Solfeggio, in Music, a vocal exercise, in which the syllables Ut (or Do), Re, Mi, Fa, Sol, La, Si—corresponding to C, D, E, F, G, A, B—are employed in lieu of words. Their use as a method of nomenclature originated, as far as the first six are concerned, in the 11th century with Guido Aretinus (q.v.), who substituted his hexachord system for the old Greek tetrachords. Observing in the melody of an ancient hymn for the festival of St John the Baptist, beginning
Ut queant laxis Resonare fibris
Mira gestorum Famuli tuorum,
Solve polluti Labii reatum
Sancte Ioannes, that the notes on which the successive phrases began were identical in order with the sounds of the hexachord, he adopted the syllables to which they were allied in the above stanza as names to represent the degrees of his new scale. When, early in the 17th century, the octave was completed by the seventh or 'leading note,' the syllable Si, formed of the initials of 'Sancte Ioannes,' was added; while Do generally took the place of Ut, as being more easily sung. The art of thus illustrating the construction of the musical scale by the use of syllables is called solmisation.