GUIDO D'AREZZO, da-retso, or GUIDO ARETINO (c.995-c.1050). A famous reformer of music, and a monk of the Benedictine Order. Nothing is known absolutely of his life, the only source of information being the frequently contra dictory traditions of the Middle Ages. He has the reputation of being the inventor of musical nota tion, and has been styled 'The RegeneratOr of Music.' But the circumstances which led to this invention are differently stated by nearly every narrator. The most plausible and possibly the most reliable account is that on one occasion, while chanting with the monastery choir a hymn in honor of Saint John, he was struck with the gradual and regularly- ascending tones of the opening syllable sounds of each hemistich in the first three verses: Comprehending the fitness of these sounds to his proposed system of solfeggio, he promptly systematized the idea. The fame of Guido's musi cal invention, and the success he achieved with it, particularly among the youthful choristers of his own monastery, while it gained for him consid erable and subjected him to much jeal ousy in his own and neighboring monasteries, finally brought him to the attention of the Pope (John XIX.), who invited him to Rome. Guido
immediately accepted the invitation, and met with a very gratifying reception. The Pope be came a student of the new system and did much to help the cause.
Research and tradition are united in ascrib ing to him the introduction of the four-line staff, which was a combination of the former red f line and yellow c line, with the addition of a black a line between them, and a black e line above them; the mensural notes being written on the lines and spaces. Extra lines were added either above or below, whenever necessary. By this invention a uniformity of pitch was obtained, which in itself marks one of the most important steps in the history of music. Ill health com pelled Guido to leave Rome, and he reentered the Monastery of Pomposa, where he had spent his younger days. He left many interesting writings explanatory of his musical doctrines, among which' may be mentioned the Microlologus and the Argymentunt Nevi Cantus Inveniemli. See MUSICAL NOTATION.