Harmony, << HAHR muh nee, >> is the study of musical chords and their relationships. Most chords consist of three or four notes sounding at the same time. A melody is harmonized when chords are added to it.
Composers used traditional harmony from about 1680 to 1900. In traditional harmony, chords are built in thirds (two steps apart in the scale). The bottom note is called the root of the chord. Chords consisting of two thirds are triads. Those with three thirds are sevenths.
One form of traditional harmony is called functional harmony. In functional harmony, all chords are related to one of three basic chords of a key. The main chord is the tonic, which is based on the first note of the scale. The others are the dominant, based on the fifth note, and the subdominant, based on the fourth note. All other chords in a key are related to one of these basic chords.
A major or minor triad is called a consonant chord. All other chords are called dissonant and, in traditional harmony, must be smoothly resolved (connected) to a consonant chord.
The history of harmony is the development of chromatic chords and modulations. Chromatic chords include tones outside the key. Modulation is changing from one key to another. Many composers use chromatic chords and modulations to add expression and harmonic variety to a composition.
After 1900, many composers abandoned traditional and functional harmony. Some have used streams of triads or sevenths in parallel motion. Some have built their chords out of intervals other than thirds. Many modern composers have also used triads in two or more keys sounded at the same time, or mixtures of notes sounded as chords.
