Hucbald (840–930), a Flemish monk, first wrote a second part, always a fifth above or a fourth below the tenor or “subject.” (The Latin name for the subject is _cantus firmus_—fixed song.) Hucbald probably used the fifth and fourth because they were perfect intervals, and all others except the octave, were imperfect. There were often four parts including the _cantus firmus_, for two parts were doubled. This succession of fourths and fifths sounds very crude and ugly (just try the example), but these people of the Middle Ages must have liked it, for it lasted several centuries and was an attempt at making chords. This music was called _organum_ or _diaphony_ (dia-two, phony-sound: two sounds). As early as 1100, singers tried out new effects with the added parts and introduced a few imperfect intervals, thirds and sixths, and tried singing occasionally in contrary motion to the subject,—this was called _discant_ from a Greek word meaning discord. Maybe at first it sounded discordant but soon it came to mean any part outside of the _cantus firmus_ or subject. (See musical illustrations.) [Illustration: Organum (IXth and Xth Centuries)] [Illustration: Diaphony] [Illustration: Discant (XIIth Century) Example of Organum, Diaphony, Discant ] There was also a kind of diaphony in which a third voice was written as a bass, a fifth below the _cantus firmus_, but it was actually sung an octave higher than it was written and sounded much better that way. As it was not a bass at all it received the name of false bass or _faux bourdon_. This was the beginning of chords such as we use. So, Hucbald started the science of harmony,—the study of chords. Hucbald called this _ars organum_—the art of organating or organizing. Hucbald also invented a system of writing music on a staff. It was not a staff such as we use today for he wrote in the spaces the initials T and S. T meant that the singer was to sing a whole tone, S, a semitone or half-step. He used a six line staff and wrote words in script instead of notes like this: [Illustration: Staff] GUIDO D’AREZZO AND HIS ADDITIONS TO MUSIC The next great name in music history is Guido d’Arezzo, a Benedictine monk (995–1050), famous for his valuable additions to music. He invented the four-line staff, using both lines and spaces and giving a definite place on the staff to each sound: Yellow line C———————————— Black line ............. Red line F———————————— Black line ............. In the Middle Ages, the men did most of the singing so the music was written in a range to suit their voices. C is middle C, and F the bass clef.