Although harmony is non-existent in many world musics, it is found extensively in the music of the West where it has gained complexity with the passage of time. Many world cultures employ only melody in their music. Western music began as a melodic music only. It was not until the Renaissance period that harmony was introduced as a basic element in the music of the West. As a basic element of music, harmony continued to evolve in complexity until the beginning of the 20th century in the West.
Chords exist in a scale-tonal infrastructure.
Certain chords project a quality of instability and tension and are known as dissonant chords while other chords project a quality of stability and repose and are known as consonant chords . A series of successive chords in time is known as a chord progression . A three-tone chord is a triad . Chords may contain as few as three tones and as many as seven or more. The effect of three or more different tones sounding at the same moment in time creates the sense of greater mass and intensity of sound as compared to the effect of the sound of a single note.