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A chord is three or more different notes sounding together. Harmony, in the broadest sense, is the sound of chords. A specific harmony is the sound of a specific type of chord. To play a C-major chord, for example, is to create the harmony of C major.

Harmony is also the overall practice, or science, of creating chords and chord progressions according to certain rules and principles. It's in this sense that one speaks of "fifteenth-century harmony," for example, or "late-nineteenth-century harmony," or "the system of tonal harmony." Systems of harmony have changed enormously from century to century, and sometimes from decade to decade, along with notions of what's possible, or acceptable, or beautiful. To describe a harmonic system, or a harmonic language, is to describe both what kinds of chords are commonly used in that system — how notes are combined — and the principles that underlie the system's chord progressions — how the harmonies relate to one another and to the other elements of musical composition.


Harmony is called, metaphorically, the "vertical" element in music, because on a printed page of music, notes that sound simultaneously are lined up vertically. Melody is the "horizontal" element: as a melody proceeds, the notes follow each other from left to right on the page.

Any given melody may be "harmonized" in different ways. A melody consists of single notes, but each of those notes may fit into a variety of different chords. To harmonize a melody, a composer decides which chord progression will work with the melody most effectively and then "builds" the desired chords by adding notes that will be heard together with the melody notes. These chords are called a "harmonic accompaniment" to the melody. The harmony isn't usually just plugged in after the melody is written, however. More often than not, melodies come to a composer's imagination with at least some of the harmonies already attached. And sometimes it happens entirely the other way around: the idea that first comes to a composer's head is a chord progression, and he or she creates a melody to fit the chords.

In fact, one of the greatest problems in using language to describe music is that we can say or write only one thing at a time, so that when we discuss such things as melody, harmony, and rhythm they sometimes seem like separate, and separable, elements. But they're not. They exist simultaneously. They're part of one another.

There is no melody without rhythm, for example, because the notes of a melody are all measured in time, and are therefore related to one another by duration as well as by pitch. And even when we're just humming a simple melody to ourselves, we somehow "hear" or imagine the harmonies at the same time. (You're not sure? Try listening to a familiar melody with someone playing the "wrong" chords, or even one wrong chord, and you'll realize how well you know, and how completely you expect, the right ones.) What we think of as a beautiful melody, in other words, is most often inseparable from its harmony. Harmony, too, has its rhythm: the beauty of a chord progression depends not just on how the harmonies change, on which specific chords form the progression, but on when they change — on how long the harmonies last relative to one another and to the notes of the melody.


The instruments on which it's most practical to play chords are keyboard instruments like the piano and organ, where all ten fingers are available to play at the same time, and plucked instruments like the guitar and harp. Composers often write chords for bowed stringed instruments like the violin, viola, cello, and double bass, but in actual performance such chords are usually "broken" into two consecutive parts because the physical arrangement of the strings allows the player to sustain a maximum of only two notes at once. Percussion instruments like the xylophone and the glockenspiel can play chords when the player uses two mallets in each hand, but wind instruments can generally play only one note at a time.

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[NPR Logo] The NPR® Classical Music Companion: Terms and Concepts from A to Z by Miles Hoffman, published by Houghton Mifflin Company. Copyright © 1997 by Miles Hoffman and National Public Radio. All rights reserved.