Taking the first note of each line of Ut quent laxis (Hymn to St.John the Baptist) Guido of Arezzo, around the year 1000, has established the system of mutating hexachords, which serves as the origin of the Kodaly system of solmization. The 20 notes of Guido's mutating hexachords fitted in The Hand: the rules of music harmony in the late Middle Ages and the Renaissance were based on The Hand. Recommended reading:
- Hoppin, Richard: Mediaeval music, W.W.Norton, 1978
- Rastall, Richard: The Notation of Western Music, Dent, 1983
- Berger, Karol: Musica Ficta, Cambridge University Press, 1987
