Guido d'Arezzo (c. 990–c. 1050)

Italian Benedictine monk and music theorist. He greatly advanced solmization and mutation by adapting the syllables Ut, Re, Mi, Fa, Sol, and La to the hexachord and by demonstrating the hexachordal positions on the fingers by the use of the ‘Guidonian hand’.

He lived in Pomposa and Arezzo, and visited Rome. He was once, rather doubtfully, credited with the invention of the music stave, the use of which he certainly encouraged. His chief theoretical work, written about 1026, is entitled Micrologus de musica.