Chapter 18. On the three parts of music.
1. There are three parts of music, namely, harmonica, rhythmica, metrica. Harmonica is that which distinguishes in sounds the high and the low. Rhythmica is that which inquires concerning the succession of words as to whether the sound fits them well or ill.
2. Metrica is that which learns by approved method the measure of the different metres, as for example, the heroic, iambic, elegiac, and so on.
Chapter 19. On the triple division of music.
1. It is agreed that all sound which is the material of music is of three sorts. First is harmonica, which consists of vocal music; second is organica, which is formed from the breath; third is rhythmica, which receives its numbers from the beat of the fingers.
2. For sound is produced either by the voice, coming through the throat; or by the breath, coming through the trumpet or tibia, for example; or by touch, as in the case of the cithara or anything else that gives a tuneful sound on being struck.
Chapter 20. On the first division of music which is called harmonica.
1. The first division of music, which is called harmonica, that is, modulation of the voice, has to do with comedians, tragedians, and choruses, and all who sing with the proper voice.[260] This [coming] from the spirit and the body makes motion, and out of motion, sound, out of which music is formed, which is called in man the voice.
2. Harmonica is the modulation of the voice and the concord or fitting together of very many sounds.
3. Symphonia is the managing of modulation so that high and low tones accord, whether in the voice or in wind or stringed instruments. Through this, higher and lower voices harmonize, so that whoever makes a dissonance from it offends the sense of hearing. The opposite of this is diaphonia, that is, voices grating on one another or in dissonance.