GUIDO OF AREZZO (c. 99o), a musician who lived in the I I th century, is also known as Guido Aretinus, Fra Guittone, and Guy of Arezzo. He has been called the father of modern music, and a portrait of him in the refectory of the mon astery of Avellana bears the inscription Beatus Guido, inventor musicae. Of his life little is known, and that little is chiefly derived from the dedicatory letters prefixed to two of his treatises and addressed respectively to Bishop Theodald of Arezzo, and Michael, a monk of Pomposa and Guido's pupil and friend. At his first appearance in history Guido was a monk in the Benedic tine monastery of Pomposa, where he taught singing and invented his educational method, by means of which, according to his own statement, a pupil might learn in five months what formerly it would have taken him ten years to acquire. Envy and jealousy, however, drove him from the monastery and he went to live at Arezzo; where, about io3o, he received an invitation to Rome from Pope John XIX. Ite obeyed the summons, and the pope himself became his first and apparently one of his most pro ficient pupils. In Rome he met again his former superior, the abbot of Pomposa, who seems to have induced him to return to Pomposa. Thenceforward the particulars of his life are scanty but it is known that at one period he worked in the Benedictine monastery of St. Maur des Fosses where he invented his novel system of notation and taught the brothers to sing by it. In codex 763 of the British Museum the composer of the "Micrologus," which gives an account of his method and other works by him is always described as Guido de Sancto Mauro.
But whatever the details of his life there is no room for question as to the importance of his musical reforms and innovations. He it was who for the first time systematically used the lines of the staff, and the intervals or spatia between them. There is also little doubt that the names of the first six notes of the scale, ut, re, mi, fa, sol, la, still in use in France and Italy, were introduced by him. They were derived from the first syllables of six lines of a hymn addressed to St. John the Baptist, the initial notes of each line of which happened to form the scale, C, D, E, F, G, A, the lines in question being as follows :— Ut queant laxis resonare fibris Mira gestorum famuli tuorum, Solve polluti labii reatum, Sancte Joannes.
Further Guido is generally credited with the introduction of the F clef and with writings on music which are amply sufficient to account for the high esteem in which he was ultimately held by his contemporaries. The precise year of his death is unknown.
The most important of Guido's treatises, and those which are generally acknowledged to be authentic, are Micrologus Guidonis de discipline artis musicae, dedicated to Bishop Theodald of Arezzo, and comprising a complete theory of music, in 20 chap ters ; Musicae Guidonis regulae rhythmicae in antiphonarii sui prologum prolatae, written in trochaic decasyllabics of anything but classical structure; Aliae Guidonis regulae de ignoto cantu, identidem in antiphonarii sui prologum prolatae; and the Epistola Guidonis Michaeli monacho de ignoto cantu, already referred to. These are published in the second volume of Gerbert's Scriptores ecclesiastici de musica sacra. A very important manuscript un known to Gerbert (the Codex bibliothecae Uticensis, in the Paris library) contains an antiphonarium and gradual undoubtedly be longing to Guido. (See SOL-FA and TONIC SOL-FA.) See L. Angeloni, G. d'Arezzo (1811) ; Kiesewetter, Guido von Arezzo (184o) ; Kornmuller, "Leben and Werken Guidos von Arezzo," in Habert's Jahrb. (1876) ; Antonio Brandi, G. Aretino (1882) ; G. B. Ristori, Biogra la di Guido monaco d'Arezzo (1868) ; and a life by Gastoue in the Dict. d'archeologie (Paris, 1924) . (See also HEXACHORD, Music and MUSICAL MOTATION.)