harmony involves chords and progressions and the principles of connection that govern them.Dahlhaus, Carl. "Harmony". In Sadie, Stanley; Tyrrell, John (eds.). The New Grove Dictionary of Music and Musicians London: Macmillan Publishers, 1995. 175.
History
Between the 16th and 18th centuries, chords developed into primary musical elements that were distinct from their polyphonic origins.Cohn, Richard, Brian Hyer, Carl Dahlhaus, Julian Anderson, and Charles Wilson. "Harmony." Grove Music Online. Oxford University Press, 2001. In early church polyphony known as organum, a plainsong was paired with another melody. This two-part counterpoint developed gradually into ever more complex polyphonic writing.Britannica Editors. "organum". Encyclopedia Britannica. November 12, 2010. Accessed February 21, 2026.
In organum's simplest form, the plainchant was doubled in a perfect interval like the fourth, fifth, or octave.Duarte, John. Melody & Harmony for Guitarists. Mel Bay Publications, Incorporated, 2010. 49. Chords were incidental results of the melodic lines.Benward, Bruce, and Saker, Marilyn. Music in Theory and Practice, Volume 1. McGraw-Hill Education, 2008.
During the Renaissance, polyphony became more complex. Seventh chords started to appear in the 16th century. In the Baroque era, seventh chords started to function in specific ways that enabled smooth voice leading and complex cadences. The dominant seventh chord in particular became a fixture of classical music during the common practice period.
For Baroque composers, counterpoint was no longer imperative, and melodies were often accompanied simply by chords. The era also saw the rise of a shorthand notation known as figured or thorough bass. The bass melody is accompanied by numbers which indicate the harmony that should be played above each note.Schonberg, Harold C. The Lives of the Great Composers. United Kingdom, WW Norton, 1970. 25.Dunstan, Ralph. Basses and Melodies for Students of Harmony and Players from Figured Basses: Selected from the Works of the Great Composers. London: Novello, Ewer, and Company, 1894. 1.
As tonality expanded, structures like Neapolitan and augmented sixth chords used chromatic notes outside of the diatonic scale.Drabkin, William. "Neapolitan sixth chord." Grove Music Online. Oxford University Press, 2001. Such altered chords complicated voice leading and led to more eclectic cadences and modulations. Composers began to strip the function from such chords and embrace them purely for their sonic qualities.DeVoto, Mark. "Harmonic Analysis", The New Harvard Dictionary of Music. Edited by Don Randel. Belknap Press of Harvard University Press, 1986. 362f."Cadence", The New Harvard Dictionary of Music, 1986. 122f. 20th century music greatly expanded chords, adding tones and often dissonance. Jazz has a particularly eclectic chord vocabulary.Pachet, François. "Surprising Harmonies", Journées d'Informatique Musicale. May 1999, Paris, France. 187–206.
Structure The major chord occurs in harmonics 4, 5, and 6 of the harmonic series.Schoenberg, Arnold. Theory of Harmony. Translated by Roy E. Carter. University of California Press, 1983. Adding harmonic 7 creates a seventh chord. A common triad has three notes: the root, third, and fifth. The intervals are identified by their distance from the root of the chord. The notes that form a chord are sometimes called members or factors.Neidhöfer, Christoph, and Peter Schubert. "MELODY OR HARMONY?" Baroque Counterpoint: Revised and Expanded Edition. State University of New York Press, 2023. 14.Solomon, Jason W. Music Theory Essentials: A Streamlined Approach to Fundamentals, Tonal Harmony, and Post-Tonal Materials. United Kingdom, Taylor & Francis, 2019.
Continuing up in thirds yields a seventh, ninth, eleventh, and thirteenth before returning to the root again. Complex sonorities larger than a tetrad are sometimes called polychords because they can be seen as combinations of two different chords.Haerle, Dan. The Jazz Language: A Theory Text for Jazz Composition and Improvisation. Columbia Pictures Publications, 1980. 30. Extended chords are one of the central characteristics of jazz harmony.Sadie, Stanley, ed. "Ninth chord". The New Grove Dictionary of Music and Musicians. vol. 13. MacMillan Publishers, 1980. 252.
Chords are identified by their intervals. The four basic triad qualities are major, minor, diminished, and augmented. Major and minor chords derive from the quality of their thirds. Diminished and augmented chords describe the quality of the fifth.Hutchinson, Robert. "Introduction to Triads". Music Theory for the 21st-Century Classroom. University of Puget Sound, 2025. Additional intervals like sevenths are also described by their quality in relation to the root.
Composers began expanding tonality beyond the common practice and often structured chords in fourths and fifths. They were more tonally ambiguous, enabling new patterns for music.Arnold Schoenberg, Structural Functions of Harmony, Faber and Faber, 1983, pp. 1–2. Chords also shrunk to tone clusters made of small intervals like seconds. The resulting sound mass was a common feature in the 20th century.Cope, David. New Directions in Music. Waveland Press, 2001. 55–66. Microtonal chords are also used by many contemporary composers.Lerdahl, Fred. Composition and Cognition: Reflections on Contemporary Music and the Musical Mind. University of California Press, 2019. 102.The Oxford Handbook of Spectral Music. Oxford University Press, 2025. 853.Gilmore, Bob. Harry Partch: A Biography. Yale University Press, 1998. 207.
Theorists began to analyze the structure of chords in the 16th century. Jean-Philippe Rameau developed the nomenclature for chord inversion that is still in use today.Mitchell, William J. "Chord and Context in 18th-Century Theory." Journal of the American Musicological Society, vol. 16, no. 2, 1963. 222–5.
Root position is when the lowest note of a chord is the root, regardless of how the other members are arranged above it. The chord is considered inverted when the root is not the lowest voice. When the third is the lowest sounding pitch, the chord is in first inversion. The second inversion puts the fifth in the bass and was widely seen as dissonant, even as composers put it into frequent practice."Inversion", The New Harvard Dictionary of Music, 1986. 403f.Bartlette, Christopher, and Steven Laitz, Steven. Graduate Review of Tonal Theory. Oxford University Press, 2010. 58.
Function +Roman Numerals and Scale Degrees for Major KeysRollinson, Thomas H.Treatise on Harmony, Counterpoint, Instrumentation and Orchestration Philadelphia: J.W. Pepper & Son, 1886. 12. RomanNumeral Scale Degree I tonic II supertonic III mediant IV subdominant V dominant VI submediant VII subtonicviileading tone The names for each scale degree were bestowed on the triads above them. The dominant fifth scale degree is the root of the dominant fifth chord. Chords retained similar relationships to the tonic as their scalar forbearers. The dominant functioned as a counterweight to the tonic. A simple progression away from the tonic to the dominant and back again is the template for countless short pieces.Piston, Walter. Harmony New York: W.W. Norton & Company, 1978.
Hugo Riemann built on Rameau's work to develop an idea of functional harmony where every chord was analyzed by its relationship to the tonic or dominant.Mickelsen, William C. Hugo Riemann's Theory of Harmony: A Study. University of Nebraska Press, 1977. His work was widely adapted by other theorists.Holtmeier, Ludwig. "The Reception of Hugo Riemann's Music Theory", The Oxford Handbook of Neo-Riemannian Music Theories. Oxford University Press, 2011. 6.
Chords inherited their behavior from the part writing traditions of polyphony. The inner voices of chords reflected the same relationships as their melodic counterparts. The dissonance of the tritone in a dominant seventh chord is resolved stepwise in traditional part writing, with the seventh stepping down to the third and the leading tone stepping up to the tonic.Benjamin, Thomas, et al. Techniques and Materials of Music from the Common Practice Period Through the Twentieth Century. Australia, Cengage, 2015. 46–49.
As music became more chromatic, composers broadened the vocabulary of chords. Chords were often borrowed from other keys without modulation.Prout, Ebenezer. Harmony: Its Theory and Practice. United Kingdom, Augener & Company, 1903. 198f. Altered chords obscured the root relationships in music to the point where tonality could be asserted simply by a composer's emphasis.Erickson, Robert. The Structure of Music: A Listener's Guide. New York: Noonday Press, 1977. 85–88.