Musical harmony

Musical harmony was invented in the late 800s A.D. Singers in monasteries like St. Gall in Switzerland improved the basic chant by adding a voice in parallel motion in order to sign in mostly perfect fourths or fifths along with the original tune. This was the beginning of musical harmony, and is known as organum. It later developed into counterpoint.

The music written during this early medieval period (the Dark Ages) is mostly anonymous.

In A.D. 1100, an improvement known as the "florid organum" occurred, as inspired by a monastery in south-central France known as St. Martial. In the "florid organum" the original tune is sung in long noets accompanied by a voice that sings many notes for each original one, emphasizing the perfect consonances (fourths, fifths and octaves)

Groves defines a chord as: "The simultaneous sounding of two or more notes."